polper maw composites- materiuh, processing...
TRANSCRIPT
Polper M a w Composites- Materiuh, Processing, Characterization and
w e n t Advances
Scope of tlie chapter
@is chapter gives a brief intmdiution of the subject and highlights the recent advances in polymer mat* composites. I t also gives a 67ief description of the important tliennosettiqj a d thmop(&Ftic mat* resim, &lierent types a d
fonm of reinforcements and the effect of interface qua& on the performance of the composites. '71ie method3 adoptedfor the quality /perfoormance evaluation of the composite and interphase, mocijication of intefaces a d toughening of th mat* have been highlighted: A brief account of the recent advances in the composite arena, including nano-composites and syntactic foam composites, is aho given Tina$, the techniques adoptedfor the fomuliztion andchnracteniatwn of hI&h pefomance m a t e resim and the advantages of using reactive4 6fended m a t e resim for advartced composite appl iatww are aho presented: Qie chapter concCuds with the current dmeIbpments in thejielii of hI&h pe$omance m a t e resitls inc ld ing epogis, 6ismahimides and their co-reactive b&n& and indicates the prospects of RaZ 'D in this area:
Chapter I 2
1.1 Introduction With the advancement in science and technology a drive for higher and higher
performance materials is being felt in aerospace, military, defense and engineering
applications. As a result, the conventional structural materials are being replaced by
different types of composite materials, the properties of which can be tailored to meet
any specific requirement by proper selection and modification of the matrix,
reinforcement, interface and processing technique. A composite material can be
defined as a macroscopic combination of two or more distinct materials having
recognizable interface between them. The requirement for a composite material was
felt because no single homogenous structural material can be found that has got all
the desired attributes for a specific application. Composite technology is of an
interdisciplinary nature, which extends over a wide range of subject fields like
chemistry, physics, engineering, polymer science and engineering, material science
etc.
The world is witnessing a spectacular growth in the application of composites
in every conceivable use. In today's world, market demand for cost effective material
solution$ for replacing metals, alloys and ceramics for a wide spectrum of applications
is increasing every day.
Composites are classified by the type of matrix material (metal, ceramic.
polymer and carbon') or by the geometry of the reinforcement (particulate, flake or
fiber). The structure, properties and applications of various composites are
investigated worldwide by several authors2". Composites possess a combination of
properties like high specific strength and specific modulus, good design flexibility, high
fatigue endurance limit and thermal cycling tolerance, corrosion and wear resistance.
tailorable coefficient of thermal expansion etc. which make them superior to most of
the conventional structural materials.
The term advanced composite has been coined to cover those reinforced
plastics having more than 50% by volume of fibers. These have been developed
primarily for aerospace industry in which the demand for strong and stiff lightweight
structures overcomes the prohibitive costs of early composite materials.
The composite products, successfully tried out towards missile programmes
fall under three major categories namely structural, electromagnetic and ablative
areas. The primary structural domain includes airframe sections, foldable wing and
frame, canister and rocket motor casing. Electromagnetic components are basically
redomes for various frequencies. The ablative products consist of thermal protection
liners for rocket motors, flex nozzles, re-entry heat shields, blast tubes etc.
The carboncarbon (C-C) composites are the most sought after in satellite
applications. Satellite in orbit dissipates tremendous amount of waste heat from
absorbed solar radiation and internal heat sources. The C-C radiator panel conducts
thermal energy more effectively than other materials currently in use for dissipating
thermal energy on satellite. They are used in satellite structures like solar panels,
antenna reflectors, yoke, optical support structures etc. They also have markedly
higher specific thermal efficiency compared to aluminium and offer improved
performance for lower volume and mass. Carbon composites are used extensively in
ablative applications in re-entry vehicle nose cones, heat shield etc. and in launch
vehicles for solid rocket motor case (C- epoxy), rocket nozzles and liners, pressure
bolts, heat shields and exit cones. Carbon fiber-phenolic composites can withstand
the high temperature and erosive gases of solid rocket motor operation and the high
temperatures generated by aerodynamic heating in re-entry systems.
Extensive use of fiber reinforced polymer matrix composites has been
identified as a viable means of reducing weight and thus increasing the fuel efficiency
and payload in aerospace applications. In the development of reusable space
transport systems, one of the major challenges is the development of materials and
structures to meet the flight requirements, and withstand the loads and adverse
conditions like high temperature and aggressive plasma environment. The clear and
confident answer to these requirements is a composite. Composites, the wonder
materials with light weight, high strength to weight ratio and stiffness properties, have
Chapter 1 4
come a long way from their inception, in replacing conventional materials like metals,
woods etc8.
1.2 Polymer Composites
The rapid advancement in the field of macromolecular materials has helped to
expedite the technological revolution in the field of aerospace, telecommunication,
micro electronics, defense and transport. At present, more than 60% of the advanced
composite market is within aerospace industry, identified primarily with aircraft I
aerospace and in sports1 leisure applications. The high specific strength, easy
processability and corrosion resistance have given prime place for polymer
composites as structural materials in aerospace. Weight reduction in aircrafts I
spacecrafts and launch vehicles can obviously lead to benefits like improved
performance and fuel economy, increased range and payload capability. Some of the
superior properties and resulting applications of advanced polymer composites in
contrast to conventional materials are given in Fig 1.1
Parabolic antenna Machinery Biocompatibility
Cryogenic application Sporting goods Chemical apparatus
Measuring instruments Music instruments Pipelines
Fig.1 .l Advantageous properties of advanced composites (Carbon Fiber Reinforced Plastics) in contrast to conventional materialsq0
Chapter I 5
Polymer matrix composites (PMCs) constitute several vital components of satellite
and launch vehicles ranging from motor cases and nozzle components to systems like
honeycomb structures, equipment panels, cylindrical support structures, pressure
bottles, solar array substrates and antenna reflector^""^. In Launch vehicles meant
for small satellites, the structure is reported to be composed of PMCs to the extent of
80%".
Composites have been used in space application from the start of 1950s.
Building up on the first successful use of composite solid fuel rocket motor case in
1950s, composites have been continually developed for aircraft, launch vehicles,
missiles and spacecraft structures. The key spacecraft environment includes
transient, steady state, vibration, acoustic, pyro shock, pressure, handling and
transport. In addition, the structural design may be affected by other environmental
conditions such as salt and fog, humidity, ambient temperature and space
environment. The space environment includes naturally occurring phenomena such
as atomic oxygen, very low density atmosphere, ionizing radiation, plasma, charged
particle plasma, neutral, atomic and molecular particles. The composites meant for
aerospace applications must be capable of surviving in this hostile environment for
sufficient length of time. Advanced composites have already started to play a major
role in the game of weight saving, where every pound or fraction of a pound weight
saved may spell the cliff between success and failure. Polymer matrix composite
(PMC) materials in the form of braided, woven or stitched laminates are increasingly
being used in critical aircraft structural parts that must be damage tolerant for reasons
of safety, reliability, maintainability and supportability. This means that PMC structures
must be durable and reliable under service conditions that can expose aircraft
structure to many types of damage mechanisms.
Space launch vehicles of expendable type experience severe thermal
environment during the ascent phase in the atmospheric regime of the flight. The
reusable launch vehicle face a similar environment during the ascent phase but are
subjected to a more severe and hostile environment during the re-entry phase. With
Chapter 1 6
the high speed advancements in science and technology, the urge for the
development of miracle materials to survlve in these hostile environment and loading
conditions is badly felt. The effects of changing the reinforcements and matrix
materials for producing composites with the properties essential for the system
requirement have been studied extensively. An overview of the myriad material and
configuration options available for polymer based composites was reported by many
researchersi4.
1.3 Principles of Polymer Reinforcement
Composites are combinations of a reinforcement material such as particles,
fiber or whisker and a matrix or binder material. This also implies that the materials
are macroscopically identifiable, retaining their distinctive component properties.
Composites reinforced with dispersed fillers, fibers and fabrics are widely used to
manufacture structural components and load bearing elements in space technology
and in aircraft, automotive and ship building industries. Therefore, the measurements,
calculations and predictions of the strength of such materials are of great interest to
engineers and researchers. The main feature of fiber and fabric reinforced composites
is the strong anisotropy of properties like strength and elastic modulus. Greatest
progress in exploitation of properties of continuous fiber reinforced composites has
been made, owing to a relatively simple mechanism of failure.
The three important factors determining the performance of a composite
material are the matrix, reinforcement and interphase.
1.4 Matrix Materials and Classifications
Matrix materials are generally classified in to four groups, ceramics, metals.
carbon and polymers. Choice of the matrix depends upon performance requirement.
service environment, available processing facilities, cost and several other factors.
The matrix constitutes approximately 40% (by volume) of the composite and performs
two major roles. The matrix component of these composites dictates many key
features like toughness, resistance to heat, corrosive environment and service
temperature. The matrix material transfers loads to the reinforcement and protects it
from adverse environmental effects. In addition, matrix controls the thermo-
mechanical behavior of the composites. The resin matrix spreads the load applied to
the composite between each of the individual fibers and also protects the fibers from
damage caused by abrasion and impact.
1.5 Polymer ~atrices"
The matrix controls the processibility, upper use temperature, flammability
characteristics and corrosion resistance of the composite. The composite mechanical
performance depends to a large extent on the resin modulus, failure strain, and the
fiber- matrix bond-strength.
Polymers are broadly classified into thermoplastics and thermosets. A number
of polymer systems under each categoly have been utilized as matrices. The merits
and demerits of each of these should be evaluated based on its chemical nature, ease
of transformation into pre-preg, processing and fabrication and also on the resultant
composite properties.
1.5.1 ~hermoplastics'~
Thermoplastics permit easy repair of structures made out of them. Joints can
be made by heating together and cooling, without need for cutting or welding. Owing
to their excellent toughness and thermal performance even to cryo-temperatures,
thermoplastics are being increasingly used in high performance applications. Unlike
thermosets, thermoplastics do not require reactive cure cycles. They require only heat
and pressure with subsequent cooling for composite fabrication. Some of the
commercially available advanced thermoplastics are poly ether ether ketone (PEEK),
poly phenylene sulfide (PPS), poly sulfide (PS), poly ether imide (PEI) and poly amide I
imide (PAI). Their glass transition temperatures normally range from 140 - 275°C and
Chapter I 8
processing temperature up to 350"~". High performance thermoplastics frequently
contain rigid aromatic and I or heterocyclic repeating segments. These repeating
segments have low mobility and thus provide high glass transition temperature, which
in turn give good heat resistance and retention of material strength at elevated
temperatures. Polymers containing high aromatic or heterocyclic structures require
high energy for thermal degradation process and thus give a high char residue in the
thermal break down process. These characteristics give polymers high decomposition
temperatures and low flammability that meet major requirements needed for
advanced structural applications. Typical high performance uncrosslinked polymers
include polyimides, polybenzobisthiozoles, polybenzobisoxazole, aromatic
polyamides, polybenzimidazoles, liquid crystalline polyesters, polyether sulphons,
polyquinolines, polyamide imides, polyether ketones, polycarbonates etciattS.
1.5.1.1 ~ o l ~ c a r b o n a t e s ~ ~
Polycarbonate has got exceptional total package of inherent properties such
as impact strength, heat resistance, clarity, inherent flame retardance and good
processability. Standard grade of polycarbonates are made from bisphenol A and
phosgene. It can be blended with other polymers to enhance the specific properties
such as chemical resistance. Co- polymers of polycarbonate have also been recently
employed to achieve high thermal performance approaching that of high-end
thermoplastics. Its superior impact strength and resistance to breakage and damage
makes it suitable for appliances, automotive, computers, business equipments,
electrical and electronic components, medical devices, transportation equipments,
outdoor fixtures and household utensils. Its excellent electrical properties remain
relatively constant over a wide temperature range.
1.5.1.2 ~ol~ethersu lphones~ '
The polyether sulphone belongs to polysulphone group of thermoplastics. Its
chemical structure consists of aromatic sulphone units linked through ether bridge.
Chapter I 9
The former is mainly responsible for the high temperature stability and mechanical
strength, while the later introduces sufficient chain mobility to permit melt processing
at reasonable temperature. The properties of polyethersulphone (PES) that
distinguish it from most other thermoplastics are its high temperature performance,
good mechanical strength and low flammability. These properties are achieved
without the penalty of difficult fabrication since PES can be melt processed in
conventional moulding equipments. The thermal stability as measured by the half life
of the tensile strength at a given temperature is very high for PES making it a
candidate for class H electrical application. PES has got very high glass transitin
temperature (220°C) and hence its properties show small dependence on
temperature. It is inherently flame retardant and does not require a flame retardant
additive. Its dielectric constant and loss factor show minimum variation with
temperature up to its glass transition temperature (T,), Most of the moulding, extrusion
and finishing operations associated with thermoplastic fabrication are applicable to
PES. It has got very good creep resistance which is one of the important attributes of
engineering thermoplastics. It is a very good electrical insulator. Little variation in
dielectric constant or loss factor is shown in the range of 0 -180 'c. Its high J temperature performance, dimensional stability and inherent fire / flame retardency
make it suitable for electronic and electrical industry. They have excellent
therrnoforrnability and mechanical properties.
1.5.1.3
Polyesters (PE) are produced by the condensation polymerisation of
difunctional acids or anhydrides with difunctional alcohols or epoxy resins. Different
classes of polyester resins are general purpose resins, chlorendic resins, bisphenol A
fumerate resins, vinyl ester resins etc. Within these classes of resins, specific
polyester can be formulated by varying the starting materials. The physical properties
of the resin do affect their durability and thermal performance. PE resins are generally
used in the elevated temperature applications, especially in the electrical and
Chapter I 10
corrosion resistant areas. Monomer type also plays a vital role in the thermal stability
of PE resins. PE resin is for application in corrosion resistant tanks, pipes, ducts and
liners in chemical processes and in pulp and paper industry. Their improved UV
resistance makes them a candidate material for outdoor applications.
1.5.1.4 Polyether ether ketonez3
Among the thermoplastics, polyether ether ketone (PEEK) is a selection
candidate for many important high performance applications because of its special
properties. It does not absorb significant amount of moisture. PEEK has got 25-40 %
crystallinity. It is relatively costly thermoplastic with good mechanical properties and
toughness, and hence most apt to be employed in high performance composites. For
example Carbon- PEEK is a competitor for carbon reinforced epoxy and Aluminium-
Copper and Aluminium - Lithium alloys in aircraft industry. PEEK has got many
essential qualities required for aerospace applications. The outstanding feature of
PEEK is its excellent fracture resistance. PEEK and other aromatic hydrocarbon
matrices have low hydrogen to carbon ratio and hence do not produce large amounts
of combustible volatiles. Limiting Oxygen Index (LOI), which is a measure of
inflammability, is as high as 35 for PEEK and its composites. Owing to its high T, and
melting point (T,), it is difficult to set fire to PEEK.
1.5.2 Thermosetting Resins
Thermosets are currently the predominant matrix resin for composites due to
their availability, well established processing technologies, existence of large
database and low material cost. The advancement in the area of high performance
composite has led to a number of related R 8 D activities and availability of abundant
literature on the topic2'. The widely used classes of thermosetting resins are
polyesters, phenolics, polyimides and epoxies.
Chapter 1 11
1.5.2.1 Phenolic ~ e s i n s "
Among the thermosetting high temperature resistant polymers, phenolics
have a unique place in terms of their chemistry, applications, thermal and chemical
resistance, and processability. Phenolic resins, both novolacs and resols are widely
used commercially due to their excellent flame retardance and low c o ~ t ~ ~ . ~ ' . The low
smoke and toxic evolution on burning make phenolics the material of choice for
nonstructural applications like aircraft interiors. Phenolics have broad range of
applications varying from construction to electronics and Addition-cure
phenolics offer viable alternatives to condensation type phenolics, avoiding need for
high pressure cures0. However, most of them require high cure temperature, posing
processing difficulties. Phenolics excel over other matrix resins in terms of resistance
to fire and the very low smoke and toxic evolutions1. Good heat and flame resistance.
ablative characteristics and low cost are the major advantages of phenolics which find
numerous applications apart from aircraft interiors, automotive components, rocket
nozzles, appliance moulding etc.
Brittleness, poor shelf- life and need for high pressure curing are the major
short comings of phenolic resins for structural applications. Brittleness is obviated by
blending it with elastomers", risking the thermal properties. Blending the phenolic with
polyesterss5 and engineering thermoplastic like po~yethersul~hone" is reported to
yield tougher systems. Cyanate esters of novolac phenolic resin (Phenolic Tr iazins
have the combined advantages of high temperature resistance and flame retardancy
of phenolic resins, epoxy- like processing and handling convenience coupled with
excellent high temperature performance comparable to that of polyimides35.
1.5.2 .2 polyimides3$
Among the numerous high-temperature resistant polymers, the polyimides(P1)
have achieved by far the greatest commercial success, due to their ability to maintain
acceptable mechanical properties at elevated temperatures together with the thermal
stability for long term use at temperatures around 300°C"~~~. Polyimides are the most
Chapter 1 12
popular heat resistant polymers due to their thermal stability, solvent resistance and
retention of properties over a wide temperature range and hence have gained
acceptance for use in aerospace composites, electrical electronic and industrial
applications. It has wide-spread application as thermal control films, coatings,
sealants and adhesives. New monomers based on different types of aromatic
diamines, and aromatic di anhydrides have been synthesized with various specific
properties such as processability and improved stability under thermal, chemical,
electrical and radiation environment^^^^'. They offer improved high temperature
properties compared to the epoxy systems. Shao et a14' reported the synthesis and
properlies of fluorinated polyimides from new unsymmetrical diamine. These
polyimides showed outstanding solubility and good dielectric properties.
Thermoplastic polyimides are less expensive than their thermoset versions.
However, their maximum use temperature is comparatively low. Condensation
polyimides are formed by a two - step process involving formation of a polyamic acid
followed by its imidisation. Thus, the processing times are much longer and require
the application of high pressure for consolidation, due to evolution of water or alcohol
as condensation by-products. Condensation polyimidesU are thermoplastics and
remain melt fusible. Consequently, they are having good tractability. Structure 1.a
gives the structure of a condensation polyimide. A number of polyimide systems have
been developed that are well suited for use as matrix resins, adhesives and coatings
for high performance applications in aerospace and electronic industriesu. However,
major disadvantages of these thermoplastic systems include poor precursor shelf-life
and processing difficulties, hydrolytic instability and need for removing volatiles. The
growing demand for polyimides that are processable, solvent- resistant with good
thermal stability provided a strong incentive for developing processable addition-type
polyimide systems. These are low molecular weight, multifunctional monomers or pre-
polymers that carry functional reactive terminations and imide functions in their
backbone. The bismaleimides, itaconimides and nadimides are the versatile ones in
this category. The structure of typical addition polyimides with nadimide terminals are
given in Structures.1.b. A large variety of addition polyimides, with good processibility
and thermal stabil~ty has been successfully used as matrix reslns in high performance
and high temperature resistant composite applications
b)
Structures 1 (a) condensation polyimide (b) addition polyimide
In addition to the condensation and thermoplastic family of polyimides, the third type
based on imide pre-polymers also has gained considerable importance recently
because of their ease of processabilty. Among these, bismaleimides have been
studied extensively mainly because they offer greatest benefits in terms of cost
effectiveness and enhanced processability.
1.5.2.3 Bisrnaleirnides
Among the addition type polyimides, bismaleimides (BMls) still dominate the
high temperature polymer scenario due to their thermal and oxidative stability, flame
retardence, low propensity for moisture absorption, ease of synthesis and cost
effectiveness4'. Bismaleimides are best defined as low molecular weight, atleast
difunctional monomers or pre polymers or mixtures there of, that carry maleimide
terminations. The general structure of bismaleimide is given in Structure.2.
Chapter 1 14
Structure.2 General structure of Bismaleimide resin
The key to the improved BMI system is the properties of the co monomer employed
for the BMI resin.The building blocks used in commercial BMI resins are 4, 4'-
bismaleimido diphenyl methane, 2, 4- bismaleimido toluene. 1. 3-bismaleimido
benzene etc. Because of the toxicity problems associated with methylene dianiline
(MDA) (4, 4'-diaminodiphenylmethane), polyaromatic diamines and the BMls based
on them are of increasing interest. The structure of some of the bismaleimides based
on specific polyaromatic diamines are given in Structure. 3.
Structure 3 Bismaleimides based on polyaromatic diamines
Cross linked BMI polymers are infusible, rigid, brittle and are insoluble in all
solvents.. They have relatively high densities (1.35 -1.40 gtcc) and exhibit T,s
generally in the range of 250-300°C. The strain to failure is typically below 2%. The
moisture absorption levels in BMI resins tend to be much the same as in Epoxy resins
Chapter 1 15
(4-5%by weight) but saturation occurs faster than in epoxy resins. New products such
as Narmco X 5250" aim for superior hot wet performance, compression-after-impact
in composite, coupled with good processibility and longer shelf- life over currently
used epoxy and BMI composites.
Polymerisation of BMI resins: BMI resins are reactive towards various reactive
species. Such reactivities provide BMI resins with high versatility for various
application through proper formulation with other thermosetting oligomers. A few
curing reactions, such as thermal polymerization, addition reactions, Diels- Alder
reactions etc have been developed to increase the application performance of BMI
resins.
Thermal polymerization: The most important curing reaction of BMI resins has
been their homo polymerisation at elevated temperatures (thermal polymerisation).
The reaction produces no volatile byproducts and provides void-free thermosets. The
BMI resins thermally set to rigid, solvent resistant, highly crosslinked thermosets.
G ~ n d schober4' first reported their homo polymerization by simply heating the
monomer to a temperature between 150-400°C.
Michael Additions: BMI resins contain reactive unsaturated olefinic groups that are
further activated by two strong electron withdrawing carbonyl groups and are known to
undergo Michael additions with hydrogen active moieties such as phenols, thiols and
amines. The reactions have been used to prepare not only high molecular weight
linear polymers but also high performance thermosets4'. The properties of BMI resins
strongly depend on synthesis conditions. It can undergo a chain extension reaction
with amino compound through Michael addition of the structure (Structure.4).
Structure 4 Bismaleimide-MDA Michael addition product
Ene reaction: One important class of high performance thermosets is derived from
BMI resins and allyl phenyl oligomers. Upon thermal curing, the mixture co-polymerize
to produce polymers of high glass transition temperature. The applicability of BMI-allyl
phenol resins as matrices for advanced composites have been studied e x t e n s i v e ~ y ~ ~ . ~ ~
CIBA-GEIGY introduced a unique cross linking chemistry into bismaleimide system
by utilizing the so called "Ene" reaction with the maleimide double bond5'
Diets-Alder polymerization: Diels- Alder polymerization requires reaction of a diene
monomer and a monomeric dienophile, which is normally activated by electron
withdrawing substituents. During the polymerization, a stiff, heat resistant ring
structure is formed by every Diet-Alder reaction unit. Diels Alder reactions have been
developed to increase the application performance of BMI resins. The type and extent
of each reaction depend on the chemical and molecular characteristics of the
bismaleimide.
Alder-ene reaction: Maleimides are known to react with allyl phenols through an
Alder-ene reaction5"" to give rise to cyclic network structures and are used as matrix
resin with improved high temperature perforrnan~e~~". A number of polymer systems
based on the co reaction of BMls and allyl phenols have been reported5'. Matrimide
(Biismaleimido diphenyl methane +diallyl bisphenol A) is a typical formulation. A few
patent claims have been made on the blends of allyl phenol based novolac and
EMIS". The Alder-ene type reaction in such systems proceeding via an intermediate
Wagner-Jauregg reaction, leads to thermally stable, crosslinked, cyclic structuresm,
High performance BMI resins are based on rigid aromatic structures and thus
possess high melting points and a narrow processing window. Detailed studies were
carried out on thermal behavior of different types of bismaleimide monomers in neat
and blended forms using various thermo analytical techniques for composite
applicationsg
The major disadvantage of all bismalimide resins is their extreme brittleness.
Much research is still being directed towards toughening of EM1 resins. Tough
compositions need blending with elastomers and lor chain extension using diamines.
Several modified versions, particularly the PMR-type resins (with service
temperatures up to 300°C for long duration) are currently in use in aerospace industry.
The various members of the PMR family are designated by numbers, the PMR-15
being the best known. Ethynyl terminated imide and isoimide and norbornene
terminated imide (PMR-15) oligomers are commercially available for high temperature
applicati~ns~~. Modifications of the PMR type addition polyimides with nadic8',
paracyclophane8z and cyclobuteneS3 terminations also have been reported
1.5.2.4 Cyanate ~ s t e r s ' ~
Cyanate esters (CE) emerged as a compromise thermosetting matrix system
~n the late 80's, which encompasses several of the characteristics required for an ideal
matrix. They possess the heat and fire resistance of phenolic resins, processing and
handling convenience of epoxies and hlgh temperature performance of polyimides.
The cyanate compounds are stable at room temperature and undergo trimerisation to
form s-triazine rings at elevated temperature in presence of catalysts and generate
h~gh crosslink densty, which in combination with rigid aromatic rings, provide
excellent high temperature properties, solvent resistance, electrical properties and
mechanical strength. Moreover, highly desirable properties like built-in toughness, low
dielectric constant and dissipation factor, radar transparency and low moisture
absorption make them the resin of choice in high performance structural composites
for aerospace applications and in electronic industry. The low out-gassing, minimal
dimensional changes during thermal cycling, low moisture absorption, low shrinkage.
good long term stability, self adherend properties to honeycomb and foam corese5 and
high service temperature are the key advantages of cyanate esters over state- of- the-
art epoxy resins. Despite thew high cost they find appl~cation in electronics, printed
circuit boards, satellites and aerospace structural composites. They have been
successfully employed in composite structures in INTELSAT". Cyanate esters can be
reactively blended with other high performance matrices such as bismaleimides, and
epoxies, wherein, the w-reaction or interpenetrating networks (IPNs) formation
facilitates imparting a wide spectrum of properties to the blend, depending on
composition and nature of the additivee7. One of the potentially and commercially
important oligomers terminated with cyanate ester group is based on phenolic
(novolac) resinss8. Novolac-cyanate provides an aerobic char yield of 58% at 800°C
and an oxygen index of about 45. Novolac cyanate-graphite composite has got short
beam shear strength of 74 MPa and flexural strength of 1300 MPa at 1 7 7 ' ~ . Novolac
-cyanate based composite is reported to give good property retentione9 after 12
weeks of air heat ageing at 240°C.
Basically cyanate ester resins have good rheological properties to meet the
processing needs for laminate and composite preparation. One of the most serious
concerns of current high-performance thermosetting resins, such as epoxy resin,
BMls, nadimides, and phenolics is their ability to pick up high percentage of moisture.
Cyanate ester linkages are very resistant to hydrolysis at ambient service conditions
and hence cyanate ester homopolymers absorb less water at saturation than epoxy,
BMI and polyimide resins. Their high T, (260-28O0C), low shrinkage, excellent
adhesion, excellent dielectric properties, low moisture uptake (<I%), and higher
tensile strain (2-6%) make them a material of choice for many important
applications". The most effective way to broaden the application scope of cyanate
ester resins is the development of co-polymerisation systems. Copolymers of cyanate
Chapter 1 19
ester with polyphenols, polyamines, cyanamides, organic anhydrides and epoxy
resins yielded useful systems suitable for variety of applications.
1.5.2.5 Epoxy ~esins"
Since their introduction in 1940% epoxy resins have found a myriad of
applications due to their good thermal and chemical resistance, superior mechanical
properties and excellent adhesion to variety of substrates. These materials are
characterized by terminal epoxide groups. The alfa epoxy is the most common variety.
Di-and multifunctional glycidyl compounds play a unique role among the thermosetting
resins. Depending on the chemical structure of the synthesized epoxy component, the
structure of the curing agent and curlng conditions, uncured epoxy resins can be
synthesized in a broad variety of physical forms ranging from low viscosity liquids to
solids and from well defined di-, tri- and tetra functional glycidyl ethers to
advancement products of oligomer type. It is possible to obtain toughness, good
chemical and corrosion resistance, high adhesive strength, mechanical properties.
good heat resistance and high electrical properties. The current state -of - the - art
matrix resin in structural aerospace composites is epoxies. Their attractive features
include ease of processing and handling convenience, good mechanical properties,
excellent adhesion to a variety of reinforcements, toughness and low cost. In addition
to applications in high performance aerospace composites, they are used in coatings,
adhesives, floorings and electrical applications. Versatility in form, modification.
properties, hardening methods, curing conditions and application is probably the most
outstanding characteristic of epoxy resins. The thermoplastic bisphenol A type
novolac re~in'~.~' was sequentially reacted with epichlorohydrin in alkali media to
generate a bisphenol- A type novolac epoxy resin. Its molecular back bone consists of
aromatic rings and as a result it can achieve excellent mechanical and thermal
performance.
Nature and amount of curing agent and its concentration are critical in
deciding the properties of the cured network. Common curatives are aliphatic and
Chapter 1 20
aromatic amines, dicyandiamide, acid anhydrides and Lewis acids such as BF3, which
are selected based on the applications of the final cured network. Fluorine-based
epoxy systems exhibit low moisture uptake, improved toughness and heat
re~istance'~. Epoxy resins are not generally recommended for applications in severe
conditions due to poor hotlwet performance and high moisture sensitivity.
Epoxy resins dominate the structural composites in aerospace applications.
Light weight motor cases use combinations of Kevlar and epoxy system. Satellite
support structures, antena, yoke and solar panel substrates are preferably made of
epoxy-composites. The novolac epoxy resin being multy functional, can produce a
denser crosslinked network compared to the common epoxy resins7'. They are
characterised by an outstanding combination of both mechanical and chemical
properties in terms of high modulus, thermal stability, solvent resistance and therefore
find wide spread application as a sealing material for semiconductor devices. The acid
anhydrides are characterized by long pot life, better heat ageing in air at elevated
temperatures and better electrical properties. Principal Lewis acid used in epoxy
composite is boron tri fluoride. Phenolics have been used as curing agent for epoxy
resins where the epoxy is usually the major comp~nent~' .~~. In many cases, these
systems make up the base resins for the semiconductor packaging due to their
improved hydrophobicity relative to amine- cured epoxies, and their low cost. Ogata et
a~~~ studied in detail the effect of cross link densities on the physical properties of the
epoxy networks. The primary resin in epoxy technology is the diglycidyl ether of
bisphenol A (DGEBPA) and its higher homologues. The glycidyl ethers of various
novolac resins are the second most important class of epoxy resins. The glycidyl
n0~0laCs are characterized by better elevated temperature performance than
bisphenol A (BPA) based systems. The diglycidyl ether of bisphenol F (DGEBPF) has
a lower viscosity than the BPA epoxies with minimal loss in T,. The triglycidyl ether of
triphenyl methane (TGETPM), a relatively new comer to the epoxy family is said to
have high T,, thermal oxidative stability and excellent moisture resistance.
Tetraglycidyl methylene dianiline (TGMDA) is the most widely used epoxy resin for the
Chapter I 2 1
fabrication of carbon fiber composites for aerospace industry. The structures of some
of the higher functional epoxies are given in Structures.S.a, b 8 c.
Epoxies can be cured with various types of hardners to obtain a wide range
of physical and mechanical propertiese0. Most common curing agents are aliphatic
amines, aromatic amines, acid anhydrides, lewis acids and dicyan diamine (DICY).
Aliphatic amines and their derivatives are recommended for ambient temperature
curing. Diethylene tetramine (DETA) and triethylene tetramine (TETA) are common
aliphatic amines. Cyclo aliphatic amines are curing agents at moderate temperature
and have got good elevated temperature properties. Aromatic amines are high
temperature curing agents. Their major advantages are long pot life, excellent
chemical resistance, good electrical properties, and good elevated temperature
performance. eg. methylene dianiline (MDA), m-phenylene diamine (MPDA). In epoxy
amine curing, the reaction takes place in two steps. The efficiency of secondary
reaction of amine with epoxy is generally 25% of that of primary reaction and hence
takes more time for completion. Sulphone diamines are normally used in conjunction
with a Lewis acid accelerator. They provide the best elevated temperature
performance. 4, 4' -diamino diphenyl sulphone is a typical example. Combination of
DDS with TGMDA resin is widely used in aerospace industry for carbon fiber
composites. Acid anhydrides are characterized by long pot- life, better heat -ageing in
air at elevated temperature and better electrical properties. Eg. n-hexa hydrophthalic
anhydride (HHPA) and methyl tetra hydmphthalic anhydride (MTHPA) perform well at
elevated temperatures. They have excellent electrical properties and give colourless
laminates with superior weathering properties. But anhydrides of high functionality
cause handling pmblem and have poor solubility. The chemistly of curing of epoxies
with anhydrides is complex. It was found that Lewis acids and bases act as catalysts
for this reaction.
Chapter 1 22
a ) EPN
b) TGETM
c) TGMDA
Structure.5 Higher functional epoxy resins (a) Epoxy resin based on novolac (Poly functional) - EPN. (b) Tris (4-glycidyloxy phenyl) methane ( TGET M) (c) N, N'-tetra glycidyl methylene dianiline (tetra epoxy) - TGMDA
At first, anhydride reacts with the catalyst to form a carbonyl anion, then the
anionic process continues up to the completion of cure. The principal Lewis acid used
in epoxy composition is boron trifluoride in the form of its mono ethyl amine complex
(BF3-MEA). It has long pot life and high T, and a storage life of over six months. Many
critical produck based on epoxies were designed and developed for launch vehicles
viz. SLV, ASLV, PSLV, GSLV and INSAT programmes of ISRO. Multifunctional - tri-
Chapter 1 23
and tetra functional - epoxies are used in most of the aerospace composites" A
comparison of properties of conventional high performance thermoset matrix resins is
given in Table 1.1 and in Fig. 1.2.
Tablel.1 Comparison of Common High Performance Thermosetting Polymer Matrices
1 property I Epoxy I Phenolic I Toughened BMI
1 Tensile modulus 3 . 1 - 3 . 8 f 3-5 3 1 ; 3;;;; ( ~ ~ l r n ~ )
Use temperature RT-180 200-250
Density (glcc)
Cure Temperature ("C)
Mould Shrinkage
( mmtmm)
1.5.3 Miscellaneous Thermally Stable Systems
High temperature heterocyclic polymers like acetylene terminated polyphenyl
quinoxaline and polybenzimidazoles are of limited application due to difficulty in
processing. Other themlally stable polymers reported include poly oxazole,
polyphenylene oxide, polythiadiazole, propargyl ether resin etc. However, few have
found commercial acceptance because of their high cost and poor processability.
1.2-1.25
RT - 180
0.0006
TGA onset ('C)
Dielectric constant
1.24-1.32
150-190
~ ~ - ~ ~ - 0.002
260-340
3.8-4.5
300-360 360-400 400-420
1.2-1.3
220-300
0.007
1.1 - 1.35
180-250
0.004
Chapter 1 24
Mast 10 Daircrtrte
8
6
4
2
'Least EAra6lc 0
Emission Strength Tempernlure
Fig. 1.2 Comparison of performance of common matrices used in PMCS'~
The rigid aromatic backbones result in highT,, high melt viscosities and low solubility
and therefore, these are more intractable. Thus, the emphasis in recent years has
been to introduce structural variations that allow improved processibility, solubility, etc.
with no sacrifice of thermal properties.
The reinforcement of the composite plays a major role in determining its strength,
stiffness and dimensional stabilitya4. The different forms of reinforcements are
particles, nano particulates, whiskers, continuous and short fibers and woven
fabricsas. Fibers are the most common type of reinforcement.
1.6.1 Particulates
Particles are used as fillers to improve strength, toughness, processability,
dimensional stability, flame retardance and to lower the cost. Particles are available in
Chapter 1 25
different forms like sphere (glass), cube and block (calcite) and flakes (talc, mica,
wood flour) and the resulting composites are macroscopically isotropic. Whiskers are
single crystals with aspect ratio >I. Typical lengths are in the range 2-50 nm. They
have extra ordinary strength (up to 1000 ksi).
Ceramic whiskers like Sic, A1203, B,C and Si3N4 exhibiting high temperature
capability upto 2000°C. However, the difficulty to collect, sort and distribute them,
together with high costs have limited the application of whiskerss8. The knowledge of
the filler properties such as its size (Surface area, size distribution), shape
(crystallinity, anisotropy) and surface characteristics (roughness, particle aggregation
8 chemical structure) is essential for its effective utilization in the composite material.
The mechanical loss factor can be used to characterize the properties of the
interface region formed in the matrix around each filler particle, as well as the
effectiveness of various coupling agentss7-89. It is also known that the other factors
such as filler particle shape, particle diameter, modulus ratio of filler to polymer, also
have effect on polymer reinforcement.
Choice of the reinforcement for a particular application depends on a large
number of parameters including strength, stiffness, environmental stability, long term
characteristics and cost. At present carbon, glass and aramid fibers account for over
95% of industrial market. The stiffness, strength, and mechanical properties of the
composite along the reinforcement direction are dominated by the properties of the
reinforcements.
1.6.2 Low Density Fillers
Hollow micro spheres have recently evoked a lot of attention as low density
fillers for the fabrication of syntactic foam composites. The syntactic foam composites
have recently attracted lot of attention as low density composites for wide range of
applications go.~yntactic foams are composites consisting of hollow micro spheres
dispersed in resinous matrix so as to have porosity at the microscopic level. Bibin et
Chapter 1 26
als' studied the effect of shell thickness and concentration of hollow glass
microballoon on the physical. thermal and mechanical properties of modified epoxy
and cynate ester syntactic foam composites. This micro porous foam material has got
additional advantages like lesser anisotropy and mechanical property enhancement
including specific strength, shear strength, impact resistance and energy absorptionw.
Their favourable thermal, dielectric and damping characteristics makes these foams
multifunctional, and suitable for applications like bulkheads of ships, submarines,
automotive and personal protection, heat shielding of missiles heads and aerospace
structures. They find application in aerospace and automotive industries where
reduction in energy conservation is one of the important factorso3. Syntactic foams as
core material find application in the construction of sandwich structures.
Sankaran et a t 4 studied the effect of incorporation of small amounts of carbon
nanotubes (CNTs) on microballoon filled epoxy- arnine syntactic foam composites.
The incorporation of small percentage of CNT was found to improve the storage shear
modulus of the system by 50% while in the case of multiwalled carbon nano tube
(MWCNT), the reported increase was 24%. The scanning electron micrograph (SEM)
images indicated that the CNTs tend to occupy the interstitial spaces in the foam
thereby decreasing the void- content. The property improvement in epoxy resin by
nano-silica reinforcement was reported recentlys5.
Continuous fiber composites routinely have strengths 2-3 times greater than
discontinuous fiber composites. The fibers for resin matrix application should have the
highest modulus, lowest density and highest tensile, compressive and interfacial bond
strength between resin and fiber, while still failing in a non-catastrophic mode. The
significantly higher strength of fibers in the longitudinal direction is provided by the
orientation of molecules along the axis during drawing.
1.6.3 Inorganic Fibers
These have been developed with inorganic lattice structures. lnorganic fibers
are extremely strong although inextensible and are intended for ultra high temperature
uses. The inorganic fibers commercially available mainly include glass, boron, silicon
carbide, nitrides and alumina.
1.6.3.1 Glass ~ i b e r s ~ ' ~ ~ '
Glass fibers have been known and used for decades. Different types of glass
fibers like E. S, C and quartz, depending on their chemical composition, are
manufactured. The popularity of glass fibers results from their high tensile strength
and durability, dimensional stability, low dielectric constant and relatively low cost,
making them attractive in automotive, submarines and motor boat applications. Fibers
are usually supplied with a finish or sizing with chrome complexes and silanes for
bener handleability and adhesion to the matrix E glass fibers (Electrical grade) have
relatively high energles to failure, provid~ng their composites with good impact
resistance compared to those of other fibers. The impact resistance of composites
made from S-glass fibers is the highest of all fiber reinforced materialssg. The major
limitation of glass fibers is their relatively low modulus.
1.6.3.2 Boron and Silicon Carbide ~ i b e r s " ~
Boron (B) and silicon carbide (Sic) fibers find selective placement in the high
value aerospace market where cost is often secondary to performance. Both are high
modulus fibers, prepared by chemical vapour deposition process. The current
principal use of B fibers is as reinforcement for Blepoxy composites for high
performance applications, whose property retention at elevated temperatures is
dictated by the epoxy matrix. Boron fibers being too expensive, are replaced by
graphite fibers for commercial use. Sic fibers are also suitable for high temperature
appli~ations'~'es~ecial1y in ceramic matrix
1.6.3.3 Alumina Fibers
Alumina fibers with very high modulus ( 2 . 7 ~ 1 0 ~ MPa) are specialty fibers
introduced by Du Pont. These are used as reinforcements for metal and ceramic
Chapter 1 28
matrices owing to their stability in molten metals, as well as radar transparent nature.
Their strength and modulus are similar to Boron fiber but density is higher by around
10%'02.
1.6.4 Organic ~ibers'"
Organic fibers commonly used as reinforcements include aramids, ultra high
molecular weight polyethylene and carbon. Most of the natural organic fibers- cotton,
jute, sisal - and many synthetic organic fibers with the exception of aromatic
polyamides (aramides), are of little interest for structural applications, because of their
low modulus and modest mechanical properties.
1.6.4.1 Aramide ~ibers"'
Du Pont has developed high strength and high temperature liquid crystalline
fibers based on aromatic amide structures, by the name Kevlar in 1971. Kevlar is
made by solution spinning in three different types, high toughness Kevlar-29, high
modulus Kevlar 49 and ultrahigh modulus ~evlar-149"'. Kevlar - 49 has an axial
modulus (124GPa) in between that of E-glass and high strength graphite and specific
gravity of 1.44. Because of its higher stiffness, this is used more widely. Their
compressive behavior is unique. The onset of compressive non linearity starts at
lower stress I strain value and hence the compressive strength of composites
reinforced with Kevlar-49 fibers is significantly lower than those using other
reinforcements such as glass and graphite. The fiber has got excellent fatigue
resistance and they are strongly anisotropic, with transverse extensional modulus and
shear modulus about an order of magnitude lower than axial extensional modulus.
Due to their good strength and modulus, light weight, toughness and excellent rigidity,
they find key applications in ballistic protection, motorized combat vehicles, tire belts,
high performance pressure vessels and rocket motor cases (hoop stress for filament
wound Kevlar 49lepoxy is 450 ksi'06
Chaoter 1 29
Aramide fiber is an insulator of both electricity and heat, resistant to organic
solvents, fuels, and lubricants. As unprotected fibers, they are highly tenatious and do
not behave in brittle manner as do both glass and carbon. Eventhough they have very
high specific strength and specific modulus, they have inferior compressive properties.
1.6.4 .2 Poly Ethylene ~ibers'"
Polyethylene fibers like Spectra 900 and Himont 1900, with excellent specific
strength and modulus are manufactured respectively by extrusion and gel spinning'08.
These low density fibers have very high molecular weights (3x10~) and approximately
45% crystallinity. The fibers possess abrasion and solvent resistance, high impact
toughness even at cryogenic temperatures and resistance to radiations. But their high
temperature performance is inferior to Kevlar owing to low T, and creep problem'0s.
The major applications are in radomes, ballistic penetration prevention and low
dielectric applications.
1.6.5 Carbon Fibers 'lo
Carbon and graphite fiber technology have made enormous strides in recent
yean in combination with high performance synthetic resin matrices. Carbon fibers
were developed as reinforcements with higher strengths and modulii than glass fibers.
They are used for reinforc~ng composites for critical aerospace applications like re-
entry vehicle structures, rocket motor cases, satellite structures, tanks and pressure
vessels. Today, carbon fibers are among the highest strength and modulus materials
and have become the dominant reinforcement for advanced composites because of
their tailorable mechanical properties, strength retention at extreme high temperature
(in non-oxidising environment) and reasonable cost. The mechanical properties of the
carbon fiber are determined by the type of precursor and the temperature-time profile
of the manufacturing process.
Chapter 1 30
The carbon fiber-reinforced composites are most suitable for cry0
temperature applications. The interlaminar shear strength of carbon fiber composites
improves with lowering of temperature. They have good thermal and electrical
conductivity and these properties do not disappear at the lowest temperature,
because, the contribution by electrons is completely eliminated. These properties offer
promising application in pulsed super conductive electromagnets. The specific
stiffness of carbon fiber composite is 9.7 times that of glass composite"'. Carbon
fibers can be prepared from mesophase pitch '12 (P-100, P-120, P-75), polymers like
polyacrylonitrile (PAN)"' and rayon (T300, T600, T1000) or carbonaceous gases like
acetylene (vGcF)"'. PAN and pitch based fibers comprise 80% of the carbon fiber
market as they are more graphatisable and therefore can attain high thermal
conductivity and low electrical resistivity. The black, thin (5-lomicron dia) man made
fiber embedded in polymer matrix has initiated a "revolution in materials" even they
are reported to be a "Miracle material" having extremely low thermal expansion, better
fatigue resistance and high corrosion resistance. The family of carbon fibers
consisting of high tensile, high modulus and intermediate modulus cover a Youngs
modulus value ranging from 200-700 GNlm2 and strength 2 - 4 GNI~~. The use of
vapor grown carbon fibers in composites is reported to yield unprecedented high
thermal conductivity and caused significant reduction in coefficient of thermal
expansion of the polymer matrixH5.
1.6.5.1 Graphite ~ibers"'
Carbon I graphite fiber is rapidly establishing itself as a top candidate for high
performance applications. It is available in forms that offer high strength, high
modulus, dimensional stability, electrical conductivity, inherent lubricity, excellent
corrosion resistance, heat resistance and low density. Good adhesion between fiber
surface and matrix resin is critical in maximizing properties and minimizing sensitivity
to moisture"'. Many critical products made of epoxies were designed and developed
for launch vehicles viz. ASLV, PSLV, GSLV and INSAT programmes. Since ASLV.
Kevlar-Epoxy has been replacing glass epoxy in many of their applications such as
rocket motor cases, pressure bottles etc. due to 50% of their weight saving.
Graphite fiber sometimes referred to as carbon fiber, comprise one of the
most important classes of reinforcement with enormous potential for future growth.
Their primary advantages over glass fibers are higher modulus, lower density, better
fatigue properties, improved creep rupture resistance and lower coefficient of themlal
expansion '18. Creep at mom temperature is generally considered to be negligible. On
the negative side, because of their low strain to failure ratio, failure energies are
relatively low and hence the impact resistance of graphite fiber composites is low.
Graphite fibers of commercial importance are made from poly acrylonitrile (PAN)
fiberi1', rayon fiber, and petroleum pitchlZ0. The high strength and moduli of graphite
fiber regardless of precursor, result from their high degree of crystallinity and
orientation. Because of their high degree of internal structure orientation, graphite
fibers are strongly anisotropic. Transverse extensional modulus and shear modulus of
most fibers are generally an order of magnitude lower than axial modulus.
1.6.5.2 Carbon ~anotubes '~ '
Since the discovery of carbon nanotubes, having extremely small physical
size (diameter approximately lnm) and many unique mechanical and electrical
properties, they have been appreciated as ideal fibres for nano -composite structures.
Carbon nanotubes (CNT) are long graphine sheets wrapped in different angles (chiral
angles) with different circumferential lengths (chiral vector) depending up on which
they are able to offer wide range of mechanical, electrical and thermal properties.
Based on the number of such sheets, these carbon allotropes may be classified as
single walled nanotube (SWNT) or multy wall nanotube (MWNT). The versatility of
these materials made them attractive candidates for reinforcing polymer matrices. It
has been reported that nanotubes own remarkable mechanical properties with
theoretical Young's modulus and tensile strength as high as 1 TPa and 200 GPa
respectively. Lau et alqZ2 has given a review of the recent researches and appliiatiins
Chapter I 32
of carbon nano tubes. The surface co-valent encapsulation of MWCNT and formation
of various grafted polymers using the same is reported by Liu et allz3 The important
mechanisms of load transfer are micromechanical interlocking, chemical bonding and
Vander Waal bonding between the matrix and the nano tube.
The influence of nanotube / matrix interfacial interaction was evidenced by
Gong et alqz4. It was also reported that coating carbon fiber with Multiwalled carbon
nanotubes prior to their dispersion into an epoxy matrix improves the interfacial load
transfer possibly by the local stiffening of the matrix near the interface '16. Jianyu
~uang"', has demonstrated its stretchability to four times its original length at
2o0o0c.
1.6.6 Hybrid and Speciality Reinforcements 127,128
Hybrid reinforcements are commonly used for improving the properties,
getting some specific properties and / or lowering the cost of conventional composites.
The best properties of each of the reinforcements can be utilized. E.g. carbon fiber is
used in conjunction with ductile fibers like glass or aramid (enhanced failure strain),
PEEK (better drape and toughness), polyethylene fibers (toughness and damping
ability), elastomer particles (toughness), alloy particles and whiskers (wear and fatigue
resistance, increased transverse strength) and coating with niobium carbon nitride
(super conducting fiber)"'. The potential advantage of combining two kinds of fibres in
a single matrix has been described by many re~earchers''~~'. Investigations in the
field of hybrid composites reveal that most of the studies were concentrated on
systems which have been re~nforced with carbon fibers.
Hybrids composites of glass fiber-epoxy laminates and aluminium foil (glare)
are commonly used to obtain hybrid fiber-metal laminates (FMLS), which are
candidates for the next generation structural materials for advanced air craft^"^. The
static mechanical performance and fatigue behavior of the hybrid composites is
dominated by the behavior of the lower strain phase j3', often carbon fibers. The fiber
arrangement is an important parameter in determining the strength of the composite.
Various types of fiber arrangements are possible in hybrid composites'". Additional
possibilities are the use of woven fabrics with one fiber in the warp and another in the
weft and further variations using interspersed tows in woven configurations. Plies
containing different fibers or mixture of fibers may be stacked with the fibers aligned in
different directions to form different combination.
Owing to their unique properties, several fibers like carbon I fluoride, nitrides,
polyether ether ketone (PEEK), poly benzoxazole (PBO), poly benzothiazine (PBT)
are being developed for specific applications. Carbon1 fluoride fibers having good
thermal conductivity and electrical resistivity (100 to 10 - cm) are used as
semiconductors. Boron and silicon nitrides are reported to possess high thermal
shock resistance, low coefficient of thermal expansion and good retention of stiffness
and strength at elevated temperatures. PEEK fibers, developed by melt spinning of
aromatic PEEK are resistant to acid and alkali hydrolysis but susceptible to UV
radiation. Liquid crystalline polyester fibers like Ekonol and Xylar are noted for high
tensile strength and modulus'35.
1.6.7 Woven ~ a b r i c s " ~
Woven fabric composites are characterized by better impact resistance,
damage tolerance, dimentional stability over a large range of temperatures, subtle
conformability and ease of manufacturing. But their in- plane properties are
compromised by using the reinforcement in fabric form. The mechanical behavior of
woven fabric (W.F) composites depends upon the type of weave, fabric geometry. 137-39 fiber volume fraction, laminate configuration and the material system used . The
fiber reinforcing efficiency depends on the percentage of curved fiber length and the
severity of curvature. Two main forms of curvature are Twist and crimp. The fabric
construction determines the reinforcing efficiency, conformability to complex surfaces
(drape), resistance to distortion (stability) and extent of anisotropy. The fabric
geometry should be so chosen that it should give the best possible properties for the
application under consideration. The important fabric parameters are strand cross
Chapter 1 34
sectional geometry, strand fineness, number of counts and the weaving conditions like
balanced or unbalanced.
1.7 ~nterphase'~' The inter phase represents an interfacial region of finite volume between the
fiber and the matrix wherein the material properties vary (either continuously or in a
step-wise manner) between those of the fiber and the matrix material. The properties
of the inter phase are governed largely by the chemical I morphological nature and
physical I thermodynamic compatibility between the two constituents. Hence, a
thorough knowledge of the microstructure - property relationship at the interphase
region is an essential key to the successful and proper use of composite materials.
The importance of inter phase in composite technology has caused ever increasing
research interests in both experimental and micro-mechanical I numerical
characterisation of the inter phase. The optimization of the mechanical properties of
composites is influenced by the behavior of interface / inter phase"'. A great deal of
research has, therefore, been focused on the analysis of interfacial phenomena in
composite materials 14244
The interface is always involved in the failure of the composite, either as an
initiation point or as a locus of failure. Its potential to have large influence on the
composite performance arises from its large area compared to the composite area'".
The complexity of the inter phase can best be illustrated with the use of a schematic
model, which allows many different characteristics of this region to be enumerated as
shown in Fig.l.3. There is now considerable evidence available which demonstrate
the outstanding influence of interfaces on fracture toughness, in both transverse and
inter laminar fractures, strength and stiffness of fiber composites in various failure
modes and loading configurations. The sensitivity of the composite properties to fiber-
matrix adhesion will be governed by, how matrix and fiber are connected and how the
applied load is transferred and distributed in composite.
Chapter 1 3 5
Thermal. chsmlarl. and mecbankal ew~mnments
BUR liber
Fig 1.3 Schematic representation of fiber -matrix Inter phasef4'
In the case of transverse tension, the matrix and fibers are connected through the
fiber- matrix interface in series and all the three components fiber, matrix and
interface1 inter phase carry equal load. In such cases, the fiber -matrix adhesion
should not be expected to have a dominant effect on composite properties'40. A
comparison among the transverse flexural, tensile and short beam shear strength of
composites made of epoxy matrix and three types of carbon fibers is shown in
~ig.1.4a'~'. There is a significant difference between transverse flexural and
transverse tensile strengths. Not only is the transverse flexural strength more
sensitive to fiber matrix adhesion, but it is also significantly higher than the transverse
tensile strength. The mode-l and mode-ll -inter laminar fracture toughness of
composites are shown in Fig.l .4bI4O. The fiber- matrix adhesion in the carbon fiber is
varied by different surface treatments and is in the order AS-4C > A S 4 > AU-4.
Chapter 1 36
Fig-1.4 (a) Effect of fiber-matrix adhesion Fig.l.4 (b) Effect of fiber-matrix adhesion on transverse flexural, tensile and short on the mode I and mode II inter laminar beam shear strength of epoxy- carbon fracture toughness of epoxy- carbon composites composites
A number of experimental techniques have been developed to characterize
the interface1 inter-laminar properties of fiber reinforced ~ o m ~ o s i t e s ' " ~ . These
techniques in general are classified in to (1) testing of single fiber micro composites
and (2) testing of laminates'". The stress distributions in fibers and fiber matrix
interface have also been measured extensively using novel techniques based on
Laser Raman spectroscopy for various combinations of fibers and polymer 150.63 matrices . The fiber I matrix interfacial degradation is generally reflected in short
beam shear (SBS) testsqs4. Surface roughness, surface functional groups and
adhesion at the lnterface are some of the factors influencing the performance of the
inter-phase.
1.7.1 Adhesion at the Interface
In order to get a complete picture of the properties of a composite, intensive
study on the active involvement of interfaces is necessary. Adhesion between the
matrix and fiber (physical, chemical and frictional) should be good for maximum stress
Chapter 1 37
transfer. Higher the resistance to shear, higher will be the stresses that can be applied
to the specimen. Normal and shear stresses are effective at the interface, the latter
arising from residual thermal stresses and difference in Poisson's ratio.
Work of adhesion is expressed as,
where, y is the surface tension and 0 is the contact angle. Matrix also plays an
important role in adhesion. Usually adhesion is stronger in polar polymers like epoxy,
owing to their capability of hydrogen-bonding with the functional groups on
reinforcement surface. Ductility also is important as it provides resistance to crack
propagation.
1.7.2 Theories of Adhesion
The fiber matrix interface adhesion can be attributed to five main
mechanisms. a) Adsorption and wetting b) Interdiffusion c) Electrostatic attraction, d)
Chemical bonding and e) Mechanical adhesion. Schematic representation of Fiber-
matrix interface adhesion is shown in Fig. 1.5.
1.7.3 Fiber Surface and Interface hlodifications'"
The interaction of fiber with a matrix material, depend strongly on the
chemical / molecular features and atomic composition of the fiber surface layers as
well as i b topographical nature. A number of factors affect the microstructure of the
inter phase, which in turn control the mechanical and physical properties of the
composite. They are the topology and the chemical composition of the fiber surface,
silane structure in the treating solution and its organ0 -functionality, acidity, drying
conditions and homogeneity.
Chapter 1 38
Fig 1.5 Schematic representation of Fiber- matrix interface adhesion1"
In recent years a surface technique. Time of Flight Secondary Ion Mass
Spectroscopy (TOF SIMS) in combination with XPS has been extensively used by
Wang et al 16' to observe the chemical reaction in the silane interface region during
cure.
The inter phase material tends to have a lower glass transition temperature,
higher modulus and tensile strength and lower fracture toughness than the bulk
matrix. Since the details of the interface reaction is specific to each cornbination Of
fiber and matrix material, with totally different chemical and atomic compositions and
morphological nature, no general conclusions can be drawn regarding the ductility
and fracture toughness of the inter phase relative to the surrounding matrix. Suzuki et
al '" reported that the interlaminar fracture toughness of the glass fiber composite is
influenced by the type and concentration of the silane solution. A schematic model for
interdiffusion and inter-penetration in a silane treated glass fiber polymer matrix
composite is shown in Fig.l.6.
The interface adhesive behavior can be visualized in to three. i) A sharp
interface with a weak molecular force as in the case of a non-polar polymer with a
polar polymer ii) A sharp interface with a strong molecular force, such as dispersion
force between a nonpolar polymer and a high energy material and iii) Diffuse interface
with any molecular force; if there is sufficient molecular diffusion and entanglement,
interfacial slippage will not occur.
Chemically bonded 8 Diffused interface ---h - --, +----------.
Polymer o coupling agent
Fig.l.6 Schematic model for interdiffusion and IPN i75f silane treated glass fiber polymer matrix composite
The interfacial interaction depends on the physical and chemical structure
and polarity of the components. The interfacial adhesion will be enhanced by
chemically coupling the matrix to the reinforcement. Several processes such as
chemical treatments, photochemical treatments, plasma treatments, surface
grafting etc, have been developed to modify polymers and fiber surfaces. These
cause physical and chemical changes on the surface layer without affecting the
bulk properties. The plasma treatment"', acetylation, benzoylation, acrylation,
permanganate treatment, peroxide treatment e t ~ . ' ~ ' " ~ were found to effectively
enhance the compatibility of fibers with polymers. Tethered chain is also reported to l a 4 5 improve the mechanical properties of polymer blends .
The degree of adhesion between carbon fiber and matrix depends considerably on
the quality and state of carbon fiber surface, wh~ch in turn depend on the internal structure
of graphite (which is highly anisotropic on a nano scale). The techniques used for the
Chapter I 40
characMzaWn of c a m fiber surface like inverse gas chromatography, at infinite and finite
dilution1", surface energy measurement^'^.'" and detefmination of active s k concenb-abn
are discussed in the case of virgin, plasma treated and anodically oxidized PAN and pitch
based carbon fibers. ESCA specboscopy deconvo~ution~~ is suggested to be a very
inkresting way to assess the Oxidation Degree of Spherical CaMn (ODSC) index. This index
expresses the ratio of the surface concentration of more oxidized groups such as carboxylic
acids and esters to less oxidied groups such as alcohols and ketones. The most e w e
surface treatment of carbon fiber- epoxy resin system are reported to be oxidative in natureqm.
Schematic model for the chemical reaction between oxidized carbon fiber surface and epoxy
matrix is given in Scherne.1. These m t s have been mnjunctured to improve the b r -
mabix adhesion primally through increased chemical bonding'" or by enhanced mechanical
interlodting between the fiber and the m a d n .
Scheme.1 Schematic model for the chemical readion between oxidzed carbon fiber surface and epoxy mabixl"
~eviews'" on the surface treatment of carbon fibers show that a range of
active functional groups can be produced by different surface treatment methods,
which can be classified into oxidative and non-oxidative treatments. The oxidative
treatments are further divided in to dry oxidation in presence of gases, plasma etching
and wet oxidation, the last of which is carried out chemically or electrolytically.
Deposition of more active forms of carbon such as the highly effective whiskerization,
plasma polymerization and grafting of polymers are among the non oxidative
treatments of carbon fiber surfaces. The surface treatment of carbon fibers results in
substantial changes in the fiber surface area with associated variation in regocity,
removal of weak surface layer ( the removal being more serious in plasma etching
than in wet oxidation), increase in the polar surface energy and chemical modification
by the formation of carboxyl, hydroxyl and carbonyl groups on the fiber surface.
To improve interfacial interaction and hence compatibility, the in situ reactive
mixing of the two polymeric phases has been shown to be one of the most effective
ways"5. The interaction between component phases may, however, be brought by
addition of an agent that interacts with both the phases, and render them mutually 'I76dl compatible and by specific reaction between the two phases . The occurrence of
reaction between the two polymeric components at the inter phase is expected to lead
to a reduction in interfacial tension. The factors which directly influence the extent of
reaction that happens include the intensity and time of mixing, functionality level,
kinetics of reactive groups, and stability of the covalent bond to the processing
conditions"'. In the future, micro engineering of the fiber-matrix inter phase will be
used to optimize the properties and performance of composite materials
1.7.4 Fiber Surface and Interface ~haracterizatjon'~
Spectral and microscopic methods are mostly resorted to the fiber
surfaces and interface characterization. The characterization gives evidence of
chemical composition of the surface region as well as information on interactions
between fiber and matrix. Electron spectroscopy for chemical analysis (ESCA)"',
Mass spectroscopy. X-ray diffraction, electron induced vibration spectroscopy and
photo acoustic spectroscopy are shown to be successful in polymer surface and 103,184 interfacial interaction chara~terization""'~~. Apart from Infrared spectroscopy ,
frequently used thermodynamic methods such as wettability studies, inverse gas
chronuitography measurement, zeta potential measurement, contact angle
measurement and Neutron activation analysis are used for the characterization of
reinforced polymers.
Chapter 1 42
1.8 Fabrication of ~ornposites'~~ Different processing techniques are used for composite fabrication,
depending on the desired properties, nature and properties of the matrix and shape of
the product. Different manufacturing processes used for the fabrication of the
composite leads to varying amounts of imperfections and air inclusions eventhough all
manufacturing methods aim to avoid entrapment of air or formation of voids since
these represent gross defects.
1.8.1 Thermoset Processing
The impregnation mechanisms and consolidation quality have got profound
influence on the mechanical properties of composites. The main goal of consolidation
is to produce a monolithic structure by inducing intimate contact and adhesion
between individual plies and to minimize void content inside the composite.
Cosolidation is accompanied by applying pressure and heat at the system to squeeze
the air and volatiles out of the composite.
The simplest method of consolidation is manual lay up (wet and pre-preg).
High strength parts with irregular shapes can be manufactured by vacuum bagging.
Application of vacuum assists in compressing the plies, simultaneously removing the
volatiles. Autoclave molding gives better compression and elimination of volatiles as
these are pneumatic pressure vessels with built-in-heatei and blower units. Therefore,
this technique is used for molding complex and critical parts.
The impregnation techniques followed irre generally classified in to pre-
impregnation techniques and post-impregnation techniques. 'The former includes melt
impregnation and solvent aided impregnation and the later constitutes film stacking,
powder coating, co -weaving and hybridization.
Another important technique for fabrication of compositss is filament winding.
This method is suited for manufacture of pressure vessels, rocket motor cases, etc.
Pultrusion method is employed for the production of rods, sheets, tubes, ek. In this,
Chapter 1 43
continuous fibers are passed through a resin bath and then through the heated die so
that the resin cures in the die itself.
Compression molding (matched die molding) is performed under heat and
pressure. Depending on the form in which material is placed inside the mold, preform,
sheet molding (SMC) and batch molding compound (BMC) methods are available to
make complex shapes with good consolidation. Small parts with powder or short fiber
reinforcements are manufactured by transfer molding. Reaction injection molding is
also a fast growing process.
1.8.2 Thermoplastic ProcessinglB6
The processing of thermoplastics is similar to that of thermosets with minor
modifications depending on the matrix and fiber chosen. Instead of curing.
thermoplastics are heated into molten stage and cooled during fabrication. Pultrusion,
matched die molding, injection molding and extrusion are the common methods for
processing of a thermoplastic resin.
1.8.3 Process Monitor ing
Many process monitoring techniques are used to track the chemical reactions
that take place during the processing of composite materials. Variety of techn~ques
such as, differential scanning ca~orimetry'~'"~~, thermal scanning rheometry'",
dielectric spectroscopy'92 Raman spectroscopy'g3and F T I R " ~ ' ~ have been used to
monitor cure reaction of epoxies. Epoxy -amine reaction was reported to follow auto
catalytic mechan i~m '~ ' "~~~
The chemical reactivity and kinetics are controlling factors for the successful
polymerization of composite resin matrix. Since chemical reactivity is related
exponentially to the temperature, the heat-up rate and temperature difference within
the laminate, the knowledge of its chemical kinetics is very important for obtaining
acceptable composites. One of the mechanisms of understanding the chemical
Chapter 1 44
kinetics of a resin system is the experimental determination of its time-temperature-
transformation (TTT) diagram. These diagrams are made by subjecting the resin to
pre determined conditions and measuring the response usually by rheometric
methods. The results are usually plotted as viscosity vs. time for various
temperatures.
1.9 Nano ~ o r n p o s i t e s ~ ~ ~
The goal of nano composite developments in composite industry is to create
new materials that have unprecedented properties due to their small size. Nano-
composite technology has been described as the next great frontier of material
science. Polymer layered nano-composites represent a rational alternative to
conventional filled polymers. The field of polymer nano-composites is stimulating both
fundamental and applied research, because a minimal addition of 40% nano-scale
materials often exhibit physical and chemical properties that are dramatically different
from conventional micro composites. The polymer layered nano-composites can
exhibit increased modulus, decreased thermal expansion coefficient, reduced gas
permeability, increased solvent resistance and increased ionic conductivity compared
to the polymer.
Hackman et a1 studied the basic concepts of nano composites, the physical
and chemical requirements for attaining nanocomposites, the types of property
improvements that have been generated by researchers in this field and nano
composite fabrication techniques viz. conventional filling, intercalation and exfoliation.
The incorporation of nano particles for the modification of fiber- reinforced composites
also yielded high performance compositeszo2.
Wang et a1203 reported the improvement in barrier properties of the nano
composites over the pristine polymer. The nano particle addition was found to give
extensive improvement in mechanical properties for the polymer having sub ambient
T, while modest improvement only was observed in the case of polymers of high T,.
Weiping Liu et a1204 evaluated the performance of organo clay filled high performance
Chapter 1 45
epoxy nano composites and reported an improvement in compressive strength and
fracture toughness (Gi, and K,3 with filler concentration while the T, and yield strength
were found to be reduced.
Epoxy-nano clay composites are being studied extensively by various
researchers which include the studies on filler concentration '05, mixing methods-direct
mixing method (DMM) vs. high pressure mixing method (HPMM) 'O' and types of
smectite clays "'. Subramonian et alZos have obtained improved properties for the
exfoliated nano composites compared to the intercalated nanoclay- glass fiber
composites.
1.10 Fiber Reinforced Composites
The fiber reinforced composites are classified in to three, based on the type of
fiber used viz. chopped, continuous or woven. The fibers are the load carrying
members and the matrix which binds the fibers together, acts as a load transfer
medium and protects the fiber from environmental damages due to elevated
temperature, humidity and damage due to handling. The stiffness, strength and
mechanical properties of the composites along the reinforcement direction are
dominated by the properties of the reinforcement.
The continuous fiber composites are usually subdivided into straight fiber
laminates that have only in-plane fiber orientations and braided or woven textile
composites that have both in-plane and out-of-plane fiber orientations. Straight fiber
laminates are used extensively in aircraft structures. However, the potential for
delamination is a major problem because the interlaminar strength is matrix
dominated. Textile composites that do not have distinct laminae are not susceptible to
delamination, but their strength and stiffness are sacrificed due to fiber curvatures.
Predicting crack propagation in PMC structure is further complicated by the
existence of a multiplicity of design options arising from the availability of numerous
choices of fibers, fiber coatings, fiber orientation patterns, matrix materials, constituent
material combinations, and hybridizations207. The performance of 3D woven
Chapter 1 46
composites was found to far outstrip that of conventional 2D laminates or stitched
laminates in many important regards. Thus, 3D braided fiber reinforced PMCs can be
expected to exhibit similar, superior performance to 2D braided PMC materials.
Further, tow size, strength and distributions in space of geometrical flaws are found to
be key design and manufacturing parameters for controlling performance
characteristics of 3D woven and braided PMCs.
The bidirectional fiber arrangement in a woven composite restricts matrix
shrinkage. The small voids may not significantly affect the mechanical properties but
show considerable effect on diffusion behavior. Moisture absorption is a matrix
dominated propertyzo7. Unlike the neat resin and uni-weave composites, the first stage
diffusion of the woven fabric composite deviate from Fickian diffusion which predicts
the moisture uptake to increase as a linear function of square root time during the
early period208.
Different mechanisms have been suggested to explain the matrix to
reinforcement stress transmission. Klaus Friedrich et alZo9 have given a detailed
picture of different deformation mechanisms in knitted fabric composites. Continuous
fibers bear the maximum applied stress. Assuming a strong fiber-matrix interface, the
tensile Stress applied along the fiber direction will be distributed as
where subscripts c, m and f refer to composite, matrix and fiber and E. V, o and E
represent modulus , volume fraction, stress and strain respectively . In the case of discontinuous fibers, stress transmission depends on the critical
fiber length I,, which depends on the ultimate strength, &of the fiber and its diameter.
Chapter I 47
Where, r = shear strength between matrix and interface.
d = diameter
The critical fiber length, I, is very important since in cases where the fiber
length is shorter than this, the fiber will not be able to reinforce the matrix. For
example the typical I, for carbon I epoxy is 4mm. The properties of the ~0mposite are
affected by several factors like the size, structure and distribution of reinforcement,
matrix morphology and molecular restructuring during processing and residual
stresses that can lead to dewetting2".
The properties of the woven fabric composites are determined by the fabric
material, fiber orientation, stacking sequence, weaving pattern, void content, etc. The
effect of fiber orientation on the work of fracture obtained by notched charpy impact
test of commercial GFRP laminates are shown in Fig.1.7'"
1 2 5 10 20 50 100 200 500 F R a C T U R ENFRGY. k J
unlBlrect~onn1.V 0 . b ~ ( 8 = 0 d e t ~ n e s tlbre sxls) E
A Cl-088 plled, non-woven, V = 0.67 f Woven cloth imrnate, V, - 0 . 4 7
Fig 1.7 Work of fracture of GFRP (by notched charpy impact test)
Chapter 1 48
1.1 1 Characterization of Fiber Reinforced Composites
The composite materials are being extensively used in different areas where
they are subjected to different loading and climatic environments. Hence a thorough
understanding of their thermal, physical, mechanical and dynamic mechanical
properties under different climatic and loading environments is essential for assessing
its suitability for the specific application. The knowledge of their on -axis and off-axis
mechanical properties, fracture properties and behavior under fatigue loading
conditions are essential for their performance prediction. The properties of different
types of composites and the factors influencing their properties were extensively
studied by several authors 212-216
1.11.1 Thermophysical characterisation2"
The thermal properties of a material are characterized by its glass transition
temperature, thermal and thermo oxidatiie resistance. flame resistance, ablative
resistance, coefficient of thermal expansion, thermal decomposition temperature in
nitrogen and air, and char yield. The highly polar groups will increase the inter-
molecular attraction. The stiff and bulky groups in the polymer backbone or sidechains
inhibit the free rotation of the chain segments and increase T, and heat resistance.
1.11.1.1 Thermo Mechanical Analysis
Thermo mechanical analysis (TMA) is useful in determining the softening
point, thermal expansion coefficient and glass transition temperature of materials.
TMA is used in expansion, flexure and penetration modes to determine the glass
transition temperature of the polymers and composites. Since the composite is a
blend of the matrix and reinforcement having different thermal expansion coefficients,
and the mismatch in their expansion coefficients can lead to the failure of the
composite at the interface, the determination of expansion coefficient of composite
and its constituents is of special concern. The coefficient of linear thermal expansion-
a, undergoes a marked change in the T, region and it is determined by the point of
Chapter 1 49
intersection of the lines fit to the expansion data above and below the T, range.
Flexural TMA analysis is sensitive to the modulus of reinforcing fibers in the
composite and this will give different results depending on the nature of the fibe?".
Uniaxially oriented fiber composites have different a values in different directions
which can be computed knowing the volume fractions, a values and Poisons ratios of
the individual component^^'^. In the transverse direction, a can be more than that of
the matrix material because of the fact that the rigid fiber prevents the expansion of
the matrix in the longitudinal direction, so that the matrix is forced to expand in the
transverse direction more in this case2".
1.11.1.2 Thermo Gravimetric Analysis
Thermo gravimetric analysis (TGA) of the polymer matrix gives information on
its thermal stability, char formation, and decomposition kinetics. The preferred method
for determining the short-term thermal stability or thermo oxidative stability of high
temperature polymers has been dynamic TGA. The weight loss in dynamic TGA is
sensitive to experimental variables like heating rate, sample mass and atmosphere.
Long-term stabilities have been most conveniently determined by iso-
thermogravimetric analysis. Thermal stability is primarily determined by the bond
energies between atoms in the chain. High thermal stability in polymers has been
achieved by making full use of resonance stabilization. Cross linking generally results
in improvement in thermal stability.
1.11.1.3 Differential scanning calorimetry
Differential scanning calorimetry (DSC) monitors the enthalpy changes in the
polymeric matrix as a function of temperature. It gives useful informations on its cure
and transition temperatures and enables to define processing window and fabrication
conditions of the composite based on the cure behavior of the resin. Since the heat
capacity of a polymer changes at T,, the differential scanning calorimeter is used to
determine its T,. The temperature corresponding to the base line shifl in heat flow vs
Chapter 1 50
temperature curve gives the To of the system which dictates the performance of the
resin system under different climatic conditions.
1.11.1.4 Dynamic Mechanical Thermal ~ n a l ~ s i s ~ ' ~
Dynamic Mechanical Thermal Analyser (DMTA) is a powerful tool for
determining the glass transition temperature, understanding the cure behavior, and
hence providing the processing conditions for the polymer matrix composite. The
dynamic mechanical properties, especially damping, are sensitive to all kinds of
transitions, relaxation process, structural heterogeneities, and morphology of the
multy phase systems such as composites. Damping is often the most sensitive
indicator of all kinds of molecular motions which are going on in the material. The
DMA is the most common and preferred method of characterizing T, of organic matrix
composites. The DMA technique provides curves of dynamic storage and loss
modulus and loss tangent as a function of temperature and frequency. The tan 6
reflects the amount of energy dissipated during each cycle of loading and goes
through peak values during the To region. The damping properties of the composite
results from the inherent damping properties of the constituents especially that of the
matrix material. It is associated with the movement of small groups and chains of
molecules within the polymer structure. Laurence E Neilson "' has given a detailed
picture of the effect of various parameters like temperature, test frequency, stress /
strain amplitude, thermal history, molecular weight, crosslinking, crystallinity,
crystalline morphology, copolymerization, plasticization, molecular ori@ntation,
strength of intermolecular forces and polymer blending and grafting on the dynamic
mechanical properties of different polymer systems. In polymer mahix composites the
damping characteristics of the polymer is altered by the incorporation of the
reinforcement. The relationship between temperature and frequency for composites
are well explained by Arrhenius relationship. The apparent activation energy H for the
relaxation process at To region is calculated using the following equationm.
Where f is the measuring frequency, f,, the frequency when T approaches infinity T is
the temperature corresponding to the tan 6 peak. The activation energy Of the
composites is less than that of the neat resin. The composite damping property
depend on the inherent damping properties of the constituents. The damping of
composites can be expressed by the rule of mixtures equation2"
tan 6, = V, tan 6, + (14,) tan 6,- (1.5)
Where V, is the volume fraction of fiber and tan$, tan6, and tan& are the damping
values of the composite, matrix and the fiber respectively. In the case of rigid
inclusions the first term can be neglected and the equation becomesz2'
tan 6, = (I - V,) tan 6, (1.6)
Several methods are reported to calculate the T, from DMA data. The temperature.
heating rate and frequency employed will also affect the results. ASTM D - 4065 covers both forced and resonant vibration techniques for DMA analysis. The modulus
in the glassy state is primarly determined by the strength of the intermolecular forces
and the way the polymer chains are packed. The increase in modulii indicates good
adhesion between the matrix and the fiber. The higher value of storage modulus
below T, indicate the reinforcing ability of the matrix in that temperature range.
Equations are available, which enable the calculation of mechanical
properties from the dynamic mechanical properties and vise versazz5.
1.11.2 Mechanical ~haracter isat ion~~'
Chapter 1 52
For structural applications, a material can be designed to maximize its mechanical
properties that are normally defined by tensile, compression and flexural
characteristics under various service environments. All of these three characteristics
are defined by ultimate strength (yield and break strengths), modulus (stiffness) and
extensibility. High cross-link density combined with rigid molecular structure embrittles
a high performance thermoset and can cause early catastrophic failure of the material.
Sankar ~ a 1 1 ~ ~ ' has reported the influence of different types of fibers -glass, carbon,
graphite & aramid- on properties of epoxy unidirectional (UD) composites and also
the influence of matrix type on the high and intermediate modulus graphite fiber
composites. The effect of different types of reinforcements on the stress-strain
properties of the composite was investigated by several authorszz8
The on-axis properties (longitudinal tensile, compressive and flexural
properties) are dominated by fiber properties whereas the off-axis properties
(transverse tensile and flexural, in-plane and inter laminar shear) and inter laminar
fracture toughness are dominated by matrix and interfacial properties. The sensitivity
of the composite properties to fiber matrix adhesion is governed by how the matrix
and fibers are connected and how the applied load is transferred and distributed in the
composite. Laurence T Drzal has explained clearly the interphase and fiber- matrix
adhesion effect on the composite mechanical propertiesz2' The mechanical
properties of the PMCs under all loading environments are temperature dependent.
1.11.2.1 Tensile strength
The tensile properties of the composites depend among other things on the
properties of the individual components, their volume fraction, interface characteristics
and the quality, distribution and orientation of reinforcement. Laurence T ~rzal''' has
given a comparative evaluation of the on-axis and off-axis tensile, compressive and
flexural properties of carbon-epoxy composites without and with different surface
treatments. The fiber/ matrix volume fraction and the testing mode determine whether
the failure is fiber dominated or matrix dominated
The fiber-matrix adhesion does not play a dominant role in the case of
longitudinal tensile behavior. On the other hand, in the case of transverse tension, the
matrix and fibers are connected through the fiber- matrix interface in series and since
all the three components carry equal load, the fiber-matrix interface1 interphase is
expected to have a dominant effect.
Extensive studies were reported indicating the influence of stress directionzH
and constituent volume % on the tensile strength of CFRP I GFRP UD compo~ i tes?~~
1.11.2.2 Compressive Strength
Kink band formation is the most common compression mechanism in graphite
-epoxy composites. With the help of Micro Raman Spectroscopy (MRS) which is
capable of measuring fiber strain with 2 micrometer spatial resolution, Narayan et a12"
could monitor the strain in individual fibers in graphite -epoxy composites and
correlate the inter phase behavior and strain concentration behavior to its kink band
fomlation in compressive failure. Depending on the matrix properties, service
environment and processing, the fiber, matrix or interphase can be the critical factor in
initiating compressive failure
1.11.2.3 Flexural Strength
Flexural properties are generally evaluated by determining the strength and
modulus of the material in flexure mode either by three point bending or by four point
bending method depending on the stiffness of the material. Not only is the transverse
flexural strength more sensitive to changes in fiber- matrix adhesion, it is higher than
the transverse tensile strength. It is reportedzs4 to be due to the non uniformity in
stress distribution in the flexure test.
1.11.2.4 Inter Laminar Shear strengthz3'
The inter-laminar strength (ILSS) characteristics of the composite materials
are generally determined by Short Beam Shear (SBS) test. In the case of short beam
Chapter 1 54
shear test, increase in fiber matrix adhesion increases the ILSS, but levels off or
shows slight decrease with highest level of adhesion. The interlaminar shear strength
(ILSS) has been used for the assessment of bond strength between fiber and matrix
resin in a laminated composites. The differences in the thermal expansion coefficients
of the fiber and matrix and cure shrinkage in thermosetting matrices result in the
development of residual stresses at the fiber 1 matrix i n t e r f a ~ e ~ ~ ' ~ ~ ' . The fiberlmatrix
interfacial degradation may be reflected in such short beam shear (SBS) testszJ8.
Interfacial debonding is expected to introduce the intraiaminar crack initiation for
composite that contains weak fiberlmatrix interface bonds"'. The interlaminar shear
properties are correlatable to many of the composite strength characteristics. Dai Gil
et aiZw correlated the short beam shear properties and impact energy absorption
characteristics of fiber reinforced polymer composites. The ILSS is sensitive to poor
material fabrication practices and damage induced by improper coupon machining
and fiber alignment relative to loading direction.
1.11.2.5 Impact Resistance 243,242
The effective use of polymer matrix composites for high performance
applications demands a thorough understanding of its damage resistance
characteristics. Since the reinforcing fibers- glass, carbon or aramid - have elongation-
to-break values of 3.5 % or less and such fibers constitute significant fraction of the
structural composite, brittle failure will always be the primary mode of mechanical
degradation. The laminated UD composites used for high performance structural
applications are highly susceptible to impact damages because of their lower
transverse tensile strength. Woven fabric composites are characterized by superior
impact resistance and damage tolerance characteristics and higher fracture
toughness.
The damage mechanisms due to an ~mpact involve delamination, matrix
cracking, and fiber breakage. The first two damage modes are purely matrix
dependent. It is now widely accepted that the increase in failure strain or area under
the stress-strain curve of the matrix material could improve the residual strength of the
composite after impact. The composites with tougher matrix have better impact
resistance. This is also related to the interlaminar fracture toughness. G1, and Gllc
which are strain energy release rates to quantify resistance against delamination in
tensile or shear modes respectivelyz4. The impact resistance show systematic
increase with GI, and Gllc.
The techniques used for the evaluation of impact resistance can be classified
in to three categ0ries.i) Drop weight tests ii) Pendulum tests and iii) Ballistic testszu.
Several parameters may affect the impact behavior, including the type of impact test
machine, characteristics of the impactor, velocity and mass of the impactor, and the
specimen configuration. Many of the elastomers245 and thermoplasti~sz~~z47 used to
toughen the epoxy resin have reactive functional groups. Impact tests enable the
determination of important characteristics such as incipient damage, ductile to brittle
transition point, maximum load and total energy absorbed in fracture. It is determined
by the energy absorbed by the specimen at different stages of fracture, the relative
contribution at different stages depending on the size and geometry of the specimenz4
1 .I 1.2.6 Fracture ~ o u ~ h n e s s ' ~ ~
Basic to the evaluation of durability and reliability of the composite is the
analysis of fracture initiation and progression under static or fluctuating thermo-
mechanical loading and fast rate of loading in variable environments. Fracture
initiation is associated with defects such as voids, machining irregularities, stress
concentrating design features, damage from impacts with tools or other objects
resulting in discrete source damage (DSD), and non-uniform material properties. The
toughness evaluation of unidirectional (UD) carbon fiber composites showed that the
stiffness is largely determined by the type of fiber and the fiber content. Raghava et al
2M has given a detailed account of the effect of different toughening mechanisms
/matrix toughening on the impact strength and fracture toughness. He has given the
equations for the energy absorption by fiber, matrix and interphase. A detailed picture
Chapter 1 56
of the effect of curing agents, concentration of reactive functional groups, type and 262,253 extent of elastome?" I thermoplastic/ hard particle modification , strain rate and
test temperatureZY on the fracture toughness of thermosets was also given with
special reference to epoxies. ~ u n s t o n ~ ' ~ examined the effect of toughening of twenty
one matrix resins (thermoset, toughened-thermoset and thermoplastic) on the fracture
energy of the composites and concluded that the increase in resin toughness
enhanced the fracture toughness of their composites.
Important fracture properties are strength and strain-to-failure, fracture
toughness, strain energy release rate, interlaminar fracture energy, fatigue crack
growth resistance and compression-after-impact? The different energy absorbing
mechanisms in the composites are fiber failure- Uf, resin crazing or cracking-U,.
fiber-resin debonding-&, fiber pull out from the matrix across a failure surface-Up,
fiber relaxation and stress distribution to the matrix-U,, multiple fiber fracture- U,,,, and
multiple matrix failure-U,. If all the failure mechanisms occur in one failure situation,
the total energy absorbed (U,) is given by '"
If the interfacial strength is stronger than the matrix strength, the crack will prefer to go
through the weaker resin rather than breaking the stronger fiber and the pnmary
failure mode changes from the intelfacial failure to matrix failure. When the fiber-
matrix adhesion is strong, several energy absorbing phenomena, such as matrix
deformation, matrix cracking, fiber pull out, interfacial failure and so on take place.
The toughness of thermoplastic matrix composite is higher than that of the thermosets
and the property more commonly characterized is the inter-laminar fracture toughness
(G.) obtained using the double cantilever beam test (DCB). Several techniques are
available for evaluating the interlaminar fracture toughness in different modes such as
t ode-lZM. Mode- 11 and mixed modes269.
The low interlaminar fracture toughness of thermosetting matrix composites
has been one of the main limitations to their use in service, due to the ease with which
delamination can initiate and propagate. The matrix properties play a vital role in
controlling the interlaminar fracture resistance of composites. The role of matrix
properties on the toughness of and thermosettingz6' composites has
been reported by several authors. Latest publications on the toughening studies on
the DDScured epoxy (DGEBA)~'~ claims more than 50% increase in fracture energy
for the DDScured epoxy (DGEBA) system using PEEK with pendent ditert- butyl
group. In toughened matrices the type of reinforcement, resin- reinforcement
interaction, ply stacking sequence, fatigue properties, interleaving etc. play significant
role in determining the toughness of the laminate composite.
Hedrick et a12" used phenolic hydroxyl and amine terminated polysulphone
oligomers to toughen epoxy resin. High molecular weight PSF increased fracture
toughness (FT) by 100% without any loss in high temperature propertiesz". Epoxy
modification using several thermoplastics -poly s u ~ ~ h o n e ~ ~ ' , polyetherimide 'B8.267
polycarbonate26s~268. polyester?m'z7', poly ether ether ketonez7z, polymethyl
methacrylate z73 and poly ethylene oxide 274 was tried earlier by several others.
The important mechanisms responsible for enhancement of F.T of
thermoplastic modified epoxies are crack pinning or bowing, crack deflection and
bifurcation, shear banding, and micro cracking. The generally observed toughening
mechanisms in rubber toughened polymers are shown in Fig.l.8. It was reported in
literature that the flexibility of short glass fiber reinforced epoxy resin was improved
with HTPB modification2". Barcia et al reportedz7' that the reinforcement of epoxy
resin using carbon fiber grafted with HTPB,when used to reinforce epoxy resin,
improved the toughness and impact resistance of the composite.
The interphase also plays a significant role and a strong interphase is
required in order to achieve the potential toughness of the polymer matrix. The effect
of temperature and test rate on the fracture toughness has been examined.
Chapter 1 58
The rubber toughening was found to increases the mode-l delamination
energy more than that of mode l l It was found that generally the improvement in
G,, was considerably less than GI1, and hence GI, is not as good an indicator of
impact resistance as GI,,.
Fig.l.8 Toughening mechanisms in rubber toughened polymers. 1) Shear band formation near rubber partides 2) Rubber particle hadure after cavitation 3) Stretching 4) Debonding 5) Crack deflection by hard partide & shearing of rubber pafides 6)Trans particle fracture 7) Debonding of hard oarticles.9) Voided I cavitated Nbber oarticks 10) Crazing 11) Plastic zone at Me crack tip 12) d i s e d shear yielding 13) Shear bandl craze interactionm
The most interesting approach taken towards the toughening of BMI resin is
by the incorporation of a high modulus, high T, thermoplastic to form a semi inter
penetrating net work after cross linking of the BMI resin. ~riedrich"' concluded in his
studies that the reinforcement geometry and matrix ductility are important fracture
toughness considerations..Although various attempts have been made to increase the
toughness by adding a ductile third phase material either dispersed in the matrix or
selectively located at the interphaseZe0,there is still no good format for predicting,
apriori, the toughness of the composite system.
1.11.2.7 Fatigue Resistance 2LH.282
Fatigue is defined as the degradation of the integrity of the material as a result
of external conditions that vary with time. These external conditions can be fluctuating
Chapter 1 59
mechanical stress1 strain, thermally induced cyclic stress or cyclic moisture exposure.
Fatigue resistance is measured to understand its behavior under cyclic loading
environments encountered under certain service conditions. Extensive studies were
carried out on the fatigue resistance of different structural materials"'.
The fatigue life is determined by number of experimental, environmental and
molecular variables. The temperature, pressure and humidity are among the
environmental variables. The test frequency, type of loading -tensile, compressive.
flexure, shear and their combinations -come under the experimental variables while
the surface characteristics of the reinforcement, matrix type and its properties and
inter phase quality come under the molecular characteristics. Fatigue damage in
composite materials is very complex due to several damage mechanisms occurring at
many locations, throughout a laminate. Matrix crack, fiber fracture, longitudinal
cracking, crack coupling and delamination growth are the five major damage
mechanismsz". The S - N culves quantify the relationship between fatigue life and
applied stress amplitude.
Thermo mechanical fatigue (TMF) tests simulate the combined effect of
thermal cycling and mechanical fatigue on advanced materials to ensure that they can
withstand the arduous operating conditions (temperatures of the order of 200O0C,
under hypersonic heating rates and dynamic loading conditions) expected to be
encountered by the various structural components of the space vehicle during the
different phases of ascend, in-orbit manuaring, re-entry and landing phases. The
stiffness reduction during the fatigue of the woven material appeared to have regions
of damage (Fig. 1.9) as described by ~eifsnide?.
From experimental obse~ations, the authors hypothesize that the damage
progressed in the following way. The rapid modulus decay at the beginning of the
fatigue process was caused by the initiation and accumulation of debonds in the weft
and matrix cracks. This behavior is similar to that commonly observed in orthotropic
laminates. However, the woven system behavior differs in that these debonds occur at
Chapter 1 60
each region surrounding a fiber undulation. Matrix cracking and weft debonding were
observed to stop progressing.
Various authors have studied the effect of test frequency on the fatigue of
polymer composites. The fatigue properties of composites have been reviewed by
~ o o r e " ~ and Dickinso et a12" examined the behavior of PEEK composite in
comparison with epoxy matrix composites. The studies confirmed superior fatigue
properties for PEEK in comparison with epoxies. Considerable reduction in fatigue
resistance is reported for [+I- 451 lay up
Fig. 1.9 Damage progression during fatigue lifez6'
1.11.3 Chemical resistance
Depending on the requirement for specific application the composite should
have excellent chemical resistancezsg including resistance to solvent, adjacent
materials, solubility, solvent crazing, and swellability
1.11.4 Dielectric Properties
In addition to mechanical, thermal and chemical properties, the polymer
should resist electric failure under service conditions. The electric storage ability for a
material can be quantitatively expressed by the dielectric constant that may be viewed
as the average energy stored per unit volume per unit electric field strength. The
polymer breakdown under electric potentials can be from three possible mechanisms:
electrical, thermal and electro-mechanical breakdowns2*. High performance
thermosets used for fabricating electronic components should possess good thermal
conductivity, so as to dissipate heat, high electric strength, high surface break down
strength, low dielectric constant, low dielectric dissipation factor, and low water
absorption in addition to the necessary thermal and mechanical properties
1 .I 1.5 Physical properties
Composite physical properties of particular interest to designers and fabrkabrs
include density, fiber volume hctbn and vo!d volume. The fiber vdume fracbn can influence
the slrength chamchish of the composite. The inaease in fiber volume taction was found
to ilxxease the area under the load displacement curve and mused the change in failure
mode from propagationdominated delamination to inMiondominated delaminationm. Many
apphtions require knowledge of hygmthernnal propetties of the composite including thenal
conducliv~Q, thermal expansion and moisture expansion. The water absorption and moisture
expansion of composite materials influence the composite performance to a mnsiderable
extent
1.11.6 Scanning Electron Microscopy
The defects in the laminates like delamination, disbands, porosity or bond
lines, fiber mis-orientation, missing plies, variation in fiber volume fraction, and resin-
rich and resin-starved areas and foreign inclusions determine its performance. SEM
Chapter 1 62
photographs enable the detailed surface and inter-phase characterization of
composites 2s2.
1.11.7 Moisture resistance
Water acts aggressively on polymer - reinforcement bonds and leads to the
movement of the locus of failure from being cohesive in adhesive to pwely interfacial.
The amount of moisture absorbed by the organic matrix depends on the polymer type.
exposure time, component geometry, temperature, relative humidlty and exposure
conditions.
A number of effects results from the ingress of moisture to an adhesive joint
and these include plasticization of the system and disruption of the interfacial region
between the substrate and the organic phase. The moisture uptake characteristics of
the resin are extremely important. The absorption of water lowers T, and produces
changes in matrix and interphase related properties. There are two moisture
properties- moisture diffusivity and equilibrium moisture content. These are
determined by gravimetric methods (ASTM D 5229 1 D 5229M). The rate of moisture
absorption is controlled by moisture diffusivity. It usually follows an Arrhenius type
exponential relation with absolute temperature. It is a function only of temperature and
weakly related to relative humidity. But equilibrium moisture content is weakly related
to temperature and is a function of relative humidity of the environmentzs3.
The hygmthermal effects not only induce moisture expansion or contraction,
but also change properties such as strength, modulus, impact and fatigue resistance.
The absorption rate of the composite can be reduced drastically when diffusivity of the
outer plies is reduced 2e4. In all composites, both the neat resin and composite exhibit
similar two stage diffusion behavior, suggesting moisture diffusion in the composite is
matrix dominated. The initial fast process may be related to the cure induced voids
and the later slow process is due to the intrinsic diffusion in the matrix.
Chapter 1 63
1.12 Advances in Epoxies, Bismaleimides and their co-cured
Systems
A high performance thermoset 285 is designed for use in highly demanding
environments. The ideal high temperature polymeric system for use as a laminating
resin for structural composites should have the following characteristics: easy tape
and pre-preg preparation, good shelf life, acceptable tack and drape, acceptable
quality control procedures, no evolution of volatiles during processing, retention of
mechanical properties over the specific temperature-time ranges and environmental
conditions and acceptable repair. Its performance criteria include processibility,
fabrication procedure and physical properties. Various high performance oligomeric
segments, such as imide, quinoline, quinoxaline, amide, amide- imide, ester,
sulphone, ether- sulphone and ether- ketone have been synthesized from a number of
different monomers to meet the performance requirements. As a result of the
molecular weight reduction, the properties of a high performance thermoset become
significantly dependent on the type of reactive functional groups. The high content of
aromatic and heterocyclic segments in a thermosetting resin reduces the solubility
and increases the melting point and melt viscosity. Hence, poor processibility is a
common concern for high performance thermosetting resins. High melting
temperature causes increase in rate of polymerization at high temperature. A wide
processing window is desired to provide more room for fabrication design and
performance control. A good account of the various thermoset systems have been
given in section 1.5.2 of this chapter.
BMI constitute one class of high performance polymer. The research in the
area of improved BMI resin systems is still ongoing. Among the addition polyimides.
bismaleimides are the most important system currently used for advanced material
applications due to its high performance to cost ratio. Various arylenediamines have
been used for the preparation of BMls to provide high stiffness and heat and thermal
resistance after crosslinking. The properties of the BMI resin vary with synthetic
Chapter 1 64
conditions. The introduction of rigid rings in the structure increases its melting point
and narrows down its processing window which is of concern and unless solution
processing is employed. Lin et alZg6 have given a detailed picture of the different
characterestics of several BMI resins.
The thermally cured bis (4-maleimidophenyl) methane has excellent
mechanical properties and heat resistance. It has got high property retention at
elevated temperatures, good electrical properties-dielectric strength, volume
resistivity, dielectric constant and dissipation factor- and is useful as insulation
material in radiation environments. However, low elongation to failure and poor
toughness are concerns for structural applications. They suffer from high brittleness
due to their high crosslinking densities. Toughness improvement of the cured BMI
resin can provide the required fatigue resistance and prevent the fracture propagation.
Several approaches have been developed to toughen I increase the impact resistance
of the cured BMI resins. Many chemical concepts to modified BMI systems have been
published "'. But only few combine all the desired properties required for use in
advanced fiber composites.
1.12.1 Toughening of Bismaleimides
1.12.1.1 Changing the basic structure
The first approach towards the improvement of toughness and other physical
properties is to change the basic structure of the backbone between two maleimide
end groups. Generally, the aromatic linkages have higher rigidity than the aliphatic
ones. This rigidity normally contributes to high melting point, glass transition
temperature, thermo oxidative resistance, decomposition temperature and modulus of
these polymeric materials. However, the processability and fracture resistance of
aromatic BMI resins are drastically reduced by the increased molecular rigidity. The
introduction of ether linkages to a BMI molecule increases the strength and flexibility
of the cured resin. The undesired effect is the reduction in heat resistance related to
the decreased glass transition temperature. The modification of BMI resins with
Chapter 1 65
aromatic amines has been the most attractive and important approach for practical
use. MIS Technochemie has synthesized poly-phenyl-group functionalised poly-
arylene ether ketone high polymers and could demonstrate that these are excellent
tougheners for BMls.
1.12.1.2 Thermoplastic modification
The most interesting approach taken towards the toughening of BMI resin is
the incorporation of a high modulus, high T, thermoplastic to form a semi
interpenetrating net work after cross linking of the BMI resin. The introduction of
engineering thermoplastic segments between two maleimide groups is an attractive
way to achieve high heat resistance and improved toughness. Poly (arylene ether
sulphones) and Poly (arylene ether ketones) are important industrial high temperature
thermoplastics which possess excellent tensile properties and fractural toughness.
Polybenzimidazole (PBI) is a high temperature thermoplastic polymer with T, of 435 'C
has an excellent chemical resistance and does not melt or bum in air. The addition of
PBI causes very little difference in the thermal and mechanical properties. But it helps
in enhancing the toughness of the system. Polysulphone is reported to provide
excellent improvement in toughness, but reduces heat resistance298.
1.12.1.3 Chain Extensions
Two approaches have been generally adopted to change the performance of
the BMI thermoset- the extension of an oligomer structure between two maleimido
groups and the reaction of a basic BMI resin with modifiers.
Extension by bridging segment: The chain extension between two crosslinking
sites is one of the ways for achieving improved toughness. The increase in molecular
weight between two maleimide groups decreases the crosslink density. This
technique generally provides improvement in toughness and strength but reduces the
T,, modulus and processability.
Extension by Michael addition: The modification of BMI resins with aromatic
amines has been the most attractive and important approach for practical use. The
performance of the cured BMI resin depends on the structure of the BMI resin and the
extender, the ratio of the BMI to the diamine modifier and the curing conditions. Many
diamines have been used to modify the properties of various BMI resins. The diamine
terminated amide resins were used to modify bis (Cmaleimido diphenyl) methane to
lower the crosslinking density and to increase the t o ~ g h n e s s ~ ~ ~ . ~ h e same resin was
chain extended with aliphatic amines300. In general, the onset of curing occurs at a
reduced temperature when the aliphatic amine is used as the chain extender. The
heat of curing also decreases significantly by chain extension.
1.12.1.4 Co polymerisation
The simplest way for polymer modification is the use of two or more
monomers in a thermosetting compound. High performance BMI resins are based on
rigid aromatic structures and thus possess high melting point and a narrow processing
window. An approach using eutectic mixture has been applied to improve the
processibility and performance of the final thermoset. BMI resins are reacted with
other high performance thermosetting compounds such as cyanate ester and
bisbenzocyclobutene (BCB) resins. Mixtures of precursors of BMI resins with cyanate
esters known as BT resins are important commercial products for high performance
thermosets. BCB- BMI mixtures can be cured to high heat resistant thermosets
through a rearrangement and Dlel- Alder reaction at elevated temperatures. A Diels-
Alder co-monomer for BMI is bis (o--propenyl phenoxy) benzophenone available from
MIS Technocheme under the trade name Compimide TM123. The BMll Compimide
TM123 copolymer resin is attractive because of its extremely high temperature
stability. It shows better thermal oxidative stability than all other commercially
available BMI systems.
Chapter 1 67
Of the several approaches reported for BMI matrix toughening, co-reaction
with allyl phenol is now gaining wide spread acceptance3". Alkenylphenyl compounds
are used as co-reactants and toughners for BMI resins. The most effective method
developed so far for the toughness improvement of BMI resin is the incorporation of
alkenylphenyl compounds such as allylphenyl and propenylphenyl derivatives as co-
reactants and toughenersm2. The final crosslinked products provide improved
toughness and heat and thermal resistance due to the formation of cyclic structures
and high crosslinking density through Diels-Elder reaction, addition polymerisation
and ene reaction. A technology using alkenyl phenols or alkenyl phenol ethers to react
with BMls to form processable pre-polymers was developed by Zaire et awl to
improve the toughness and humidity resistance of BMI resins.
Zhongming Li et ato4 reported the synthesis of modified bismaleimido
diphenyl methane (BDM), with high heat and hot I wet resistance and high mechanical
properties by modifying the Bismaleimide resin using diallyl bisphenol A and diallyl p-
phenylene diamine. A copolymer of bismaleimide and a new allyl compound
containing diglycidyl ether of bisphenol A backbone, with improved tack and drape
properties was prepared by Aijuan Gu et a~'~'. Takao luima et a13" modified a three
component bismaleimide resin system composed of 4, 4'-bismaleimido diphenyl
methane (BDM), o, 0'-diallyl bisphenol A (DABA) and o, 0'4iethallyl bisphenol A
(DBA), by blending it with poly(ether ketone ketone)^ like poly(phthaloy1 diphenyl
ether) (PPDE), poly(phthaloy1 diphenyl ether -co - isophthaloyl diphenyl ether)
(PPIDE) and poly(phthaloy1 diphenyl ether-co - terephthaloyl diphenyl ether) (PPTDE).
so that the new system gave an improvement in K,, with no deterioration in flexural
strength and modulus. Co-reactive curing agents act as a monomer in the
polymerization process.
Yehai Yan et developed and characterized a resin system based on
novolac and bismaleimide by curing the allylated novolac resin using BMI and using
allyl phenyl ether as the diluent and the woven fabric composites based on this
system showed very good flexural properties and high retention rates at 200 and
Chapter 1 68
300°C. Kancheng Mai et alM' attempted the stability studies on bismaleimide- o, 0'-
diallyl bisphenol A (BMI-DABA) blends modified using thermoplastic bisphenol A
polysulphone (PSF). Polyether ketone (PEK-C) and polyether sulphone (PES-C) and
found that the stability of the thermoplastic can be ~mproved by the formation of semi-
interpenetrating polymer networks (SIPN). An alkenylphenol compound is reactive in
both maleimide and epoxy resins and a thermoset compound of these three resins
have been developed provid~ng high performance characteristics3? The Michael
addition adduct of BMI resins using excess diamines should produce amino end
groups useful for reacting with other species, such as epoxy resins, unsaturated
olefins and The combination of rigid rod benzimidazole structure. Michael
addition of BMI resin, and BMI- allylphenyl reactions has resulted in the preparation of
molecular composites with simultaneous improvement of tensile strength, modulus
and elongation. No phase separation was observed in these matrix systems3".
Modified epoxies are used in many high performance applications. Dual
photo and thermally initiated cationic polymerisation of epoxy monomers has been
reported by Crivello et.al3I2. These dual cure systems have potential application in
adhesives, potting resins and composites. The flame retardence of epoxy resin can be
improved by incorporating bromine in to the structure, but bromine increases the toxic
smoke emissi~n"~. Fluorine containing bismaleimides find application in multilayer
printed circuit boards. The chemical nature of two fluorine containing bismaleimides
investigated in Hitachi Research institute, ~ a ~ a n ~ ' ~ are given in Structure 6 Tyberg et
alms carried out cure reaction of phenolic resin using epoxies to achieve an improved
void-free system, as strong as epoxy net work, which retain the fire retardance of
phenolicss1s. Gonzalez et a1317 reported the synthesis and propertes of an epoxy
thermoset with reduced shrinkage and thermal degradability with increase in ratio of
the co-monomersdiglycidylether of bisphenol A and 6, 6 dimethyl-(4, 8 dioxaspiro
[2.5] octane- 5.7 dione).
Chapter 1 69
Structure 6 Fluorine contaming bismaleimides
Blending of trifunctional solid epoxy with difunctional liquid epoxy was found to reduce
its viscosity to a level suitable for the pre-pregging operation3".~he dry T, was found
to be lowered from 310 to 3 0 2 ' ~ by the addition of 25 weight % of the difunctional
epoxy when cured using DDS. Blending with epoxy monomer can also be used to
impart good processing quality to more interactable thermosetting resins such as
polyimides or to reduce the intrinsic brittleness of b i s m a l e i m i d e ~ ~ ' ~ ~ ~ ~ ~ . The lower
crosslink density of the epoxy component will result in the lowering of the thermal
performance of the polyimide.
The best known way to alter the properties of an epoxy resin, both in terms of
its cure kinetics and the properties in the cured state, is by changing the nature of the
chemical agent used for its polymerization. at ridge'^' has studied the effect of DDS
and dicy hardner on the chemoviscosity and T, of TGDDM epoxy. A mixture of these
two hardners can also be used so that dicy acts as an accelerator for the DDS cure.
An alternate approach to epoxy cure, which aids the introduction of flexible
crosslinks, is to use an isocyanate compound. This type of cure gives rise to both
chain extension and crosslinking via stiff heterocyclic structures, the oxazolidone and
isocyanurate ring respectively. Nevertheless the epoxy resin cured in this way
combine toughness and high T, values.
A rapid development in the formulated high performance epoxies and
bismaleimides based on the principle of dissolving a high temperature thermopiastic
Chapter 1 70
or rubber additive in the monomer often with the aid of a common solvent. Good
adhesion between the two phases can be obtained by sufficient grafting between the
additive and the monomer. The polymeric modifiers such as functionalized
thermoplastics32z yield sufficient toughness without much deterioration in high
temperature performance.
Novel thermosetting resin with very high T, based on bismaleimide and
allylated Novolac (BMAN) has been reported by Yuan Yao et atz3. BMAN -15 resin
with high allylation degree and low BMI proportion was found to give high
performance composite matrix with high strength and modulus retention at 350%. The
thermosetting resin based on BMI and allyl compounds such as bisphenol A diallyl
ethe?"allylated novolac 3258'2Band allylated xylok showed T,s up to 350%. Diallyl
bisphenol A novolac was cured with BMI to get high temperature resistant matrix
which retained its lap shear strength up to 2 0 0 ~ ~ ~ ~ ~ . Bindu et reported a co-cured
matrix composed of novolacs derived from maleim~do phenol and phenol-allyl phenol.
A dual cure maleimido phenol- epoxy system exhibited excellent thermo-adhesion
profile in contrast to novolac cured epoxy resin329.
Scope and Objective The increasing need of materials for high performance, high temperature
resistant aerospace structural composite applications pose great demand for the
development of speciality thermoset matrix resin systems which can outdo the mast
commonly used epoxy resin in terms of thermal capabilities, toughness and moisture
resistance, and bismaleimide in terms of toughness and mechanical properties.
Epoxy-based laminates largely find applications as aerospace structural components.
The most important property that has made epoxy composite laminate as a competent
aerospace material is its ease of processing, superior heat ageing, lower laminating
pressures, freedom from condensation volatiles, less complicated cure cycles and
superior flexural strength. Epoxy composites find numerous other applications in
marine, construction, tooling, electrical and sports goods. The use of epoxy
composites is increasing rapidly in commercial and military aircrafts, light compact
aircrafts, helicopters, launch vehicles, satellites and spacecrafts. The BMI emerged as
an alternative matrix system with enhanced thermal capability and replaced the
epoxies to some extent in areas where their thermo-mechanical profile is of
advantage. The inherent brittleness of the system, poor impact resistance and high
cure cycles were major concern for their wide spread applications. Blending of BMI
with allylated derivatives could solve these issues to a great extent resulting in the
emergence of commercial products based on BMI and diallyl bisphenol adduct. In
many cases a compromise matrix system, with tailored properties can be derived by
way of blending one or more polymer system to form polymer blends, alloys or lPNs
depending on the physical and chemical interactions among the components and the
resultant morphological features. A control of the parameters can impart desirable
properties to the resultant blends.
This thesis concerns the research efforts to derive a blend of epoxy resin and
bismaleimide. There are limited literature on the blends of epoxies and BMI. Epoxy - phenol systems have been reported as low T,, tough, hydrophobic matrices. Allyl
phenol- BMI systems have a success story as high temperature resistant tough
matrices. It was of interest to derive a combination of epoxy- phenol and allyl phenol-
BMI through a multi reaction ternarysystem constituted by epoxy- allyl phenol- BMI.
The literature survey on matrix resin and composites and presented in chapter 1
reveals that epoxy-allylphenol- BMI systems have been little addressed in open
literature.
The effect of modification of epoxy- phenol system by co- reacting it with
bismaleimide and the evaluation of the influence of BMI concentration on the thermo-
physical, mechanical and rheological properties of the ternary blend and their fabric
reinforced composites form the major objective of the thesis. Another objective of the
study is to examine the performance and properties of the ternary reactive polymer
blend of epoxy- diallyl bisphenol-BMI system with the structural variations of the epoxy
and bismaleimide components. The thesis concerns the properties of the composites
Chapter 1 72
with different reinforcements, fillers, fiber orientation etc. Typical applications of the
ternary matrices have also been explored. The gist of the research work carried out in
this perspective and presented in the thesis is as follows.
The first chapter gives a summary of the literature survey carried out on
polymer matrix composites with special emphasis on matrix resins, reinforcements,
interphase, composite fabrication and characterization. It also throws light on the
recent trends in matrices, reinforcements and composites with special emphasis On
the epoxy- phenol- BMI constituted polymer matrix composites.
The second chapter gives a brief description of the sources and properties of
the materials used for the study, techniques used for their characterisation.
optmisation of the processing condition of the matrix resin and composites, and the
methods used for their performance evaluation.
Prelude to the evaluation of the properties of the ternary system, the
properties of the precursor epoxy- diallyl bisphenol was studied. The third chapter
gives an account of the cure kinetics of-the novolac epoxy- diallyl bisphenol system.
Studies using dynamic DSC experiments revealed the influence of catalyst
concentration on the epoxy- phenol cure reaction, which enabled the selection of
optimum catalyst concentration and cure conditions.
Studies on the mechanical characterization of novolac epoxy- diallyl bisphenol
system are dealt with in chapter four. The effect of varying the molar ratio of epoxy
resin and diallyl bisphenol on their cure behavior, mechanical and thermo-mechanical
properties was investigated. The influence of the extent of allyl group curing on the
properties of the epoxy-phenol matrix system and its glass composite was also
evaluated.
Though the epoxy- diallyl bisphenol system provided a matrix with good
mechanical properties, it was inferior in respect of its high temperature performance.
To address this, the matrix was co- reacted with BMI and the resultant resin was
characterized for its cure behavior, thermal stability and composite properties. Thus.
the fifth cha~ter focuses on the studies on the modification of stoichiometric blend
Chapter 1 73
(1:l) of the epoxy - diallyl bisphenol matrix system by co-reaction with BMI to form an
epoxy-phenolic-bismaleimide (EPB) ternary blend. The effect of BMI concentration on
the rheological, mechanical and thermo-physical properties of the ternary blend was
examined. The system was evaluated at composite level using glass fabric as
reinforcement composites. The matrix composition with optimum concentration of BMI
was chosen for further studies.
The sixth chapter mainly concentrates on the evaluation of the effect of
different types of reinforcements on the performance of the epoxydiallyl bisphenol-
bismaleimide (EPB) composite. Comparative evaluation of the performance of the
fabric reinforced EPB composites with different reinforcements such as glass and
carbon fabrics of different fiber orientations and stacking sequences was carried out
by determining their tensile, compressive, flexural and interfacial I inter-laminar
properties and fracture toughness. Their moisture absorption characteristics,
coefficient of linear expansion, constituent content and surface morphology were also
compared. To iilustrate the utility of the new matrix system in diverse compositions,
other than laminates, the resin was evaluated as a matrix for the processing of
syntactic foam composites. Syntactic foam composites with varying concentrations of
hollow glass microballoon were characterized for their physical, thermal and
mechanical properties and the performance variation of the foam composite with
microballoon type and concentration was examined. The use of blended microballoon
fillers on the properties of the syntactic foam composite was also studied. The utility of
the matrix as high temperature adhesive was also explored.
The influence of the structural variations of both the epoxy resin and
bismaleimide on the thermal, physical and mechanical properties of the ternary blend
was examined and presented in the seventh chapter. EPB compositions were
prepared using bismaleimide, diallyl bisphenol-A and three different epoxy resin
systems viz. Novolac epoxy, LY-556 and Triepoxy, having different physical and
molecular characteristics. The effect of structural variations of BMI resin on the
performance of the EPB system was studied using EPB compositions containing three
Chapter 1 74
different types of bismaleimides in combination with the novolac epoxy and diallyl
bisphenol A. The variation in high temperature performance of these EPB systems
with nature of the bismaleimide was studied by determining their strength retention at
different climatic temperatures.
The overall conclusions from the above studies are summarized in chapter
eight and the prospects for future work is also indicated.
1 .I3 References
1 Autar Kaw, Ed. Introduction to composite materials, CRC Press, Chl. 14 (1 997)
2 D. Hull. T. W. Clyne, An Introduction to Composite Materials, 2"' Ed., Cambridge University Press, Ch.12, 295-308 (1996).
3 P. I. Gonzales, R. J. Young, J. Mater. Sci.,Vol. 33, 5715 (1998).
4 M. P. Thomas, M. R. Winstone, J. Mater. Sci., 32, 5499 (1998).
5 A. Amesh, P. Zugenmaier. Polymer Bullettin, 40, 251 (1998).
6 S. V. Ranade, X. Q. Xie, A. T, Dibenedetto, J. Adhesion, 64, 7 (1997).
7 J. Raghavan, R. P. Wool, J. Appl. Polym. Sci., 71, 775 (7999).
8 The Hindu. Chennai. India. Feb.10 (2000)
9 J. K. Wessel. Handbook of Advanced Materials Enabling new designs, Wiley lnterscience Publications, New Jersy,l-63 (2004).
10 Erich Fitzer, Ed..Carbon fibers and their composites, Springer Verlag, NewYork, 5 (1995).
11 D. Tanner, J. A. Fitzgerald. W. F Knoff, J. Pigliacampi, P.G.Riewald. Proc.lntemational Symp. Fiber Sci. Tech., Hakon, Japan, August (1985).
12 D. Tanner, V. Gabara. J. R. Schaefgen, IUPAC International symp: Polymers for advanced structures- An over view, Ed. M. Levin. VCH Publishers Inc., 384 (1 988).
13 M. J. Robinson, 28Ih lnt. Natl SAMPE Tech. Conf., 530 (1996)
Chapter 1 75
K. Fried rich, R. Reinicke, 2. Zhang, J. Engineering Tribology, 216, 415- 426(2002).
T. J. Reinhart, L. L. Clements, "Introduction to composites" in Engineered
materials Hand book, Vol. 1, 31 (1987).
ASM Hand Book, Material lnformation Society of lndia , ASM International,
Vol. 21, 132 -140 (2001).
Louis A. Pilato. Michael J. Michno, Advanced Composite Materials, Springer Verlag, Ch 2, (1994).
T. E. Attwood, D. A. Burr; T. King, A. B. Newton, Polymer, 18, 359 (1977).
T. E. Attwood, P. C. Dawson, J. L. Freeman, R. L. Hoy. J. B. Rose, P. A. Stanil, Polymer, 22. 1096 (1981).
R. 0 . Carhart. Engineering Thermoplastics - Properties and Application, Ch. 3. Polycarbonate, James M. Margolis Ed., Marcel Dekker, New York, 29 -82 (1985).
R. B. Rigby, Engineering Thermoplastics - Properties and Application, Ch. 9, Polyethenulphone, James M. Margolis Ed., Marcel Dekker, New York. 235 - 254 (1 985).
ASM Hand Book, Material lnformation society of lndia, ASM International, Vol. 21,90 - 96 (2001).
Rhymer. B Rigby. Engineering Thermoplastics - Properties and Application, Ch. 12. Polyether ether ketone, James M. Margolis Ed., Marcel Dekker, New york. 299 - 314 (1985).
I. K. Patridge, Ed., .Advanced composites, Elsevier, 7- 41 (1989).
ASM Hand Book, Material lnformation Society of lndia, ASM International, Vol. 21. 120 -125. 2001
R. Antony, C. K. S. Pillai, J. Appl. Polym. Sci ., 54, 429 - 438 (1994.).
C. G. Schwarzer, Shell Oil Co. US Patent 3.369, 056 Flame Retardent Phenolic Resin Compositions, 2, 13 (1965).
A. Knopp, V. Bohmer. L. A. Pilato. Comprehensive Polym. Science, Synthesis, Characterisation, Reactions and Applications of polymers, Pergamon, New York, ch. 5. 35 (1989).
H. F .Mark, N. M. Bikalas, N. M. Overberger, G. Menges. J. I. Kroschwitz, Eds., Encyclopedia of Polymer Science and Engineering, Wiley, New York, ch.Phenolic Resins.1 I (1988).
C. P. Reghunadhan Nair, R. L. Bindu , K. N. Ninan, Recent Advances in Phenolic resins, Metals, Materials and Processes, Meshap Science Publishers, Mumbai, India, 9, No.2. 179 (1996).
I. K. Patridge (Ed). Advanced composites. Elsevier, 1 (1989)
K. Takeshi, 0. Keiji. I. Shinji. (Sumitomo Bakelite Co)., Japan Kokai Tokkyo Koho, JP. 91, 137151; C.A., 116, 84978, (1992).
A. Matsumoto, U. Akira, H. Kiichi. F. Akihori, Nippon Setchaku Gakkaishi. 29. 504, 1993 C.A..120, 32044 (1994).
M. Juichi. H. Fumitomo, (Sumitomo Bakelite Co).. Japan Kokai Tokkyo Koho, JP. 94, 12845; C.A., 121,158879 (1994).
S. Das, D. C. Prevorsek, B. T. DeBona, Mod. Plast, June, 67, 72, 1990; ibid 216 lnt. SAMPE Technical Conference, Sept, (1989).
ASM Hand Book. Composites. Material Information Society of India. ASM International, Vol. 21, 105 (2001).
J. Shaw, Hand book of Adhesion, Longman Scientific and Technical, England,
228 (1 992).
A. K. St. Clair. T. L. St. Clair, in "Polyimides: Synthesis, Characterisation and
Applications" Proceedings of Technical Conference, Vo1.2, Plenum Press,
New York, 977 (1982).
D. Tanner, V. Gabara J. R. Schaefgen, IUPAC. Int. National Symp.; Polymers for Advanced Structures- An overview, Ed., M. Lewin, VCH Publishers. Inc.. 384 (1988).
D. Tanner, A. K. Dhingra J. J. Pigliacampi, J. Met. 38, 3, 21 (1986).
M. A. Meador, P.J. Cavano. D.C. Malarik, "Structural Composites Design and Processing Technologies". Proc. of Sixth Annual ASM I ESD Advanced Camp. Conf Michigan, USA. Eds. C.F. Johnson and N.G Chavka, 529 (1 990).
Y. Shao. Y. F. Li, X. Zhao. X. L. Wang, T. Ma F. C. Yang, J. Polym. , Sci., Polym. Chem. Part A. 44, 6836-6846 (2006).
Chapter I 77
A. Brent Strong, Fundamentals of Composite Manufacturing: Materials, Methods. and Applications, Pub. Society of Manufacturing Engineers. 529, (1989).
M. E. Rogers, T. M. Moy. Y. J. Kim J. E McGrath. Mat. Res. Soc. Symp. Proc..l3. 264 (1992).
H. D. Stenzenberger, Addition Polyimides, in Adv. Polym. Sci.,Ed. P.M Hergenrother, Springer Verlag, vol. 117, 163 (1994).
J. D Boyd & T. F Biremann. Advanced bismaleimide prepreg for up to 40O0F service. Proc. 31'' Int. SAMPE Symp., Las Vegas, 977-957 - 10 (April 1986).
F. Gmndschober J. Sambeth; U. S Patent; 3380964 (1964)
S. C. Lin I Eli M Pearce, High performance Thermosets Chemistry.
Properties and Applications, Hancer Publishers, New York, 30 (1993)
I. K. Varma, A. Guptha , Sangita, D. S. Varma, J Appl. Polym. Sci.. 28. 191 (1983).
I. K. Varma, A. Gupta , Sangita, Polym. Lett., 20. 621 (1982).
H. D. Stenzenberger, Brit. Polym. J,, 383, 20 (1988).
T. Wagner- Jauregg. Tetrahedron Lett., 13, 1175. (1967)
S. A Zahir, N. A Chaudhari, J. King, Macromol Chem., Macromol Symp 25, 141 (1989).
C. P. Reghunadhan Nair, M. Sunitha, K. Krishnan, K. N Ninan.. Thermochim.
ACta. 374.2. 151- 69 ( 2001).
R. J Morgan, E. Shin, B. Rosenberg, A. Jurek, Polymer, 38, 639 (1997).
Aijuan Gu, J. Appl. Polym. Sci., Vol. 64, John Wiley & Sons, 2, 273
N. Shigeki, S. Yesuhisa , S. Hiroshi (Sumitomo Bakelite Co).. Japan, Kokka;, Koho J P 89 289 821: Chem. Abstr 112, 159870 ( 1990).
D. Reyx, L. Campistron, C. Caillau, M. Villatte , 0.Cavendon. Macromol Chem, 196,775 (1995).
K. Krishnan, T. M. Vijayan, K. N. Ninan, J. Material Sci., 34, 907 (1999)
Chapter 1 78
60 T. T. Serafina, P. Delvigs, G. Lght Sey, J. Appl. Polym. . Sci., ib, 905 (1972).
61 L. A. Pilato, Michael J. Michno, Advanced Composite Materials, Springer Verlag, 25 (1994).
62 W. Gorharn, J. Polym. Sa., PT.A- 1,4, 3027 (1966).
63 M. P. Cava, M. J. Mitchell, Cyclobutadiene and Related Compounds Academic, New York. Chapter 6, (1967).
64 ASM Hand Book, Material lnformation Society of India, ASM International, Vol. 21. 126 - 131 (2001).
65 Bryte. Techon. Inc. 408 1946 - 6477 - No.21, SAMPE J. 29,5 (1993)
66 G. Epstein, S. Ruth, SAMPE, 32,l (1996)
67 K. Sakae, T. Toshiro, K. Ishii, Netsu Kokasei, Jushi, 16, 1 (1995)
68 A. G. Farbenfabriken Bayer, French patentl, 481, 425 (1967)
69 C. B. Delano, A. H. McLeod, NASA-CR - 159724 (1979).
70 S. C. Lin, E. M. Pearce. High Performance Thermosets. Chemistry, Properties
and Application, Hanser, New York, 77 (1993).
71 ASM Hand Book. Material lnformation society of India, ASM International, Vol. 21,78 - 89 (2001).
72 T. H. Ho, C. S. Wang, J. Appl. Polym. SCI ., 74, 1905 (1999).
73 C. H. Lin, J. C. Chiang, C. H. Wang, J. Appl. Polym. Sci., 88, 2607 (2003).
74 M. Kaji, K. Nakahara, K. Ogarni, T. J. Endo, J. Polym. Sci A: Polym. Chern.. 3. 3687 (1999).
75 S. C. Lin / E. M. Pearce "High performance Thermosets Chemistry, Properties
and Applications, Hancer Publishers, New York. 256 (1993).
76 C. S. Wang, M. C. Lee, J. Appl. Polym. SCI., 70, 1907 (1998).
77 A. Hale, C. W. Macosco. J. Appl. Polym. Sci., 38, 1253 -1269 (1989).
78 H. E. Bair. Proceedings of the 21" North American Thermal Analysis Society Conference 13 -16 September, Atlanta, G.A, 60 - 71 (1992).
79 M .Ogata, N. Kinjo, T. Kawata J. Appl. Polym. Sci ., 48: 583 - 601 (1993).
Chapter 1 79
Michael Bauccio, Ed.,Engineered materials Hand Book Volume -1 Composites, ASM International, 438 (1987).
I. K. Patridge, Ed., Advanced composites, Elsevier, I 0 (1989)
Autar K. KAW "Introduction to composite Materials" Ch.lin "Mechanics of composite materials", CRC Press. 24 (1997).
D. Hull, T. W. Clyne, An lntroduction to Composite Materials, 2"6 Ed., Cambridge University Press, NewYork, ch.2, 22 - 27 (1996).
John Murphy, Reinforced plastics Hand Book. Elsevier Advanced Technology,
R. P. Sheldon, Composite Polymeric materials, Applied Science Publishers. NewYork, 8 (1985).
Stuart M. Lee, International Encyclopedia of Composites. VCH Publishers, 3, 247 (1 990).
J. Kubat, M. Rigdhahl , M. Welander, J. Appl. Polym. Sci., 39, 1527 (1990).
88 S. S. Bhagavan, D. K. Tripathy, S. K. Day. J. Appl. Polym. Sci., 34.1581, (1 987).
89 J. Ding, C. Chen , G. Xue, J. Appl. Polym. Sci., 42, 1459 (1991).
90 H. S. Kim, P. Pubrai, Comp. Part A, 35, 1009 (2004)
91 Bipin John, K. Ambika devi, C. P. Reghunadhan Nair, K.N Ninan, Proceeding of ISAMPE lnt. Conf. on Composites INCCOM - IV, 249 - 260 (2005).
92 F. Shutov, Advanced Polym. Sci., 73/74, 63 -123 (1986)
93 S. C. Sharma, Composite Mater.. Narosa publishing house, New Delhi, 19, (1 999).
94 S. Sankaran, S. DasGuptha. K. Ravisekhar. C. Ghosh, Carban nanotube based syntactic composite foams, Proceeding of ISAMPE lnt. Conf. on Composites INCCOM - IV, 82 (2005)
95 Klaus Friedrich, Stoyko Fakirov , Zhong Zhang, Polymer composites from Nano to Macro scale, Ch.6, Springer, 91 -104 (2005).
96 P. K. Mallik, Ed., Composite Engineering Hand Book, Marcel Dekker, New YO&, 61 - 69 (1997).
Chapter 1 80
97 1. K. Patridge, Ed., Advanced composites - Elsevier, 116 - 123 (1989).
98 H. S. Mark, N. M. Bikales, S. Overberger, G. Menges, Encyclopedia of Polym. Sci and Engineering, Wiley lnter Science, znd Ed., 14, 407 (1988).
99 Carl Z weben, H. Thomas Hahn,TSU. Wei Chou, Mechanical behavior and properties of composite Materials, Vol. 1, Technornic Publishing Co. Pennsylvania. USA, 5 - 6 (1989).
100 1. K. Patridge, Ed., Advanced composites, Elsevier, 123 -126 (1989).
101 Brent Strong, Fundamentals of Composite Manufacturing, Materials. Methods and Applications. Pub. Soc. Manuf. Engineers,63 (1989).
102 H. F. Mark, N. M. Bikales. S. Overberger, G. Menges, Encyclopedia of Polym. Sci. and Engineering, Wiley lnter Science. 3, 805 (1985).
103 Michael Bauccio. Ed., Engineered Materials Handbook ASM International. 79 - 81 (1994).
104 Encyclopedia of composite materials and components, Ed. Martin Grayson John Wiley and sons, New York. 97 - 126 (1983).
105. P. G. Riewald, A. K. Dhingra ,T. S. Chem, 6" Int. Conf. on Composite Materials. 2" Eur. Conf. on Composite Mater., Eds.. F. L. Mathews et al, 5, 362 (1987).
106 lvana K. Patridge, Ed., Advanced composites. Elsevier Science Publishers New York, 134 - 137 (1 989).
107 1. K. Patridge. Ed., Advanced composites, Elsevier, New York, 137 - 139, (1989).
108 Stuart. M. Lee, International Encyclopedia of Composites, VCH Publishers. 2, 153 (1990).
109 H. F. Mark, N. M Bikales. S. Overberger. G. Mendes; Encyclopedia of Polym. Science and Engineering, Wiley, lnter Science, 2 Ed., 6, 491 (1986).
110 1. K. Patridge, Ed. Advanced composites, Elsevier, 127 -134 (1989).
111 R. M. Gill, Carbon fibers in Composite Materials, Publishers ILIFFE Books, London, 189 (1 972).
112 L. S. Singer, U.S. Patent4.183 (2005).
113 A. K. Gupta. D. K. Paliwal, Pushpa Bajaj, J. Macromol. Sci.. Rev. Macromol. Chem. & Phys. 31,l. 1 - 89 (1991).
Chapter 1 8 1
Deborah, D. L. Chung, Carbon Fiber Composites, Butterworth -Heinemann. Ch.2, 13 (1994).
Chen, Yu - Mao, Ting, Jyh - Ming, Carbon 40, 3, 359 - 362 (2002).
Autar K. KAW, "lntroduction to composite Materials" Ch.lin "Mechanics of composite materials. 19 (1997).
Leif A. Carlsson, Ed., Thermoplastic compos* materials, vol 7, Composite Materials series. Elsevier. NewYork,lOS (1991).
D. Hull, An lntroduction to Composite Materials, Cambridge University press, New York, 295 - 308 (1985).
M. K. Jain. A. S. Abhiraman, J. Material Sci., 22, 278 ( 1987).
M. Endo, J. Material Sci., 23, 598 (1988).
Bharat Bhushan. "Hand Book Oi Nano Technology" Springer. 39 - 86 (2004).
Lau, Kin -Tak; Hui, David, Composites engineering, Part B, 33, 7, 9263 -27, (2002).
Y. X. Liu, Z. J. Du, Y. LiX.P. Yang, J. Polym. Sci. Part A, Polym. Chem., 44,
6880 - 6887 (2006).
X. Gong, J. Liu, S. Baskaran. R. D .Voise. J. S. Young, Chem. Mater.. 12.
1049 - 1052 (2000).
E. T. Thostenson, W. Z. Li, D. Z. Wang. Z. F. Ren. T. W. Chou Carbon nanotube - carbonfiber hybrid multiscale composites. J Appl. Phys. 91, 6034 - 6037 (2002)
New Scientist. ~an.21" (2006), B Nature, vol. 439, 281 (2005).
Z. S. Wu, C. Q. Yang, Y. H. Tobe, L. P. Ye, T. Harada, J. Composite Materials. 40, 3, 227 - 244 (2006).
Anthony Kelly, Ed., Concise Encyclopedia of composite Materials, CBE Robert Maxwell Publishers, Great Briton.142 - 146 (1989).
A. Brent Strom, Fundamentals of Composite Manufacturing, Materials, Methods and Applications, Ch.3, Pub. Soc. Mfg. Eng. (1989).
J. Summerscales , D. Short, Composites, 9, 3.157 (1978).
A. R. Bunsell , B. Harris, Composites, 5, 4,157 (1978).
Chapter 1 82
132 C. T Lin. P. W. Kao, Materi. Sci., Eng. A, 190,65 (1995).
133 1. K. Patridge (Ed.), Advanced composites, Elsevier, 356 (1989)
134 F. J. Guild. J. Sumrnerscales. Composites, Butterworth - Heinemann Ltd., 24,.5,383 - 393 (1993).
135 Stuart M. Lee, International Encyclopedia of Composites, VCH Publishers. 2,161 (1990).
136 Leif A. Carlsson, Ed.. Thermoplastic composite materials. Composite Materials series, Elsevier, NewYork, 7.182 (1 991).
137 N. K. Naik. V. K. Ganesh. J. Comp. Materials 30,1779 - 1822, (1996).
138 N. K. Naik, Composite Engineering Hand Book, Ed., P.K Mallik, Marcel Decker, New York ch. 6, 249 - 307 (1997).
139 V. K. Ganesh, N. K. Naik, Composite Sci. and Technology, 51, 387-408 (1994).
140 Lawrence T. Drzal, 'Interfaces and lnterphases' in ASM Hand Book Vol. 21, Material lnformation Society of lndia, ASM International, 169 - 179 (2001).
141 L. T. Drzal in Proceedings of lCCl 111 Controlled lnterphases in Composite Materials, edited by H.lshida (Elsevier Science Publishing Co., Cleveland). 309 (1 990).
142 E. Mader, Comp Sci. and Technol, 57, 1077 (1999).
143 D. Upadhyaya , P. J. Tsakiro Poulos, J .Mater, Proc. Technolo, 54, 17, (1995).
144 C. Marieta, E. Schulz , I. Mondragom, Comp. Sci. and Technol 62, 299, (2002).
145 M. J. Greenfield. T. F. Hunter, D. S. Kalika, L. S Penn, J. Composte Materials. Vol. 35. 02,165 (2001).
146 Lawrence T. Drzal 'Interfaces and lnterphases' in ASM Hand Book, Material Information society of lndia. ASM International, Vol. 21, 170 (2001).
147 ASM Hand Book. Material lnformation Society of India, ASM International, Vol. 21, 169 - 179 (2001).
148 J. K. Kim , Y. W. Mai, Materials Science and Technology Series, Vo1.13, ch.6 (T. W. Chou Ed.). V.C.H Publishers, Weinheim, Germany (1993).
Chapter I 83
149 Dale W. Wilson , Leif A. Carlsson "Composite Engineerig Hand Book", P.K Mallik, Ed., Marcel Dekker, New York, 11 13 - 11 18 (1997).
150 Nocholas P. Cheremisinoff, Paul N. Cheremisinoff Ed.. Handbook of Advanced Materials Testing, Marcel Dekker, New York, 367 - 389 (1995).
151 1. C. Galiotis, Compo. Sci. Technol, 43,125 - 150 (1991).
152 H. Jahankhani , C. Glaliotis, J. Compo.Mater., 25,609 - 631 (1991).
152 N. Melanitis, C. Glaliotis, P. L. Tetlow , C. K. L Davis, Interfacial, J. Comp. Materials. 26, 574 - 610 (1992).
153 L. S. Schadler, C. Laird, N. Melanitis, J. C. Galiotis. J. Mater. Sci .. 27. 1663 - 1671 (1992).
154 6. C Ray, J. Mater. Sci., Lett., 22,201 (2003)
155 J. K. Kim & Y. W. Mai, Engineered Interfaces in fiber reinforced composites. Elsevier, 6 (1998).
156 J. K. Kim, Y. W. Mai, Engineered interfaces in Fiber reinforced Composites, ch.5, Pub. Elsevier Science Ltd., UK, 171 - 228 (1998).
157 D. Wang, F. R. Jones, Denison, J. Mater. Sci.,Vol. 27, 36 - 48 (1992).
158 Y. Suzuki, 2.. Mackawa.. H. Hamada, A. Yokoyama, T. Sugihara, J Mater. Sci., 28, 1725 - 1728 (1993).
159 J. K. Kim & Y. W. Mai, Engineered lnterfaces in fiber reinforced composltes. Elsevier, 12 (1998).
160 S. R. Wu, G. S. Sheu , S. S. Shyu, J. Appl. Polym. Sci., 62, 1347 (1996).
161 R. Prasanth Kumar, S. Thomas, Polym. Intemt, 38, 173 (1995).
162 S. I. Moon, J. Jang. J Mater. Sci.. 33, 3419 (1998).
163 C. Plessier. 6. Guptha . A. Chapiro. J. Appl. Polym. Sci.. 69,1343 (1998).
164 S . Thwna, R. Prudhome, Polymer, 33,42604268, (1992)
165 C. Auxhra, R. Stadler, I. Voigt-Martin, Polymer, 34,2081-93 (1993).
166 L. Schub, J Lavielle, , C. J . Mart~n , Adh.. 23,45 (1988).
167 J. B. Donnet, G. Guilpain Carbon , 27,749-757, (1989)
168 J. B. Donnet, M Brendle, S. Dong, J. Phys. Appl. Phys., 20,269 (1987).
Chapter 1 84
169 J. 8. Donnet, G.Guilpain, Composites, 22, 1. 5962, (1991)
170 T. R . King, D. F. Adams ans D. A. Buw, Composites, 22,5,380-387, (1991)
171 J. K. Kim . Y. W. Mai, Engineered interfaces in Fiber reinforced Composites, ch.5. Elsevier Science, UK, 190 (1998).
172 X. X. Fitrer, K. H. Geigl, W. Huttner, R. Weiss, Carbm, 18,389-393 (1980).
173 L. T. Dtzal, M. J. Rich, P. F. J. Lloyed, J. of Adhesion, 16, 1-20 (1982).
174 J. B. Donnet, R. C. Bansal, Carbon Fibers, Marcel Dekker New Yo*. 109-161 (1 984).
175 A. Jalali-arani, A. A. Katbab, H. Nazockdast J. Appl. Polym. Sci., vo1.96, 155- 161 (2005).
176 G. Gurrero, T. Lozano, V. Gonzalez, E. Arroyo, J. of Appl. Polym. Sci, 82, 1382 (2001).
177 J. M Willis, B. D. Favis, C. Lavalle, J. Material Sci., 28.1749 (1993).
178 A. Bhoumic, T. Chiba, T. Inoue, J .Appl. Polym. Sci.. 50, 2055 (1993).
179 J. K. Kim. Y. W. Mai, Engineered interfaces in Fiber reinforced Composites, ch.2. Pub. Elsevier Science Ltd., UK. 5-38 (1998).
180 P. Zadorecki, T. Ronnhult, J. Polym. Sci: part A Polym. Chem.. 24, 737 (1986).
181 X. M. Cherian, P. Sayamoorthy, J. J. Andrew. S. K. Bhattacharya, Macromolecular reports, A 31, 261 (1994).
182 Kh. M. Mannan, Polymer. 34.2485 (1993).
183 M. Nitschke , J. Meichsner, J. Appl. Polym. Sci., 65, 381 (1997).
184 M. A. Khan, K. M. I. Ali , S. C. Basu, J. Appl. Polym. Sci., 49, 1547, (1993).
185 J. A. E. Manson, Advanced Thermoplastic Composites Characterisation and Processing. Ch. 9. Hans-Henning Kausch. Ed.. 282-290 (1993).
186 J. A. E. Manson, Advanced thermoplastic composites Characterisation and processing , Hans-Henning Kausch. Ed.. Hanser Publishers.273-297 (1 993).
187 S. Savier, G. V. Assche, 8. V. Male, J. Appl. Polym. Sci., 91, 2814 (2004)
Chapter 1 85
M. Ivankovic, L.lncarnato, J. M. Kenny, L. Nicolas, J. Appl. Polym. Sci. 90. 3012 (2003).
S. K. Ooi, W. D. Cook, G. P. Simon, C. H. Such, Polym., 41, 3639 (2000)
J. E. K. Schawe. Thermo chirn. Acta, 388.299 (2002).
J. M. Laza. C. A. Julian, E. Larrauri, M. Rodriguez, L. M. Leon. Polymer, 40. 35 (1998).
G. Levitha, A. Livi, P. A. Roollo, C. Culieehi, J. Polyrn. Sci.Part. B, Polym.Phys. 34. 2731 (1996).
E. V. Overbeke. J. Devaux, R. Legras, J. T. Carter, P.T Mc Grail, V. Carlier, Appl. Spectroscopy, 55, 1514 (2001).
J. Mijovic, S. Andjelic, J. M. Kenny, Polyrn. Adv. Technol., 7, 1 (1995)
G. A George, P. C Clarke, N. S. T John, G. Friend J. Appl. Polym. Sci.. 42. 643 (1991).
R. J. Varley, G. R. Heath, H. G. Harithorne, J. H. Hodkin, G. P. Simon, Polymer, 36,1347 (1995).
S. Shen, Y. Li, J. Gao, H. Sun, Int. J. Chem. Kinet., 33, 558 (2001).
V. L. Zvetkov, Polymer, 42, 6687 (2001).
W. G. Kim, J. Y. Lee, Polymer, 43, 5713 (2002),
K. Friedrich, S. Fakirov, 2. Zhang. Polymer composites from Nano to Macro scale, Ch.1, Springer, 3-22 (2005).
I. Hackman, L. Hollaway, Composites, Part A, XX.1-10 (2005).
A. Haque. M. Shamsuzzoha, J. Composite Mater., 37. 20.1827-1837 (2003).
Z. W. J. Massam. T. J Pinnavaia, Polymer clay nano composites, Wiley. NewYork, 127-149 (2000).
W. Liu, S. Vhoa, M. Pugh, Composite Sci. Tech, 65, 307-316 (2005).
A. Subramonian, Q. Biny, D. Nakaima. C. T. Sun. Proceedings of 18th Technical conference Gainsvilla FL, American society for composites Oct.20-22 (2003).
John Hyun Park. Sadan C. Jana. Polymer, 44,2091-2100 (2003).
T, W. Chou, F. K. KO, Textile Structural Composites, Elsevier, 16 (1989).
Chapter 1 86
L. R. Bao, F. A. Yee, Composite Science and Technology, 62, 2118 (2002).
K. Friedrich, S. Fakirov, Z. Zhang, Polymer composites from Nano to Macro scale, Ch.15, Springer, 263-286 (2005).
A. A. Berlin, S. A . Volfson, N. S. Enikolopian, S. S. Negmatov, Principles of Polymer Composites, Springer Verlag, Ch.1 (1986).
Bryan Harris. Engineering composite materials, Indian Institute of metals. Publishers. Ch.4. 69 (1986).
V. Sauvant, J. L. Halary, Compos. Sci. Technol., 62, 783 ( 2000).
A. Todoroki, M. Tanaka, Y. Shimamura, Compos. Sci. Tecfinol., 63, 1911 (2003).
A. B. Pareira, A. B. De Marais, Compos. Sci. Technol., 64, 2261 (2004).
F. Yang, R. Pichumani, Compos. Sci. Technol., 64, 1437 (2004).
A. Todoroki, Y. Tanaka, Y. Shimamura, Compos. Sci. Technol. 64, 749 (2004).
Stuart M. Lee, Ed., Reference Book for Composite Technology, Technomic publishing Co. Pensilvania Vo1.2, 49-80 (1989).
Composite materials Hand Book. Vol. I, Technomic Publising Co, Pensilvania. Ch. 6, 13 (1996).
Laurence E Neilson. Mechanical properties of polymers and composites, Vol.1 Marcel Dekker, New York, 435-436 (1974).
Encyclopedia of Polymer science and Engineering, vol .5, Ed., Mark, Bikales, Overberger, Menges, John Wiley and sons, New York. 299-329 (1986).
L. E Neilson, Mechanical properties of polymers and composites, Vol.1. Marcel Dekker, New York. 139-231 (1974).
M. Ashida. T. Noguchi, S. Mashimo, J. Appl. Polym.Sci.. 30,1011 (1985).
L. E Neilson. Mechanical properties of polymers and composites. Marcel Dekker, Newyork, Vo1.2, Ch.7 (1974).
L. T. Drazal, M. J. Rich, M. F Koenig, P. F. Lloyd, J. Adhes., 16, 133 (1983).
L. E. Neilson, "Mechanical properties of polymers and composites" Marcel Dekker. New York, Vol. I, 157 (1974).
Chapter 1 87
Stuart M. Lee, Ed., "Reference Book for Composite Technology" Vol.1 Technomic publishing Co. Pensilvania, 63 (1989).
Shanker Mall, Laminated polymer matrix composites in Composite Engineering Hand Book, Ed., P.K Mallik, Marcel Dekker, New York. 813 (1997).
Shanker Mall, Laminated polymer matrix composites in Composite Engineering Hand Book. Ed.. P.K Mallik, Marcel Dekker, New York, 817 (1997).
L. T. Drzal, "Interfaces and lnterphases" in ASM Hand Book, Material lnformation society of India, Vol. 21. 169-179 ( 2001).
Bryan Harris, Engineering composite materials, Indian Institute of Metals , ch.3,41 (1986).
R. P Sheldon. Composite polymeric materials, Applied science Publishers UK, 81. (1982).
Carl T. Herakovich, Mechanics of fibrous composites, John Wiley 8, sons, 306 (1998).
S. Narayan, S. Linda. Schadler composite science and Technology, Elsevier Science Ltd, 59, 2201-2213 (1999)
ASM Hand Book, Material lnformation society of lndia, Vol. 21, 177, 2001
Nicholas P. Cheremisinoff, Paul N. Cheremisinoff, Ed., Handbook of Advanced Materials Testing, Marcel Dekker, New York, 367-388 (1995).
Y. Yamashita, K. Nakao, J. Reinforced Plastics and Composites, 18, 862 (1999).
237 N. Mukherjee, P. K. Aditya, J. Reinforced Plastics and composites. 21,1271 (2002).
238 B. C. Ray, J. Mater. Sci., Lett., 22, 201 (2003).
239 B. Z. JANG. Advanced Polymer Composites: Principles and Applications, ASM International, Materials park. OH. 138-205 (1999).
240 D. G. Lee, S. S. Cheon, J. Compos. Mater, Vol. 35, No.1, 27-56 (2001).
241 N. K. Naik, Composite Engineering Hand Book, ch. 16, Ed., P.K Mallik, Marcel Dekker. New York. 847-860 (1997).
Chapter 1 88
K. Friedrich. S. Fakirov , Z. Zhang, Polymer composites from Nano to Macro scale, Springer. Ch.16, 289-306 (2005).
S. Mall, K. T. Yun. N. K. Kochhar, Composite materials: fatigue and fracture, Vo1.2, STP 1012, ASTM Philadelphia, 296-310 (1989).
S. Abrate, Impact of laminated composite materials. Appl. Mech. Rev. 44,155 (1991).
M. L. Arias. P. M. Frontini. R. J. J. Williams, Polymer. 44. 1537 (2000).
S. J. Park, H. C. Kim, J. Polym. Sci., Part 8, Polym. Phys., 39, 121 (2001).
H. Harani, S. Fellahi, M. Baker, J. Appl., Polym. Sci., 71, 29 (1999).
D. C Philips, B. Harris, Engineering Polymer Composites. Ed.. M. Richardson, London, Applied Sci., Ch.2 (1977).
I. K. Patridge, Ed., Advanced composites, Elsevier, Ch.4, 145-160 (1989).
R.S. Raghava, Reference Book for Composite Technology, Stuart M. Lee Ed., Vol. 1, 79-94 (1 989).
D. L. Huston, Composite Tech. Review., Winter, 5, 118 (1983).
J. Spanoudakis, R. J. Young, J. Mater. Sci..l9. 473 (1984).
J. Spanoudakis, R. J. Young, J. Mater. Sci.,l9, 487 (1984).
Leif A. Carlsson. Ed., "Thermoplastic wmposite materials". Composite Material Series, Vol. 7, Elsevier, New York, 268-285 (1991).
D. L Huston, Composite Tech. Review, Winter, 6, 4,176 (1984).
Leif A. Carlsson Ed., "Thermoplastic composite materials, Composite Material Series, Vol. 7, Elsevier, New York, 7, 235 (1991).
S. R. Reid . G. Zhou, Ed., Impact behavior of reinforced composite materials and structures, Woodland publishing Ltd. Cambridge, England, 21 (2000).
Leif A. Carlsson. Ed., Thermoplastic wmposite materials. Composite Material Series, Vol. 7, Elsevier, New York. 258-268 (1991).
Leif A Carlsson Ed., Thermoplastic composite materials, Composite Material Series vol -7, Elsevier, New York. 285-290 (1991).
Leif A Carlsson Ed., Thermoplastic composite materials, Composite Material Series, Vol. 7, Elsevier. New York, 295-327 (1991).
Chapter 1 89
Stuart M. Lee, Ed. Reference bodc for Composite Technology, Technomic Publishing Co., Pennsiivania. US4 79-96 (1989).
Bejoy Francis, Sabu Thomas, R. Ramaswamy, V. Lekshman Rao. Int. J Polymeric Mater, (In Press).
J. L. Hedrick, I .Yilgor, G. L. Wilkes, J. E. Mc Grath, Polym. Bull., 13, 201 (1985).
J. L. Hedrick, M. J. Jurek, I. Yilgor, J. E. Mc Grath, Polym. pre, 26, 293 (1985).
P. Huang, J. Huang , Q. Guo, Polymer, 38, 5565 (1997).
E. G Reydet, H. Sautereau, J. P. Pascault, P. Keats, P. Navard, G. Thollet,
G.Vigier, Polymer, 39, 2269 (1998).
C. C. Su, E. M. Woo, Polymer, 36, 2883 (1995).
E. M. Woo, M. N. Wu, Polymer, 37, 2485 (1996).
M. S. U, C. C. M. Ma, J. Polym. Sci. Part B. Polym. Phys., 35, 2183 (1997).
Y. Yu. J. Mater. Sci 32. 11 (1997).
P. A Oyanguren. P. M Frontini, R. J. J Williams, G. Vigier, J. P Pascault. Polymer, 37, 3079 (1996).
8. Francis. G. V Poel, F. Posada, G. Groeninckx, Y. L Rao, R. Ramaswamy, S.Thomas. Polymer. 44, 3687 (2003).
B. Das, D. Chakraborty, A. K Hajra, S. Sinha, J. Appl.Polym. Sci, 53, 1491 (1994).
2. Sixun, 2. Naibin, L. Xiaolic, M. Dezhu, Polymer, 36, 3609 (1995)
J. K. Kim & Y. W. Mai, Engineered Interfaces in fiber reinforced composites. Elsevier. 12 (1 998).
C. Kaynak, A. Arikan, T. Tineer, Polymer, 44,2433 ( 2004)
F: L Barcia, B. M Soares, M. Gorelov, J. Acid, J. Appl. Polym. Sci., 74,1424 (1 999).
Leif A Catisson Ed. Thermoplastic composite materials. Composite Material Series. Elsevier, New York, Vol. 7, (1991).
K. Friedrich, Compos. Sci. Technol. 22, 43 (1985).
Chapter 1 90
280 J. Chang, J. P. Belland, S. Shkolnik, J. Appl. Polym. Sci. 34, 2105 (1987).
281 1. K. Patridge, Ed., Advanced composites. Ch-10, Fatigue of organic matrix composite materials, Elsevier, 331 -367 (1989).
282 N. K. Naik. Composite Engineering Hand Book, Marcel Decker, New York, ch. 16, Ed. P.K Mallik, 827-847 (1997).
283 T. Car, Herakovich, Mechanics of fibrous composites, John Wiley & sons, 16, (1 998).
284 R. L. Reifsnider. Composite material series, Fatigue of composite Materials vol .4, Elsevier Science Publishing co. New York. 253 (1991).
285 K. L. Reifsnider, K. Schulte, . J. C. Duke 'Long term fatigue behavior of composite materials" ASTM, STP, 813, T.K. 0. Brien, Ed., American Society for Testing and Materials, Philadelphia, 136-159 (1983).
286 D. R. Moor, Thermoplastic composite materials, Ed., L A Calsson 23, 2 (1992).
287 R. F. Dickinson. C. J. Jones, B. Harris, D. C. Leach, & D. R. Moore, J. of Mater. Sci., 20, 60-70 (1985).
288 lvana K. Patridge, Ed.. Advanced Composites. Elsevier, Applied Science New York, 84-86 (1989).
289 Stuart M. Lee, Ed., Reference book for Composite Technology, Technomic publishins Co., Penmilvani USA, 58-63 (1969).
290 S. C. Lin & E. M. Pearce, High Performance Thermosets, Chemistry, Properties and Applications . Hanser Publishers , New York. 9 (1993).
291 D. G. Lee, S. S. Cheon, J. Composite Mater. Vo1.35, No. 1, 27 ( 2001).
292 Nocholas P. Cheremisinoff, Paul N. Cheremisinoff Ed.. Handbook of Advanced Materials Testing. Marcel Dekker, New York, 51-64 (1995).
293 "Guide lines for characterization of structural materials" Vol. .ll, Composite materials Hand Book. Technomic Publishing Co, Pennsylvania, Ch. 6, 13 (2002).
294 L. R. Bao, A. F. Yee, Composite Science and Technology, 62, 2118 (2002).
295 S- C. Lin & E. M. Pearce, High Performance Thermosets, Chemistry,
Properties and Applications, Hanser Publishers, New York. 5 (1993).
Chapter I 91
S. C Lin, E. M. Pearce, High perfomlance, Thermosets, Chemistry. Properties
and Application, Hansr, New York, 18 (1993).
H. Stenzenberger, P. Koning, High perf. Polym., Vol. 5, 123 (1993).
S. C Lin, Eli M. Pearce, High performance Thermosets, chemistry, properties
and application, Hansr, New York,.59 (1993).
I. K. Varma , S. Sharma, Eur. Polym. J., 20,11, 1101 (1984).
I. K . Varma, Angew, Macromol. Chem., 153, 15 (1987).
G. Liang, L. Lan, A. Gu, ACT0 of composites, 12, 1, 1 (1995).
S. C. Lin. Eli M Pearce, H~gh performance Thermosets, chemistry,
properties and application, Hansr, New Yo*, 48 (1993).
A. C. Zahir, A. Renner, U.S Patent,4,100, 140 (1978).
304 Z. Li, M. Yang, R. Huang, M. Zhang, J. Feng, J. Appl. Polym. Sci., 80, 2245- 2250 (2001).
305 Aijuan Gu, J. Appl. Polym. Sci., V. 64, 2, John Wiley &Sons, 273-279 (1997).
306 T. lijima, N. Yuasa. M. Tomai J. Appl. Poly Sci., 82. 2991-3000: (2001).
307 Y. Yan, X. Shi, J. Liu, T. Zhao, J. Appl Polym. Sci.. 83, 1651-1657, (2002).
308 K. Mai. J. Huang, H. Zeng J. Appl. Poly Sci. 66,1965-1970 (1997).
309 R. Schmid, et al., U S Patent 4, 826,927 (1989).
310 S. C. Lin, Eli M Pearce, High performance Thermosets . Chemistry,properties
and application, Hansr. New York. 61 (1993).
311 T. K. Kwei, ACS Polym. Prepr, 32. 3, 339 (1991).
312 J. V. Crivello , U. Bulut, J. Polym. Sci. Part A, Polym. Chem.44, 6750-6764,
(2006).
313 F. Hshieh, H. D. Beeson, Spec. Tech. Publ., STP 126, 7,152 (1995).
314 A. Nagai, A. Takahashi. M. Suzuki , A. Mukoh, Appl. Polym. Sci., Vo1.44, 159
(1 992).
Chapter 1 92
C. S. Tyberg, K . Bergeron. M. Sankarapandian, P. Shih, A. C. Loos, D. A. Dillard J. E. McGrath J. S. Rime, U. Sorathia, Polymer, 41, 5053-5062 (2000).
H. Ghassemi. H. K. Shobha, C. Sensenich. P. Shih, J. S. Rime. J. J. Lesco, J. E. McGrath, Sorathia U, Void free phenolic networks for infra structure Fibre composites in infra structure, vol 1, lCCl (1998).
L. Gonzalez , X. Ramis, J. M. Sallaand A. Mantecon, J. Polym. Sci, Part A,
Polym. Chem., 44,6869-6879 (2006).
"Experimental Tris -epoxy Novolac Resin", Dow Epoxy Resin data sheet XD- 7342 (2002).
E. M. Woo, L. B. Chen, & J. C. Seferis, J. Mater. Sci ., 22, 3665-71 (1987)
T. Gotro. B. K. Appelt & K. I. Papathomas, Polym.Composites, 8, 1, 39-45 (1 987).
I. K. Patridge, Advanced composites. Elsevier Science Publishers., 30-31. (1989).
C. B. Bucknall, I. K. Patridge, Polym. Eng. Sci., 26, 1, 54-62 (1986).
Y. Yao, T. Zhao, Y. Yu, J. Appl. Polym. Sci. 97, 443-448 (2005).
K. A. Barret, M. A. Chandhari, B .H. Lee; SAMPE J., 25, 2, 17 (1989)
B. H. Yan, B. H. Shi, J. G. Liu. T. Zhao, Y Z. Yu. J. Appl. Polym. Sci., 83, 1651 (2002).
Y. Z. Yan. Y. 2. Zhi . Y. Z. Wang. T. Zhao, Y. Z. Yu, J Appl. Polym. Sci. 86, 1265 (2002).
C. Gouri, C. P Reghunadhan Nair, R. Ramaswamy, High performance
polymers. 12. 497 (2000).
R. L. Bindu, C. P. Reghunadhan Nair, K. N. Ninan, Appl. Polym. Sci., 80, 737
(2001).
C. Gouri, C. P Reghunadhan Nair, R. Ramaswamy, Polym. International, 50,
403 (2001).