شفاء/ polymer nano powder

7/27/2019 polymer nano powder /شفاء

http://slidepdf.com/reader/full/-polymer-nano-powder 1/37

1

Introduction

The term composite refers to any multiphase, multicomponent material that

exhibits a significant proportion of the properties of the constituent phases suchthat a better combination of properties is realized. According to this principle of combined actions, better property combinations are obtained by the judiciouscombination of two or more distinct materials. Many composite materials arecomposed of just two phases, one is termed as the matrix, which is continuous andsurrounds the other phase, often called the dispersed phase. Polymer nanocomposites are materials in which nanoscopic inorganic particles, typically10-100 Å in at least one dimension,are dispersed in an organic polymer matrix inorder to dramatically improve the performance properties of the polymer. Polymer

nanocomposites have attracted interest in the last few decades providing scope for improvement of various functional properties, such as mechanical, thermal, optical,rheological, magnetic, and electrical. The improvements in functional properties of

polymers are achieved at very low loading of nanoparticles. While significant work has been done on preparation and properties of polymer nanocomposites, effort isstill needed to the interrelationship between processing, morphology, andfunctional properties of nanocomposites. The properties of nanocomposites areaffected by a large number of factors including microstructural distributions thatare generated during nanocomposite processing as well as the state of nanoparticledistribution in polymer systems. It is believed that understanding of the

relationship between processing, morphology and functional properties of nanocomposites will be very helpful in optimizing the ultimate properties of nanocomposites as well as improving the models for predicting properties of nanocomposite systems.applications in daily life due to their unique attributes such as ease of production,light weight and often ductile nature. However, polymers have lower modulus andstrength as compared to metals and ceramics and hence had restricted applications.In order to improve their mechanical properties, polymers were reinforced withinclusions (fibers, whiskers, platelets, or particles), known as fillers. This addition

of fillers into the polymer matrix to make composites was expected to result inmaterial properties (mechanic, thermal stability and expansion, fire retardant,electrical and barrier properties) not achieved by either phase alone, and oftenlower cost. This practice improved polymer properties while maintaining their lightweight and ductile nature; hence, the addition of fillers to polymers gained a lot of importance over the years. Nowadays, nanocomposites offer new technology and



2

business opportunities for all sectors of industry, in addition to beingenvironmental- friendly.



3

Classification of Nano composites

Polymeric nanocomposites can be broadly classified as:-

Nanoclay-reinforced composites Carbon nanotube-reinforced composites

Nanofibre-reinforced composites, and Inorganic particle-reinforced composites.

Nanoclay-reinforced Composites

Historically, the term clay has been understood to be made of small inorganic particles(part of soil fraction < 2 mm), without any definite composition or crystallinity. The claymineral (also called a phyllosilicate) is usually of a layered type and a fraction of

hydrous, magnesium, or aluminum silicates . Every clay mineral contains two types ofsheets, tetrahedral (T) and octahedral (O). Hectorite, saponite, and montmorillonite arethe most commonly used smectite type layered silicates for the preparation ofnanocomposites. Montmorillonite (MMT) has the widest acceptability for use in

polymers because of their high surface area, and surface reactivity. It is a hydrousaluminosilicate clay mineral with a 2:1 expanding layered crystal structure, withaluminum octahedron sandwiched between two layers of silicon tetrahedron. Eachlayered sheet is approximately 1 nm thick (10 Å), the lateral dimensions of these layersmay vary from 30 nm to several microns or larger, depending on the particular layered

silicate. The aspect ratio is about 10-1000 and the surface area is in the range6 of 750m2/g. When one octahedral sheet is bonded to one tetrahedral sheet, a 1:1 clay mineraresults. The 2:1 clays are formed when two tetrahedral sheets bond with one octahedralsheet. The aspect ratio of 1000 is possible when a clay platelet is well-dispersed into the

polymeric matrix without breaking. Practically, breaking up of clay platelets duringmixing process at high shear and large shear stress condition results in an aspect ratio of30-300.

Graphite has a similar geometry (layered structure) with nanoclay, therefore a clay- polymer reinforcement concept is applicable. Graphite flakes have been known as host

materials for intercalated compounds. By applying rapid heating, some of the graphite-intercalated compounds (GICs) expand and a significant increase in volume takes place.Many literature citations identify the expanded graphite flakes with polymer systems forlightweight and conductive polymer composites. In polymer-layered silicate (PLS)nanocomposites, stacking of the layers leads to a regular van der Waals gap between thelayers called the interlayer or gallery. Isomeric substitution (for example tetrahedral Si 4+

by Al3+ or octahedral Al3+ by Mg2+ or Fe2+) within the layers generates negative charges



4

that are counterbalanced by alkali and alkaline earth cations (typically Na + or Ca2+)situated inside the galleries. This type of layered silicate is characterised by a moderatesurface charge known as the cation exchange capacity (CEC). Details regarding thestructures and chemical formulae of the layered silicates are provided in Fig. “1”. Ingeneral, the organically modified silicate nanolayers are referred to as nanoclays ororganosilicates.

Figer”1” Basic structure of 2:1 clay minerals

It is important to know that the physical mixture of a polymer and layered silicate may

not form nanocomposites. Pristine-layered silicates usually contain hydrated Na+

or K +

ions. To render layered silicates miscible with other polymer matrices, it is required toconvert the normally hydrophilic silicate surface to an organophilic one, which can becarried out by ion-exchange reactions with cationic surfactants. Sodium montmorillonite(Nax(Al2-xMgx)(Si4O10)(OH)2 .H2O) type layered silicate clays are available as micronsize tactoids, which consist of several hundreds of individual plate-like structures withdimensions of 1 micrometer * 1 micrometer * 1 nm. These are held together byelectrostatic forces (gap in between two adjacent particles ~ 0.3 nm). The MMT particles,which are not separated, are often referred to as tactoids. The most difficult task is to

breakdown the tactoids to the scale of individual particles in the dispersion process toform true nanocomposites, which has been a critical issue in current research in differentliteratures.

Properties and Applications of Nanoclay-reinforced Composites

Theoretical predictions have shown that the modulus for well aligned platelets can bethree times that for wellaligned fibres, especially as the aspect ratio of clay layers



5

increases. Other studies however, suggest that the modulus increase is not entirely due tothe load-carrying ability of the platelets, but is caused by the volume of polymerconstrained by the platelets. This suggests that to optimize the increase in modulus, thedegree of dispersion must be optimised to maximise the degree of matrix/fillerinteraction. Work on PP nanocomposites in which adding malefic anhydride (MA) to thematrix changed the degree of filler dispersion supports this suggestion that despite the

plasticising effect of MA, the modulus improved due to enhanced dispersion of the clay.Lan and Pinnavaia found that, .as the degree of exfoliation increased by changing the

length of alkylammonium intercalating chain, the modulus and strength improved.As the polymer intercalates and swells, the layers and the area of interaction between the

polymer and the filler increases and the modulus increases significantly. Figure “2”represents three main types of composites for layered silicate materials.

Figure “2”. Scheme of three main types of layered silicates in polymer matrix

The polymer/clay interaction plays a significant role in controlling mechanical behavioris also evident from the fact that improvement in properties tends to be higher above theglass transition temperature than below it. However, proper dispersion is critical forachieving this. Hasegawa, et al. studied the dispersion of clays in polypropylene. Theyfound that the strain-to-failure ratio in nanocomposites remains high (>200 per cent) evenat reinforcement loadings of 3per cent. But even a small amount of aggregation decreasedthe strain-to-failure ratio to 5 per cent-8 per cent. A similar effect was also observed in

Phase separated



6

polyimide matrices, in which the strain-to-failure ratio decreases by 72 per cent due toaggregation.Xu68, et al.have reported similar improvements in tensile strength and impact strength ofthe composites with a nanoclay addition of 10 per cent to 15 per cent. Unprecedentedcombinations of properties have been observed in some thermoplastics too. The inclusionof equi-axed nanoparticles in semicrystalline thermoplastics has resulted in increase inyield stress, the tensile strength, and Young.s modulus of the polymers. A volumefraction of only 0.04 mica-type silicates (MTS) in epoxy increases the modulus below theglass transition temperature by 58 per cent and the modulus in the rubbery region by 450

per cent. In addition, the permeability of water in poly (å-caprolactone) decreases by anorder of magnitude with the addition of 4.8 per cent silicate by volume. Yuno, et al.showed a 50 per cent decrease in the permeability of polyimides at a 2 per cent loading ofMTS. Many of these nanocomposites are optically transparent and/or optically active.

Carbon Nanofiber-reinforced Composites

Carbon nanotubes are graphitic sheets rolled into seamless tubes (i.e., arrangements ofcarbon hexagons into tube-like fullerenes) and have diameters ranging from about ananometer to tens of nanometers with lengths up to centimeters. Nanotubes have receivedmuch attention due to their interesting properties (high modulus and electrical/thermalconductivity) since their discovery by Iijima in 1991. Since then, significant effort has

been made to incorporate nanotubes into conventional materials (such as polymers) forimproved strength and conductivity. Moreover, many potential applications have been

proposed for carbon nanotubes, including conductive and high-strength compositesenergy storage and energy conversion devices; sensors; field emission displays andradiation sources; hydrogen storage media and nanometer-sized semiconductor devices;

probes and interconnects.

Classifications of Carbon nanotubes.

Carbon nanotubes can be grouped as single-wall (SWNT), multiwall (MWNT), and thenewly established small-diameter (SDNT) material, based on the number of walls presentin the carbon nanotubes, as illustrated in Fig. “3”. By definition, SWNTs are single

walled carbon nanotubes about 1 nm in diameter with micrometer-scale lengths; MWNTsare multiwalled carbon nanotubes with an inner diameter of about 2 to 10 nm, an outerdiameter of 20 to 70 nm, and a length of about 50 (micrometer; and SDNTs havediameters of less than 3.5 nm and have lengths from several hundred nanometers toseveral micrometers. These SDNTs generally have one to three walls.



7

Figure “3” Definition of single- and multiwall carbon nanotubes.

Figure” 4”. Schematic of a: (a) single-wall and (b) multiwall nanotube.

The packing of the carbon hexagons in the graphitic sheets defines a chiral vector (m, n)and angle. The indices of the vector determine the morphology of the nanotubeVariations in the nanotube morphology can lead to changes in the properties of thenanotube. When m_n/3 is an integer, the resulting structure is metallic; otherwise, it is asemiconducting nanotube For instance, the electronic properties of an armchair nanotubeare metallic; however, the electronic properties of zigzag and chiral nanotubes aresemiconducting.



8

Figure “5”. Schematic of nanotube morphologies. (a) Armchair, (b) zig-zag, and (c)

chiral.

The behavior is determined based on a mathematical model developed using the chiralvector indices. All arm-chair and one-third of zig-zag nanotubes are metallic having acontinuous conduction band. The remaining two-thirds of the zig-zag nanotubes aresemiconductors, having an energy gap in the conduction band

Properties and Applications Carbon nanofibers

Properties of carbon nanotubes have been studied extensively. Carbon nanotubes areexcellent candidates for stiff and robust structures, because the carbon-carbon bond in thegraphite is one of the strongest in nature. Transmission electron microscopy data revealedthat carbon nanotubes are flexible and do not break upon bending. Thermal conductivityof carbon nanotubes can be extremely high, and the thermal conductivity of individualcarbon nanotubes was found to several years because of their unique potential uses forstructural, electrical, and mechanical properties. Nanotubes have high Young's modulusand tensile strength, and they can be metallic, semiconducting, or semimetallicdepending on the helicity and diameter

Synthesis of Carbon nanofibers

The three main methods of manufacturing nanotubes include direct-current arc dischargelaser ablation, and chemical vapor deposition (CVD). A thorough discussion on each ofthese production methods can be found in the April 2004 MRS Bulletin . Direct-arcdischarge and laser ablation were the first techniques used to produce gram quantities ofSWNTs. In both methods, the evaporation of solid carbon is used to condense carbon gas



9

The products of such methods are normally tangled and poorly oriented. The CVD produces nanotubes from the decomposition of a continuously supplied carbon containinggas onto a substrate. Due to the continuous supply of the gas, high-purity nanotubes can

be produced on a larger (or industrial) volume scale. Producing the nanotubes in anordered array with controlled length and diameter can also be achieved via CVDmethods. Furthermore, plasma enhanced chemical vapor deposition (PECVD) results infurther nanotube uniformity within the array. Carbon nanotubes have a wide spectrum of

potential applications. Examples:- include use in catalysis, storage of hydrogen and othergases, biological cell electrodes, quantum resistors, nanoscale electronic and mechanicaldevices, electron field emission tips, scanning probe tips, flow sensors, andnanocomposites. Single-walled nanotubes It offer incredible opportunities in electrical

properties, mechanical properties, thermal properties, and field emission, as shown below:• Electrical properties.

Electrically conductive composites for electrostatic dissipation, shield, and conductivesealants; energy storage for super capacitors and fuel cells; electronic materials anddevices for conductive inks and adhesives; electronic packaging; device and microcircuitcomponents.• Mechanical properties.High-performance composites; coatings for wear-resistance and low friction; high

performance fibers; reinforced ceramic composites• Thermal properties. Thermally conductive polymer composites; thermally conductive

paints and coatings• Field emission. Flat-panel displays; electron device cathodes and lighting



10

Figure “6” SWNTs are the perfect material with unique and extraordinary

properties.



11

Small-diameter carbon nanotubes (SDNTs).

Small-diameter carbon nanotubes are linear polymers of pure carbon with diameters lessthan 3.5 nm and lengths from several hundred nanometers to several micrometers. Smalldiameter carbon nanotubes are more cost-effective and affordable than SWNTs. TheseSDNTs generally have one to three walls. Like Bucky tubes, SDNTs are molecules, not

particles or structures like their larger multiwall or vapor-grown carbon fiber relatives, soaccordingly, they have a high degree of molecular perfection. It is this high degree ofmolecular perfection that provides SDNTs with their amazing properties. Small-diametercarbon nanotubes are the strongest, stiffest, toughest molecules available. They have theelectrical conductivity of copper and various band-gap semiconductors depending upontheir diameter and chirality, which allows them to compete with metals as well as withsilicon and other semiconductors. They are the most conductive of the inherentlyconducting polymers. Small-diameter carbon nanotubes are also the best knownconductor of thermal energy along their length, and their thermal stability in air of up to550 or 1400°C in anaerobic conditions makes them the most thermally stable polymerknown.



12

Multiwall carbon nanotubes.

Multiwall carbon nanotubes have an interior diameter of 2 to 10 nm, an exterior diameterof 20 to 75 nm, and a length of 50 micrometer, as shown in Fig. 2.29. Multiwall carbonnanotubes are produced by CVD synthesis of xylene-ferrocene composition at arelatively low temperature of 725°C, and with high purity > 95 percent xylene (Fig.2.30). Multiwall carbon nanotubes are nanoscale carbon fibers with a high degree of

graphitization. Multiwall carbon nanotubes are technically neither fullerenes normolecular. They are attractive materials intermediate between SWNT and CNF with properties vastly superior to graphite and carbon black (Figs.” 7” and “8”).



13

Figure” 7” Microstructures of MWNTs in cartoon and TEM micrographs.



14

Fig”8” Microstructures of MWNTs in cartoon and TEM micrographs. Inorganic Particle -reinforced Composites

Nanoparticles are often defined as particles of < 100 nm in diameter. Nanometer-sized particles have been made from different organic.inorganic particles and these impartimproved properties to composite materials Different particles have been used to prepare

polymer/inorganic particle nanocomposites, including:

Metals (Al, Fe, Au, Ag, etc.) Metal oxides (ZnO, Al2O3, CaCO3, TiO2, etc.) Nonmetal oxide (SiO2)52 Other (SiC)

The selection of nanoparticles depends on the desired thermal, mechanical, and electrical properties of the nanocomposites. For example, Al nanoparticles are often selected due totheir high conductivity; calcium carbonate (CaCO3) particles are chosen because of theirlow cost and silicon carbide (SiC) nanoparticles are used because of their high hardness,corrosion resistance, and strength.

Properties and Applications Inorganic Particle-reinforced Composites

Polymer/inorganic particle-based nanocomposites have shown significant improvement

in mechanical, thermal, and electrical properties. For example, in nylon-6 filled with 5Wt % 50 nm silica nanoparticles, an increase in tensile strength by 15 per cent, strain-to-failure by 150 per cent, Young.s modulus by 23 per cent and impact strength by 78 percent. Jiang, et al. investigated ABS (acrylonitrile butadiene styrene) reinforced with bothmicrosized and nanosized calcium carbonate particles through melt compounding. It wasfound that the ABS/micron-sized particle composites had higher Young.s modulus butlower tensile and impact strengths than neat ABS. However, the ABS/nano-sized particlecomposites increased the Young.s modulus as well as impact strength. Ma, et al. showedan improvement in electrical properties of polyethylene nanocomposite by introducingfunctional groups at TiO2 nanoparticles. Zhang and Singh improved the fracture

toughness of nominally brittle polyester resin systems by incorporating Al 2O3 (15 nm)An Al2O3 particle has been found to be effective in improving the dielectric constant of a

polymer in other studies also. Koo, et al. used AEROSIL (silicon dioxide, 7.40 nm) silicananoparticles to process different nanocomposites with different resin systems (phenolic,epoxy, cyanate ester) for high-temperature applications. Recently, creep tests were

performed on TiO2/PA6,6 nanocomposites by Zhang and Yang. Poor creep resistanceand dimensional stability have been improved by adding TiO2 in polyamide 6,6



15

thermoplastic composites. Chisholm, et al. investigated micro- and nano-sized SiC in anepoxy matrix system. In their study, an equal amount of loading, nanoparticle infusion

bringssuperior thermal and mechanical properties than microsized particle-basedcomposites.

Different Types of Nanoparticles.

There are different types of commercially available nanoparticles that can beincorporated into the polymer matrix to form polymer nanocom posites. Depending onthe application, the researcher must determine the type of nanoparticle needed to providethe desired effect.The most commonly used nanoparticles in the polymer nanocomposite.• Montmorillonite organoclays (MMT) • Carbon nanofibers (CNFs) • Polyhedral oligomeric silsesquioxane (POSS)

• Carbon nanotubes [multiwall (MWNTs), small-diameter (SDNTs), and single-wall(SWNTs)]• Nanosilica (N-silica)• Nanoaluminum oxide (A1203)• Nanotitanium oxide (TiC) • Others

How nanocomposites work

Polymer nanocomposites are constructed by dispersing a filler material intonanoparticles that form flat platelets. These platelets are then distributed into a

polymer matrix creating multiple parallel layers which force gases to flow throughthe polymer in a “torturous path”, forming complex barriers to gases and water vapor, as seen in Figure “9”. As more tortuosity is present in a polymer structure,higher barrier properties will result. The permeability coefficient of polymer filmsis determined using two factors: diffusion and solubility coefficients:P = D x S.Effectively, more diffusion of nanoparticles throughout a polymer significantly

reduces its permeability. According the Natick Soldier Center of the United States

Army, “the degree of dispersion of the nanoparticles within the polymer relates toimprovement in mechanical and barrier properties in the resulting nanocompositefilms over those of pure polymer films”. Nanoparticles allow for much lower

loading levels than traditional fillers to achieve optimum performance. Usuallyaddition levels of Nano fillers are less than 5%, which significantly impact weightreduction of nanocomposite films. This dispersion process results in high aspect



16

ratio and surface area causing higher performance plastics than with conventionalfillers.

Figure “9”. Schematic of nanoscale fillers.

Factors that affect the polymer nanocomposite properties

There are many factors that affect the polymer nanocomposite properties including:- Synthesis methods such as melt compounding, solvent blending, in-situ

polymerization, and emulsion polymerization. Polymer nanocomposite morphology. Types of nanoparticles and their surface treatments. Polymer matrix such as crystallinity, molecular weight, polymer chemistry, and

whether thermoplastic or thermosetting. Table “1” shows several benefits anddisadvantages when nanoparticles are incorporated into the polymer matrix.



17

Table “1” characteristics of Nanoparticles to polymers

Characteristics of Polymer Nanostructured Materials.

There are two main challenges to developing polymer nanostructured materials after thedesired nanoparticle has been selected for the polymer of interest.First ,

the choice of nanoparticles requires an interfacial interaction and/or compatibility withthe polymer matrix.Second ,the proper processing technique should be selected to uniformly disperse and distribute

the nanoparticles or nanoparticle aggregates within the polymer matrix.In most cases, polymer nanostuctured materials exhibit multifunctionality. Several of the

functions of these materials are listed below:• Thermal : increased thermal resistance, higher glass transition temperature (Tg) or heatdeflection temperature (HDT), reduced coefficient of thermal expansion (CTE).• Mechanical : increased modulus, strength, toughness, elongation (in some cases).• Chemical : improved solvent resistance, improved moisture resistance.• Electrical : improved thermal conductivity, lower resistivity (depends on thenanoparticles).



18

• Barrier : reduced oxygen, moisture transmission.• Optical : clear, transparency provided in selective systems.• Others : abrasion resistance, reduced shrinkag

Polymer Matrices

In general, polymers can be classified into the three basic families of resins namelythermoplastics, thermosets, and elastomers. Table” 2” lists several characteristics of the

thermosetting and thermoplastic resin systems.

Thermoplasti c-based nanocomposites.

Materials are often classified as metals, ceramics, or polymers. Polymers differ from theother materials in a variety of ways, but generally they exhibit lower densities, andmoduli. The lower densities of polymeric materials offer an advantage in applicationswhere lighter weight is desired. The addition of thermally and/or electrically conductingfillers allows the polymer formulator the opportunity to develop materials from insulatingto conducting type characteristics. Themoplastic materials are used in a vast array of

products. In the automotive area, they are used for interior parts and in under-the hoodapplications. The packaging applications area is a large area for thermoplastics, fromcarbonated beverage bottles to plastic wrap.

Table “2” comparisons of thermoplastic and thermosetting resion characteristic.



19

Application requirements vary widely; fortuitously, plastic materials can be formulated tomeet these different business opportunities. It remains for designers to select from thearray of thermoplastic materials that are available to meet the particular needs of theirapplications. Many thermoplastics have been nanomodified into polymer nanocomposites

by incorporating nanoparticles into the polymers as shown in Table “3”.

Table”4” Thermoplastic - based of nanocomposites.



20

Thermoset-based nanocomposites.

Thermosetting type resins consist of solid, semi-solid, or liquid organic reactiveintermediate material that cures or crosslinks into a high molecular weight product with

no observable melting point. The basic characteristic of these intermediate reactivehermosetting resins is that they will, upon exposure to elevated temperature from ambientto above 450°F, undergo an irreversible chemical reaction often referred to as polymerization, or cure. Each family member has its own set of individual chemicalcharacteristics based on its molecular structure and its ability to either homopolymerize,copolymerize, or both. This transformation process separates the thermosets from thethermoplastic polymers. The important beneficial factor lies in the inherent enhancement



21

of the physical, electrical, thermal, and chemical properties of thermoset resins becauseof that chemical cross-linking polymerization reaction, which contributes to their abilityto maintain and retain these enhanced properties when exposed to severe environmentalconditions. An intermediate reactive thermosetting species is defined as a liquid, semi-solid, or solid composition capable of curing at some defined temperature that can befrom ambient to several hundred degrees and cannot be reshaped by subsequentreheating. In general, these intermediate reactive thermosetting compositions contain twoor more components: a reactive resinous material with a curing agent that causes theintermediate material to polymerize (cure) at room temperature, or a low molecularweight resinous material and curing agent that, when subjected to elevated temperatures,will commence polymerization and cure. Several thermosetting resins have beennanomodified into polymer nanocomposites by introducing the nanoparticle into thethermosetting resin as shown in Table “5”. These intermediate thermosettingnanocomposites can be impregnated into fiber reinforcements such as glass, silica, quartz

carbon/graphite, aramid, poly(p-phenylene-2-6- benzobisoxazole) (PBO), polyethylene, boron, or ceramic and upon curing lead to laminates or nanomodified polymer matrixcomposites (PMCs).

Table “5” thermoset- based nanocomposite

Elastomer-based nanocomposites

rubberlike, known as elastomers. These elastomeric materials can be block copolymers ormulti-phase systems containing soft (low Tg) segments and hard segments (high Tg,

possibly crystalline). They are processable under thermoplastic conditions. A fewelastomers have been nanomodified into elastomer nanocomposites as shown in Table“6”. For completeness, some rubber materials (synthetic, isoprene, natural, etc.) that arenanomodified are also listed in Table “6”.



22

TABLE “6” Elastomer-Based Nanocomposite Examples

Scientists and engineers can develop formulations for a range of polymer nanocompositesto fit their requirements and applications. The challenge is to select the baseline polymerswith the proper nanoparticles to solve specific problems. Processing and morphologicalcharacterization are the keys to understanding the fundamentals of this new class ofnanomaterials.



23

Applications of polymer nanocomposites.

The improvements in mechanical properties of nanocomposites have resulted in majorinterest in numerous automotive and general/industrial applications. It includes potentialfor utilization as mirror housing on various types of vehicles, door handles, engine

covers, and belt covers. More general applications include: packaging, fuel cell, solarcell, fuel tank, plastic containers, impellers and blades for vacuum cleaners, power toolhousing, and cover for portable electronic equipment such as mobile phones and pagers.

Coatings.

Coatings are important for modifying properties of surfaces. One of the well verseddevelopments is nanoclay based polymer coatings. Nanoclay incorporated thermoset

polymer nano coatings exhibit superior properties such as superhydrophobicity, improved

wettability, excellent resistance for chemicals, corrosion resistance, improved weatherresistance, better abrasion resistance, improved barrier properties and resistance toimpact, scratch, etc.

Energy storage systems and sensors.

Fuel cells act as electrochemical `devices, which convert chemical energy of carbon,hydrogen and oxygen directly and efficiently into useful electrical energy with heat andwater as the only byproducts. Due to incorporation of nano materials their efficiencyincreases

considerably. In fuel cells, proton exchange membrane‟s role is to allow proton transportfrom the anode to the cathode, to be an electron nonconductive material and to act as agas separating barrier.

Gas barriers for plastic bottles, packaging and sports goods

Hybrids made of poly(dimethyl siloxane) rubber and nanosilica generated in-situ byhydrolysis of tetraethyl orthosilicate can be specifically shaped, giving objects such asgolf balls.

A number of polymer nanocomposites based on polymers, such as butyl rubber, styrene butadiene rubber, ethylene propylene diene monomer rubber, ethylene vinyl acetatecopolymer, ethylene-octene copolymer, have been used commercially for barrierapplications. These polymers can act as excellent barriers for many gases such as CO2,O2,N2, and chemicals such as toluene, HNO3, H2SO4, HCl, etc. Due to excellent solvent

barrier properties PNCs have been utilized in chemical protective and surgical gloves in



24

order to protect against chemical warfare agents and for avoiding contamination frommedicine.

PNCs also have been widely used in food packaging and plastic containers, both flexibleand rigid. Specific examples include packaging for processed meat, cheese, cereals anddairy products, printer cartridge seals, medical container seals for blood collection tubesstoppers for medical containers and blood bags, baby pacifiers and drinking water bottles.

Products with low flammability.

Electronics and automobile sectors.

Optical glass and membranesClay incorporated polymers have been shown, when employed to coat transparent

materials, to enhance both toughness and hardness of these materials without sacrificinglight transmission characteristics. An ability to resist high velocity impact combined withsubstantially improved abrasion resistance of PLS nanocomposites was demonstrated byTriton Systems. Owing to this reason and improved optical properties it has been widelycommercialized in contact lens and optical glass.Polymer/clay nanocomposites can also be used to fabricate various types of membranessuch as solvent filters, filters for bacteria and virus , solid electrolytes for fuel cells,membrane for gas separation, etc

Biomedical applications

The applicability of polymer nanotechnology and nanocomposites to emerging biomedical/biotechnological applications is a rapidly emerging area of development ofwhich this discussion can only briefly cover. One area of intense research involveselectrospinning for producing bioresorbable nanofiber scaffolds for tissue engineeringapplications. This might be construed as a nanocomposite as the resultant scaffold allowsfor cell growth yielding a unique composite system. Another area also involvingnanofibers is the utilization of electrically conducting nanofibers based on conjugated

polymers for regeneration of nerve growth in a biological living system.

Refractive Index Tuning

In many optical applications such as telecommunications and optical computing, polymeroptical fibres are very attractive to adjust the refractive index of the connecting opticalfibre (due to ease of mass production and low cost). This can be done by the addition ofnanoparticles with various refractive indices to the polymer. Bohm79, et al. reported



25

additions of nanoparticle zirconia, alumina, and silica to poly (methyl methacrylate) andthey were able to adjust the refractive index over a sufficient range. Levels up to 10 Wt %loading were reported. Tuning the refractive index of surface coatings is important insignature management. Damage resistance (abrasion and scratching) of the fibre is likelyto be improved by addition of ceramic nanoparticles.

Solid Lubricants

It is possible to produce inorganic fullerene-like (IF) nanoparticles of tungsten sulphide(WS2), which have a characteristic structure like a hollow onion. have reported that byadding small quantities of WS2 nanoparticles (about 100 nm dia) to two polymermatrices: epoxy and polyacetal, it was possible to reduce coefficient of dry friction

between polymer and a steel disc to less than half in both the cases. If a simple lubricantwas present, friction coefficient was further reduced significantly. Fracture toughness of

the epoxy was also improved. These lubricants may be used for rotating and sliding bearings.

Porous Nanocomposites.

The additions of nanoparticles can serve to improve the foaming properties of a polymeras reported by Siripurapu81, et al. who used additions of silica nanoparticles to act asnucleation sites for nanopore formation using carbon dioxide as a blowing agent. Adisadvantage of porous polymer foams (e.g., polyurethane) is their large surfaceto-

volume ratios, which increase the rate of heat and gas release in case of fire. Byintroducing nanoparticles with a flake-like morphology, the rate of burning can besignificantly reduced. Nanoporous polyurethane is being considered for automotive seatapplications. Other applications include shock-absorbing materials, and acousticabsorbents, etc.

Microwave Absorbers

Nanocomposites as microwave absorbers are receiving much attention. Nguyen and

Diaz78 have reported a method to synthesize polypyrrole nanocomposites containing ironoxides (g and a), tin oxide, tungsten oxide and titanium dioxide. Pyrrole containing adispersion of nanoparticle metal oxides was polymerised in situ and the magnetic

properties reported. The electrical conductivity and dielectric losses can be tuned byvarying the concentration and orientation of the nanotubes additions. Only a few weigh

per cent of nanotubes need be added to the polymer to achieve useful properties.



26

Efforts have been made to utilise CNTs for developing economical microwave (in therange 8 GHz to 24 GHz) absorbers103,104. These materials have wide applications inelectrical energy storage (condensers) integrated into load-carrying structures for UAVshigh strength CNTspolymer fibres for energy absorption, electromagnetic shielding, etc.

Ballistic Protection.

The reports of ballistic testing of PNCs are very few and this may be due to secrecyassociated with such materials and lack of suitable nanocomposite materials. Reportsfrom the US Army Research Laboratory indicate promising results when combininginorganic nanoparticles (of silica) in polyethylene glycol. When this shear thickeningfluid is impregnated into conventional Kevlar, the ability of the material to absorb energyis greatly improved. In one example, the ballistic performance (in terms of absorbed

energy) was more than doubled so that four layers of Kevlar impregnated with the shearthickening fluid absorbed as much energy as would have been absorbed by 10 layerswithout the shear thickening fluid. This will lead to a more flexible armour with reducedweight. Such materials find applications for body/personal armour where flexibility ofmovement is required besides protection against blunt weapons (stones, sticks and bars)for arms and legs.

Corrosion Protection

Corrosion protection of metals and alloys is normally achieved by a surface coatingswhich must resist both mechanical damage (scratching, impact, abrasion) and chemicalattack (salts, acids and bases, solvents). It should also not be damaged (cracked) byhaving a coefficient of thermal expansion greatly different from the metal to be protected.PNCs have improved scratch and abrasion resistance, due to their higher hardnesscombined with improved elastic modulus. Gentle and Baney87 reported preliminaryexperiments using a silica-reinforced silicone nanocomposite coating deposited to protectaluminium surfaces and electronic circuits.



27

Properties of polymer nanocomposites

Barrier properties and flame retardancy

The search for non-halogenated flame retardants has led to nanoclays, one nm thick by1000 nm diameter. Initial research showed that the addition of as little as 5% of nano-sized clay particles could produce a 63% reduction in the flammability of nylon-6. Morerecent studies have shown that flame retardancy in many other polymers can be boosted

by dispersing clay at the molecular level. Clays are believed to increase the barrier properties by creating a maze or „tortuous path‟ (Scheme 8) that retards the progress ofthe gas molecules through the matrix resin (Neilson, 1967). For example,

polyimide/layered silicate nanocomposites with a small fraction of O-MMT exhibitedreduction in the permeability of small gases, e.g.O2, H2O, He, CO2, and ethyl acetate.

.Scheme 8. Neilson‟s tortuous path model for barrier enhancement of nanocomposites

(from Neilson, 1967).

Optical clarity

The presence of reinforcement incorporation at nano-levels has been shown to havesignificant effects on the transparency and haze characteristics of films. In comparison toconventionally filled polymers, nanoclay incorporation has been shown to significantlyenhance transparency and reduce haze.



28

Clays are just into thin, albeit their micro- lateral size. Thus, when single layers aredispersed in a polymer matrix the resulting nanocomposite is optically clear in the visibleregion (Figure 10). At the same time, there is aloss of intensity in the UV region (for λ < 300 nm), mostly due to scattering by the MMT

particles. There is no marked decrease in the clarity due to nano-dispersedreinforcements.

Fig. 10. UV-visible transmittance for MA-functionalized PP and its MMTnanocomposites as

a function of MMT loading

A plausible reason for the above observations could be that the size of nanoclay particlesis less than the wavelength of visible light; hence, visible light rays are not appreciablyscattered by nanoclay particles. But, visible light rays could be appreciably scattered byregions where clay particles form agglomerates. This fact could be understood by lookingat scheme 9 (Wilson et al., 2002).



29

Scheme 9. Light rays passing mostly undeflected through an array of nanoparticlesso the array is transparent. When the particle size of the same material increases, lightrays are scattered and the material becomes .

Nanocomposite mechanical properties: reinforcementA common reason for adding fillers to polymers is to increase the modulus or stiffnessvia reinforcement mechanisms described by theories for composites [58,165 – 185]Properly dispersed and aligned clay platelets have proven to be very effective forincreasing stiffness. This is illustrated in Fig. 7 by comparing the increase in the tensilemodulus, E, of injection molded composites based on nylon 6, relative to the modulus ofthe neat polyamide matrix, Em, when the filler is an organoclay versus glass fibers [58].In this example, increasing the modulus by a factor of two relative to that of neat nylon 6requires approximately three times more mass of glass fibers than that ofmontmorillonite, MMT, platelets. Thus, the nanocomposite has aweight advantage over

the conventional glass fiber composite. Furthermore, if the platelets are aligned in the plane of the sample, the same reinforcement should be seen in all directions within the plane, whereas fibers reinforce only along a single axis in the direction of their alignment[165]. In addition, the surface finish of the nanocomposite is much better than that of theglass fiber composite owing to nanometer size of the clay platelets versus the 10 – 15 mdiameter of the glass fibers.



30

Fig. 7. Comparison of modulus reinforcement (relative to matrix polymer) increases fornanocomposites based on MMT versus glass fiber (aspect ratio w20) for a nylon 6 matrix

Nanocomposite thermal properties: dimensional stability

The high thermal expansion coefficients of neat plastics causes dimensional changesduring molding and as the ambient temperature changes that are either undesirable or insome cases unacceptable for certain applications. The latter is a particular concern forautomotive parts where plastics must be integrated with metals which have much lower

coefficients of thermal expansion, CTE.Fillers are frequently added to plastics to reduce the CTE. For low aspect ratio filler

particles, the reduction in CTE follows, more or less, a simple additive rule and is notvery large; in these cases, the linear CTE changes are similar in all three coordinatedirections.However, when high aspect ratio fillers, like fibers or platelets, are added and welloriented, the effects can be much larger; in these cases, the CTE in the three coordinatedirections may be very different.The fibers or platelets typically have a higher modulus and a lower CTE than the matrix

polymer. As the temperature of the composite changes, the matrix tries to extend orcontract in its usual way; however, the fibers or platelets resist this change creatingopposing stresses in the two phases.



31

Processing of Nanomaterials.

Synthesis Methods.After the selection of a particular polymer matrix and the appropriate nanoparticles for aspecific application, the next challenge is to determine the proper synthesis method tocreate the desired polymer nanocomposite. Figure 4.1 shows the processing challenge of

transforming ( particles into > 1 million platelets.

Figure 4.1 Processing challenge of layered silicate.

In general, for solid thermosetting reactive prepolymers or thermoplastic polymers withsolid nanoparticles, the following processing methods are recommended:• Solution intercalation • Melt intercalation • Roll millingFor liquid thermosetting reactive prepolymers or thermoplastic polymers with solidnanoparticles, the following processing methods are recommended:• In-situ polymerization• Emulsion polymerization • High-shear mixing

Structure of PNC.

Two types of structures are obtained, namely intercalated nanocomposites, where the polymer chains are sandwiched between silicate layers, and exfoliated nanocomposites,where the separated, individual silicate layers are more or less uniformly dispersed in the

polymer matrix.



32

Characterization Techniques for Nanocomposites.

Characterization tools are crucial to comprehend the basic physical and chemical properties of PNCs. For structural applications, it facilitates the study of emergingmaterials by giving information on some intrinsic properties. Various techniquesfor characterization have been used extensively in polymer nanocompositeresearch .The commonly used powerful techniques are wide-angle X-ray diffraction(WAXD), small-angle X-ray scattering (SAXS), scanning electron microscopy(SEM), and transmission electron microscopy (TEM).The SEM provides images of surface features associated with a sample.However,there are two other microscopies, scanning probe microscopy (SPM) andscanning tunneling microscopy (STM), which are indispensable in nanotuberesearch. The SPM uses the interaction between a sharp tip and a surface to obtain

an image. In STM, a sharp conducting tip is held sufficiently close to a surface(typically about 0.5 nm), such that electrons can „tunnel‟ across the gap . Thismethod provides surface structural and electronic information at atomic level. Theinvention of the STM inspired the development of other „scanning probe‟

microscopes, such as the atomic force microscope (AFM) .The AFM uses a sharp tip to scan across the sample. Raman spectroscopy has also

proved a useful probe of carbon-based material properties .Due to the easiness and availability, WAXD is the most commonly used to probethe nanocomposite structure, and occasionally to study the kinetics of the polymer melt intercalation. In layered silicate nanocomposite systems, a fully exfoliatedsystem is characterized by the absence of intensity peaks in WAXD.Therefore, a WAXD pattern concerning the mechanism of nanocomposite

formation and their structure. On the other hand, TEM allows a qualitativeunderstanding of the internal structure, spatial distribution of the various phases,and views of the defective structure through direct visualization, in some cases of individual atoms. Therefore, TEM complements WAXD data . Small-angle X-rayscattering (SAXS) is typically used to observe structures on the order of 10A ˚ or larger . For thermal characterization and to study the cure behavior (typically for thermoset resin systems) of PNCs, the commonly used techniques are differential

scanning calorimeter (DSC), DSC is an analytical tool which helps to understandthe thermal behavior of polymer nanocomposites. It helps in finding glasstransition temperature (Tg) of polymer and its polymer composites.The increase in Tg values shows the presence of inorganic materials in the polymer matrix.thermomechanical analysis (TMA), Fourier-transform infrared (FTIR), dynamicmodulus analysis (DMA), etc. Both, XRD and Thermogravimetric analysis



33

(TGA), are important techniques used to characterize the microstructure of nanocomposites. In general, TGA is used to assess the amount of organic matter exchanged on the clay surface during the surface modifi cation process. XRD isalso used to quantify increases in basal plane spacing in the filler following surfacemodifi cation, and also after composite generation.



34

Reffrencess.

NANOCOMPOSITES AND THEIR APPLICATIONS

BY,SHIVANI PANDYA CENTRE FOR NANOSCIENCE

LITERATURE SURVEY ON POLYMER NANOCOMPOSITE.

By RAVI NARAIAN PANDEY M Tech.-2nd year.DTU — DELHI.

INTRODUCTION AND APPLICATIONS OF NANOTECHNOLOGY . BY

TAHIRA IRUM M.Phil 1st

CHAPTER 9POLYMER MATRIX NANOCOMPOSITES(PMN) NoraihamMohamad, Ph.D,Department of Engineering Materials

Faculty of Manufacturing Engineering,UniversitiTeknikalMalaysia Melaka

5 - Polymer Nano-compositesRobert J Young FREng* School of Materials, University of Manchester, UK

Advanced Polymer Nanocomposites: Novel Properties and ApplicationsRamanan Krishnamoorti ,Department of Chemical&BiomolecularEngineering,University of Houston Polymer Nanocomposites: From Synthesis to Applications

S. Anandhan1 and S. Bandyopadhyay2 1National Institute of Technology Karnatak

The University of New South Wales



35

Polymer Nanocomposites: Synthesis, Microstructure,and Properties Vikas Mittal

Polymer Nanocomposites Processing, Characterization, and Applications,

by Joseph H. Koo



36

Content

Title Page

Introduction

Classification of Nanocomposite

Nanoclay-reinforced composite.

Inorganic particale reinforcedcomposition

Different type nanoparticles

How nanocomposite properties

Factors that affect the polymer nanocomposite properties

Characteristic of polymer

Applications of polymer nanocomposite

PROPERTIES OF PNC.

PROCESSING OF PNC

STRUCTURE OF PNC



Characterization Techniques for Nanocomposites

شفاء/ polymer nano powder

Documents