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Thermo-mechanical characteristics of thermally aged

polyethylene/polypropylene blends

Abdel-Hamid I. Mourad*,1

Mechanical Engineering Department, United Arab Emirates University, Al-Ain, P.O. Box 17555, United Arab Emirates

a r t i c l e i n f o

Article history:Received 11 April 2009

Accepted 20 July 2009

Available online 23 July 2009

Keywords:

Polyethylene/polypropylene blends

Blend ratio

Mechanical properties

Thermal aging

Thermogravimetric analysis (TGA)

a b s t r a c t

Polyethylene (PE), polypropylene (PP) and their blends have attracted a lot of attention due to theirpotential industrial applications. Therefore, the current work has been carried out with the main objec-

tive of investigating the impact of the thermal aging/treatment and blend ratio (composition range) on

the mechanical (tensile and hardness) and thermal characteristics (using thermogravimetric analysis

in a dynamic air atmosphere) of PE, PP and PE/PP binary blends. Samples of PE/PP blends containing

100/00, 75/25, 50/50, 25/75 and 0/100 wt.% were prepared via injection moulding technique and ther-

mally treated/aged at 100 °C for 0, 2, 4, 7, 14 days. The tensile measurements indicated that the yield

strength and the modulus decrease with increasing PE content. It was also observed that PE, PP and their

blends deform in ductile modes. They undergo a uniform yielding over a wide range of deformation,

which is followed by strainhardeningand then failure. The strainto break forpure PE is found to be much

higher than that for pure PP and for their blends, intermediate values have been observed. The hardness

measurements have also revealed that increasing PE content in PE/PP blends reduced the hardness value

of PP, however, thermal aging at 100 °C has not affected the polymers hardness which holds also true for

the tensile properties, showing a good correlation between tested mechanical properties. The thermo-

gravimetric analysis (TGA) in a dynamic air atmosphere and derivative thermogravimetric analysis

(DTA) were conducted to study the thermal degradation and stability of thermally unaged and aged

PE, PP and PE/PP blends in terms of the initial (T d and T d(1%)) and final (T d(99%)) decomposition tempera-tures and maximum decomposition rate temperature (T max). All polymers start to decompose at no less

than 365 °C. As for mechanical properties, the blend ratio has affected the thermal properties however,

aging time has not.

Ó 2009 Elsevier Ltd. All rights reserved.

1. Introduction

In the last few decades, polymers have been widely used mate-

rials in industry and their utilization in engineering applications is

widely growing all over the world. Their versatility makes them

suitable for a whole range of applications, and comes from the

capability of manufacturers to tailor microstructures and therefore

properties through control of the processing conditions. As an

example, the use of plastic pipes in piping systems applications

[1] (pressure vessels and in pipelines for potable water, irrigation,

and sewage) represent an important area in which polymers are

becoming predominant against other materials and has increases

considerably and rapidly. Pipes made out from polymers have sev-

eral special features in comparison to metallic pipes. Their rela-

tively low cost, ease of installation, transportation, and long-term

durability against environmental degradation (harmful environ-

mental attack such as corrosion, rust and higher thermal stresses)

make plastics an attractive alternative to metals in such applica-

tions). Among the most common polymers utilized in such applica-

tions are polyethylene (PE) and polypropylene (PP).

Though, polymers have offered many useful advantages over

metals (they have in general good thermal and electrical insulation

properties, low density and high resistance to chemicals), but they

are mechanically weaker and exhibit lower elastic modulus than

metals. In order to overcome these limitations, numerous studies

have been carried out in the recent years to improve the mechan-

ical behaviour of polymers, e.g. [2–6]. There have been also a large

number of reports describing the methods for producing polymers

with improved properties, e.g., polymer blending, in the form of

rods, sheets and tubes.

Blending of different plastic resins has long been practiced in the

manufacturing industry for various reasons including: (i) tailor-

made blends to meet specific processing and performance require-

ments that cannot be satisfied by a single component; (ii) blending

of polymers can be used in the field of recycling post-consumer

0261-3069/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.doi:10.1016/j.matdes.2009.07.031

* Tel.: +971 3 7133574; fax: +971 3 7623158.

E-mail address: [email protected] On leave from Mechanical Design Department, Faculty of Engineering, El-Mataria,

Helwan University, P.O. Box 11718, Cairo, Egypt.

Materials and Design 31 (2010) 918–929

Contents lists available at ScienceDirect

Materials and Design

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / m a t d e s

http://dx.doi.org/10.1016/j.matdes.2009.07.031

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wastes to upgrade their properties, (iii) scientific interests; and (iv)

financial incentives [7].

As generally known, having fast-growing application areas,

polyolefin are the most widely used cheap plastic materials [8,9].

Polyethylene (PE) and polypropylene (PP) are of considerable

industrial relevance, especially in the form of a blend. Over the

years, their blends are among those binary systems that have at-

tracted a lot of attention.

Jose et al. [10] investigated the phase morphology, crystallisa-

tion behaviour and mechanical properties of isotactic polypropyl-

ene (i-PP)/high density polyethylene (HDPE) blends. They used

different compositions of blends, namely, i-PP and HDPE (H10,

H20, H30, H40, H50, H60, H70, H80 and H90), where H denotes HDPE

and subscript denotes the percentage composition by weight of

HDPE. They found that the properties are related to each other.

They have found that, as the percentage of HDPE increased the size

of the dispersed HDPE domains increased due to the coalescence

phenomenon [11]. Jose et al. measured the mechanical properties

of the PP/HDPE blends (tensile strength, tensile strength at break,

elongation at break, impact strength, hardness and tear strength).

They also reported that, all the properties except Young’s modulus

and hardness showed negative deviation from the additivity line

and minimum values of mechanical properties are observed for

blends exhibiting co-continuous morphology. This is due to the

incompatibility of these blends. The most important result they

have found is the variation of Young’s modulus with composition,

which shows a positive synergism with maximum corresponding

to 80% PP. This behaviour was explained by considering both the

morphology and crystallinity of the blends.

The mechanical behaviour/tensile properties, morphology and

crystallisation from the melt of high density polyethylene

(HDPE)/syndiotactic polypropylene (sPP) blends were investigated

byLooset al. [12]. They found that the mechanical behaviour of the

blends changed drastically compared to pure HDPE and sPP, and

for HDPE concentrations between 10 and 70 wt.%, they found that

no neck formation was observed. Both pure sPP and pure HDPE

showed usual plastic deformation via necking with elongationse% 300–800%. But already for samples containing only 5 wt.%

HDPE, the drawing behaviour of the blends changed, and for the

90/10 blend samples, brittle fracture took place before necking

after approximately 10% elongation. For low concentrations of

HDPE, a synergetic increase in the Young’s modulus with a maxi-

mum of about 20 wt.% HDPE was measuredand for blends contain-

ing more than 20 wt.% HDPE a slight decrease in tensile strength

was observed. The crystallization behaviour of these blends was

characterized by transmission electron microscopy and in situ

Raman spectroscopy. For all investigated sPP/HDPE blends, the

start temperature of the sPP crystallization significantly increased

with increasing HDPE content. The start temperature of crystalliza-

tion increases more than 10 °C when HDPE was present, which re-

flected the favoured nucleation of sPP in the blends.Study and characterization of virgin and recycled LDPE/PP

blends were carried out by Bertin and Robin [7]. First, they made

a model composition of virgin LDPE/PP blend to study the effect

of process parameters and that of different types of compatibiliz-

ers. Second, they applied the results to plastic wastes coming from

industrial post-consumer plastic wastes. By adding compatibilizing

agents, elongation at break and impact strength were improved for

all blends. The effect of these various copolymers was different and

was related to chemical structure. The recycled blends exhibited

suitable properties, which lead to applications that require good

mechanical properties. In the specific case of LDPE/PP blends, EP-

CAR 847 (EPM) was used as a compatibilizer. Its presence in the

blend efficiently improved the elongation at break and decreased

the Young’s modulus [13]. Some EPDM and EPM grafted withmaleic anhydride (EPDM-g-MAH) were tested to compatibilize

LDPE/PP blends [14–16]. Also, the addition of fibers, such as short

polyamide fibers, in LDPE/PP blends allowed the improvement of

tensile, flexural and impact behaviour [17].

The characteristics of polypropylene/polyethylene (PP/PE) bin-

ary blends at the microscopic level have been widely studied by

different researchers over the years. Wong and Lam [18] discussed

the empirical results obtained from a series of DSC and TGA tests

on the selected thermal properties of PP/PE blends. They usedDSC to investigate the effects of different blending ratios of PP

and PE on the melting and crystallinity behaviour of the blend sys-

tems. TGA was used to study the degradation properties of the

blends in terms of their induction time. An empirical equation

was proposed and was proved to offer a convenient means for

the estimation of the overall crystallinity percent of a PP/PE sys-

tem. The TGA study showed that the effect of temperature on

induction time of PP/PE blends followed the trend of the Arrhenius

equation.

One of the most obvious effects brought about by the blending

process is the density of the blends. A Techne Density Gradient Col-

umn was employed by Wong [19] for density measurement. He

found that the density of the blends may be accurately described

by an additive rule that was reported to be applicable for PP/PE

systems.

Blom et al. [20] investigated the mechanical and rheological

properties of PP/HDPE blends. In this investigation, the properties

of two types of PP/PE blends (PP/HDPE and PP/LDPE) were studied.

The PE contents in both types of blends were kept at a low percent-

ageÀ20 wt.%.

In general, in systems composed of two polymers the tensile

strength depends linearly on the concentration of one component,

but antagonistic and synergistic effects were also reported [21].

Incompatible and immiscible polymers may exhibit a broad mini-

mum in tensile strength over the composition [22]. The term

‘immiscible’ means that the Gibbs free energy of mixingDGm is po-

sitive, whereas ‘incompatible’ is defined with respect to properties

and means that the properties of the blend are inferior to those of

the pure polymers. Since polyethylene and polypropylene aregenerally immiscible and incompatible [23,24], their mixtures are

expected to be poor in mechanical properties. However, the high

density polyethylene (HDPE)/isotactic polypropylene (i-PP) blend

is one of the few immiscible systems which has a maximum in ten-

sile strength at a certain composition [22], i.e., it is not incompati-

ble. Moreover, the addition of a small amount HDPE into i-PP

improves the impact strength of i-PP [25], and the addition of a

small amount of i-PP into HDPE enhances the transparency of solid

PE [26] (at the expense of environmental stress cracking resis-

tance). These effects depend on the blend preparation conditions.

For HDPE/i-PP blend samples, a surprisingly high impact strength

compared to the single components was observed at a specific

range of HDPE content. This phenomenon raises questions as to

thestructure, morphology and theinterphasesbetween thecompo-nents and their possible correlation with the impact strength [27].

Mechanical properties, structure and morphology of high den-

sity polyethylene (HDPE) and isotactic polypropylene (i-PP) blends

were studied by Schurmann et al. [27]. Young’s modulus was mea-

sured for blends with a wide range of compositions. Evidently their

values follow the mixing rule over the whole range, and the com-

patibilizer had almost no effect. The impact strength, however,

exhibited a very pronounced deviation from a simple linear depen-

dence [27]. The blends exhibit a maximum in impact strength at

specific mixing ratios. An explanation was found by analysing the

morphology. For a mixing ratio of 60% HDPE/40% i-PP, the impact

strength was twice as high as for the single component i-PP. For

the blends containing a compatibilizer (ethylene–propylene

copolymer), the impact strength became five times higher thanthat of i-PP and 10 times higher than that of HDPE [27].

Abdel-Hamid I. Mourad/ Materials and Design 31 (2010) 918–929 919



Waldman and De Paoli [28] reported the thermomechanical

degradation of (i-PP) and (LDPE), and the effect of the specific deg-

radation processes of each polymer on the degradation of a 1:1

blend of these polymers by using a conrotatory double-screw mix-

er coupled to a torque rheometer. The products were characterized

by Fourier transform infra-red spectroscopy and thermogravimetry

under inert and oxidative atmospheres. Data for the blends were

compared with curves simulated from a combination of the results

for the single polymers. LDPE was shown to form 3–4 times more

carbonyl-containing products than i-PP in the processing condi-

tions used to prepare the blend. The main reason for this difference

was the stabilizers added to i-PP by the producer before its pellet-

ization. Blending with LDPE stabilized i-PP, even at temperatures

well above its melting point.

Kesari and Salovery [29] studied the mechanical behaviour of

ternary blends of polyethylene (PE), isotactic polypropylene (PP)

and ethylene–propylene-diene terpolymer (EPDM). The variation

of the tensile and impact behaviour of compression mould ternary

blends with compression moulding time was reported. The blends

showed variations in tensile and impact behaviour after periods of

compression moulding. These variations resulted from changes in

structure. Changes in the mechanical behaviour were associated

with rearrangements of phase morphology in the blends due to

the compression moulding process. They also reported that ternary

blends of PP/PE/EPDM are complex mixtures of immiscible phases,

crystalline spherulites, and amorphous domains.

Although the polyolefin phases in the ternary blends are immis-

cible, considerable interaction occurs between the phases [30]. For

example, the effect of amorphous ethylene–propylene copolymers

on spherulitic crystallization in isotactic PP was described [31], and

considerable synergism in mechanical behaviour was reported for

PP–PE binary blends. Moreover, the mechanical properties of such

binary blends were very sensitive to processing [32]. Unlike binary

blends of PE and PP which do not show an evidence for adhesion

between dispersed PE droplets and PP matrix, ternary blends with

a random ethylene–propylene copolymer indicated adhesion be-

tween the composite droplets and the matrix [33].Rubbery polymers such as EPDM are frequently added to glassy

or semicrystalline polymers to enhance the impact resistance [30].

Morphological changes that affect the size and composition of the

dispersed phase should alter the mechanical properties. Here we

report the variation of the mechanical properties with the blend

compositions and the thermal treatment period.

In the study of Kukaleva et al. [34], homoPP, coPP and LDPE

were blended with recycled HDPE (wt.% = 75 and higher). They at-

tempted to produce blends of these polyolefins that are suitable for

large-scale moulding and are capable of providing appropriate

physical properties without the use of compatibilisers. The data

from MDSC experiments showed that, only one peak at 130.3 °C

[T m(HDPE)=132.2 °C and T m(LDPE)=106.4 °C] was present in the to-

tal heat-flow curve of 85HDPE/15LDPE blend on melting and oncrystallization, which is unexpected: the miscibility of linear and

branched types of polyethylene is a rare phenomenon. They spec-

ulated that the recycled HDPE was more compatible with LDPE

than virgin HDPE and this might be explained by the less regular

molecular structure and higher polydispersity index of the former

resulting from oxidation and chain scission undergone during

material’s reprocessing. The main conclusion from their MDSC re-

sults was that the presence of some partial miscibility in the solid

state may be suggested in blends–H1/LDPE, H1/coPP, H1/LDPE/

homoPP, but not in the H1/homoPP blend. They also concluded

that the blends were mechanically compatible, i.e., they are capa-

ble of providing compositions with a good balance of stiffness

and toughness. The degree of compatibility was the highest for

the recycled HDPE/LDPE blend, followed by the ternary blend recy-cled HDPE/LD/homoPP and recycled HDPE/coPP blend, and then

the recycled HDPE/homoPP blend. Although the last blend is the

least compatible system, simultaneous crystallization of its com-

ponents and the decreased PP crystallinity in the blend provided

better toughness than normally expected from the HDPE/PP

combination.

Although polymers are, nowadays, widely used in many struc-

tural products given their low costs and ease of processing, the

end use in engineering applications is often restricted by their

macroscopic mechanical performance. Mechanical properties such

as impact strength, tensile strength, Young’s modulus, strength and

elongation at the stretching limit as will as processing properties

need to be optimised. An understanding of polymer crystallinity

is important because the mechanical properties of crystalline poly-

mers are different from those of amorphous polymers. Polymer

crystals are much stiffer and stronger than amorphous regions of

polymer. Therefore, the mechanical response of semicrystalline

polymers is generally greater than of amorphous polymers [35].

This is mainly due to the coexistence of amorphous and crystalline

phase, if two different semicrystalline polymers are mixed, more

complicated mechanical response are expected. The aim of this

study was to lead us to better understand this class of materials.

It is understood that the manufacturing of i-PP is rather difficult

due to its inherent crystallinity which requires high relatively pro-

cessing temperatures. However, blending i-PP may result in an

undesired deterioration of its mechanical behaviour. This repre-

sents a point of motivation for the present research work. Another

reason for the interest in studying PE/PP blends is due to the fact

that complete separation of post-consumer PE and PP is very diffi-

cult, it is necessary to have a good understanding of the behaviour

of PE/PP blends. The huge worldwide annual consumption require-

ments of PE and PP is also thought to be responsible for the contin-

uous research efforts directed towards the various blending issues

of these two thermoplastics. The interests and needs in this area of

polymer science and engineering have grown.

Miscible or compatible blends are called homogeneous blends.

They give rise to a single phase, in which individual components

are mutually soluble in one another. In most cases, compatibleblends have mechanical properties superior to those of incompat-

ible blends. Therefore, a lot of efforts have been made to develop

experimental techniques, such as electron microscopy, light scat-

tering, small-angle X-ray diffraction and dynamic mechanical anal-

ysis, to determine the compatibility of a pair of polymers. On the

other hand, immiscible or incompatible blends are called heteroge-

neous blends. The majority of these blends contain a matrix phase

of rigid resin and a dispersed phase of flexible resin. The character-

istics of the blend will be directly influenced by the chemical struc-

ture, molecular weight, molecular weight distribution of each

component and by the ratio of each component in the blend. They

have many interrelated variables that affect their rheological

behaviour, processability and the mechanical/physical properties

of the finished product. For instance, the method of blend prepara-tion, like the method of mixing and the intensity of mixing, con-

trols the morphology of the blend (e.g., the state of dispersion,

the size of the dispersed phase, and the dispersed phase size distri-

bution), which in turn controls the rheological properties of the

blend. On the other hand, the rheological properties strongly dic-

tate the choice of processing conditions, which in turn strongly

influence the morphology and therefore the mechanical/physical

properties of the finished product. The Miscibility of vLDPE and i-

PP has been addressed in a previous work, sent for publication.

These two polymers have been found to be partially miscible.

The effect of that on the mechanical behaviour is investigated in

the current work.

The conducted literature survey reveal that, in the recent years,

blending of PE and PP polymers is receiving and attracting increas-ing attention from researchers for various reasons including the

920 Abdel-Hamid I. Mourad/ Materials and Design 31 (2010) 918–929



possibility of creating a material or product for new and more

industrial applications to meet specific processing and perfor-

mance requirements that cannot be satisfied by a single compo-

nent. Considering all the above, many attempts have been made

to improve the mechanical properties of polymers by blending.

However, there is a need for further studies that might widen

the scope of knowledge on the influence of blending parameters

on the mechanical behaviour of polymer blends. Furthermore,

most of the studies addressed the issue of thermally unaged/un-

treated polymers, however, the work related to thermally aged

blends is very lacking. This study is thus carried out to investigate

the effect blending ratio PE/PP and thermal aging on the mechan-

ical properties of PE/PP blends. Tensile and hardness tests were

conducted on injection molded and thermally aged PE/PP blend

samples to study the influence on the mechanical properties (elas-

tic moduli, strengths, percent elongations, and hardness values)

and to determine their macroscopic response. All these efforts have

offered additional information to the pool of existing knowledge

and experience accumulated by other workers in similar fields.

Thermogravimetric analysis (TGA) is a helpful technique for

studying the thermal decomposition of polymers and its applica-

tion can be expanded to the determination of the kinetic features

of degradation. Detailed survey on the TGA for PE, PP in both nitro-

gen and air atmospheres are presented by Mourad et al. [36].

In this study, blends of very low density polyethylene (vLDPE)

and isotactic polypropylene (i-PP) were used to prepare vLDPE/i-

PP samples of 100/0, 75/25, 50/50, 25/75, 0/100 weight ratios.

The samples were thermally aged by oven method for periods of

0.0, 2, 4, 7, and 14 days. The main objective of this work is to study

the thermo-mechanical performance of thermally aged vLDPE/i-PP

blends.

2. Materials and experimental procedure

2.1. Materials

The polymers used in this study are commercially available and

provided in the form of pellets with the courtesy of DSM, Inc., The

Netherlands. It has been confirmed that they are very low-density

polyethylene (vLDPE) and isotactic polypropylene (i-PP). The com-

pany did not provide further details such as molecular weight dis-

tribution, melt flow index (MFI) and density. for the purpose of

confidentiality. The basic physical properties of the polymers se-

lected for the study are: density (g/cm3) values are 0.893 and

0.930 and melt flow index (MFI) (g/10 min) values are 9.505 and

4.425 for vLDPE and i-PP, respectively.

2.2. Preparation of molded strips

Injection moulding technique was used for fabricating themolded strips which will be subjected to aging process. Vertical

injection moulding apparatus (Test Sample Moulding Press-hand

operated model-supplied by Norwood Instruments Ltd.) with a cyl-

inder of 20 mm bore and 180 mm length was used. The correct

amount of pelletized material was fed into the cylinder/barrel of

apparatus. This charge was pushed forward into the cylinder by

the motion of a plunger or ram, at which point the charged mate-

rial melts to form a viscous liquid (plasticize). Next, the molten

plastic was impelled, again by ram motion, through a nozzle into

the enclosed molt cavity; pressure was maintained until the

molded strip has solidified under a forced air cooling using electric

fan. The mould assembly (tool) was opened, the strip was ejected.

Finally, the mould was assembled for the next strip injection. Four

strips can be produced from each batch/blend ratio. The entirecycle was repeated for the subsequent mixture. The operation

variables or parameters that to be precisely controlled included

mould and cylinder temperatures, injection pressure and the

mould temperature at strip ejection. This is to ensure that the pure

polymers and their blends all had similar thermal history, so as to

minimize any possible effects on the subsequent tests due to pro-

cessing discrepancy in the upstream preparation work. The mould

(with cavity dimensions of 80Â 25Â 1 mm) is fabricated and used

to produce rectangular strips with the cavity dimensions.Salient

points in preparing the molded strips are as follows.

The respective virgin pellets of PE and PP were first carefully

weighed separately and manually mixed at various fractions, to

produce mixtures of 20 grams each, Five different mixtures and

strips of PE/PP (wt.%) were obtained (100/0, 75/25, 50/50, 25/75,

0/100). The machine was provided with two-zone digital tempera-

ture controller for barrel and mould. The barrel and mould temper-

atures are controlled by digital controller and leave to stabilize

before dispatch. The barrel temperature is controlled at 180 °C

for pure PE and 190 °C for pure PP, while the mould temperature

is controlled at 115 °C. Sufficient time (approximately from 8 to

10 min) was allowed for the material to plasticize. The molten

material was carefully mixed mechanically using a specially de-

signed stirrer. The molten polymer, or melt was injected into the

closed mould cavity where it cooled and solidified. When the tool

temperature reaches %75 °C (within approximately 10 min), the

tool (mould assembly) is opened with care from its location so that

the product could be removed, Forced air cooling with electric fan

was used while cooling and solidification process of the molded

material. This process improved the ease with which the strip

can be removed from the mould cavity and the quality of the

molded strip as well. When moulding was complete, the cylinder

liner was removed and cleaned in a suitable solvent. Then the pro-

cess is repeated for the next batch (blend ratio).

2.3. Aging process

This was performed by the oven method as described by theASTM 0573-99. The molded stripes were placed in a preheated

oven at 100 °C (OSK 9500 M-Electric Oven-Type C-OGAWA-SEIKJ-

Co. Ltd.). The aging interval began at the time the specimens were

placed in the oven and continued for time intervals of 2, 4, 7 and

14 days at 100 °C. At the end of each aging interval, the strips were

removed from the oven, cooled to room temperature on a flat sur-

face and allowed to stand for not less than 24 h prior to further

processing. Then samples were characterized after the aging

process.

2.4. Tensile testing

A dumbbell test samples in accordance with ISO 527 (con-

formed also to IEC 923/01 and ASME D 638) were punched fromthe aged injection molded strips. Two or three (if possible) speci-

mens were punched side by side from each strip using a hydraulic

press. All specimens have a gauge length of 17 mm, width of 4 mm,

thickness of 1 mm and overall length of 50 mm.

The dumbbell shaped specimens were tested according to ISO

527. The tests were carried out on a 30 kN Zwick universal testing

machine (MTMT1-FR0303THA1k) under displacement controlled

conditions. They were stretched at a constant cross head speed of

25 mm minÀ1 until they fail. All tests were carried out at a room

temperature (23 ± 5 °C) and atmospheric pressure. The total length

between the grips is about 34 mm for the used dumbbells and the

rate of separation was 25 mm minÀ1. At least two valid results are

to be achieved in order to calculate the tensile properties; other-

wise the test is repeated and any unsatisfactory test result was ig-nored. The average value of the results is presented.




The tests were conducted to determine the tensile properties

(e.g., modulus of elasticity E , yield strength ry and elongation at

break) of the material. The Young’s modulus E is determined as

the tangent modulus at 1% strain; which is almost the tangent

slope to the first portion of the curve and also as the secant mod-

ulus at 2% strain. In the absence of a distinct yield point, yield

strength is defined as the 0.5%-offset stress r0.5. Also it was deter-

mined at the initial peak load on the curves; if exists.

2.5. Hardness testing

Hardness was measured using shore durometer type D. In mea-

surements the recommendations of the standard SFS-ISO 868:E

was used for hardness test. All tests were conducted at room tem-

perature and atmospheric pressure. Test specimens of 1 mm thick-

ness were cut from the aged and unaged injection molded strips.

The surface of the specimen was examined carefully to make sure

that it was flat and clean. At least three test specimens were pre-

pared for each condition and at least five readings have been re-

corded for each specimen. The average value of the fifteen

readings, for each condition, is presented.

2.6. Thermogravimetric analysis (TGA)

The thermal decomposition/degradation was studied by ther-

mogravimetry in a PERKIN ELMER thermogravimetric instrument

(TGA 7). Samples of a mass ranged between 10 and 20 mg were

cut from both aged and unaged strips. The samples were heated

from room temperature up to 600 °C (873 K) in a dynamic air

atmosphere with a flow rate of 60 ml minÀ1 and a heating rate of

10 °C/min in the thermal analyser. The degradation (% weight loss)

of the samples was monitored and measured as a function of tem-

perature and analyzed with the TGA analysis program. The first

derivative of the weight loss (i.e., derivative thermogravimetric

analysis DTA/derivative thermogravimetry DTG) of the weight loss

was recorded simultaneously. The TGA thermograms and their firstderivatives (DTA) were then plotted. Hence, the onset of degrada-

tion or initial decomposition temperature T d(1%) (the temperature

at which 1% of weight has been lost), the final decomposition tem-

perature T d(99%) (the temperature at which 99% of weight has been

lost), and the maximum decomposition rate temperature T max (the

temperature at which the rate of mass loss is at a maximum were

evaluated for each sample. Another initial/onset decomposition

temperature T d obtained directly from the thermogravimetric

instrument (TGA 7). T d is obtained at the intersection of the two

tangents of the 1st and 2nd portions of the thermogramme. The

method is demonstrated in the results section.

3. Results and discussion

3.1. Tensile and hardness testing

Stress–strain curves show the response of the tested materials

to applied stress. They reveal important information such as

Young’s modulus, yield strength and yield strain. Accurate knowl-

edge of these parameters is paramount in engineering design.

These curves allow us explore the different stages in the curves

as the strain is increased.

It was observed while conducting the tensile tests on the spec-

imens of PE, PP and their blends that all tested specimens exhibited

necking and cold drawing. The region of necking are evident for all

pure PE, PP and their blends tested specimens. It was noted also

that all specimens remained transparent as they were stretched.

Stress–strain data from a tension test on PE, PP and their blendssamples and for different aging durations (2, 4, 7 and 14 days) are

plotted in Figs. 1–5. The figures show all data to fracture and the

initial part of the data were also plotted (not presented here) at a

sensitive strain scale (up to 50% strain) to facilitate the measure-

ments of the modulus of elasticity. The values of modulus of elas-

ticity E (based on tangent and secant methods), yield strength ry

(based on 1st zero gradient and offset methods), percent yield

strain ey, tensile strength at break r f and percent strain at break

e

f for the tested samples have been obtained (and collected in a

0

2

4

6

8

10

12

14

16

18

0 100 200 300 400 500 600 700 800 900 1000 1100 1200

Strain (%)

S t r e s s ( M P a

)

0:10025:7550:5075:25100:0

Fig. 1. Stress–strain curves for untreated PE/PP blends.

0

2

4

6

8

10

12

14

0 100 200 300 400 500 600 700 800 900 1000 1100 1200

Strain (%)

S t r e s s

( M p a )

0:10025:7550:5075:25100:0

Fig. 2. Stress–strain curves for PE/PP blends of 2 days thermal treatment.

0

2

4

6

8

10

12

14

16

18

0 100 200 300 400 500 600 700 800 900 1000 1100 1200

Strain (%)

S t r e s s ( M p a )

0:10025:7550:5075:25100:0





table, which is not presented here) from the curves for the purpose

of analysis.

Figs. 6–10 show the stress strain curves for all PE/PP (wt.%) per-

centages (100/0.0, 75/25, 50/50, 25/75, 0.0/100) and for the differ-

ent aging durations. Figs. 7 and 10 show two distinctive tensile

behaviours for pure PP and PE. For pure PP (Fig. 10), after signifi-

cant yielding in the 1st part of the stress–strain curve, the stress

drops to the drawing stress (in the 2nd part) and remains constant

in the 3rd region up to a certain value of engineering strain when

work hardening commences again. In the last, 4th part, almost lin-

ear hardening is evident. It is seen in the graphs that the 1st partrepresents almost linear behaviour. At the end of this part, the

stress has reached an instability limit. After reaching this maxi-

mum load (1st peak load), a reduction in area appears somewhere

along the gage section. Rather than being stationary, as in the case

of metals, the neck travels along the gage length to produce a ‘‘sec-

ond specimen” of reduced cross section and increased gage length.

A further increase in the displacement tends to untangle the long

molecules that cause the stress to decrease (2nd part) to the level

of the drawing stress. In the 3rd region, the deformation is such

that it can develop through the untangling of the molecules with-

out incurring any further increase in the stress. The molecules be-

come untangled and to accommodate further elongation the

molecules have to be stretched which causes an almost linear in-

crease in stress level (4th part). This trend of tensile behaviour isobserved regardless the period of thermal aging.

Not all polymers undergo the elongation and the necking pro-

cess described above for pure PP. For pure PE the necking process

is closer to that found in metals than that of polymers. The

stress–strain diagrams for pure PE (Fig. 6) show that the stress

never decreases and the specimen fracture at a particular strain.Here the neck forms before the maximum load is reached at a

0

2

4

6

8

10

12

14

16

18

0 100 200 300 400 500 600 700 800 900 1000 1100 1200

Strain (%)

S t r e

s s ( M p a )

0:100

25:75

50:50

75:25


0

2

4

6

8

10

12

14

16

18

0 100 200 300 400 500 600 700 800 900 1000 1100 1200

Strain (%)


0:100

25:7550:5075:25100:0


0

2

4

6

8

10

12

14

16

18

0 100 200 300 400 500 600 700 800 900 1000 1100 1200

Strain (%)


14 days

4 days

2 days

0 day

Fig. 6. Stress–strain curves for untreated and thermally treated pure PE samples.

0

2

4

6

8

10

12

14

16

18

0 100 200 300 400 500 600 700 800 900 1000 1100 1200

Strain (%)


14 days

7 days

4 days2 days0 day

Fig. 7. Stress–strain curves for untreated and thermally treated 75% PE/25% PPblend samples.

0

2

4

6

8

10

12

14

16

18

0 100 200 300 400 500 600 700 800 900 1000

Strain (%)


14 days

7 days4 days

2 days0 day

Fig. 8. Stress–strain curves for untreated and thermally treated 50% PE/50% PP

blend samples.




certain axial position. As in the case of pure PP, pure PE samples ex-

hibit the same tensile behaviour trend regardless the period of

thermal aging.

The tensile test curves for pure PP (Fig. 10) show a clear yield

point where the slope of stress–strain curves reached zero. In con-trast, a clearly observable yield point was not able to be obtained

for pure PE stress–strain curves (Fig. 6), as no maximum/peak point

was observed. The clearly observed yield point for pure PP disap-

pears gradually as polyethylene weight percent increases (Figs.

1–5). This observation might reveal that the two polymers are par-

tially miscible. Therefore, and for the purpose of unification, the

yield strength for all PE, PP and their blends are defined as the

0.5% offset stress, which is the stress determined by the intersec-

tion of the stress–strain curve and an imaginary line parallel to

the onset gradient of the stress–strain curve shifted to the 0.5%

strain value. Tensile yield strength is also determined from themaximum point/peak point (if present) where the slope of

stress–strain curve reached zero.

When comparing yield strengths which are determined for dif-

ferent blend ratios, interesting trends are observed. It is found from

Fig. 11 (which shows the variation of ry with PE content) that ten-

sile yield strength decreases with increasing PE ratio. This is as a

consequence of the lower yield strength of pure PE (r0.5% = 1

MPa) than pure PP (r0.5% = 5.2 and rpeak = 10 MPa) and the partial

miscibility of the two polymers. Although, the peak stress of pure

PP samples increase by as much as 2.3 MPa (23%), the results indi-

cate that the thermal aging has not affected significantly the yield

strength of blends. Moreover, there is no clear trend of variations of

the yield strength with the thermal aging period.

The tensile modulus (based on both tangent and secantmethods) is plotted as a function of PE content for various thermal

0

2

4

6

8

10

12

14

16

18

0 100 200 300 400 500 600 700 800

Strain (%)


14 days

7 days4 days

2 days

0 day

Fig. 10. Stress–strain curves for untreated and thermally treated pure PP samples.

0

1

2

3

4

5

6

7

8

0 25 50 75 100

PE weight (%).

Y i e l d s t r e n g t h ( M P a ) .

14 days

7 days

4 days

2 days

o day

Fig. 11. Variation of offset yield strength r0.5 with PE content for untreated and

thermally treated blends.

0

100

200

300

400

500

600

0 25 50 75 100

PE weight (%).

M o d u l u s o f

e l a s t i c i t y ( M P a ) .

14 days

7 days

4 days

2 days

o day

Fig. 12. Variation of modulus of elasticity (tangent) with PE content for untreated

and thermally treated blends.

0

2

4

6

8

10

12

14

16

18

0 100 200 300 400 500 600 700 800

Strain (%)


14 days

7 days

4 days

2 days

0 day

Fig. 9. Stress–strain curves for untreated and thermally treated 25% PE/75% PP

blend samples.

0

100

200

300

400

500

600

0 25 50 75 100

PE weight (%).

M o d u l u s o f e l a s t i c i t y ( M P a ) .

14 days

7 days

4 days

2 days

o day

Fig. 13. Variation of modulus of elasticity (secant) with PE content for untreated

and thermally treated blends.




treatment periods in Figs. 12 and 13. the values for pure PP

(255 MPa using 1% strain tangent and 225 using 2% strain secant)

are much higher than that for PE (50 MPa and 42 MPa using the

same two techniques), i.e., five times. The tensile modulus, as yield

strength, decreases with an increase in PE content. However, the

periods of thermal aging have no significant effect on the modulus

(Figs. 14 and 15) as in the case of yield strength.

The yield strain of untreated and thermally treated pure poly-

mers and their blends was found to vary in the range 2%:3.5% with

no specific trend of variation with PE content. It was also observedthat PE, PP and their blends deform in ductile modes similar to rub-

ber. They undergo a uniform yielding over a wide range. This yield-

ing is followed by strain hardening and failure. The test data show

that the strain to brake of pure PE is much higher than pure PP and

intermediate values for their blends have been observed. Never-

theless, some specimens have been observed to fail prematurely.

We infer that the origin of the decrease in modulus and yield

strength lies in the blend structure. In contrast to our observation

for PP, Lee et al. [37] reported that PP polymer prepared by metal-

locene catalyst undergoes brittle failure. This behaviour is ob-

served during the stretching of PP films of 0.1 mm thickness

prepared by hot pressing for 5 min at 190 °C under one metric

ton. The polyolefin films were characterized after 3 days of physi-

cal aging of room temperature. These films develops localisedstress whitening (necking) in a small region (usually) less than

2 mm, followed by the abrupt failure of the region in the brittle

failure of PP, crazing (or at least craze-like deformation) is thought

to play a major role. There observations agree with our observation

for PE. They reported that films of polyethylene copolymers pre-

pared by metallocene deform in ductile modes similar to rubber.

Some others investigators reported also that the strain-to-break

of the PE films [38–40] is much higher than PP films.

In the present work, a Shore Durometer type D hardness tester

was used. The average value of the fifteen readings, for each condi-

tion, has been presented in Figs. 16 and 17 show the effects of the

blending ratio and aging time on the hardness of different samples.

Fig. 16 shows that the measured hardness values for pure PP at dif-

ferent aging times are larger than that of PE and their blends have

intermediate values. Generally, aging time has not affected thehardness as shown in Fig. 17. These observations are correlated

to the observation of the tensile tests.

The tensile and hardness tests results indicate the presence of

some partial miscibility in the PP and PE blends. This has been ob-

served by Mourad et al. [36] through differential scanning calorim-

etry (DSC) and thermogravimetric analysis (TGA), in a dynamic

nitrogen atmosphere. The results show that, addition of PE had

caused the crystalline melting temperature heat of fusion and per-

centage crystallinity of PP main crystalline peak to decrease. Sim-

ilar observations have been also reported in [41,42].

3.2. Thermogravimetric analysis (TGA)

The thermogravimetric analysis (TGA) in a dynamic air atmo-sphere and derivative thermogravimetric analysis (DTA) were

0

100

200

300

400

500

600

0 2 4 6 8 10 12 14

Aging time.

M o d u l u s o f e l a s t i c i t y ( M P a ) .

100:0 75:25 50:50 25:75 0:100

Fig. 15. Independence of modulus of elasticity (secant) from the aging time for

different PE/PP blend samples.

50

55

60

65

70

75

80

100/0 75/25 50/50 25/75 0/100

Blending ratio

H

a r d n e s s

0 days

2 days4 days

7 days

14 days

Fig. 16. Variation of hardness with blending ratio.

0

100

200

300

400

500

600

0 2 4 6 8 10 12 14

Aging time.

M o d u l u s o f e

l a s t i c i t y ( M P a ) .

100:0 75:25 50:50 25:75 0:100

Fig. 14. Independence of modulus of elasticity (tangent) from the aging time for

different PE/PP blend samples.

40

45

50

55

60

65

70

75

80

0 2 4 7 14

Aging time, days

H a r d n e s s

100/0

75/25

50/50

25/75

0/100

Fig. 17. Hardness variation with aging time.




performed on all thermally unaged and aged neat polymers and

their blends in order to investigate the effect of blending ratio

and the aging time on the thermal decomposition. The thermo-

gravimetric curves are grouped into five collective figures each of

which for a particular aging time. The same was done for the deriv-

ative thermogravimetry (DTG) curves. All measurements were

made in duplicate with good repeatability. The TGA in a dynamic

nitrogen atmosphere has been investigated by Mourad et al. [36].

3.3. Decomposition temperatures T d(1%), T d, T max and T d(99%)

A typical thermogravimetric analysis (TGA) and the derivative

thermogravimetry (DTG) curves, obtained from the apparatus,

showing the different decomposition temperatures are shown in

Fig. 18. The figure shows also how the onset/initial degradation

temperature based on the machine definition T d (°C) (at the inter-

section of the two tangents of 1st and 2nd TGA curve), the maxi-

mum rate of decomposition temperature T max (°C) (at the DTG

curve peak), the final decomposition temperature T d(99%) (°C) (atwhich 99% of weight has been lost). Another initial decomposition

temperature at which 1% of the sample weight has been lost also

calculated from the raw data of the TGA thermogramme. T d(99%)

identifies the temperature at which the polymer starts to degrade

at an early stage and eliminates the discrepancy that might occur

due to the construction of the two tangents while calculating T d.

Three representative TGA thermogram groups, for thermallyunaged and aged (for 2 and 14 days) blends are shown in Figs.

19–21. It is seen that all TGA curves are single-stage mass decrease

(loss) curves (e.g., single-stage decomposition). The T d(1%), Td, Tmax

and T d(99%) decomposition temperatures for all blends are summa-

rized in Table 1. It is seen that all samples started to decompose at

no less than 365 °C. Although the thermal stability in the industrial

applications depends on operating temperature and exposure time,

this relatively high temperature might indicate the thermal stabil-

ity in a wide operating temperature range. A higher corresponding

decomposition temperature (i.e., 380 °C), in a dynamic nitrogen

atmosphere, for the same blends has been reported by Mourad

et al. [36] which shows less thermal stability in the real service

conditions. Table 1 shows also that the T d, T d(1%) and T max decompo-

sition temperatures of neat unaged PP are relatively higher thanthat for neat unaged PE. However, the T (d99%) is found to be

Fig. 18. A typical apparatus TGA thermogramme (in a dynamic air atmosphere) and its first derivative (DTG) for thermally aged (for 14 days) pure PP showing onset of

decomposition T d (390.33 °C) and max decomposition rate (415.91 °C) temperatures.

0

20

40

60

80

100

120

0 100 200 300 400 500 600 700

0.0/100

25/75

50/50

75/25

100/0.0

W e i g h t ( % )

Temperature (oC)

Fig. 19. TGA thermograms (in a dynamic air atmosphere) of degradation (weight

loss) as a function of temperature for thermally unaged blends (0.0 days).

0

20

40

60

80

100

120

0 100 200 300 400 500 600 700

0.0/100

25/75

50/50

75/25

100/0.0

W e i g h t ( % )

Temperature (oC)


loss) as a function of temperature for thermally aged (for 2 days).




relatively higher for neat PP than PE. These observations of the

decomposition temperatures reveal that the PP has a relatively

higher thermal stability than PE. Fig. 22 shows the variation of

the in air atmosphere initial decomposition temperature T d(1%)

with PE content within thermally unaged and aged blends. The

thermally unaged and aged pure PE samples have relatively higher

T d(1%) than pure PP samples and the blends of PE%/PP% (75%/25%,

50%/%/50% and 25%/75%) have intermediate values. It is worth not-

ing also that, the 50%/50% blend has relatively lower values than

other two blends. This behaviour is consistent for all thermally un-

treated and treated samples as shown in Fig. 22. As the content of

either PE or PP increases (i.e., 75%/25% and 25%/75%), decomposi-tion is slightly retarded and hence the T d(1%) increases if compared

with pure PE samples. This may be explained on the basis that the

two polymers are partially miscible and is also consistent with the

fact that PE and PP decompose to structure like products and the

lower values of 50%/50% blend may be a consequence of the co-

continuous phase effect. Fig. 23 shows the independence of T d(1%)

from the aging time within thermally unaged and aged blends

(i.e., the aging time has not influenced the T d(1%) of various ther-

mally unaged and aged polymers. Table 1 shows also that the pre-

vious observations for T d hold true for T d(1%).

Fig. 24 demonstrates that the unaged and aged pure PE samples

have relatively higher maximum decomposition rate temperature

T max than pure PP samples as for T d(1%). Also, the trend of variation

of T max with PE content is almost similar to that for T d(1%). Further-more, the results demonstrated that, T max is independent of aging

0

20

40

60

80

100

120

0 100 200 300 400 500 600 700

0.0/100

25/75

50/50

75/25

100/0.0

W

e i g h t ( % )

Temperature (oC)


loss) as a function of temperature for thermally aged (for 14 days).

Table 1

The decomposition temperatures in air atmosphere for unaged and aged blends.

PE/PP (wt.%) aging times (day) T d (°

C) T d(1%) (°

C) T max (°

C) T d(99%) (°

C)0.0/100 0.00 381 308 427 573

2.00 381 306 417 574

4.00 385 304 412 582

7.00 376 303 404 576

14.00 390 302 400 578

25/75 0.00 379 306 425 573

2.00 375 305 415 574

4.00 380 302 412 580

7.00 370 302 402 582

14.00 382 300 399 580

50/50 0.00 376 297 394 570

2.00 365 296 392 567

4.00 375 295 390 581

7.00 377 295 385 583

14.00 369 293 380 585

75/25 0.00 372 297 420 567

2.00 369 294 417 5734.00 368 295 412 580

7.00 371 295 407 575

14.00 375 293 395 583

100/0.0 0.00 372 290 398 568

2.00 368 289 397 577

4.00 370 289 392 575

7.00 367 291 391 578

14.00 367 288 391 580

T d = the onset of degradation temperature based on the machine definition (°C);

T d(1%) = the initial/onset decomposition temperature at 1% sample weight loss (°C);

T max = the maximum rate of decomposition temperature (°C); T d(99%) = the tem-

perature at which 99% of weight has been lost.

260

270

280

290

300

310

320

330

340

0 25 50 75 100

0 day

2 days

4 days

7 days

14 days

T d ( 1 % ) ( o C )

PE content (wt %)

Fig. 22. Variation of the in air atmosphere initial decomposition temperature T d(1%)

with PE content within thermally unaged and aged blends.

260

270

280

290

300

310

320

330

340

0 2 4 6 8 10 12 14

0 %

25 %

50 %

75 %

100 %

T d ( 1 % ) ( o C )

Aging time (day)

Fig. 23. Independence of the in air atmosphere initial decomposition temperature

T d(1%) from the aging time within thermally unaged and aged blends.

300

320

340

360

380

400

420

440

460

480

500

0 25 50 75 100

0 Day

2 Days

4 Days

7 Days

14 Days

T m a x

( o C )

PE content (w%)

Fig. 24. Influence of the in air atmosphere maximum decomposition rate temper-

ature T max from theblendPE content withinthe various thermally unaged andaged

blends.




time which is analogous to that for T d(1%). Similar results have been

reported by Mourad et al. [36] for the same blends in dynamic

nitrogen atmosphere.

The values of the T d(1%) and T d are very critical in the design and

processing of polymeric components, since they could indicate

which would be the processing and manufacturing temperatures

without continuing or initiating a process of decomposition, espe-

cially in blends of recycled material. The results obtained regarding

the initial temperature of the decomposition process show that the

introduction of VLDPE results in the degradation beginning at

slightly lower temperatures.

Table 1 illustrates also that, the T d(99%) for unaged pure PP(573.4 °C) is little higher than that for unaged pure PE (567.7).

The values for unaged and aged samples vary within difference

range of 17 °C (3% of the maximum value). This reflects again al-

most an independent variation of T d(99%) from PE content and aging

time.

The decomposition temperature range (DT = T d(99%) À T d(1%)) is

calculated and presented in Table 2, from which it is clear that

the degradation temperature range varies from DT = 267 up to

DT = 293 °C. The pure and unaged PP sample has the lowest degra-

dation temperature range (265 °C) among all samples. This is also

consistent for all aging times, because of the higher T d(1%) it has and

almost same T d(99%) value as other blends. The 50% PE/50% PP blend

of 14 days aging time has the maximum degradation temperature

range, this is due to its lower value of T d(1%) (early start of decom-position) and almost same T d(99%) as other blends. This is also pos-

sibly due to a cooperative effect resulting from less dominance in

either of the blend components. Similar observation has been re-

ported for dynamic nitrogen atmosphere [36].

For all examined blends, residues were not obtained, based on a

sample weight of 9 mg:10 mg, as seen in the TGA thermograms of

Figs. 18–21. This illustrates that nearly all the sample weight sub-

jected to degradation was transformed into volatile material and

the decomposition led to a complete vaporization of the sample.

This could be because the investigated material is of organic

nature.

4. Conclusions

The main goal of this work was to investigate the effect of ther-

mal aging and blend composition on the thermo-mechanical

behaviour of unblended vLDPE and i-PP and their blends. Based

on the results of this study the following main conclusions could

be drawn:

All tested specimens exhibited necking and cold drawing. Strain

to break/percentage elongation (e%) for pure vLDPE samples was

much higher than that for pure i-PP samples and their blends

had an intermediate performance.

Two distinctive tensile behaviour trends were observed for

vLDPE and i-PP samples and an intermediate behaviour trend

was observed for their blends.

Addition of vLDPE to i-PP caused the modulus of elasticity andyield strength of i-PP to decrease.

The addition of vLDPE to the i-PP by the weight ratio of 25:75

reduced the percentage crystallinity by ca. 20% [36] while

retaining almost the same values for the modulus of elasticity

and yield strength. Further addition of PE content dramatically

diminished the mechanical performance of the i-PP. It is highly

recommended that no further addition of PE should take place

beyond the 25% mark, while it is equally important to further

study the structure–property relationship for blends of less PE

content in later studies.

The tested thermal aging periods had no influence on tensile and

hardness behaviour of pure and blend samples.

The decomposition temperatures from the TGA in a dynamic air

atmosphere illustrate that all samples started to decompose at

no less than 365 °C.

The tested thermal aging periods had no influence on the ther-

mal behaviour of pure and blended polymers, However, the PE

content has found to have some influence on the thermal stabil-

ity/decomposition temperatures.

The decomposition temperatures variations with blend ratio and

aging time in both dynamic nitrogen [36] and air atmospheres

are analogous,

The thermo-mechanical properties reveal that the i-PP and

vLDPE are partially miscible/compatible and the resulting

blends were not fully homogeneous. These results are supported

by the observation of other investigators [41,42].

Acknowledgements

The author appreciate the help of Eng. Jayarajan Kadachi and

Mr. Francis Corriea of DUCAB company, Jabel Ali, Dubai, in con-

ducting the tensile tests and also the assistance of Eng. R. Akkad

in plotting the tensile curves.

References

[1] Mendell JF, Roberts DR, MGarry FJ. Plane strain fracture toughness of

polyethylene pipe materials. Polym Eng Sci 1983;23:615–51.

[2] Mourad A-HI, Bekheet N, El-Butch A, Abdel-Latif L, Nafee D, Barton DC. The

effects of process parameters on the mechanical properties of die drawn

polypropylene. Polym Test 2005;24:169–80.

[3] Fouad H, Mourad A-HI, Barton DC. Irradiation and aging effects on nanoscale

mechanical properties of ultra high molecular weight polyethylene for

biomedical implants. Plast Rubber Compos Macromol Eng 2008;37:346–52.

[4] Fouad H, Mourad A-HI, Barton DC. Effect of pre-heat treatment on the static

and dynamic thermo-mechanical properties of ultra-high molecular weight

polyethylene. Polym Test 2005;24:549–56.

[5] Fouad H, Mourad A-HI, Barton DC. Semicrystalline polymers deformation and

fracture behaviour under quasistatic strain rates and triaxial states of stress.

Strength Fract Complex 2004;2:149–62.

[6] Mourad A-HI, Elsayed HF, Barton DC, Kenawy M, Abdel-Latif L. Ultra high

molecular weight polyethylene deformation and fracture behaviour as a

function of high strain rate and triaxial state of stress. Int J Fract

2003;120:501–15.

[7] Bertin Sylvie, Robin Jean-Jacques. Study and characterization of virgin and

recycled LDPE/PP blends. Eur Polym J 2002;38:2255–64.[8] Deng M, Shalaby SW. Properties of self-reinforced ultra-high-molecular-

weight polyethylene composites. Biomaterials 2007;18:645–55.

[9] Lewis G. Properties of crosslinked ultra-high molecular weight polyethylene.

Biomaterials 2001;22:371–401.

[10] Jose S, Aprem AS, Francis B, Chandy MC, Werner P, Alstaedt V, et al. Phase

morphology, crystallisation behaviour and mechanical properties of isotactic

polypropylene/high density polyethylene blends. Eur Polymer J

2004;40:2105–15.

[11] Plochocki AP, Dagli SS, Andrews RD. The interface in binary mixtures of

polymers containing a corresponding block copolymer: effects of industrial

mixing processes and of coalescence. Polym Eng Sci 1990;30:741–52.

[12] Loos L, Bonnet M, Petermann J. Morphologies and mechanical properties of

syndiotactic polypropylene (sPP)/polyethylene (PE) blends. Polymer

2000;41:351–6.

[13] Barlow JW, Paul DR. Polym Eng Sci 1984;8:24.

[14] Chang-Sik H, Hae-Dong P, Youngkyoo K, Soon-Ki K, Won-Jet C. Polym Adv

Technol 1996;7:483–92.

[15] Fortelny I, Krulis IZ, Michalkova ZD, Horak Z. Effect of EPDM admixture and

mixing conditions on the morphology and mechanical properties of LDPE/PPblends. Die Angew Makromol Chem 1996;238:97–104.

Table 2

The decomposition temperature range (DT ) for thermally unaged and aged samples.

PE/PP ratios DT = (T d(99%) À T d(1%)) (°C)

(0 day) (2 days) (4 days) (7 days) (14 days)

0.0/100 265 268 278 273 276

25/75 267 269 278 280 280

50:50 273 272 286 289 293

75/25 270 279 285 281 290

100/0.0 279 288 286 286 292




[16] Chunley Si, Chen Wei. Shenyang Huagong Xueyuan Xuebao 1996;10:65–6.

[17] Arroyo MR, Lopez-Manchado MA. J Polym Eng 1995;14:237–52.

[18] Wong AC-Y, Lam F. Study of selected thermal characteristics of polypropylene/

polyethylene binary blends using DSC and TGA. Polym Test 2002;21:691–6.

[19] Wong AC-Y. The study of the relationships between melt index, density and

blend ratio of binary polyethylene blends. Polym Eng Sci 1991;31:549.

[20] Blom HP, Teh JW, Rudin A. IPP/HDPE blends: interactions at lower HDPE

contents. J Appl Polym Sci 1995;58:995–1006.

[21] Teh JW. Structure and properties of polyethylene–polypropylene blend. J Appl

Polym Sci 1983;28:605–18.

[22] Teh JW, Noordin R, Low AKY. Recycling of mixed plastic wast – is separationworthwhile. In: Proceedings, international plastics conference, Kuala Lumpur,

Malaysia, 22–24 October 1985.

[23] Krause S. In: Paul DR, Newman S, editors. Polymer blends, vol. 1. New

York: Academic Press; 1978. p. 15.

[24] Solc K, editor. Polymer compatibility and incompatibility, principles and

practices. New York: MMI Press Symposium, Harwood Academic; 1982.

[25] Plochocki AP, Paul DR, Newman S. Polymer blends, vol. 2. New York: Academic

Press; 1978.

[26] Kostoski D, Babic D, Stojanovic Z, Gal O. Mechanical and thermal properties of

gamma irradiated iPP-LDPE blends. Int J Radiat Appl Instrum, Part C: Radiat

Phys Chem 1986;28(3):269–72.

[27] Schurmann BL, Niebergall U, Severin N, Burger CH, Stocker W, Rabe JP.

Polyethylene (HDPE)/polypropylene (i-PP) blends: mechanical properties,

structure and morphology. Polymer 1998;39:5283–91.

[28] Waldman WR, De Paoli Marco A. Thermo-mechanical degradation of

polypropylene, low-density polyethylene and their 1.l blend. Polym Degrad

Stab 1998;60:301–8.

[29] Kesari Jaisimha, Salovey Ronald. Mechanical behaviour of polyolefin blends.

Advances in chemistry series 206 polymer blends and composites in

multiphase systems 1984;vol. 34:211–9.

[30] Ho W, Salovey Ronald. Polym Eng Sci 1981;21:829.

[31] Bucknall CB. Toughened plastics. London: Applied Science Publishers, Ltd.;

1977.

[32] Martuscelli E, Silvestre C, Abate G. Morphology crystallization and melting

behaviour of films of isotactic polypropylene blended with ethylene–

propylene copolymers and polyisobutylene. Polymer 1982;23:229–37.

[33] Barlett DW, Barlow JW, Paul DR. Mechanical properties of blends containing

HDPE and PP. J Appl Polym Sci 1982;27:2351–60.

[34] Kukaleva Ntalia, Simon George. The effect of blending on the viscosity

reduction of recycled milk bottle grade HDPE. CRC for polymers. Department

of Materials Engineering, Monash University, Australia; 2000.[35] Mizutani Y, Nago S. Microporous polypropylene films containing ultrafine

silica particles. J Appl Polym Sci 1999;72(11):1489–94.

[36] Mourad A-HI, Akkad R, Ahmad S, Tarek M. Characterization of thermally

treated and untreated polyethylene–polypropylene blends, accepted for

publication in plastics, rubber and composites. Macromol Eng 2009;1:1–5.

[37] Lee Jonghwi, Macosko Christopher W, Bates Frank S. Development of discrete

nanipores. 1: Tension of polypropylene/polyethylene copolymer blends. J Appl

Polym Sci 2004;91:3642–50.

[38] Chaffin KA. Ph.D. Thesis, University of Minnesota, Twin Cities; 1999.

[39] Chen YY, Lodge TP, Bates FS. Entropically-driven phase separation of highly

branched/linear polyolefin blends. J Polym Sci, Part B: Polym Phys

2000;38:2965–75.

[40] Chaffin KA, Knutsen JS, Brant P, Bates F. High strength welds in metallocene

polypropylene/polyethylene laminates science 2000;288:2187–90.

[41] Li J, Shanks RA, Long Y. Miscibility and crystallisation of metallocene

polyethylene blends with polypropylene. J Appl Polym Sci 2003;87:1179–89.

[42] Li J, Shanks RA, LongY. Miscibility and crystallisation of polypropylene – linear

low density polyethylene blends. Polymer 2001;42:1941–51.


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