Effect of MMT concentrations as reinforcement on the properties of recycled PET/HDPE nanocomposites

DOI 10.1515/polyeng-2013-0107 J Polym Eng 2013; aop

Rizuan Mohd Rosnan and Agus Arsad *

Effect of MMT concentrations as reinforcement on the properties of recycled PET/HDPE nanocomposites Abstract: The objective of this research is to investigate

the effect of incorporating montmorillonite (MMT) on the

mechanical, morphological, rheological, and thermal

properties of recycled poly(ethylene terephthalate) (rPET)

and high-density polyethylene (HDPE) nanocomposites.

The MMT contents in 90:10 rPET/HDPE and 70:30 rPET/

HDPE ranged from 1 to 5 wt.%. rPET/HDPE nanocom-

posites were prepared by using a single screw extruder,

and injection molded to prepare mechanical test speci-

mens. The samples underwent rheological tests by using

a capillary rheometer, and the morphology of the nano-

composites was investigated by scanning electron micro-

scopy (SEM). The thermal stability of the nanocomposites

was tested using thermogravimetric analysis (TGA). The

results showed that MMT acts as compatibilizing agent

and improves phase dispersion and interfacial adhesion

in the nanocomposites. The maximum tensile strength

was found at 3 and 1 wt.% of MMT for the 90:10 and

70:30 rPET/HDPE blends. However, the tensile modulus

decreased significantly with the incorporation of MMT.

The impact strength for both the 90:10 and 70:30 blends

reached a maximum at 3 wt.% and started to decrease

beyond 3 wt.%. The incorporation of MMT increased

the shear viscosity of the 90:10 and 70:30 blends, which

reached a maximum value at 3 and 1 wt.%. SEM micro-

graphs showed a good interaction of MMT that improved

the adhesion between the two phases of blends and led

to an increase in the mechanical properties of rPET/HDPE

nanocomposites.

Keywords: nanocomposites; recycled PET; rheological;

rPET/HDPE.

*Corresponding author: Agus Arsad, Faculty of Chemical

Engineering, Department of Polymer Engineering, Universiti

Teknologi Malaysia, 81310 Skudai, Johor Bahru, Malaysia,

e-mail: [email protected]

Rizuan Mohd Rosnan: Faculty of Chemical Engineering, Department

of Polymer Engineering, Universiti Teknologi Malaysia, 81310

Skudai, Johor Bahru, Malaysia

1 Introduction Polyethylene terephthalate (PET) is considered one of the

most important technical plastics. The blends of PET with

other polymers, in particular with polyolefins, may offer an

attractive balance of mechanical and barrier properties and

processability [1] . The amount of PET used in the plastics

industry (especially for beverage bottles) has significantly

increased. Hence, the problem of sufficient recycling has

become more and more challenging. Recycling offers an

alternative solution for handling plastic wastes. Moreover,

recycling plastics can reduce manufacturing resources,

conserve energy in production and shipping, and minimize

the overall impact on the environment. Thus, recycled PET

with high-density polyethylene (PET/HDPE) blends has

attracted increasing interest. Studies on rPET/HDPE blends

are mainly focused on improving the compatibility of rPET

and HDPE, as they are inherently incompatible [2] owing to

the great difference in solubility between them [3] .

Most of the studies are based on the PET matrix with

a minor portion of HDPE. It has been shown that PET/

HDPE blends are less brittle than PET, and are stiffer,

faster to prepare for processing, better flowing, and faster

cooling than HDPE [4, 5] . Satisfactory performance in

immiscible blends is usually attained by minimizing the

interfacial tension and improving the adhesion between

the two phases. Therefore, the recycled blends must have

reinforcement agents to achieve the desired properties. To

date, various polymer/montmorillonite (MMT) blends have

shown promising combinations that have brought about

enhancements in PET/MMT nanocomposite development

[6 – 8] .

Nevertheless, being thermodynamically immiscible

because of the coarse morphology, which corresponds to

very poor mechanical properties, is one of the drawbacks

of rPET and HDPE blends [9, 10] . Therefore, to overcome

this situation, compatibilizers were introduced, such as

polyethylene grafted with maleic anhydride (PE-g-MAH)

[11] . In this study, an attempt was made to develop rPET/

HDPE nanocomposites compatibilized by HDPE-g-MAH.

The effects of various MMT contents on the mechanical,

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2 R. Mohd Rosnan and A. Arsad: Effect of MMT on rPET/HDPE nanocomposites

morphological, thermal, and rheological properties of

rPET/PE nanocomposites were investigated.

2 Experiments

2.1 Materials

There are four main components used in this research:

rPET, HDPE, PE-g-MAH, and MMT. rPET was collected

from excess material, rejected products, and leftovers

from the plastics industries [Texchem-Pack (Johor) Sdn

Bhd, Johor, Malaysia]. This material was bought directly

from the factory. The general-purpose HDPE resin Titanex

was manufactured by Titan Chemicals (Malaysia) Sdn

Bhd. MMT was obtained from Nanocor Inc., Arlington

Heights, IL, USA (Nanomer 1.28 E), organically modified

with quaternary amine with a mean dry particle size of

16 – 22 μ m. PE-g-MAH resin was bought from Sigma Aldrich

with a melt flow rate of 115 g/10 min (190 ° C/2.16 kg) and

0.6% maleic anhydrite.

2.2 Sample preparation

PET pellets were dried at 90 ° C for 24 h before com-

pounding. All constituents were compounded by a

single screw extruder (local custom made – Johor,

Malaysia) with an length/diameter (L/D) of 30. The

barrel temperature profile adopted during compound-

ing for formulations was from 200 ° C to 250 ° C at the die

head with a screw rotation speed of 30 rpm (0.02 g ). The

extruded materials were injection molded into standard

tensile, flexural, and Izod impact specimens by using a

JSW (Muroran, Japan) Model NIOOB II injection-molded

machine with a barrel temperature ranging from 220 ° C

to 260 ° C. All test specimens were kept under ambient

conditions in desiccators for at least 24 h before testing.

2.3 Characterization

2.3.1 Mechanical analysis

Tensile test was carried out according to ASTM D638 using

an Instron 5567 (Bucks, UK) machine under ambient

conditions with a crosshead speed of 50 mm/min. Izod

impact tests were carried out on notched impact speci-

mens according to ASTM 256, using a Toyoseiki (Tokyo,

Japan) impact testing machine under ambient conditions.

Five specimens of each formulation were tested and the

average values were calculated.

2.3.2 Rheological analysis

In this study, the extrusion flow tests were conducted

by using a capillary rheometer (Rheograph 2003; Gott-

fert, Germany) at Malaysian Rubber Board (LGM), Sungai

Buloh, Selangor at 230 ° C, and the apparent shear rate was

varied from 10 to 1700 s -1 to measure the melt flow curves

(relationship between shear stress and shear rate). All

data were Bagley corrected.

2.3.3 Morphological analysis

A scanning electron microscope (SEM) type JEOL JSM-6390

LV with an intensity of 9 × 10 -9 A, 25 kV, was employed to iden-

tify the distribution and phase separation of the nanocom-

posite. The sample was obtained from impact test samples

and cut to 1-mm thickness. These samples were then coated

with a thin layer of gold before conducting the test.

2.3.4 Thermal analysis

The nanocomposites then underwent thermal analysis

by using a thermogravimetric analyzer (TGA) to study the

degradation and stability of the organoclay and compat-

ibility between rPET and HDPE phases. The tests were

carried out using a Perkin Elmer Pyrist 6 TGA analyzer at

the Polymer Laboratory, Faculty of Chemical Engineering,

UTM Johor Bahru, Johor. The samples were scanned from

30 to 850 ° C at a heating rate of 20 ° C/min.

3 Results and discussion

3.1 Mechanical analysis

Figure 1 shows the reduction in tensile strength of the

blends by the introduction of HDPE content. In 70:30

rPET/HDPE nanocomposites, the tensile strength was

reduced as compared with 100% rPET, followed by the

90:10 ratio. The decrease of tensile strength is dependent

on lower PET and higher HDPE contents [12] , in which the

tensile strength of the blend increased proportionally with

PET concentration. Therefore, by increasing the HDPE

content in rPET, the tensile properties were decreased.



R. Mohd Rosnan and A. Arsad: Effect of MMT on rPET/HDPE nanocomposites 3

However, by incorporating MMT into the system,

it has shown a small improvement in tensile strength.

The tensile strength for the composition of 90:10 rPET/

HDPE showed an increment from 1 to 3 phr of MMT

with a maximum at 24.9 MPa. It was the highest peak of

tensile strength in the composition before the properties

were decreased when 5 phr of MMT loading was reached.

However, the tensile strength of 70:30 rPET/HDPE nano-

composites was maximum at 34.8 MPa with 1 phr of MMT.

It was the best tensile strength among these compositions.

The tensile strength was maintained at 32.1 MPa with

3 phr of MMT before being drastically reduced to 22.1 MPa

at 5 phr MMT loading, contributing to 30% reduction of

the properties.

This result has shown that addition of small

amounts of organoclay in the system can help increase

the mechanical properties of rPET. The tensile strength

decreased when the MMT loading was at 5 phr for the

70:30 ratio of rPET/HDPE nanocomposites. Thus, a higher

content of MMT did not give rise to further improvement.

This might be assumed to be because the agglomeration

of MMT layers occurred at higher MMT loading of > 3 phr

and caused a reduction of tensile and flexural strength,

elongation at break, and impact strength properties.

This result is in agreement with the study by Wang et al.

[13] . A similar effect was also shown by the 90:10 rPET/

HDPE nanocomposites. However, the introduction of 1

phr of MMT contributed to the drastic increase in tensile

strength, and no further increment was found beyond the

MMT addition of 1 phr. In conclusion, the result showed

that the optimal nanoclay concentration for the tensile

strength of either 70:30 or 90:10 rPET/HDPE nanocom-

posites was 3 phr.

Figure 1 Effect of MMT concentrations on tensile strength at

different ratios of rPET/HDPE. Figure 2 Effect of MMT concentrations on tensile modulus at

different ratios of rPET/HDPE.

Figure 2 shows the performances of the tensile

modulus of rPET/HDPE nanocomposites of different MMT

contents. From the figure, it can be seen that the tensile

modulus was decreased by increasing the HDPE content

of nanocomposites. It can be seen that the tensile modulus

for both formulation has resulted in a proportional reduc-

tion in properties when HDPE was added. The tensile

modulus for 100% rPET decreased from 2.40 to 2.18 GPa at

10% HDPE. The tensile modulus was further decreased to

1.83 GPa by the addition of 30% HDPE. This is an indica-

tion of increasing HDPE content in the rPET matrix, which

implies that the system obeys the rules of mixture [14] .

From the figure, it can be seen that the tensile modulus

decreased by the addition of MMT into the system. The

composition of 90:10 rPET/HDPE has shown a decrease in

stiffness at 1 phr of MMT addition. The stiffness was further

decreased by the addition of 5 phr MMT. This reduction

indicates that MMT had no significant effect in increas-

ing the tensile modulus due to composition dependence.

A similar trend has also been found for the 70:30 rPET/

HDPE ratio when the increment of MMT content up to

5 phr caused a reduction in the tensile modulus.

Figure 3 shows a plot of strain at break for rPET/HDPE

vs. the addition of MMT into the nanocomposites. By

adding HDPE into the system, it was found that the elon-

gation experienced a reduction from 100% rPET, followed

by the 70:30 and 90:10 rPET/HDPE nanocomposites. From

the figure, 100% rPET showed the highest value of elonga-

tion at break at 2.8%, followed by 2.2% for the 70:30 and

1.1% for the 90:10 rPET/HDPE nanocomposites. By refer-

ring to the result, it shows that the incompatibility of rPET

and HDPE was attributed to poor strain at break proper-

ties and also because of the higher HDPE content [15] .




The properties experienced an improvement for

the 90:10 rPET/HDPE nanocomposites when the MMT

was incorporated into the system. The properties were

slightly increased when MMT was loaded up to 3 phr.

It showed that the agreement of the statement of strain

at break has followed the trend of tensile strength

( Figure 1 ). The strain at break for 70:30 rPET/HDPE nano-

composites decreased with further addition of 3 phr of

MMT. This result contradicted with the finding reported

by Dimitrova et al. [16] , and they stated that the improve-

ment of strain at break might be due to a good dispersion

of MMT in the system that was able to promote a better

adhesion of the two phases and help enhance the prop-

erties. Unfortunately, the given reason was not applica-

ble for this study.

However, the properties of 70:30 rPET/HDPE nano-

composites achieved the ultimate improvement when the

highest percentage of elongation at break was observed.

Hence, it has shown the best performance compared with

100% rPET and has been the ideal composition among

others. The improvement would be due to the presence of

MMT in the composition that has contributed to the incre-

ment of the property by achieving a maximum percentage

at 3.6% of elongation at break up to 3 phr of MMT before

decreasing to 2.5% at 5 phr of MMT.

Figure 4 shows the effects of MMT concentrations on

the Izod impact strength of rPET/HDPE nanocomposites.

From the figure, the decrement of impact strength of the

blends by increasing the HDPE contents in the system

can be clearly seen. The impact properties of the blends

depended on the ratio of HDPE and rPET, in agreement

with the previous study [17] . The trend of impact strength

with the addition of HDPE into rPET was in agreement

with tensile strength and strain at break. However, the

introduction of 3 phr MMT into 70:30 rPET/HDPE nano-

composites increased the impact strength to higher than

that of 100% rPET.

The 90:10 rPET/HDPE nanocomposites has shown

a slight reduction of properties before 1 phr of MMT was

loaded into the system. The reduction of impact strength

could be attributed to the immobilization of the macromo-

lecular chains by the MMT particles, which limited their

ability to adapt the deformation and promoted embrittle-

ment. However, the impact strength increased at 3 phr of

MMT before the properties slightly decreased at 5 phr of

MMT. The increment was assumed to be due to the good

dispersion of MMT within the polymer matrix, which

contributed to the improvement in adhesion at the inter-

face [13] . Hence, a high dispersion degree and interfacial

adhesion between the components are expected to signifi-

cantly enhance the impact properties of 90:10 rPET/HDPE

nanocomposites, which is relative to the improvement of

tensile strength at 3 phr of MMT loading.

A similar trend has been plotted at a composition of

70:30 rPET/HDPE nanocomposites. The improvement

was observed when the impact strength increased with

≥ 1 phr of MMT loaded. The impact strength of 70:30 rPET/

HDPE compositions without MMT has shown a lower

value compared with MMT loaded by assuming poor

adhesion between the blends. Then, the impact strength

was continuously increased by incorporating the blend

with 3 phr of MMT. The result showed the highest value

of impact strength at a maximum of 5.87 kJ/m 2 . Interest-

ingly, the substantial increases of tensile strength were

also contributed by the incorporation of 3 phr of MMT at

this composition.

Figure 4 Effect of MMT concentrations on impact strength at

different rPET/HDPE ratios.

Figure 3 Effect of MMT concentrations on strain at break at

different rPET/HDPE ratios.




From the finding, it may be assumed to be due to the

good dispersion of MMT, which improved the adhesion

between the two phases of the components and led to an

increase in the mechanical properties. However, the prop-

erty was slightly decreased to 5.08 kJ/m 2 when 5 phr of

MMT was loaded into the 70:30 rPET/HDPE composition.

Agglomeration of organoclay at high loading may induce

local stress concentration in the composites [18] . In addi-

tion, in agreement with a previous study [13] , the MMT

dispersion is not ideal in higher loading and incomplete

intercalation will reduce the properties.

3.2 Rheological analysis

Shear viscosity, η , is the viscosity coefficient when the

applied stress is shear stress. Shear viscosity is the ratio of

the shear stress to the shear rate. In the current work, the

shear viscosity of samples were analyzed and discussed

to understand the effect of nanoclay composition on the

polymer blends. The effect of 0, 1, 3, and 5 phr of MMT

to those of rPET/HDPE compositions at 230 ° C at various

shear rates are shown in Figures 5 and 6 , respectively.

The 90:10 rPET/HDPE nanocomposites in Figure 5 show a

typical pseudo-plastic non-Newtonian property by reduc-

ing the shear viscosity with increasing shear rate.

In general, the increment of melt viscosity from

unfilled blends to nanoclay-filled blends up to 5 phr MMT

was shown to be in agreement with the Newtonian behav-

ior in the lower shear rate region. The increment of the

shear viscosity of polymer was due to the good interac-

tion between the polymer blends and the nanoclay. rPET

alone showed the lowest shear viscosity owing to the no

Figure 5 Plots of shear viscosity as a function of shear rate for the

90:10 rPET/HDPE blends at different loadings of MMT.

Figure 6 Plots of shear viscosity as a function of shear rate for the

70:30 rPET/HDPE blends at different loadings of MMT.

additional polymer composition or nanofiller as a rein-

forcement as expected. The SEM micrograph of this struc-

ture has been proved to show a strong incompatibility

evidenced by the rheological tests. Moreover, it was attri-

buted to the immiscible composition between rPET and

HDPE due to the inherent incompatibility between the two

phases. Figure 5 shows that the highest shear viscosity was

at 3 phr of MMT, followed by 1, 0, and 5 phr, respectively.

The highest shear viscosity of 3 phr MMT was due to the

sufficient amount of MMT to form a packed arrangement,

which provided good dispersion and distribution in the

rPET phase. This finding is an agreement with the study

by Razak et al. [19] , where MMT was more well dispersed

in the rPET phase than in the in ABS phase, as MMT was

increased to the optimum amount to achieve a maximum

shear viscosity. However, 5 phr of MMT showed the lowest

shear viscosity among the nanocomposites owing to the

excess amount of MMT contributing to the combination

of agglomeration and small particles to form non-uniform

MMT dispersion and distribution in the system, and low-

ering the adhesion between the two phases of MMT and

the matrix.

The flow curves of all the nanocomposites containing

MMT showed an increment of melt viscosity owing to the

surface adhesion that has been successfully generated.

The composition of 90:10 rPET/HDPE nanocomposites has

shown better properties of tensile and impact at loading

up to 3 phr of MMT through a morphological study, com-

pared with others. This might be due to the good interac-

tion of the composition with 3 phr MMT addition, which

enhanced the properties. The SEM micrograph showed

more uniform particles in dispersed phase with smaller




dimensions, resulting in better adhesion as compared

with the blend without MMT.

Figure 6 shows the rheological flow curves for the

70:30 rPET/HDPE nanocomposites. A similar trend has

been shown in 90:10 rPET/HDPE compositions when the

curves of unfilled blends were lower than those of the filled

blends. The composition of 70:30 rPET/HDPE nanocom-

posites has shown better properties of tensile and impact

at a loading of 1 phr of MMT. However, the nanocompos-

ites showed a different result with the incorporated blend

of 5 phr of MMT. The blend with 5 phr MMT showed the

lowest viscosity curve among the nanocomposites, and it

might be assumed that the higher content of HDPE and

MMT can be attributed to the inhomogeneous disper-

sion in the molten phase and reflected to the decrease of

mechanical properties. In this case, it was suggested that

the interfacial adhesion of the blends filled with 5 phr

MMT was poor owing to the high viscosity of HDPE that

potentially agglomerated, and attributed to the poor dis-

persion of MMT with the polymer matrix phase. The ten-

dency of MMT agglomeration influenced the organoclay

function to play its role in improving the properties.

From the research done, it was found that the 90:10

rPET/HDPE nanocomposites have a good reaction with the

incorporation of 3 phr of MMT, whereas 70:30 rPET/HDPE

was only effective with 1 phr of MMT loading. Therefore, the

conclusion that might be suggested is that by increasing

HDPE content, the effectiveness of MMT will be decreased.

This might be due to the hyperphobic behavior of HDPE

that affected the interaction of MMT with the system. Thus,

the percentages of effectiveness of MMT were decreased by

increasing the HDPE content of the system.

3.3 Morphological analysis

Figures 7 A and 8 A show that there was almost no inter-

action and adhesion between rPET and HDPE. Without

the presence of MMT as a reinforcement, the investigated

blends for all compositions showed the typical morpho-

logy of incompatible systems with a poor distribution of

the components and no adhesion between the matrix and

the dispersed phase. The clean surface of the dispersed

particles and voids was observed in the SEM micrographs

of impact fractured surfaces and indicates the weak-

ness of the interaction between these two materials. The

inherent incompatibility of HDPE with rPET is the cause

for the blends producing two-phase materials. Moreover,

the voids occurring at places where the dispersed parti-

cles were located showed that rPET and HDPE were sepa-

rated, and the possibility of a weak mechanical adherence

between them.

However, a different scenario can be seen when 1

phr of MMT was added into rPET/HDPE nanocompos-

ites. Figures 7 B – D and 8 B – D show a different surface of

fracture in which it became smoother than that without

A B

C D

90-10 rPET-HDPE-0 phr MMT100 μm 100 μm

100 μm 100 μm

90-10 rPET-HDPE-1 phr MMT

90-10 rPET-HDPE-3 phr MMT 90-10 rPET-HDPE-5 phr MMT

Figure 7 Morphology of the fracture surface of 90:10 rPET/HDPE with (A) 0 phr, (B) 1 phr, (C) 3 phr, and (D) 5 phr.




MMT in the matrix, indicating enhancement of interfacial

adhesion. The 90:30 rPET/HDPE blends without MMT in

Figure 7 A was characterized by domains clearly segre-

gated from the matrix and by wide voids in the domain

boundary. It is different in the other compositions with

MMT addition, as shown in Figures 7 B – D and 8 B – D, in

which the dispersed phase was strongly adhered to the

matrix and the fracture was propagated throughout both

phases. It is also evidenced that MMT could act as a com-

patibilizer that has the ability to attach or penetrate into

the rPET phase instead of the HDPE phase because of the

similarity in hydrophilic properties [19] . The formation of

voids in the uncompatibilized blends can be explained by

different volume shrinkages during the thermal transition

of polymers in fast cooling [20] .

Figures 7 and 8 show that HDPE appeared as an island

or in droplet form surrounded by the molten rPET phases.

This is because HDPE with a higher viscosity has the

opportunity to form agglomeration into an island form in

the molten rPET phase [21, 22] . The virgin HDPE with long

molecular chains was forced to agglomerate because of

limited mobility. This is also because of different melting

points that showed two phases of materials trying to attach

to each other to form a good combination in the presence

of MMT in order to be wet. This statement is true when the

melting range of PET (220 ° C – 260 ° C) is far higher than that

of HDPE, which solidified as a continuous phase [23] .

The HDPE phases have remained entrapped within

the rPET phase, which subsequently constituted the sub-

phase to become HDPE islands. In this case, PET is a recy-

cle-based material whose molecular structure has been

formed in short chains. Therefore, rPET has the potential

to flow very fast, owing to its short molecular chains with

lower viscosity, in order to distribute itself well and sur-

round the HDPE phases. Figure 8 C shows that the mor-

phology of 70:30 rPET/HDPE was smooth and the particle

sizes of the dispersed HDPE phase were smaller than that

of 90:10 rPET/HDPE at 3 phr of MMT addition ( Figure 7 C).

The number of voids was significantly lowered and the

morphology of the nanocomposites seemed smooth.

Some small dispersed rPET particles that appeared in

HDPE domains, however, could be ignored.

Figure 8 A – D shows that the morphologies of 70:30 of

rPET/HDPE with different concentrations of MMT were

smoother than the previous blend compositions. From the

discussion, it can be assumed that MMT influenced the

morphology of the blends by preventing the coalescence

and reduction of interfacial tension. MMT improved the

adhesion between the two phases and led to an increase

in the mechanical properties. Overall, the addition of MMT

into the system has improved the compatibility between

the rPET and HDPE phases. In another words, this pro-

vides evidence that MMT acts as a compatibilizer and also

improves several mechanical properties.

A B

C D

70-30 rPET-HDPE-0 phr MMT100 μm 100 μm

100 μm 100 μm

70-30 rPET-HDPE-1 phr MMT

70-30 rPET-HDPE-3 phr MMT 70-30 rPET-HDPE5 phr MMT

Figure 8 Morphology of the fracture surface of 70:30 rPET/HDPE with (A) 0 phr, (B) 1 phr, (C) 3 phr, and (D) 5 phr.




Figure 9 TGA curves of the 90:10 rPET/HDPE nanocomposites at

10 ° C/min in N 2 .

Figure 10 TGA curves of the 70:30 rPET/HDPE nanocomposites at

10 ° C/min in N 2 .

3.4 Thermal analysis

Figure 9 shows the TGA weight loss traces of the 90:10

rPET/HDPE nanocomposites. From the figure, it can be

seen that the trend of the composition was increased in

terms of thermal stability by increasing the MMT loading

up to 5 phr. The onset of decomposition temperature of

pure rPET was about 442 ° C, and the temperature at which

pure rPET degraded was at about 599 ° C.

As a comparison, the 90:10 rPET/HDPE nanocompo-

sites without MMT content began to degrade at 440 ° C and

degraded the fastest at about 494 ° C. This is because the

presence of HDPE limited the thermal resistance of the

polymers. However, the subsequent addition of MMT to

the blend further increased the onset of degradation tem-

perature especially at 3 phr of MMT. The nanocomposites

were extended to degrade at 442 ° C and degraded at about

520 ° C. The increase in the degradation onset tempera-

ture was possibly due to the improved thermal stability

of the rPET/HDPE component after reacting with MMT.

It is shown that the blend experienced a good disper-

sion phase and strongly adhered to the matrix. The use of

the right additives influenced the thermal stability of the

rPET/HDPE nanocomposite system, and together it linked

to achieve the highest tensile strength of 90:10 rPET/HDPE

nanocomposites with 3 phr of MMT reinforcement.

The enhancement of rPET thermal stability with the

addition of MMT is more apparent in the 70:30 rPET/HDPE

nanocomposites as shown in Figure 10 . The blend without

MMT had an onset of decomposition temperature limited

at 438 ° C and degraded at about 504 ° C. By incorporating

1 phr of MMT into the system, the thermal stability of the

70:30 rPET/HDPE nanocomposites has been improved

by the extension of decomposition temperature further

to 442 ° C and was degraded at about 512 ° C. Together,

the enhancement of thermal stability contributed to the

mechanical improvement by improving the tensile proper-

ties at the maximum peak.

A few researchers have agreed that MMT helps con-

tribute to the thermal stability of the blend system.

Nanoscale particles will show a stronger interaction with

the PET matrix, which enhanced the degradation tem-

perature [24] . A high interaction between the organoclay

and PET molecules improved the thermal stability of the

PET nanocomposites, which was attributed to the shield-

ing effects of the nanoclay layers [25] . Clays have good

thermal stability that could improve polymer thermal sta-

bilities owing to the heat insulation effect of the clay [26] .

Thus, it was proved that the presence of MMT has helped

enhance the rPET/HDPE nanocomposite system together

with increasing the mechanical properties.

4 Conclusion The tensile strength for the composition of 90:10 rPET/

HDPE showed an increment from 1 to 3 phr of MMT with

a maximum at 24.9 MPa, and decreased when 5 phr

of MMT addition was reached. However, the tensile

strength of 70:30 rPET/HDPE nanocomposites was at

a maximum at 1 phr of MMT. In contrast, the strain at

break was improved for both rPET/HDPE nanocom-

posites when MMT was incorporated into the system.

The impact strength for both rPET/HDPE blends was

slightly decreased by the addition of 1 phr MMT. SEM




micrographs showed more uniform dispersed particles

of smaller dimensions, with better adhesion compared

with the blend without MMT.

In rheological analysis, the increment of melt vis-

cosity from unfilled blends to nanoclay-filled blends for

both rPET/HDPE compositions was shown to be in agree-

ment with the Newtonian behavior in the lower shear rate

region. The thermal stability of 90:10 and 70:30 rPET/

HDPE nanocomposites were improved by incorporating

with MMT at 3 and 1 phr. The extension of degradation

onset temperature showed that the stable nanocompos-

ites experienced a good dispersion phase and strongly

adhered to the matrix of the rPET/HDPE nanocomposites.

Acknowledgments: This work was supported by the Uni-

versiti Teknologi Malaysia (research university grant).

Received May 1, 2013; accepted July 19, 2013

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