425

Middle East Journal of Applied Sciences 4(2): 425-435, 2014

ISSN 2077-4613

Corresponding Author: Soma Ahmed El Mogy, Polymer Metrology Lab, Chemistry Department, National Institute for

Standards, Giza, Egypt.

E-mail: soma.elmogy@yahoo.com

Creep Behavior of Carbon Nanofillers/Polypropylene Composites

1Nabila Darwish;

1Anhar Abd El Megeed;

2Nagwa Badawy;

2Amina El-Bayaa and

1Soma El-

Mogy

1Polymer Metrology Lab, Chemistry Department, National Institute for Standards, Giza, Egypt.

2Chemistry Department, Faculty of Science, Al-Azhar University for Girls, Cairo, Egypt.

ABSTRACT

Polypropylene (PP)/ nano carbon composites were prepared via melt blending PP with carbon fillers,

including multiwalled carbon nanotubes (MWNTs) and carbon black (CB) and further processed by hot

compression molding. This work focused on the mechanical behavior, especially creep resistance of

thermoplastic polypropylene with different ratios of the fillers (0, 0.5, 1, 3, 5 wt.%). From the results, the

MWNTs particles can aggregate and form a filler network, and the size of the aggregates increased with

increasing MWNTs content, while there is homogeneous dispersion in case of CB. Thermal stability of the

composite was found to be enhanced with increasing filler loadings. The WAXD patterns of the nanocomposites

show typical α-form PP crystals. The addition of MWNTs to PP composites enhances both the tensile strength

and young's modulus. Whereas presence of both MWNTs and CB in the PP matrix increases the creep resistance

and creep-recovery property and that nanocomposites based on 5 wt.% of MWNTs showed the best creep

resistance and recovery ratio.

Key words: polypropylene, carbon nanofillers, nanocomposites, creep.

Introduction

Polypropylene (PP) is one of the most widely used commodity thermoplastics due to its versatility to accept

numerous types of fillers and reinforcements. PP has been widely used in the household appliances, food

packaging, automotive components, and medical devices. PP nanocomposites have been extensively investigated

over a wide range of applications during the past few decades (Li et al., 2011; Wei et al., 2011; Zhu et al., 2011;

Zhang & Horrocks et al., 2003 and Sun et al., 2009). The reinforcement of PP has been studied by many

researchers to improve its performance (Funck & Kaminsky, 2007; Koval’chuk et al., 2008; Salaün et al., 2008;

Montagna et al., 2011 and Zhou et al., 2006). In particular, significant property enhancements were reported

when carbon nanofillers were incorporated into PP.

Carbon nanotubes (CNTs) are ideal fillers for polymer composites due to their high Young’s modulus

combined with good electrical and thermal conductivity. The very high aspect ratio makes it likely that the addition

of a small amount of CNTs strongly improves the electrical (Valentino et al., 2008), thermal (Bikiaris et al., 2008)

and mechanical (Ganß et al., 2008) properties of the polymer matrix. Thus, CNT/polymer composites combine the

good processability of the polymers with the excellent mechanical and other functional properties of the CNTs.

There are two types of CNTs: single-walled carbon nanotubes (SWNTs) and multiwalled carbon nanotubes

(MWNTs). Now MWNTs are being widely used to reinforce polymers because they can improve not only

electrical properties, but also thermal conductivity and mechanical properties (Lau and Hui, 2002).

Carbon black (CB) is the most widely used filler because of its abundant source, low density, predominant

electrical property, and low cost. It is a finely divided solid composed of primary particles of spherical shape with

diameters between a few tens and a few hundreds of nanometers that are fused together into aggregates.

However, MWNTs are a collection of several concentric graphene cylinders. The typical diameters of MWNTs

are in the 10–50 nm range, and the length of MWNTs is of the order of micrometers. So the effect of MWNTs

on the properties of polypropylene (PP) should be different from that of CB because of the structure difference

between MWNTs and CB.

Creep performance of traditional plastic materials, such as polyamide (PA), polyethylene (PE), and

polypropylene (PP), etc., as well as their composites, has been comprehensively studied in the past years (Ward,

1983 and Findley et al, 1989). Yang et al., 2007 found that with only 1 vol.% of multi-carbon nanotubes, creep

resistance of polypropylene could be significantly improved with reduced creep deformation and creep rate at a

long-term loading period. The creep strain and creep rate of TiO2 nanoparticles filled polypropylene could be

reduced by 46% and 80%, respectively, compared to those of the neat matrix (Yang et al., 2007). Some

researchers (Ganß et al., 2007; Pegoretti et al., 2004 and Vlasveld et al., 2005) declared that the creep

compliance could be decreased in thermoplastics filled with nanotubes and layered silicates. However, limited

knowledge is known about the recovery behavior of nanoparticle-filled polymers when the applied loading is

removed. Muenstedt et al., 2008 found the recoverable shear creep compliance became smaller with decreasing

426 Middle East j. Appl. Sci., 4(2): 425-435, 2014

nanoclay content under constant load. Jia et al., 2011 observed that incorporation of nanotubes remarkably

improved the creep and recovery property of polypropylene. From the previous mentioned investigations, there

are not many studies that report the creep behavior of CNTs and very few studies about that of CB based

composites under accelerated creep environment (high temperatures). It seems that the study of creep and

recovery properties for nanocomposites based on CB and MWNTs is still in its infancy. The aim of the present

work was to investigate that the effect of the incorporation of carbon black and nanotubes on the creep and

recovery properties of PP under the conditions of different temperatures, and comparison between results was

made.

Materials and Methods

Materials:

PP was supplied by oriental petrochemicals company, Egypt (in the form of homopolymer pellets). It has

density of 0.9 g/cm3, and melt flow rate of 12 g/10min (at 230°C/2.16 kg load). MWNTs were supplied from

Nanoscience and Nanotechnology unit, Beni-Suef University, Egypt. It is synthesized by chemical vapor deposition

(CVD) method. Iron-Cobalt/Calcium carbonate, Fe-Co/CaCO3, was used as catalyst/support mixture. These

nanotubes have an average outer diameter of 36 nm. Carbon black (SAF, having an average diameter of 28 nm) is

used, and supplied from transporting and engineering company, Egypt. MWNTs and CB are used as nanofillers

with various concentrations in the PP mixes. Irganox 1010 was supplied from Ciba (Geigy, Swizerland) in white

powder form. It has a specific gravity of 1.45, and melting point of 110-125°C. It is used to prevent

thermomechanical degradation during mixing and pressing processes.

Methods:

1. Preparation of nanocomposites

All ingredients were accurately weighed and the mixing was carried out using twin-screw extruder, new plast

company, Indian. The mixing was continued at 190 °C for 20 min. at a rotor formulations speed of 30 rpm. The

mixes are shown in Table 1.

Table 1: Formulations (in wt %) of the PP mixes containing CNTs or CB without treatment.

Sample No. Ingredient

A4 A3 A2 A1 A°

100 100 100 100 100 PP

5 3 1 0.5 0 CNTs or CB (nanofiller)

0.1 0.1 0.1 0.1 0.1 Irganox 1010 (Antioxidant)

2. Morphological Characterization:

The morphology of the composites was studied under scanning electron microscope (SEM, Philips XL 30

microscope, U.S.A). Prior to the measurement; the specimens were coated with gold. This analysis shows the

shape and size of filler particles.

3. Thermogravimetric Analysis (TGA):

Thermogravimetric analysis (TGA) was performed on an analyzer (Model TA-50, Shimadzu, Japan) on 5

mg sample for all cases, at a heating rate of 10 °C/min. TGA was conducted with the compounds placed in a

high quality nitrogen atmosphere in order to avoid unwanted oxidation. It is used to obtain the thermal stability

and degradation temperature of the composite.

4. Wide-Angle X-Ray Diffractometry (WAXD):

WAXD experiments were performed at room temperature to characterize the crystalline structure of fillers.

XRD patterns were collected using a Bruker D8 advance X-ray powder diffractometer at the wave length of

copper target= 1.54 Å, a tube voltage of 40 kV and the tube current of 40 mA.

5. Mechanical Measurements:

Different sheets of PP composites including CB, CNTs were cut out to five individual dumbbell-specimens

by a steel die of constant width (0.4 cm). The thickness of the test specimen was determined by using a dial

427 Middle East j. Appl. Sci., 4(2): 425-435, 2014

gauge. A bench mark of 15 mm length was marked on the working part of each specimen under test. Mechanical

tests including tensile strength, elongation at break, and elastic modulus were performed at room temperature

(23±2°C) using a tensile testing machine (Model Z 010, Zwick, Germany) at a crosshead speed of 50 mm/min.,

and according to ASTM D 638 standards.

6. Creep and Recovery Measurements:

Creep and recovery tests were conducted in tensile mode under different temperatures (-50, 25 and 80°C)

using dynamic mechanical analysis (DMA Q800 apparatus: TA Instrument, USA). The specimen's dimensions

were 30 mm x 8 mm x 2 mm (length x width x thickness). The creep and recoverable strain were determined as

a function of the time (tcreep= 45 min and trecovery= 180 min). Prior to the creep test, the stress level was derived

from tensile results and was fixed at 1 MPa, to ensure the creep measurements remained in linear viscoelastic

deformation regime. The recovery ratio, XR of a system at a time t is defined as shown in Equation (1):

1 % 100

,0

t

tttXR

where ɛ(t) is the creep strain and ɛ(t0,t) is the unrcovered strain

Results and Discussion

1. Morphological Characterization:

The efficiency of nanofillers in reinforcing the polymer matrix is primarily determined by the degree of its

dispersion in the matrix. Therefore, morphological characterization is very important for evaluating the

dispersion state of carbon nanofiller in the polymer matrix. In this study, dispersion of MWNTs and CB in

polypropylene composites was examined by using scanning electron microscope (SEM) as can be seen in Figs.

1 and 2, respectively. For PP/MWNTs nanocomposites, Fig. 1a-e, it can be seen that composites with different

MWNTs contents, 0, 0.5, 1, 3, 5 wt.%, exhibited different MWNTs dispersion state. In comparison with pure

PP, at low content, most of the MWNTs dispersed individually in the PP matrix, Fig. 1b. Where as at relatively

high MWNTs contents, aggregates appeared in the polymer matrix and the size of the aggregates increased with

increasing MWNTs content as can be seen in Fig. 1 (c-e). The agglomeration of nanotubes in clusters could be

due to van der waals attraction during synthesis and mixing (Vyazovkin et al., 2006). From the micrographs in

Fig. 2a-d, it can be seen that composites with different CB ratios showed good dispersion where no apparent

changes in the fracture surfaces of the composites with respect to that of the pure PP were observed. Also, the

scans did not show the presence of a significant number of micron-size carbon black aggregates, which

suggested that there was homogeneous dispersion of the particles in the matrix after the melt mixing.

2. Thermal Degradation:

The effect of carbon nanoparticles (MWNTs, CB) on the thermal stability of polypropylene was studied

using thermogravimetric analysis (TGA). Thermogravimetric curves for neat PP and the prepared PP/MWNTs

and PP/CB nanocomposites at a heating rate 10°C/min in nitrogen atmosphere are presented in Fig. 3. The

results revealed that thermal degradation of PP and its composites takes place through a one-step process with a

maximum decomposition temperature. Neat PP begins to thermally degrade at about 300°C, while the presence

of carbon nanoparticles causes a shift to higher temperature. The respective temperatures for each

nanocomposite are presented in Table 2. This shift is proportional to the amount of carbon nanoparticle. The

table also showed that pure PP degrades almost completely, while the residues of the nanocomosites are directly

related with the amount and type of carbon nanoparticles added to PP. From the figure, it can be clearly noticed

that carbon nanotubes enhance the thermal stability of the samples rather than CB and that composites

containing 3 or 5 wt.% of MWNTs had the maximum decomposition temperature. This improvement in thermal

stability can be attributed to the inherent high temperature stability of the carbon nanotube filler and its

reinforcing effect on PP matrix. Analogous behavior of thermal stability in an inert atmosphere has been

obtained in previous work for PP nanocomposites containing nanofillers (Vassiliou et al., 2008; Zanetti et al.,

2001; Tang et al., 2003; Qin et al., 2004 and Yang et al., 2011).

428 Middle East j. Appl. Sci., 4(2): 425-435, 2014

a b

c d

e

Fig. 1: SEM micrographs of PP/MWNTs nanocomposites with filler content of (a) 0 wt.%; (b) 0.5 wt.%; (c) 1

wt.%; (d) 3 wt.% ; (e) 5 wt.%.

Table 2: Therogravimetric analysis of nanocomposites as a function of filler loading.

Residue

(%)

T max

(°C)

Endset

(°C)

Onset

(°C)

Sample

78.70 610.43 735.91 472.47 MWNTs

34.21 498.97 606.60 394.61 CB

0.40 379.94 405.09 307.51 PP

0.87 416.36 436.62 374.32 PP + 0.5 wt% MWNTs

1.37 418.20 439.23 378.41 PP + 1.0 wt% MWNTs

1.87 428.71 451.19 390.64 PP + 3.0 wt% MWNTs

1.98 428.99 454.43 390.51 PP + 5.0 wt% MWNTs

0.57 383.14 405.65 325.18 PP + 0.5 wt% CB

0.83 405.70 415.55 343.70 PP + 1.0 wt% CB

0.94 412.48 444.66 358.60 PP + 3.0 wt% CB

1.04 414.01 439.87 367.56 PP + 5.0 wt% CB

429 Middle East j. Appl. Sci., 4(2): 425-435, 2014

a b

c d

Fig. 2: SEM micrographs of PP/CB nanocomposites with filler content of (a) 0.5 wt.%; (b) 1 wt.%; (c) 3 wt.%;

(d) 5 wt.%.

0

20

40

60

80

100

0 100 200 300 400 500 600 700 800

Weig

ht

Lo

ss [

%]

PP

PP + 0.5 wt% MWNTs

PP + 1wt% MWNTs

PP + 3 wt% MWNTs

PP + 5 wt% MWNTs

Temperature [ °C ]

0

20

40

60

80

100

0 100 200 300 400 500 600 700 800

Temperature [ °C ]

Weig

ht

Lo

ss [

%]

PP

PP + 0.5 wt% CB

PP + 1 wt% CB

PP + 3 wt% CB

PP + 5 wt% CB

Fig. 3: TGA curves of the pure PP; PP/MWNTs (a); and PP/CB (b) nanocomposites with 0.5, 1, 3, 5 wt% of

filler particles under nitrogen atmosphere.

3. X-Ray Diffraction Measurements:

The effect of carbon nanoparticles on polypropylene crystallization was studied with WAXD. Fig. 4

showed the WAXD patterns of PP and its nanocomposites of 2θ. Nanoparticles are known from many studies to

act as nucleating agents, causing changes in the crystallization characteristic of polymers and, subsequently, the

position and intensity of diffraction peaks are found to change in the resulting WAXD curves. PP can crystallize

in three crystalline modifications: monoclinic (α), hexagonal (β) and orthorhombic (γ) (Brückner et al., 1991).

These phases can be examined by XRD. The pure PP showed several distinct diffraction peaks in its WAXD

curve. The peaks at 2θ = 13.9°, 16.7°, 18.3°, 21.03°, 21.6°, 25.4°, and 28.44°, correspond respectively to the

(110), (040), (130), (111), (041), (060), and (220) diffraction planes of the α-form of PP crystals. In the

diffraction patterns of PP/MWNTs nanocomposites with all different contents (0.5-5 wt.%), an additional peak

is recorded at 2θ = 19.27°, which is attributed to the (130) plane of γ-form of PP crystals as shown in Fig. 4a.

Whereas the diffraction patterns of PP/CB nanocomposite with CB content (0.5 wt%) was found to be similar to

that of neat PP, as shown in Fig. 4b. However, in the nanocomposites containing 1, 3 and 5 wt%, an additional

a b

430 Middle East j. Appl. Sci., 4(2): 425-435, 2014

peak is recorded at 2θ = 19.27°, which is attributed to the (130) plane of γ-form of PP crystals. The diffraction

peak positions among various samples did not exhibit any obvious shifts, implying that the addition of carbon

nanoparticles had negligible influence on the distance between the diffraction planes of the crystallites in the PP

matrix. Meanwhile, the intensity and width of some of the diffraction peaks changed with the additional

nanofillers loading. The relative intensity of the diffraction peaks corresponding to the (110) and (111) crystal

planes of α-form decreased with increasing nanofillers content. At the same time, the relative intensity of

diffraction peak corresponding to the (060) crystal planes increased with the enhanced loading of carbon

nanofillers. Also, specifically the intensity of the diffraction peak corresponding to the (040) crystal plane

displayed a remarkable increase. The WAXD patterns of the nanocomposites show typical α-form PP crystals

and exhibits complete absence of the β-crystal form and presence of γ-form. These changes in crystallization

characteristics of the PP matrix brought about by the addition of carbon nanofillers will influence the final

properties of the nanocomposites, including mechanical and electrical properties.

10 15 20 25 30

2θ [degree]

Inte

nsi

ty [

a.u

]

PP

PP + 0.5 wt% MWNTs

PP + 1 wt% MWNTs

PP + 3 wt% MWNTs

PP + 5 wt% MWNTs

10 15 20 25 30

2θ [degree]

In

ten

sit

y [

a.u

]

PP

PP + 0.5 wt% CB

PP + 1 wt% CB

PP + 3 wt% CB

PP + 5 wt% CB

Fig. 4: XRD patterns of PP and PP/MWNTs (a) and PP/CB (b) nanocomposites.

4. Mechanical Properties of the nanocomposites:

The tensile properties of the pure PP, PP/MWNTs and PP/CB nanocomposites at room temperature have

been determined. The young's modulus, tensile strength and elongation at break are listed in Table 3. From the

results, it is deduced that the reinforcing effect of MWNTs is clearly distinct as compared to their counterpart,

carbon black. As the MWNTs content in the polymer increases, the tensile strength goes from 37.90 MPa for

pure PP to 53.51 MPa for 1 wt.% nanocomposites, i.e. increase by about 41 %. A further increase in MWNTs

proportions in the composite provides a marked decrease in the tensile strength. This may be attributed to the

presence of nanotubes aggregates. Whereas when carbon black is used as filler, the tensile strength increases by

about 28 % at 3 wt.%, then followed by a decrease in tensile. On the other hand, as the MWNTs content

increases, young's modulus gradually increases. This is because, the mobility of the polymer chain is restricted

by the addition of filler content up to 3 wt.%. As a result, the composites will be more rigid and have higher

moduli than the unfilled one (Cheng et al., 2012). Then, by increasing filler content (at 5 wt.%), modulus

deceases due to the presence of aggregates of the filler. Similar trend was found when adding CB filler to the PP

matrix, but with lower values of modulus than that obtained in case of MWNTs. Generally, adding a rigid

particle into PP matrix decreased the elongation at break (Ansari et al., 2009). In this study, the addition of

nanotubes has a little effect on the elongation of PP/MWNTs nanocomposites, while the elongation of PP/CB

composites decreases up to 1 wt.% of CB and after that values of the elongation remain unchanged.

Table 3: Tensile properties of PP, PP/MWNTs and PP/CB nanocomposites with different MWNTs and CB contents.

Sample Tensile Properties

Tensile Strength (MPa)

Modulus (MPa)

Elongation at break (%)

PP 37.90 957.69 9.42

PP + 0.5 wt% MWNTs 48.91 1725.00 10.10

PP + 1.0 wt% MWNTs 53.51 1965.88 9.90

PP + 3.0 wt% MWNTs 53.09 2002.83 9.63

PP + 5.0 wt% MWNTs 47.77 1653.69 9.29

PP + 0.5 wt% CB 41.96 1615.66 8.05

PP + 1.0 wt% CB 43.75 1793.45 7.01

PP + 3.0 wt% CB 48.53 1879.40 7.16

PP + 5.0 wt% CB 47.91 1566.51 7.16

a b

431 Middle East j. Appl. Sci., 4(2): 425-435, 2014

5. Creep and recovery behavior:

The creep and recovery tests of PP and nanocomposites were performed by using dynamic mechanical

analyzer (DMA). Creep is a time and temperature dependent phenompenon and is of importance for material

applications requiring long-term durability and reliability. The applied creep stress was 1 MPa for creep time of

45 min followed by a recovery time of 180 min. This creep-recovery experiment was performed at three

different temperatures of -50, 25 and 80°C. The creep strain, unrecovered strain and recovery ratio, which is

calculated according to Equation (1), were measured for MWNTs and CB nanocomposites and listed in Tables 4

and 5, respectively.

Table 4: Creep strain, unrecovered strain and recovery ratio for PP and PP/MWNTs nanocomposites under different temperatures.

Content of MWNTs

(wt.%)

Temperature

-50 °C 25 °C 80 °C

Creep strain (%)

0 0.5

1.0

3.0

5.0

0.30620 0.17710

0.15670

0.08241

0.06212

0.5514 0.4715

0.2810

0.2726

0.2530

1.7200 1.1840

0.9399

0.7104

0.6586

Unrecovered strain (%)

0

0.5 1.0

3.0 5.0

0.147400

0.048300 0.007990

0.003170 0.002112

0.3189

0.1795 0.0630

0.0320 0.0162

1.2018

0.6484 0.4699

0.3041 0.2497

Recovery ratio (%)

0

0.5 1.0

3.0

5.0

51.86153

72.72727 94.90108

96.15338

96.60013

42.16540

61.93001 77.58007

88.26119

93.59684

30.12791

45.23649 50.00532

57.19313

62.08624

Table 5: Creep strain, unrecovered strain and recovery ratio for PP and PP/CB nanocomposites under different temperatures.

Content of CB

(wt.%)

Temperature

-50 °C 25 °C 80 °C

Creep strain (%)

0 0.5

1.0

3.0 5.0

0.3062 0.3009

0.2656

0.1377 0.1061

0.5514 0.5319

0.4744

0.4454 0.3619

1.720 1.408

1.346

1.235 0.940

Unrecovered strain (%)

0

0.5 1.0

3.0

5.0

0.1474

0.1200 0.0814

0.0260

0.0100

0.3189

0.2600 0.1985

0.1428

0.0965

1.2018

0.9139 0.8029

0.6630

0.3987

Recovery ratio (%)

0

0.5 1.0

3.0

5.0

51.86153

60.11964 69.35241

81.11837

90.57493

42.1654

51.11863 58.15767

67.93893

73.33518

30.12791

35.09233 40.34918

46.31579

57.58511

Figs. 5 and 6 displayed the creep and recovered strains as a function of time for unfilled and filled

composites with 0, 0.5, 1, 3, and 5 wt% MWNTs and CB nanofillers, at three different temperatures,

respectively. In these curves, the creep stages (instantaneous deformation, primary and secondary creeps) can be

clearly observed. On the other hand, there was no evidence of tertiary creep, i.e. creep rupture, which would

require longer time and larger stress. It is visibly apparent that with the raising of the temperature from -50 to

80°C, the creep strain increased with increasing temperature for all composites at the same time. The results

indicate that creep strains of nanocomposites were lower than that of the neat matrix at all test temperatures and

this implies that the creep behavior is improved by the presence of nanofillers. However, creep strains of

nanocomposites with carbon nanotubes were lower than those of nanocomposites with carbon black at the same

concentration. i.e. carbon nanotubes enhanced creep behavior of the composite owing to the exceptionally high

aspect ratio of the reinforcing phase (MWNTs). For example: the strain values at 80°C were reduced by 31, 45,

58 and 61 % compared to polypropylene when the contents of MWNTs were 0.5, 1, 3 and 5 wt.%, respectively.

Whereas, the strain values at the same temperature were reduced by 18, 21, 28 and 45 % compared to PP when

the contents of CB were 0.5, 1, 3 and 5 wt.%, respectively (see Tables 4 and 5). The recovered strain as a

432 Middle East j. Appl. Sci., 4(2): 425-435, 2014

function of time was also represented in the same figures. The curves also indicated that incorporation of

nanotubes as well as CB improves the elastic recovery and decreases the recovered strain remarkably when

compared to pure PP matrix. This result is in consistent with that discussed by Jia et al., 2011. It was found that

the recoverable strain of the nanocomposites decreases with increasing the content of MWNTs and CB over the

whole relaxation time range. At the same time, it was found that higher imposed temperature resulted in lower

recovery ratio. The figures also showed clearly that the presence of MWNTs enhances to great extent the

recoverable strains and the recovery ratio rather than in case of CB, as indicated in Tables 4 and 5. The results

indicate that adding both MWNTs and CB to the PP matrix can increase the creep resistance and creep-recovery

property. Based on the observation, however, it becomes clear that the creep and recovery properties of

PP/MWNTs composites are better than PP/CB ones. Especially at 5 wt.% of MWNTs and at -50°C, the

nanocomposite gives the best creep resistance.

-0.4

0

0.4

0.8

1.2

1.6

2

0 50 100 150 200 250

Time (min)

Strain

(%

)

PP (-50°C)

PP (25°C)

PP (80°C)

-0.4

0

0.4

0.8

1.2

1.6

2

0 50 100 150 200 250

Time (min)

Stra

in (

%)

PP/1 wt.% MWNTs (-50°C)

PP/1 wt.% MWNTs (25°C)

PP/1 wt.% MWNTs (80°C)

-0.4

0

0.4

0.8

1.2

1.6

2

0 50 100 150 200 250

Time (min)

Strain

(%

)

PP/5 wt.% MWNTs (-50°C)

PP/5 wt.% MWNTs (25°C)

PP/5 wt.% MWNTs (80°C)

-0.4

0

0.4

0.8

1.2

1.6

2

0 50 100 150 200 250

Time (min)

Stra

in (

%)

PP/3 wt.% MWNTs (-50°C)

PP/3 wt.% MWNTs (25°C)

PP/3 wt.% MWNTs (80°C)

Fig. 5: Temperature dependent creep strain: (a) neat PP; (b) PP + 0.5 wt.%; (c) PP + 1 wt.%; (d) PP + 3 wt.%;

(e) PP + 5 wt.% of MWNTs

-0.4

0

0.4

0.8

1.2

1.6

2

0 50 100 150 200 250

Time (min)

Stra

in (

%)

PP/0.5 wt.% MWNTs (-50°C)

PP/0.5 wt.% MWNTs (25°C)

PP/0.5 wt.% MWNTs (80°C)

a

b c

a

e

d

433 Middle East j. Appl. Sci., 4(2): 425-435, 2014

Fig. 6: Temperature dependent creep strain: (a) PP + 0.5 wt.%; (b) PP + 1 wt.%; (c) PP + 3 wt.%; (d) PP + 5

wt.% of CB.

Conclusions:

PP/nanocarbon filler composites were prepared using melt mixing. The creep and recovery behavior of the

nanocomposites were studied. From our observations, the following he results revealed that the composites

filled with CB showed better dispersion than that filled with MWNTs. The thermal stability of the composite

increases with increasing filler loading. Also, the results showed that MWNTs enhanced thermal stability of the

composites rather than CB. The nanocomposites showed typical α-form PP crystals and exhibits complete

absence of the β-crystal form and presence of γ-form in nanocomposites filled with both MWNTs and CB.

Significant improvements in Young's modulus and tensile strength of the PP/MWNTs composites were obtained

in comparison with that of the PP/CB composites. Addition of nanofiller to PP matrix can influence the creep

and recovery property of the nanocomposites in different temperature conditions. The results showed that

PP/MWNTs nanocomposites have better creep and recovery properties than PP/CB nanocomposites and that the

PP nanocomposite contains 5 wt.% of MWNTs showed the best creep resistance and recovery ratio at -50°C.

References

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properties of Feldspar Filled Polypropylene Composites. Journal of Reinforced Plastics and Composites,

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-0.4

0

0.4

0.8

1.2

1.6

2

0 50 100 150 200 250

Time (min)

Stra

in (

%)

PP/1 wt.% CB (-50°C)

PP/1 wt.% CB (25°C)

PP/1 wt.% CB (80°C)

-0.4

0

0.4

0.8

1.2

1.6

2

0 50 100 150 200 250

Time (min)

Stra

in (

%)

PP/0.5 wt.%CB (-50°C)

PP/0.5 wt.%CB (25°C)

PP/0.5 wt.% CB (80°C)

-0.4

0

0.4

0.8

1.2

1.6

2

0 50 100 150 200 250

Time (min)

Stra

in (

%)

PP/5 wt.% CB (-50°C)

PP/5 wt.% CB (25°C)

PP/5 wt.% CB (80°C)

-0.4

0

0.4

0.8

1.2

1.6

2

0 50 100 150 200 250

Time (min)

Stra

in (

%)

PP/3 wt.% CB (-50°C)

PP/3 wt.% CB (25°C)

PP/3 wt.% CB (80°C)

a b

d

c

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