The roles of process parameters on structures and mechanical properties of polypropylene clay nanocomposites

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The Roles of Process Parameters on Structures and Mechanical
Properties of Polypropylene/Clay Nanocomposites
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IUMRS-ICA 2018
IOP Conf. Series: Materials Science and Engineering 553 (2019) 012044
IOP Publishing
doi:10.1088/1757-899X/553/1/012044
1
The Roles of Process Parameters on Structures and
Mechanical Properties of Polypropylene/Clay
Nanocomposites
Annisa Rifathin1*
, Onny Ujianto1
, Nurul Jamilah1
, Bambang Afrinaldi1
1
Center for Polymer Technology, Agency for Assessment and Application of
Technology, Building 460, Puspiptek Area, Setu, South Tangerang, Banten, Indonesia
15314
annisa.rifathin@bppt.go.id
Abstract. Process parameters are crucial to produce targeted qualities in polypropylene
(PP)/clay nanocomposites, due to their roles on the generation of shear and diffusion. Thus,
this research aims to observe their effects on structures and properties of PP/clay
nanocomposites. Samples were produced by mixing PP, PP grafting maleic anhydride (PP-g-
MA), and Cloisite 20A at fixed compositions, 88/9/3 wt%, respectively, in an internal mixer
with variations on temperatures (210, 220, 230 °C) and speeds (60, 80, 100 rpm). Effect of
mixing parameters on nanocomposite structures and properties were investigated from XRD,
SEM and flexural properties. The results showed that all samples had intercalated as well as
agglomerated structures. Further analysis on XRD and SEM showed that samples produced at
high conditions (230 C or 100 rpm) had similar structures. In contrast, low setting sample (210
C and 60 rpm), despite its similarity on dispersion level, had longer agglomerates than that of
mixed at high settings. Correlated both increase of d-spacing and agglomerates length to
flexural properties suggested that modulus was more influenced by dispersion level, while
strength was affected by agglomerates. However, it was worth to note that improvement on d-
spacing, with availability of long agglomerates might not guarantee modulus and strength
improvement due to low interfacial bonding.
Keywords : Polypropylene, clay, internal mixer, XRD, SEM, flexural
1. Introduction
Polypropylene (PP) is widely applied to produce various applications as automotive, packaging,
building component, etc. Due to its large applications, studies on enhancement properties of PP are
still interesting field for many researchers. One possible technique that growth rapidly in the last two
decades to improve PP properties as physical, mechanical, fire retardancy, and barrier is the addition
of nanofiller as clay to PP matrix [1-5], due to its low loading. In order to mix this two different polarity
materials, compatibilizer is needed [6, 7], and process parameters should also be considered as their
contribution to disperse the fillers [8-11].
The processing parameters might provide shear, diffusion, and degradation mechanisms that
influence clay exfoliation [12]. Our previous study on PP/clay nanocomposites showed that interaction

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doi:10.1088/1757-899X/553/1/012044
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between temperature and mixing time was crucial to disperse nanoclay [13]. However, correlation
between this interaction and structures and properties was still unclear.
This study aimed to explore interaction effects of process temperatures and mixing speeds on clay
dispersion and mechanical properties in Polypropylene matrix. Analysis on the role of mixing
conditions was done according to flexural properties. The dispersion level was investigated from X-
ray diffraction (XRD), while agglomerations were observed under Scanning Electron Microscopy
(SEM).
2. Experimental method
2.1 Materials
Polypropylene (PP), 5169 MAS 2158 from PT. Politama Indonesia was used as matrix. It was PP with
melt flow index (MFI) 1.8 g/10 min. Epolene Wax G 3015P, polypropilene-grafted-maleic anhydride
(PP-g-MA), from Eastman Chemical Company was used as a compatibilizer. A commercial
organophillic montmorillonite clay, Cloisite 20A (Southern Clay Product) was added as filler.
2.2 Nanocomposite preparations
Haake Rheomix 600 was used for mixing PP, PP-g-MA and clay according to process conditions
presented in Table 1. All samples were produced at identical composition with 88% of PP, 9% of PP-
g-MA, and 3% of clay to produce the best tensile strength [8]. Before mixing, overnight drying (80°C)
was perform on clay to reduce its moisture. Nanocomposite specimens were prepared by compression
molding (Collin P300P) with setting conditions shown in Table 2. Two steps of compression molding
were applied to produce smooth surface as trials done in our lab.
Table 1. Setting Conditions used in an Internal Mixer.
Samples Temperature [°
C] Speed [rpm] Time [min]
Control 220 80 10
1 210 60 10
2 210 100 10
3 220 80 10
4 220 80 10
5 220 80 10
6 230 60 10
7 230 100 10
Table 2. Setting Conditions used in Compression Molding.
Parameters
First Step Second Step
1 2 3 4 5 1 2 3 4 5
Temperature [°
C] 205 205 205 205 40 205 0 195 0 40
Pressure [Bar] 0 1 1 0 0 0 0 0 0 1
Time [Min] 10 5 5 0 15 10 0 3 0 15
2.3 Characterizations
Flexural modulus and strength testing were performed using Shimadzu AGS 10 kN, Universal Testing
Machine, according to ASTM D 790. Flexural speeds were calculating by considering samples
thickness as stated in standard. The support span distance was set at 25.4 mm. At least five specimens
were tested, and the average values were reported.
The structures of clay were observed from agglomeration analyzed using Scanning Electron
Microscope (SEM) and d-spacing increase using X-Ray Difraction (XRD). The agglomerations of clay

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doi:10.1088/1757-899X/553/1/012044
3
were observed to analyze the present of agglomerations in the mixtures using JEOL JSM-6510LA
SEM with accelerated voltage of 15 kV. Measurement and analysis were done in 5 surface area of
flexural sample number 1, 2, 6, and 7, with at least 1 measured agglomerate for each surface. Specimens
were cooled with liquid nitrogen and cut. Specimens were sputter coated with Platinum to increase
surface conductivity and reduce charging. The clay dispersions were analyzed using Simadzu X-Ray
Diffractometer 7000 Maxima-X with Cu kα radiation. Analysis wes performed at scan speed 2.4
deg/minute, λ = 1.54 A˚, 40 kV and 20mA. The intensity peak were intergrated from 1° - 10° of 2 theta.
3. Results and discussions
3.1 Effects of processing parameters on flexural properties
Flexural modulus and strength of PP/clay nanocomposite samples are presented in Table 3. It is shown
that the average modulus and strength increase about 12% and 6%, respectively, attributed to clay
dispersion. However, despite the increase of flexural properties for most of samples, it is shown that
there was one sample (sample 1, produced at low temperature and low rpm) experiencing decrease on
both modulus and strength. These phenomena were also reported in another previous study [14]. The
decrease might be produced by poor polymer - clay bonding due to availability of big agglomerates.
These might be happened in case of very low generated shear applied to disperse the clay [15, 16] and
very high polymer viscosity that difficult to penetrate clay galleries [17]. This suggested that setting
combination between low temperature (210 °C) and low rpm (60 rpm) applied to mix sample 1 might
not enough to disperse most of the clay in this nanocomposite system, and resulted in some big
agglomerates.
Table 3. Flexural modulus and strength of PP/clay nanocomposite samples.
Sample
Temperatures
[°
C]
Speed
[rpm]
Time
[min]
Modulus [MPa] Strength [MPa]
Control 220 80 10 1764 ± 86.0 (± 5%) 49.15 ± 1.66 (± 3%)
1 210 60 10 1512 ± 55.0 (± 4%) 41.10 ± 2.05 (± 5%)
2 210 100 10 1974 ± 131 (± 7%) 53.20 ± 5.65 (± 11%)
3 220 80 10 2090 ± 158 (± 8%) 55.14 ± 1.13 (± 2%)
4 220 80 10 2113 ± 205 (± 10%) 56.46 ± 2.59 (± 5%)
5 220 80 10 2084 ± 184 (± 9%) 57.33 ± 2.60 (± 5%)
6 230 60 10 2119 ± 57.0 (± 3%) 50.70 ± 6.42 (± 13%)
7 230 100 10 2169 ± 105 (± 5%) 52.90 ± 7.89 (± 15%)
Average all nanocomposites 1978 ± 123 (± 6%) 52.00 ± 3.75 (± 7%)
Average of mid setting 2096 ± 182 (± 9%) 56.31 ± 2.11 (± 4%)
Figure 1. Effect of mixing speeds on flexural
modulus and strength.
Figure 2. Effect of mixing temperatures on
flexural modulus and strength.
30
40
50
60
1200
1400
1600
1800
2000
2200
2400
40 60 80 100 120
Modulus at Low Temp Modulus at High Temp
Strength at Low Temp Strength at High Temp
Modulus(MPa)
Strength(MPa)
Mixing Speed (rpm)
30
40
50
60
1200
1400
1600
1800
2000
2200
2400
200 210 220 230 240
Modulus at Low Speed Modulus at High Speed
Strength at Low Speed Strength at High Speed
Modulus(MPa)
Strength(MPa)
Temperatures ( C)

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Figure 1 and 2 show the effects of processing parameters on flexural properties. In general, both
modulus and strength increased as the higher settings. These improvements were clearly obtained
especially at higher setting (either mixing speed (Figure 1) or temperatures (Figure 2)) when the other
parameter was set at low condition. At low temperature and low mixing speed, polymer viscosity is
still high so it difficult to penetrate the interlayer galleries. At the same time, low mixing speed might
unable to disperse clay agglomerates effectively. Combination these two conditions resulted in low
modulus and strength. In contrast, at low temperature, higher mixing speed generated higher shear that
able to disperse the clay and improve modulus and strength. However, there were slight improvements
at higher mixing speed when temperature was set at high setting, and vice versa. This suggested that
the effect of shear and diffusion in these boundaries might not significant change flexural properties
due to competing mechanisms between shear and diffusion that work simultaneously.
3.2 Effects of processing parameters on nanocomposite structures
The structures of PP/Clay nanocomposites are presented in Figures 3 to 7. In general, all
nanocomposite samples have nanostructures as well as agglomerated structures. Nanostructures were
observed from peaks shifted to lower angle compared to clay peak on XRD diffractogram, while
agglomerated were analyzed from the length and width of microstructures available on SEM
micrographs.
Figure 3. XRD diffractograms of PP/clay nanocomposites
Figure 3 shown that all samples have peaks at lower degree suggested intercalated of some clay
structures. The best improvement on the increase of interlayer spacing was obtained by samples 6 and
7 produced at high temperature (230 °C) and either at low or high mixing speed. The peaks were shifted
from 3.26° represented 2.71 nm of d-spacing to 2.34° represented 3.77 nm of inter-gallery distance.
The increase of intergallery spacing from 2.71 nm to 3.77 nm suggests that the nanocomposites
structure is available on sample 6 and 7. In contrast, the lowest increase was produced by sample 1
prepared at low temperature and low mixing speed (210 C and 60 rpm) that increase from 2.71 nm to
3.39 nm, and also suggests nanocomposite structures. However, this did not support to negative results
of modulus and strength. So it was hypothesized that there were both nanostructures and agglomerates
available on the system and competing each other. For this reason, further analysis on the size of
agglomerates were done using SEM.
-1
0
1
2
3
4
5
6
1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0
Intensity
2-Theta
PP
Clay
Sample 1
Sample 2
Sample 6
Sample 7
XRD Diffractogram of PP/Clay Nanocomposite Samples
Samples 6 and 7
Sample 2
Sample 1
Clay

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5
(a) (b)
(c) (d)
Figure 4. SEM micrograph (a) Sample 1 (210°C, 60 rpm); (b) Sample 2 (210°C,
100 rpm); (c) Sample 6 (230°C, 60 rpm); (d) Sample 7 (230°C, 100 rpm).
Figure 5. Size of agglomerates available on PP/clay nanocomposites.
Figures 4 and 5 show selected surface area of microstructures available on each observed samples
and agglomerate size. The length of microstructures ranges from 1.6 to 6.9 µm, while the width varies
from 1.0 to 3.8 µm. The smaller agglomerates were available in samples 2 and 7 those were produced
at high mixing speed. On the contrary, the bigger agglomerates found at low mixing speed samples
(Sample 1 and 6). The size even more than twice for sample 1 (low mixing speed, low temperature)
compare to another samples, attributed to limited shear in the process. This data explains the reason
behind the decrease on modulus and strength for this sample compare to control, despite the
6.9
2.2
3.4
1.6
3.8
1.7
2.2
1.0
0.0
2.0
4.0
6.0
8.0
1 2 6 7
Length
Width
Sample No.
AgglomerateSize(µm)

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improvement on d-spacing. This finding also suggests that there is minimum ratio between level of
dispersion and agglomerate size to improve both modulus and strength that is not covered in this
research. For this reason, it is suggested that further experiment should be done in the future.
Combination analysis on XRD and SEM suggested that high dispersion level and small agglomerates
can be achieved if there was minimum one parameter that be set at high condition (temperature or
rpm). The fact that the high dispersion level was produced at high temperature or rpm, and small
agglomerates were available on high rpm samples, suggested that there was synergism between shear
and diffusion in order to produced desired nanostructures. The results of this research show that the
shear is crucial to break the agglomerates, however this mechanism would not go further if there was
no diffusion mechanism that runs simultaneously and need optimum viscosity to work.
3.3 Effects of nanocomposite structures on mechanical properties
Figure 6. Effect of interlayer spacing increases
on flexural modulus and strength.
Figure 7. Effect of agglomerate sizes on
flexural modulus and strength.
Structures and mechanical property of PP/clay nanocomposites are shown in Figure 6 and 7. In general,
the increase on d-spacing and reduction on agglomerate length would improve modulus and strength.
This is caused by the increase on aspect ratio that improves interfacial bonding between matrix and
fillers. From the figures, it is also suggested that the d-spacing increase (Figure 6) has more influence
to modulus (R2
= 0.88) than to strength (R2
= 0.61). In contrast, the reduction of agglomeration sizes
(Figure 7) has more contribution to strength (R2
= 0.99) than to modulus (R2
= 0.87).
4. Conclusion
The roles of mixing conditions on structures and flexural properties of PP/clay nanocomposites have
been explored. The samples were produced using an internal mixer with temperatures (210, 220, 230
°C) and mixing speeds (60, 80, 100 rpm) variations, and fixed composition. The structural of
nanocomposites were investigated from XRD diffractograms and SEM micrograms, while mechanical
properties were represented by flexural test.
The results showed that the average flexural modulus and strength of all nanocomposite samples
increased by adding nanoclay on PP. These increases were influenced by the combination of
intercalated structure and small agglomerate size. The samples produced at high conditions (230 C or
100 rpm) had similar intercalated and agglomerate structures. On the other hand, bigger
microstructures were found in the sample produced at low settings (210 C and 60 rpm), despite its
similarity on dispersion level. Analysis on structures and flexural property relationship shows that the
intercalated structures have more contribution on modulus improvement, while agglomerates size
contributes to strength. The findings of this research also suggest that the improvement on d-spacing
might not successfully increase modulus and strength, if huge microstructures presents on the system.
R² = 0.86
R² = 0.51
30
40
50
60
70
0
500
1000
1500
2000
2500
0.60 0.70 0.80 0.90 1.00 1.10 1.20
Modulus Strength
D-spacing Increase (nm)
Strength(MPa)
Modulus(MPa)
Effect of Interlayer Spacing Increase on Flexural Properties
R² = 0.87
R² = 0.99
30
40
50
60
70
0
500
1000
1500
2000
2500
0 5 10 15
Modulus Strength
Length of Agglomerates (µm)
Strength(MPa)
Modulus(MPa)
Effect of Agglomerates on Flexural Properties

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doi:10.1088/1757-899X/553/1/012044
7
Acknowledgment
Authors would like to thank you Center for Polymer Technology, Agency for Assessment and
Application of Technology for supporting us to conduct this research.
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