Extrusion-Compression molded isotactic polypropylene (iPP) composites containing 10 wt%, 20 wt%, 30 wt%, 40 wt% and 50 wt% of talc filler were studied by scanning electron microscopy (SEM), simultaneous thermal analysis (STA) and physical testing. The scanning electron microscope (SEM) micrographs of neat iPP and composites with 10 wt%, 20 wt%, 30 wt%, 40 wt% and 50 wt% talc content show that neat PP, 10 wt%, 20 wt%, and 30wt% talc composites surface is smooth in comparison to 40 wt% and 50 wt% talc composites. It is also observed that talc is dispersed uniformly in the matrix and this uniform dispersion is not decreased even with talc content as high as 30 wt% talc. The composites of 40 wt% and 50 wt% talc contain more crack, agglomerates or larger particles. Bulk density of the composites decreases with the increase of talc content. With the increase of percentage of talc and period of immersion, the water absorption (WA) increases. Thermal analyses indicate a considerable increase of thermal stability of the composites with filler addition.
Fillers-reinforced polymer composites have attracted much attention to the researchers due to the fact that inclusion of fillers in polymers remarkably alters structural, physical, mechanical and thermal behavior of final products [
Isotactic polypropylene (iPP) has found a wide range of applications in the food packaging, electrical, and automotive industries. Inorganic fillers, such as talc, mica and silica, ceramics, etc. are widely used in iPP to improve their mechanical and thermal properties [
Composites used in this work were prepared from iPP and talc. Commercial grade iPP was purchased from BASF, Germany. The density of PP is 0.91 gm/cc and its melting temperature is 438K. Talc is collected from local market and is in the form of powder. Different chemical component of talc are presented
Five different composites were prepared by iPP and talc powder according to the mass ratio (10-X) PP: X talc, Where X =1, 2, 3, 4, 5. Besides these one pure iPP sample was also prepared. The mixtures were kept in separate pot and then mixed uniformly as much as possible. The different mixtures were melted by extrusion machine. Three heaters of extrusion machine were switched “ON” for about one hour. The barrel was heated for about one hour at 513K. After heating for one hour the mixture was put into the feed hopper. The motor was then switched on to feed the batch from the feed hopper into the barrel. The molten composite material was then collected through the die in the form of rod. For easier handling these were cooled in a water bath during collection. The rods were then cut with a hacksaw. For converting the rod shape samples into disc shape sample 450kN Press (machine Paul-Otto Weber GmbH. Germany) were used. The rod shape samples were molded by this machine. The heating temperature and initial pressure were set at 180˚C and 50kN, respectively. After reaching the set temperature, the pressure was increased up to 100kN, continued heating at that temperature for 15 min and stopped the heating system.
The morphology of the iPP sample and composites with 10 wt%, 20 wt%, 30 wt%, 40 wt%, 50 wt% talc was studied by a scanning electron microscope (SEM) (Philips XL 30, Netherlands) with a maximum operating voltage of 10kV of the apparatus. The sample surface was coated with a thin gold layer by a sputtering prior to SEM measurement.
Bulk density was calculated using following formula
Constituents | Amount(%) |
---|---|
MgO | 31.7 |
SiO2 | 63.5 |
H2O | 4.8 |
where,
BD = Bulk Density of the specimen in Kg/m3,
Ws = Weight of the specimen in Kg, and
V = Volume of the specimen in m3.
In this way the bulk density of each sample is measured[
Water intake specimen was prepared according to ASTM Designation [
where
Wd = Dry weight of the specimen,
Ws = Saturated weight at the specimen after submersion in distill water.
In all cases a protective gel coat (araldite) was applied on the cut sides to prevent penetration of water from cut sides.
Melting and degradation temperatures of the neat iPP sample and the composites were monitored by a thermo gravimetric-differential thermal analyzer (TG-DTA) [Seiko-Ex-STAR-6300, Japan]. The measurements using TG-DTA were carried out from room temperature to 600˚C at a heating rate of 20˚C∙min−1 using nitrogen gas flow. While the DTA traces give the melting and degradation temperatures as determined from the DT signal versus temperature curves, the TGA runs exhibit the weight retained of the sample with temperature.
The SEM micrographs of iPP and composites with 10 wt%, 20 wt%, 30 wt%, 40 wt% and 50 wt% talc content are shown in figure 1. It is observed that the surface structure changes due to the percentage of talc in PP. It can also be seen from micrographs that iPP, 10 wt%, 20 wt% and 30wt% talc compotes surface is smooth in comparison to 40 wt% and 50 wt% talc composites. It is also observed that talc is dispersed uniformly in the matrix and this uniform dispersion is not decreased even with talc content as high as 30 wt% talc. On the surface of the composites of 40 wt% and 50 wt% talc composites contain more crack, void, agglomerates or larger particles. These observed agglomerates were created during fracture by extraction of some talc crystals from their places on fractured surface.
In figure 3 it is observed that water absorption (WA) increases with increasing period of immersion and increase of percentage of talc. Since talchas more affinity for water than iPP, so with the addition of talc, the water absorption of the composite fairly rises. Similar effect was found by M. Maniruzzaman et al. [
From
Sample (wt%) | On setTemperature (˚C) | Temperature of 50% degradation (˚C) | Ash content (%) |
---|---|---|---|
0 | 389.6˚C | 415.9 | 2.4 |
10 | 407.1˚C | 431 | 8.2 |
20 | 398.2˚C | 427.5 | 26.3 |
30 | 423.7˚C | 446.5 | 23.3 |
40 | 391.7˚C | 417.2 | 35.5 |
50 | 403.2˚C | 432.4 | 34.6 |
Sample (wt%) | 1st peak(˚C) | 2nd peak(˚C) | 3rd peak(˚C) |
---|---|---|---|
0 | 166.4 | 431.7 | _ |
10 | 174.2 | 442.8 | _ |
20 | 166.9 | 434.7 | _ |
30 | 167.8 | 450.6 | _ |
40 | 166.7 | 391.4 | 430.8 |
50 | 171.7 | 326.6 | 438.1 |
Sample (wt%) | MaximumDegradation temp(˚C) | Degradation rate(mg/min) |
---|---|---|
0 | 432.8 | 1.169 |
10 | 442.8 | 2.84 |
20 | 435.1 | 1.97 |
30 | 454.8 | 3.36 |
40 | 430.8 | 1.976 |
50 | 447 | 1.73 |
different wt% of iPP-talc composites. From DTG curve it is also noticed that the maximum degradation occurs for 30% talc at the temperature 454.8˚C with the rate of 3.36 mg/min. The reason for increasing degradation temperature of the composites may be based on the influence of impurity. If it is assumed that talc has higher volumetric heat capacity and thermal conductivity than iPP, then the composite materials will preferably absorb more heat as compared to the pure iPP sample. As a result of the colligative thermodynamic effect, the temperature of the composite material will increase and the iPP chains start to degrade at higher temperatures in the composites than the iPP sample. So figure 4analyses show that with addition of talc in different concentration iPP-talc composite become more thermally stable. Such increase of thermal stability in copper filled low density polyethylene, talc filled polypropylene and TiO2 filled PP was observed by Luyt et al.[
The structural, physical and thermal properties of iPP-talc composites are studied. The SEM micrographs of iPP and composites with 10 wt%, 20 wt%, 30 wt%, 40 wt% and 50 wt% talc content show that PP, 10 wt%, 20 wt%, and 30wt% talc surface is smooth comparison to 40 wt% and 50 wt% talc composites. The composites of 40 wt%and 50 wt% talc contain more crack, agglomerates or larger particles. Bulk density of the composites decreases with the increase of talc content. With the increase of percentage of talc and period of immersion, WA increases. From the TGA, DTA, and DTG curves it is seen that composites become more thermally stable than neat iPP and composites with 30 wt% talc is the most thermally stable than others.
In conclusion, it is seen that a thermally stable iPP-talc composite can be developed for industrial and scientific application.
The authors thank the authority of the Bangladesh University of Engineering and Technology (BUET) to provide financial support for this investigation. The authors are grateful to the department of materials and metallurgical Engineering, BUET and Bangladesh Council of Scientific & Industrial Research (BCSIR) to allow facilities for this research.
RahimaNasrin,M. A.Gafur,A. H.Bhuiyan, (2015) Characterization of Isotactic Polypropylene/Talc Composites Prepared by Extrusion Cum Compression Molding Technique. Materials Sciences and Applications,06,925-934. doi: 10.4236/msa.2015.611093