Chemical and Material Engineering 2012 ISBN : 978-602-097-281-7
MSD.09 - 4
Department of Chemical Engineering Diponegoro University September 12
– 13, 2012, Semarang Indonesia
Vickers method of hardness was determined by Wolpert DIA Testor 2RC instrument. Tensile strength were determined by Instrontester Seri Strograph-RI Toyoseiki. Structure and morphology was tested by Scanning
Electron Microscope.
3. Results And Discussion
In this paper, thermoplastics polymer polypropylene were used as binder in order to produce of BPP by injection molded method. Polypropylene PP, also known as polypropene, is a thermoplastic polymer used in a
wide variety of applications including packaging and labeling, textiles e.g., ropes, thermal underwear and carpets, stationery, plastic parts and reusable containers of various types, laboratory equipment, loudspeakers,
automotive components, and polymer banknotes. An addition polymer made from the monomer propylene, it is rugged and unusually resistant to many chemical solvents, bases and acids.
Polypropylene is normally tough and flexible, especially when copolymerized with ethylene. This allows polypropylene to be used as an engineering plastic, competing with materials such as ABS. Polypropylene is
reasonably economical, and can be made translucent when uncolored but is not as readily made transparent as polystyrene, acrylic, or certain other plastics. It is often opaque or colored using pigments. Polypropylene has good
resistance to fatigue.
The composition of graphite powders were done in 5:1 to acetylene black as filler for increasing the hardness and conductivity. The third component is polymer whereas polypropylene were easily obtained. Synthesis method
in slurry condition is easily obtained homogenous composition of composite materials. The BPP should be strong enough to withstand the compressive stresses generated during assembling the
stacks of the plates in a fuel cell. This is one of the reasons for replacing the conventional monolithic graphite plates which are brittle and have low-strength. The BPPs should depend upon the nature of filler contents and the
bonding with the resin system used. Herein we focused the composition of polymer as binder in graphiteacetylene black powder is 5 to 25 wt in order to get light weight and high strength.
Table 1. Properties of BPPs without PANi
Composition Hotpress
pressure Density gcm
3
Porosity Conductivity
Scm Tensile strength
kgcm
2
Hardness kgmm
2
95:5 75
1.219 1.075
66.240 27.709
7.536 150
1.346 3.614
74.709 35.190
4.051 90:10
75 1
.391 1.163
56.958 50.899
4.051 150
1.482 1.219
74.170 45.792
4.207 85:15
75 1.315
3.030 41.290
55.455 4.207
150 1.429
2.500 56.482
81.923 4.139
80:20 75
1.402 6.173
23.588 90.842
4.139 150
1.462 1.163
26.978 69.403
4.518 75:25
75 1.364
3.960 27.894
83.019 4.518
150 1.421
4.819 20.717
60.449 4.314
In compression molded methods the slurry composite was preheated in hotpress tools with mold size of 14 cm diameter in 15 minutes, then in order to remove air inside the composite the slurry was pressed slowly and
pressed at 200 C with 75 and 150 kgfcm
2
in 15 minutes. The results of BPPs components properties are shown at Table 2. The polymer type of PS was choosen as thermoplastics polymer. A density of all variant composites are
less than 2 gcc that was consider to many references. The electrical conductivity decresed with increasing of polymer contents [8]. And high presure of 150 kgfcm
2
were give a good effect to increase all variants conductivity.
Chemical and Material Engineering 2012 ISBN : 978-602-097-281-7
MSD.09 - 5
Department of Chemical Engineering Diponegoro University September 12
– 13, 2012, Semarang Indonesia
Table 2. Properties of BPPs with PANi
Composition Hotpress
pressure Density gcm
3
Porosity Conductivity
Scm Tensile strength
kgcm
2
Hardness kgmm
2
95:5 75
1.266 3.488
99.269 21.429
4.649 150
1.359 5.940
59.213 23.811
7.572 90:10
75 1.333
5.825 35.315
43.081 4.416
150 1.113
2.752 47.279
31.393 4.656
85:15 75
1.377 2.531
44.189 49.886
5.669 150
1.343 2.678
38.161 43.436
5.410 80:20
75 1.258
4.396 31.131
88.147 5.641
150 1.532
6.186 36.208
88.258 5.194
75:25 75
1.325 6.667
44.108 104.014
6.902 150
1.352 3.797
29.880 59.639
4.566
The density of all variant composites is less than 2 gcm
3
that was consider in many references. The electrical conductivity increased with increasing of graphite contents because graphite has good conductivity. The electrical
conductivity reaches 66.2402 Scm by combination 95 GCB and 5 PP. To increase electrical conductivity, Polyaniline PANi as conductive polymer was added by 5 weight of total polymer. Adding of PANi to the
composite gives higher electrical conductivity as shown in Table 1 and Table 2. The electrical conductivity increase from 66.2402 Scm to 99.2688 Scm for 95 GCB and 5 PPPANi. While the commercial bipolar plates require
100 Scm electrical conductivity. This observation appears to agree with that of Kakati B.K., et al. [9], who found a positive influence of the PANi on the electrical conductivity of GPP composites. These synergistic effects were
explained by enrichment of the PANi at the interface between G and PP. High pressure of 150 kgfcm
2
were shown to give a good effect to increase all variants conductivity.
As comparison, commercial bipolar plate from local industry paralel model and serpentine and electrochem bipolar plate were measured by the same method. It results electrical conductivity 40.646 Scm, 87.291 Scm and
98.013 Scm, respectively. The electrical conductivity of ABS composite is approaching the commercial ones.
Figure 5. SEM surface micrographs of GCBPP at: a 25 wt PP; b 20 wt; c 15 wt; d 10 wt; e 5 wt.
Figure 6. SEM surface micrographs of GCBPPPANi at: a 25 wt PPPANi; b 20 wt; c 15 wt; d 10 wt; e 5
wt.
The scanning electron micrographs in Fig 5-6 reveal that graphite primary particles aggregate into larger clusters with low aspect ratios. These tend to disperse more evenly into the polymer matrix, thereby resulting in
fewer particle contacts at given loading level and, consequently, a lower conductivity polymer composite. In other words, the filler particles do not make contact with the nearest neighbor due to partial wetting by the polymer.
Dawson and Adkins [10] proposed that conductivity in G-filled polymers is regulated by inter-particle electron transfer at low filler loadings and by intra-particle electron transfer at high filler loadings. Solution blended
Chemical and Material Engineering 2012 ISBN : 978-602-097-281-7
MSD.09 - 6
Department of Chemical Engineering Diponegoro University September 12
– 13, 2012, Semarang Indonesia
GCBPPPANi has higher conductivity than of GCBPP. This can be attributed to better distribution of graphite rather than to the addition of PANi.
It was difficult, however, to prepare well-dispersed PPG composites with simple mixing techniques. The surface properties of the filler and polymer have a significant effect on the conductivity of the composite by
influencing the interaction between them. How well the polymer wets the surface of the filler can be quantified by the difference between the surface energies of the two materials. Smaller differences between the two surface
energy values lead to better wetting of the filler by the polymer. Better wetting means that larger amounts of the polymer are coating the filler surface, which will alter the distribution of the filler within the matrix. This will
increase the percolation threshold and the overall resistivity of the composite because larger amounts of the filler are required before the particles will come in to contact with each other. PP is hydrophobic and has relatively low
surface free energy ~20-25 mJm
2
[11]. G is also strongly hydrophobic these may be a small difference between its surface energy and that of PP [12] which might lead to partial wetting and hence lower conductivity. This would
explain why a somewhat larger difference between the surface energy of the filler and the polymer is desirable. As described in results properties, the graphite-carbon black powder with various polymer matrixes
composite have an opportunity as new BPP materials. However, on the concept of commercial manufacturing for fuel cells, they are associated with major problems of high fabrication cost and insufficient reliability of fuel cells.
The BPP is one of the most costly component hence this research should be continued to get optimum formula of matrix contain and has become a critical research issue.
4. Conclusion
