Lowering The Percolation Threshold In Carbon Blackfilled Polymer Composites
- PDF / 1,323,094 Bytes
- 5 Pages / 417.6 x 639 pts Page_size
- 84 Downloads / 205 Views
University of Minnesota
-
Twin Cities, Minneapolis, MN 55455, [email protected]
ABSTRACT In an effort to lower the percolation threshold of carbon black-filled polymer composites, various polymer microstructures were examined. Composites prepared with a polyvinyl acetate
(PVAc) latex and a poly(vinyl acetate
-
ethylene) water-dispersible powder showed a
significantly lowered percolation threshold relative to an equivalently prepared composite that used a polyvinyl alcohol (PVA) solution to form the matrix phase. The percolation threshold of the dispersion-based composites occurred at 5 vol.% carbon black, while the equivalent solutionbased composite produced a threshold at 14 vol.%. By excluding the carbon black from regions occupied by polymeric particles, the dispersion-based composites lead to preferential aggregation of carbon black, as evidenced by SEM, and a lowered percolation threshold. INTRODUCTION The use of carbon black-filled polymers in applications such as electromagnetic 2 1 interference shielding and anti-static layers has created an interest in altering the percolation threshold of these conductor-insulator systems. Electrical conductivity is not achieved in these composite systems until the volume fraction of carbon black exceeds the percolation threshold. Classical percolation theory3 predicts the insulator-metal transition to occur at a 0.15 volume 3 fraction of conductive filler, and several binary composite systems experimentally support this value.4'•' 6'7 Efforts to lower the amount of conductive filler required to produce a conducting with composite have been fueled by the desire to have an electrically conductive system 8 9 mechanical properties identical to those of the polymer matrix alone. Polymer blends ' and 1 semi-crystalline polymer systems ° have shown that the percolation threshold can be lowered when a phase incompatible with the carbon black is added to the microstructure. Another option that may prove more efficient is to force carbon black into regions between polymer particles as the composite microstructure evolves. This method has already demonstrated lower percolation thresholds in composites molded from polymer particles and finer conductive particles."l In this
paper, this principle is explored for composites created from dispersions of carbon black with a water-dispersible polymer powder and water-based emulsion. EXPERIMENTAL METHODS
Polymer-carbon black composites were prepared from aqueous dispersions of (i) polyvinyl acetate (PVAc) latex, (ii) polyvinyl acetate-ethylene water-dispersible powder and (iii) polyvinyl alcohol (PVA) solution. Vinac XX2 10 polyvinyl acetate (PVAc) homo~polymer emulsion (provided by Air Products, Inc.) is a poly-disperse latex system with a Tg of 35 C. This 50 vol.% polymer latex was diluted with distilled water to 25 vol.%, to reduce viscosity before
adding carbon black. AirflexT RP-245 polyvinyl acetate-ethylene (PVAc-PE) redispersible
powder (provided by Air Products, Inc.) was dispersed in water to create a 20 vol.% polymer
Data Loading...
