Incompatibility and stress have been known to cause rifts in many an otherwise perfect union. Take polypropylene, for instance. This thermoplastic is often wedded with inorganic fillers such as talc or kaolin to increase heat resistance and stiffness. But the resulting union responds poorly to the stress of impact. Shock waves tend to start cracks around the filler particles—mostly because the plastic doesn't cling to the filler. It just surrounds it. Our polymer scientists here at the General Motors Research Laboratories set out to strengthen the plastic-filler composite by introducing a compatible, shock absorbing interface. The trick was to get the interface material to stick to the filler. How did they do it? First they adsorbed a monomer, 2-ethylhexyl acrylate, on the filler particles. Then they irradiated the coated filler, under vacuum, with high energy electrons (photo above). The radiation did two things: It polymerized the monomer coating. And it chemically linked this coating to the filler, as revealed by thermogravimetric analysis and carbon-14 tracer techniques. As a result, some s POLYPROPYLENE WITH plastics are now able f to bond tightly to fil- i lers through an elas- I OLYfcROPYLENE WITH tic interface. In the f ^;P N0QAT;E,D;TALG case of polypropylene & and talc, that means I about twice the im- ^ pact strength as bePERCENT TALC BY VOLUME fore (see graph). We call this experimental technique "radiation grafting on fillers!' It's only one of the approaches we're exploring to help make plastic products live happily ever after.
Making plastic-filler marriages last longer.
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C&EN Oct. 3, 1977
GM
General Motors Research Laboratories Warren, Michigan 48090
