Thermal degradation and combustion of polymeric blends

The thermal stability of polymer blends was investigated by means of gas chromatography-mass spectroscopy (GC/MS) and thermal analysis. Evaluated changes in thermal stability can be attributed to blending. On the other hand, we were interested in whether blending may provide a method to control thermal stability and combustibility of polymeric materials. A new scheme of thermal degradation for polystyrene-polydimethylsiloxane (PDMS) blend was suggested. In the case of polystyrene (PS) as a part of the blend, the products of degradation of PS diffuse through the phase boundary, which cause interaction with PDMS polymers. Apparently, PDMS acts as an inert component, slowing down the termination reaction by dilution of macroracticals formed in random scission degradation process of the PS component. On the other hand, it stabilizes the PS by means of interpolymer recombination, which leads to cross products of thermal degradation. Two of the degradation products: 2-phenyl-4(1',3',3',5',5'-pentamethylcyclotrisiloxane)-butane and 2-phenyl-4(1',3',3',5',5',7',7'-heptamethylcyclotrisiloxane)-butane were assigned to the products of cross-interpolymer recombination which can accelerate the process of PDMS depolymerization by means of radical initiation of PS* fragments. The connection between a polymer thermal oxidative degradation and its combustion under diffusion flames condition was shown by using composition of polypropylene-polypropylene-copolyethylene (PP/PP-co-PE). In general, the solid-phase polymer reaction can play a very important role in the reduction of polymer combustibility. It was shown that the composition of PP/PP-co-PE (62 : 38) has the highest induction period of autooxidation, which correlates with its combustibility. (C) 2002 Wiley Periodicals, Inc.