FLAME RETARDANCIES OF OLEFINS AND POLYSTYRENE WITH CONTROLLED MOLECULAR WEIGHTS

摘要

The thermal degradations and flammabilities of three kinds of polyolefins [polyethylene (PE),polypropylene (PP), and polybuthylene (PB)] and polystyrene (PS) have been researched for severaldecades and these polymers are considered to burn easily. However, this study showed that it isdifficult for PE to continue combustion under limited conditions such as the vertical configuration ofthe materials, air circumstance and small molecular weight. The results suggested the possibility thatthere is a critical molecular weight that would enable PE to continue its combustion because PE doesnot burn directly but rather the scission products react with the oxygen in the air. The combustionstates and scission products of the linear straight-chain hydrocarbons of PP, PB and PS were comparedwith PE. As a result, 1) the strong relation between the position of the flames during combustion andthe distribution of scission products was observed for polyolefin and PS, 2) the peak of PS's molecularweight was shifted from high molecular weight to low molecular weight after pyrolysis. Thesephenomena show that the combustion of PE, whose molecular weight is relatively low, was stronglyrestrained by the thermal degradation rate and the distribution of the scission products.