Recovery of mechanical properties of aged polystyrene after reprocessing

Abstract

A combined procedure of thermal ageing followed by injection molding has been applied for ten times to simulate the repeated recycling. The processability of the recycled material was somewhat improved and the mechanical parameters were rather retained. Regular oscillations in strength characteristics of the successively aged and recycled samples have been registered. Namely, stress at break was repeatedly decreased and restored again after ageing and reprocessing steps, respectively. The very similar zig-zag pattern has been observed for elongation at break. Similarly, impact strength of the remolded samples shows on average better values than those of the aged samples. On the contrary, z-average molecular weight and melt flow rate were changed rather monotonically - a decrease and on increase, respectively. Considering the above, the observed phenomenon of alternating deterioration and recovery of the strength parameters has been attributed to material homogenization under the reprocessing steps.