Heat Degradation of Poly(propylene) in Extruding Cycles

Poly(propylene) samples were reprocessed in multiple cycles by a single-screw extruder. The heat degraded samples reprocessed were characterized by dynamic viscoelasticity and stress-strain measurement.The decrease (Mw/Mw0) in molecular weight of poly(propylene) with reprocessing was expressed by the product (f(n, T)·g(t, T)) of a function of cycles number (n) of extrusion consisting of virgin and degraded samples and a function of time (t) required in extrusion at a given temperature (T). Especially, at a temperature below 190°C, Mw/Mw0 was expressed only by f(n, T). In blend system Mw/Mw0 was expressed by similar relationship, suggesting that the synergy effect of blend on the heat degradation was absent. Young’s modulus (E) and yield stress (σy) obtained from stress-strain curves did not change regardless of the virgin, heat degraded and blend samples.