Mechano-radical formation in polypropylene by an extruder action and its after-effects

Abstract

Free radical (mechano-radical) formation caused by the mechanochemical effect of an extruder was experimentally proved on polypropylene by (ESR) combined with the spin trapping method. In this experiment the commonly used spin-trapping agents were found to be useless because of the higher temperature in the extruder, but the hindered amine light stabilizer (HALS), bis-(2,2,6,6-tetra-methyl-4-piperidinyl) sebacate, was found to be a good spintrapping agent in the extruder action. The enhancement of the photodegradation was found for the fractured polypropylene, which had experienced the extruder action. The series of reactions initiated by the mechano-radicals formed in the extruder are discussed. It is most reasonable to assume that the polypropylene is contaminated with ketons after passing through an extruder, even if the sample has been pure before the passing through the extruder. Since the ketons play the role of chromophore, the presence of ketons in the fractured samples is an origin for the enhanced photodegradation of the fractured polypropylene.