Ageing of polypropylene: processes and consequences

Based on information available in the literature and new investigations, th e ageing behaviour of poly propylene at room temperature and in annealing w as studied. Two effects have to be discerned: changes in the amorphous and/ or mesomorphic regions of the material at room temperature, which lead to a n increase in density and modulus in connection with embrittlement on the o ne hand, and relaxation- and recrystallization-processes at higher temperat ures, which positively influence heat deflection temperature and impact str ength alongside with modulus and density on the other hand. Use of elevated temperatures to accelerate ageing for the determination of long-term prope rties is therefore not possible in the case of polypropylene. (C) 1999 Else vier Science Ltd. All rights reserved.