CRYSTALLIZATION KINETICS OF POLYPROPYLENE .1. EFFECT OF SMALL ADDITIONS OF LOW-DENSITY POLYETHYLENE

In order to analyse the effect of small additions (up to 20 wt%) of lo w-density polyethylene (LDPE) on the crystallization kinetics and ther modynamics of an isotactic polypropylene (iPP), morphological studies of iPP/LDPE blends have been carried out. The results have shown that at LDPE percentages above 10% in the blend, the LDPE aggregates pass o ver the spherulitic limits and go into the intraspherulitic domains of the PP. The half-crystallization times (tau(1/2)) as well as the Avra mi exponent (n) and the chain folding energy for PP crystallization (s igma(e)) increase markedly at LDPE percentages above 10% in the blend. The isothermal radial growth rate, G, of the PP in the blends is one- third of the plain polymer, although it remains constant at any blend composition. However, the overall kinetic rate constant seems to be in fluenced by the presence of the melt LDPE phase. In all cases, and acc ording to the obtained results, an instantaneous nucleation takes plac e. Copyright (C) 1996 Elsevier Science Ltd.