CRYSTALLIZATION KINETICS OF POLYPROPYLENE .2. EFFECT OF THE ADDITION OF SHORT GLASS-FIBERS

The effect of short glass fibres on the polypropylene (PP) crystalliza tion kinetics and thermodynamics has been investigated. Although at hi gh fibre percentages in the composite the spherulitic limits are not c learly defined, the presence of crystalline entities is evident. A mar ked decrease of the half time of PP crystallization, tau(1/2) as well as a sensible increase of the overall crystallization rate, K-n, has b een observed in the presence of fibres. However, at any crystallizatio n temperature, a maximum of tau(1/2) is reached at 20% glass fibre con tent in the composite followed by a continuous decrease as fibre perce ntage increases. A slight increase in the Avrami exponent as temperatu re increases is obtained although it is relatively independent of comp osite composition. In all cases an instantaneous nucleation takes plac e, a nucleant effect of fibres is evident, and no transcrystallinity h as been observed with these short glass fibres. Fibres give rise to a marked increase in the crystallinity of the samples. The chain folding energy for PP crystallization (sigma(e)) decreases with fibre content , and a minimum is observed at 20% fibre content. (C) 1997 Elsevier Sc ience Ltd.