Crystallization kinetics of polypropylene III. Ternary composites based on polypropylene low density polyethylene blend matrices and short glass fibres

The effect of, simultaneously, both short glass fibres (SGF) and low density polyethylene (LDPE), on PP crystallization kinetics and thermodynamics has been investigated. Glass fibres tend to initially compensate the delaying effect of LDPE on the PP crystallization as is shown by the values of the crystallization half time, tau(1/2), as well as by the overall crystallization rate, K-n. However, at high glass fibre percentages in the composite (30-40%) a considerable increase of tau(1/2) values is observed although they remain always below the corresponding values of the plain polymer. The isothermal radial growth rate of PP spherulites is hardly affected by both the fibres and the LDPE. According to the values of the Avrami exponents, it can be established that the spherulitic development arises from an athermal, instantaneous and heterogeneous nucleation with two-directional diffusion controlled growth. No transcrystallinity has been observed. (C) 1998 Elsevier Science Ltd. All rights reserved.