Relaxation processes in polyethylene fibre-reinforced polyethylene composites

The dynamic mechanical properties of filament-wound composites comprising ultrahigh-molecular-weight polyethylene (UHMWPE) extended-chain fibres in matrices of linear low-density polyethylene (LDPE), high-density polyethylene (HDPE), and thermally treated HDPE have been studied in tensile mode over a wide frequency range. The study focused on the additional effects of the fibres, for three winding angles of 26 degrees, 34 degrees and 45 degrees, on the dynamic properties of the polyethylene-fibre-reinforced polyethylene composites. These effects were expected to result from transcrystallinity, which is induced in the matrix and which may invade a significant proportion of the composites, and from the extra restraint imposed by the reinforcement. The effects of the fibres are expressed by the real and imaginary moduli and the loss tangent and are analysed in terms of frequency dependence and activation energies for the alpha, beta and gamma transition processes. The effects of the fibres and of the crystallinity are evident in significantly higher moduli and activation energies of the relaxation processes. (C) 2000 Elsevier Science Ltd. All rights reserved.