Abstract

Substantial improvements in the mechanical and physical properties of thermoplastic polymers as a result of molecular orientation have initiated the development of a number of solid state thermoforming processes such as free tensile drawing, die-drawing, hydrostatic extrusion etc. Though these processes have attracted significant scientific and practical interests over the years, commercialising these processes in a normal industrial environment requires detailed investigations of the various process parameters and the properties of the oriented product. Recently detailed property evaluations and computer simulations have been used at Leeds to predict the response of polymers in solid phase thermoforming processes and also to optimise the thermoforming conditions. However successful quantitative predictions are difficult due to the sensitivity of the polymer to temperature, strain, strain-rate and hydrostatic pressure as well as to microstructural changes.

This seminar will present recent results arising from studies on three classes of polymer systems that have successfully undergone solid state orientation at Leeds as follows: • polyoxymethylene (POM) for wire rope applications, looking particularly at the deformation and damage arising from the die-drawing process • wood-polypropylene (WPP) composites, including micromechanical modelling of the properties • silane-grafted polyethylene (PE), considering the effect of the silane grafts on the practical limits of the drawing process.

In each case, the important process parameters are reviewed as well as the tensile, physical and microstructural properties of the highly oriented product. Where appropriate, theoretical and empirical models of the material behaviour are derived and compared with the experimental results. SEM , SAXS and WAXS are used to help in the interpretation of the mechanical property data.