Keynote paper to 17th Annual Meeting of the Polymer Processing Society, Montreal, Canada, 21st-24th May 2001

J M Methven with S F Bush and A J Hulme

Summary

The conventional pultrusion process allows continuous manufacture of a fibre-reinforced composite profile of constant cross section. Important refinements to the basic process have been made within the UMIST Polymer Research Laboratory over the past few years and this work describes a further development.

For manufacture of hollow profiles, the outer surface of a mandrel forms the inner surface of the profile while the inner surface of the die forms the outer surface of the profile. Many profiles are made hollow to increase the bending stiffness-to-weight ratio. This can also be achieved by making a solid profile with a centre section composed of a light organic polymeric foam such as a polyurethane or a cross-linked phenolic resin. However, synchronising the blowing and chemical cross-linking of the foam with the gelation of the outer glass-reinforced resin as it passes through the die is difficult to achieve reproducibly in a factory environment. The paper describes an alternative approach in which the organic foam is replaced by resin impregnated inorganic particles such as clay or glass which are expanded by vacuum rather than by reaction. This creates, in effect, a controllable, low density, low cost mandrel which is incorporated into the profile.

The paper describes the techniques used to establish the conditions for manufacturing 30 mm simulated hardwood poles in a factory. By using a conventional mix of glass fibres, unsaturated polyester with a relatively high maleic element, and a peroxide catalyst to create the outer annulus of the profile, together with a decorative PET film on the outside film, a pole of acceptable quality and cost has been made at a line speed of 1.2 m/minute. Broader conclusions are drawn for applications of the technology to other shapes and moulding processes.