Glass-fibre Reinforced Acetal Co-polymer

Abstract

The glass fibre reinforced acetal copolymer system has been studied in detail. An attempt has been made to investigate some of the variables affecting the mechanical properties of the composite and evaluate their relative importance: these variables included processing methods, coupling agents, glass content and polymer viscosity. These variables were first investigated using a compression moulded test system, but a rather poor level of properties was obtained and the results proved inconclusive. It was decided that compression moulding did not offer a useful evaluation of glass reinforced acetal and so an injection moulded system was investigated as well. Injection moulded test pieces showed a considerably higher level of mechanical properties, An investigation of the effect of processing method revealed that a dry blended material showed generally superior mechanical properties to a material prepared on the two roll mill which in turn was superior to material prepared in the Buss Ko-kneader. It was shown that this resulted from increasing shear in the three processing methods, giving rise to a reduced fibre length in the composite. Tensile properties and hardness have been shown to increase linearly with increasing glass content whereas impact strength goes through a definite minimum, which moves to a higher level of glass content with decreasing fibre length. Polymer viscosity has been shown to have little effect on mechanical properties. Coupling agents exert a marked effect on tensile strength but no effect on tensile modulus - this is inexact accordance with theoretically predicted behaviour. Methacrylato — chromic chloride and Y-methacryloxypropyl trimethoxy—silane appear to be the most effective coupling agents of those investigated. One incidental result of this work has been to yield materials having, in the optimum direction, tensile strengths of up to23,500 psi and moduli of nearly 2,700,000 psi - substantially higher than previously recorded for glass reinforced polyacetal. An extensive literature survey has been carried out over the whole field of glass reinforced thermoplastics.