Interconnected fibre masses precipitated from solutions of polymers

Abstract

IN studies to increase the mechanical strength of polymeric encapsulants for high voltage electronic devices we have formed fibre masses of unusual structure from isotactic polypropylene. The method for producing these three-dimensionally interconnected fibrous structures is described here and involves agitation of a solution of the polymer at sonic frequencies with simultaneous cooling. This process has since been observed for polyethylene and polybutene-1. Furthermore, the process has been extended to other polymers, both crystalline and non-crystalline, through a process we call ‘seeding’. Uniform reinforcement of encapsulating resins through the addition of high strength, short fibres, is not practical because of the complex shapes and numerous small interstices of the devices to be encapsulated. We therefore set out in 1973 to form fibres in situ by precipitation from low viscosity solutions which would readily impregnate a device of complex geometry. As a secondary objective, we hoped to polymerise the solvent to form a matrix around the fibres thereby producing a self-reinforced composite.