Pultruded fibre-reinforced polyurethane composites. III. Static mechanical, thermal, and dynamic mechanical properties

Abstract

A proprietary process has been developed for the manufacture of polyurethane (PU) pultruded composites. The blocked isocyanate (NCO)-terminated PU prepolymer synthesized in this study was prepared from ϵ-caprolactam blocked blends of toluene diisocyanate and branched polyester. The static mechanical and thermal properties of various fibres (glass, carbon and Kevlar-49 aramid fibre) reinforced blocked PU composites have been studied. Results show that the static mechanical properties (i.e. tensile strength, specific tensile strength, flexural strength, specific flexural strength, flexural modulus and impact strength) and thermal properties (heat deflection temperature (HDT) increase with fibre content. Kevlar-fibre/blocked-PU composites possess the highest impact strength, specific tensile strength and HDT, whereas carbon-fibre/blocked-PU composites show the highest tensile strength, flexural strength, specific flexural strength and flexural modulus. Experimental results for tensile strength of all composites except carbon-fibre/blocked-PU composites follow the rule of mixtures. The deviation from the mixtures' rule of the properties of the carbon-fibre/blocked-PU composite is due to fibre breakage during processing. The glass-transition temperature (T g) increased slightly and the damping peak (tan δ) was broadened as a consequence of fibre reinforcement. The dynamic mechanical moduli (G', G“) of pultruded blocked PU composites are apparently higher than those of the matrices. The moduli (G', G“) increase with increasing fibre and filler content, and the damping peak becomes broad. The effect of postcuring on the degree of crosslinking, T g and dynamic modulus will be discussed.