Prepregs and laminates of polyetherimide-reinforced by a thermotropic LCP

Abstract

Unidirectional sheets (prepregs) of blends of polyetherimide (PEI) with a liquid crystalline polymer (LCP) are prepared. The mechanical properties of prepregs at directions of 0°, 45°, and 90° to the machine direction are investigated as a function of draw ratio and LCP concentration. The results show that drawing significantly increases the tensile strength and modulus of prepregs in the machine direction and only slightly decreases these properties in the transverse direction. An increase in the LCP content greatly enhances the tensile strength and modulus in the machine direction but decreases these properties in the 45° and 90° directions. The strain at break of prepregs decreases with LCP content in all directions tested. An abrupt drop in the tensile strength, modulus, and strain at break of prepregs occurs in the 45° and 90° directions when LCP content reaches 40%. Prepregs are used to manufacture unidirectional and quasi-isotropic laminates. Unidirectional laminates show mechanical properties close to those of the corresponding prepregs. The tensile modulus of quasi-isotropic laminates exhibits a continuous increase with increasing LCP content while the tensile strength increases with an LCP content up to 30%, then it decreases rapidly. The morphology of LCP in prepregs is observed to change from disperse to continuous at LCP contents of 40 and 50%. This effect is found to be responsible for the large decrease in tensile strength of prepregs in the 45° and 90° directions and quasi-isotropic laminates at higher LCP concentration. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:329–340, 1997