Shelf-Life Determination of Epoxy Prepregs and Film Adhesives

摘要

Epoxy prepregs and film adhesives are composed of partially cured (''B'' staged) epoxy resins and, in the case of the prepregs, a fiber matrix. Purchased epoxy prepreg lots typically are accepted or rejected on the basis of resin content, gel time, and resin flow. The shelf-life storage conditions of both materials generally are based on vendor recommendation. At The Bendix Corporation, Kansas City Division, there has been concern recently with shelf-life aging of a Kevlar/epoxy prepreg. At present, lot acceptance of this prepreg is partially based on flow test data which was considered of questionable merit for shelf-life extension determinations. Film adhesive lots are generally accepted or rejected on the basis of lap shear strength data. When film adhesive is bought as a small preformed shape, whose size and configuration prevent lap-shear testing, it must be lot accepted by vendor certification only. Differential scanning calorimetry (DSC) is a method for performing thermochemical analysis. DSC can readily be applied to epoxy prepregs for acceptance testing and observing the kinetics of the curing reaction. In this study, the practical aspects of such methods were further investigated, and additional ways for determining the effects of ''B'' stage conditioning on the processing parameters of epoxy prepregs and predicting the shelf-life of these materials, as well as film adhesives, were developed. (ERA citation 04:016734)