The Influence of Prepreg Ageing on the Chemorheology of Carbon Fibre Laminate Processing

Abstract

The ordinary working procedure of laying-up of composite laminates involves the exposure of the prepregging materials for several days in an ambient held at controlled temperature and humidity. The ageing of the material influences the reactivity of the epoxy prepolymer. The laminates are then subjected to high temperatures in order to provide the heat required for initiating and maintaining the chemical reactions needed for the epoxy polymerization and cross-linking. The changes of the molecular structure and weight distribution induced by the chemical reactions modify the rheological properties of the system. The cure cycle is generally optimized for assigned viscosity modifications, sorbed moisture devolatilization rate, resin flux, and laminate thickness; however, the hygrothermal ageing of the prepreg alters the chemorheological behaviour of the epoxy system leading to undesired local modifications of the actual cure process. First, an integrated analysis procedure providing the base for the optimization between resin chemistry, factory operations and curing is developed; and the calorimetric and rheological behaviours of aged prepreg are experimentally and theoretically illustrated.