Influence of moisture on the thermal and mechanical properties of autoclaved and oven-cured Kevlar-49/epoxy laminates

Moisture absorption behaviour and the influence of moisture on the thermal and mechanical properties of Kelvar-49/epoxy-resin laminates have been studied. The laminates were prepared by two different routes, namely autoclaving and oven-curing, and their properties were compared. The oven-cured laminates contained a greater percentage of voids which resulted in a greater amount of moisture absorption and higher values of moisture diffusivity. Moisture absorption caused an associated depression in the glass-transition temperature and deterioration in mechanical properties. Furthermore, two distinct relaxation transitions were indicated beyond a certain level of moisture absorption. Strongly hygroscopic Kevlar fibre is considered to provide an easy route for moisture ingress and led to the observed inhomogeneity in the plasticisation of specimens. (C) 1997 Elsevier Science Limited.