The effect of environmental ageing on the interphase in glass fibre - vinyl ester composites

The results of a study of environmental ageing on the apparent interfacial shear strength of glass fibre – vinyl ester microbond samples are presented. The scale related issues of estimating water absorption levels in microbond samples are reviewed and discussed and a solution based on Fickian diffusion is given. Interphase strength of microdroplets aged in water at 23 °C was relatively stable up to 6 days exposure after which strength degradation was fairly rapid. Immersion in water at 50 °C resulted in an immediate 20-30% irreversible loss of strength. Further exposure beyond 2 days led to total loss of integrity of the microbond samples. Electron microscope images of aged microdroplets appeared to show the development of a bi-phasic microstructure. The presence of two phases in small scale vinyl ester polymer samples was confirmed by DMA on thin films.