Effects of Hygrothermal Cycling on Properties of Glass–Vinyl Ester Composite

Abstract

Hygrothermal freeze–thaw cycling exposures were performed on glass–vinyl ester composite to simulate harsh temperature and moisture conditions that the composite might encounter during their lifetime in services. The cycling conditions used were 80°C/saturated steam/48h⇔−17.8°C/dry/24 h. A characteristic moisture absorption behavior observed was that each time when the composite was taken out of the warm and humid environment and put into freezer, it exhibited a fast absorption of moisture, while the composite underwent an obvious desorption when moved from freezer to a warm humidity chamber. After the desorption at the very beginning of the thaw process, the composite showed a moderate absorption in the saturated steam at 80°C. This phenomenon was explained by the difference in thermal expansion rates of the fibers and the resin. Compression tests were conducted to investigate hygrothermal cycling effects on mechanical properties of the composite. The results showed that the degradation in compression strength for hygrothermally cycled composites was less significant than that of samples simply experienced isothermal holding at the same temperature and with the same exposure duration. Thermal analysis results indicated that glass transition temperature of the composite increased with an increase in hygrothermal cycling duration and leveled off after about 1000 h of the exposure, while thermal decomposition temperature of the composite was only slightly influenced by the hygrothermal exposures.