Effect of Time-Temperature Path of Cure on the Water Absorption of High T sub g Epoxy Resins

摘要

The effect of different time-temperature paths of cure on the water absorption of high t sub g epoxy resins has been investigated. The resins were cured isothermally at elevated temperatures for different times, with the following results: as extent of cure increased, the glass transition temperature (t sub g) increased, the room temperature (RT) modulus decreased, the RT density decreased. the RT diffusion coefficient appeared to decrease, and RT equilibrium absorption of water increased. The decrease in RT density is related to an increase in volume, which controls the amount of water absorbed. A qualitative model accounts for the increase in RT volume with increasing cure. The model is based on a restricted decrease of free volume on cure due to rigid molecular segments in the cured resin systems. A thermodynamic approach, independent of the absorption mocel, can correlate sorption data at different temperatures. The diglycidyl resin was also cured for extended times at three temperatures in an effort to achieve full cure at each temperature. Their equilibrium water absorption increased with increasing cure temperature, consistent with the decrease in RT density. The systems studies were a diglycidyl ether of bisphenol A cured with an aromatic tetrafunctional diamine, trimethylene glycol di-p-aminobenzoate (T sub g infinity = 156 C), and a triglycidyl ether of tris(hydroxyphenyl)methane cured with the same amine (T sub g infinity = 268 C).