3Influence of water absorption on the mechanical properties of a DGEBA (n=0)/1, 2 DCH epoxy system

The diffusive, calorimetric, and mechanical behavior of a system composed o f a diglycidyl ether of bisphenol-h (DGEBA, n = 0) and 1, 2 diamine cyclohe xane (1, 2 DCH) were investigated during water sorption at different temper atures (23, 47, 58, 77, and 100 degrees C). Experimental results showed tha t the water absorption at these temperatures fitted well to Fick's law. The water moisture content at the equilibrium temperature and the water moistu re content at the equilibrium-curing conditions dependences have been check ed. The activation energy for diffusion was calculated obtaining a value 26 .01 kJ/mol. Dynamic mechanical analysis of several samples immersed in wate r at 100 degrees C during different periods of time showed no significant c hanges in the glass transition temperature, and a decrease in the storage m odulus at 2% of water content was observed. Storage modulus remained essent ialy constant above that water content. Values of glass transition temperat ure were corroborated by differential scanning calorimetric measurements. ( C) 1999 John Wiley & Sons, Inc.