THE DEPENDENCE OF FRACTURE PROPERTIES ON CURE TEMPERATURE IN A DGEBA DDS EPOXY SYSTEM/

The glass transition temperature (T(g)), water- and solvent-absorption characteristics, fracture toughness, and tensile properties of a digl ycidyl ether of bisphenol-A (DGEBA) -based epoxy resin (Epikote 8283) cured with an aromatic amine curing agent, 4,4'-diaminodiphenyl sulfon e (DDS), were studied as a function of cure temperature and cure cycle (one-step or two-step cure). The glass transition temperature (which depends on the extent of cure) shows a linear increase with increasing cure temperature and levels off toward the cure temperature of 200-de grees-C. Water and solvent uptake tended to increase with increasing c ure temperature and, hence, with cross-linking level. Fracture toughne ss, tensile strength, strain to break, and tensile fracture energy als o increased significantly with increasing final cure temperature regar dless of cure cycle. In contrast, the small strain properties such as modulus, yield stress, and yield strain were not influenced greatly by cure temperature and cure cycle. From these results, we infer that th e large strain properties of the resin are not inversely proportional to the cross-link density of the network as reported in many publicati ons,1 but, rather, that they are dependent on other structural paramet ers such as free volume and the flexibility of the cross-linked chains .