Using data generated by a differential scanning calorimeter, the heat of reaction, the rate of cure, and the degree of cure of Fiberite 976 resin were determined at the constant temperatures of 413, 423, 433, and 443°K (isothermal scanning). The ultimate heat of reaction was also measured at the constant heating rate of 2°K/min (dynamic scanning). Using a disc and plate type viscometer, the viscosity was measured as a function of time at the temperatures of 413, 423, 433, and 443°K. Expressions were also developed which represent the rate of cure, the degree of cure, and the viscosity data.
The parallel‐plate test fixture on a Rheometrics viscometer was electrically isolated so that the rheological and dielectric properties of a thermoset polymer system could be simultaneously measured. This enabled the relationship between the dielectric properties and the rheological properties to be directly examined. A close relationship was established between the dielectric properties (dipole relaxation time and specific conductivity) and the pre‐gelation bulk viscosity. This relationship suggested that models similar in form to those used to describe the change in viscosity might be used to describe the changing dielectric properties. The limitations and advantages of two such models, which attempt to describe the time‐temperature behavior of the dielectric properties, were then tested for use with a typical aerospace epoxy resin system.
SynopsisA model epoxy matrix resin was analyzed using differential scanning calorimetric and rheological techniques. The data was used to construct a time-temperature-phase transformation diagram to investigate the thermoset curing phenomena. Experimental techniques were developed to generate similar data on a carbon/epoxy prepreg material. The data were then compared to study the effects of the presence of the reinforcement on the processing characteristics of the epoxy matrix resin.
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