The effect of molding time and temperature on the modulus and glass transition of phenolics

The effects of molding time and temperature on the dynamic mechanical behavior of a novolak phenolic molding compound were measured using the DuPont Dynamic Mechanical Analyzer. Large differences were found in the modulus-temperature response over the range of curing times (10 to 1800 s.) and temperatures (132 to 218°C) employed. Glass transition temperatures increased well beyond cure temperatures at long cure times. In the asmolded condition, samples cured at lower temperature had higher room temperature modulus than those cured at higher temperatures, and the lower modulus corresponded to lower density. Postbaking by steps up to 232°C increased the glass transition above 280°C, and also served to normalize the modulus differences found in as-molded samples.