The effect of isothermal aging on the relaxation spectra of AFR700B

A variety of environmental factors, acting individually or synergistically, can have a profound influence on the performance of advanced polymers and composites. In particular, exposure to a combination of moisture and elevated temperature can significantly alter properties; the extent of chemical and physical changes is a function of exposure time and the temperature and humidity of the environment. Changes in the relaxation time spectrum can be related to chemical or physical alterations which occur in the polymer. Chemical degradation can result in a broadening of the relaxation time spectrum due to a widening of the molecular weight distribution resulting from the generation of lower-molecular weight species. Physical aging may be reflected in a shift in the relaxation time spectrum to longer times. This paper discusses the effect of chemical and physical aging on the relaxation time spectra of AFR700B, a high-temperature polyimide resin. Neat resin samples were isothermally aged for 500 hours at 250 degrees C in dry air, humid air and dry nitrogen. Changes in the dynamic mechanical properties of the resin after these different exposures are discussed.