Thermomechanical Testing of Plastics for Environmental Resistance

Abstract

Abstract A thermomechanical analysis (TMA) technique has been developed for evaluating effects of moisture on mechanical behavior of plastic materials after short exposures to humidity environments. The key to shortening environmental conditioning time is the capability to test very thin, micro-size specimens which provide a high surface area to volume (S/V) ratio. The weight percentage of moisture absorbed by a material in a given time is directly proportional to the S/V ratio; therefore, thin specimens exhibit faster rates of bulk weight and, consequently, bulk property changes. The TMA method involves measurement of deflections in specimens loaded in three-point flexure while the temperature is increased at a constant rate. The technique is similar to that described in ASTM D 648 for determining temperatures at which arbitrary amounts of deflection have been reached. In addition to its sensitivity in detecting environmental effects on short term environmental exposure, the TMA method has other advantages over the D 648 procedure. These include faster and more uniform specimen heating and continuous recording of deflection versus temperature and time.