Application of TMA For Determination of In-Service Exposure Temperatures in Thermoformed Sheets

摘要

Thermoplastics are frequently thermoformed into useful shapes at temperatures below their melt processing temperatures, imparting residual stresses in the part. These residual stresses will relax if exposure temperatures during use are sufficiently high relative to the glass transition temperature of the polymer. Thermomechanical analysis (TMA) was used to compare two thermoformed PVC assemblies with different exposure histories, and to determine if one part was subjected to temperatures in excess of an operational specification. The part in question and control sheets were evaluated for relaxation under isothermal conditions, as well as thermal expansion under varying temperature profiles. It was determined that the deformed sheet material was exposed to a higher in-service temperature than the control material; TMA is shown to be an effective technique for assessing dimensional stability as a function of processing history and subsequent in-service thermal exposure.