Influence of Operation Procedures on Vicat Softening Temperature of Thermoplastic Materials

Vicat softening temperature (VST) is one of the most important parameters to evaluate heat resistance of thermoplastic materials. However, the initial test temperature is difficult to control, which may reduce the testing efficiency and the precision of VST. Moreover, according to the procedure of GB/T 1633-2000, the specimen should be placed horizontally under the indenting tip of unloaded rod for 5min. After that, add a sufficient weight to the weight-carrying plate, and then set the penetration indicator to zero to start the experiment. However, the waiting period between adding the extra mass and starting the test may be different during the real operation. Such longer or shorter waiting periods can also influence the tested VST. In this paper, ultra-high molecular weight polyethylene (UHMWPE) was used to discuss the influence of initial temperature and waiting period on its final VST. The results show that, in order to satisfy the practices of standard GB/T 1633-2000, the initial temperature and the waiting period should not exceed 40 degrees C and 25min, respectively.