Optimization of Cryo-treatment Parameters for PTFE by Quantum-Chemical Approach and Its Evaluation Through Mechanical, Thermal and Structural Characterization

Cryogenic treatment of polytetrafluoroethylene (PTFE) which is a widely used polymer in automotive applications is carried out using liquid nitrogen in order to improve its wear resistance. Hence, in this paper investigations on the influence of cryo-treatment especially on mechanical, structural and thermal properties of PTFE are presented along with the optimization of cryo-treatment parameters. The selected material is treated at different temperatures (-80, -140, -185 A degrees C) for stipulated time period (4, 8, 12, 16, 20, 24 h) in the cryostat and then tested at ambient temperature. PTFE is also studied simultaneously for thermal ageing. The properties of 'un-treated' and 'cryo-treated' PTFE are evaluated in a comparative manner by experiments including wear performance, Tensile test, X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy and differential scanning calorimetery. The result of quantum-chemical calculations for vibrational frequencies is used to match with experimental data for optimization of cryo-temperature. Thus cryo-treatment parameter, where the material showed thermodynamically most stable structure is optimized through quantum chemical approach. The change in crystallinity, crystallite size, bond lengths and bond angles are found to be the most important parameter responsible for enhancement of wear performance. Maximum increase in % crystallinity and wear performance is found at 12 h and -185 A degrees C, hence it can be considered as an optimum condition for cryo-treatment of PTFE.