Structural and mechanical properties of UV-C irradiated polytetrafluoroethylene films

Abstract

In this contribution, we investigate the structural and mechanical properties of PTFE films subjected to different exposure times under UV-C rays ranging from 100 to 500 h. The Raman analyses indicate that the UV-C irradiation of PTFE for 100 and 200 h produces structural disorder with a lattice distortion detected particularly after an exposure time of 100 h, which primarily arises from the polymer chain scission. An almost recovery of the initial structural characteristics occurs after 300 h of irradiation due to the rearrangement of polymeric chains which is more pronounced for higher exposure times. The ATR-FTIR spectra showed that the absorption by the amorphous phase is higher after UV-C irradiation during 100 h and starts to decrease over the exposure time in the series of 200, 300, 400 and 500 h due to structural rearrangement which in turn reduces the amorphous content. The XRD analyses showed again that the irradiation during 100 and 200 h induces structural disorder with a lattice distortion produced after an exposure time of 100 h, in agreement with the Raman data. Moreover, the impact of UV-C rays on mechanical properties (hardness) of PTFE films have been better checked by the micro and nanoindentation experiment. It is found that the hardness is correlated with the structural properties. In particular, the hardness of PTFE is enhanced after UV-C irradiation for 100 and 200 h due to the enhancement of its toughness caused by the structural disorder. Further increase in the exposure time produces softening of PTFE due to the structural rearrangement. Overall, it is concluded from the present study that depending on the UV-C irradiation time of PTFE, the processes behind the induced changes are reversible.