Degradation study of polydimethylsiloxane gaskets exposed in research reactor environment using different analytical techniques

The aim of this research is to study the principal degradation mechanisms in Polydimethylsiloxane (PDMS) gaskets exposed in research reactor environment. For this purpose, locally available PDMS gaskets samples were purchased and labelled as G-1, G-2 and G-3. Characterization of samples was done by employing various analytical techniques such as X-ray Diffraction spectroscopy (XRD), Fourier Transform Infrared spectroscopy (FTIR), Thermo-gravimetric analysis–Differential Scanning Calorimetry (TGA–DSC), mechanical testing, Optical/Scanning Electron Microscopy/Energy-dispersive spectroscopy (SEM/EDX) analyses and chloroform immersion test. The results revealed that G-1 sample showed better thermal, mechanical and chemical properties due to homogenized blend of silica particles with PDMS polymeric structure. The qualified gasket sample (G-1) was fixed in stainless steel flanges and irradiated (neutrons, gamma) in pool of Pakistan Atomic Research Reactor (PARR-1). On monthly basis inspection, it was observed that G-1 sample deteriorated in numerous pieces after receiving an accumulated dose of ~ 16.5 KGy during 5.5 years. The irradiated sample was characterized and results revealed that PDMS chains degraded by yielding free radicals (H . and CH 3 . ) and silicon-based cyclic compounds (C 6 H 18 O 3 Si 3 ) as by-products. Furthermore, dispersed silica particles leached out and left behind pores in main matrix which also weaken the polymeric chain structure. The propagation of crack branches along the weak regions of polymeric matrix was also observed in SEM analysis. From this investigation, it was inferred that scissioning mechanism was dominant over crosslinking in PDMS gasket during their degradation in research reactor environment.