Investigation on thermal degradation mechanism of poly(phenylene sulfide)

Thermal degradation occurs inevitably during the practical processing of poly(phenylene sulfide) (PPS) due to its low thermal stability, leading to the deterioration of processability and performance of PPS products. In this study, the structural evolution of PPS during thermal degradation in nitrogen (N2) and oxygen (O2) atmospheres are investigated systematically via X-ray photoelectron spectra (XPS), fourier transform infrared spectroscopy (FT-IR), gel permeation chromatography (GPC) and dynamic rheology. A rheological measurement is proposed to distinguish the multi-stage degradation behaviors of PPS efficiently. It is found that the thermal degradation mechanism of PPS differs considerably in N2 and O2 atmospheres. Chain scission is predominant when PPS is heated in N2, while CS and CC crosslinking structures can only be initiated at extremely high temperature. On the contrary, oxidation of PPS is accelerated seriously in the presence of O2. Chain extension and branching reactions are activated even at low processing temperature of PPS, and substantial COC crosslinking structures are created which leads to the sharp increase of melt viscosity. Furthermore, the change of crystallization behaviors after thermal treatments of PPS are also studied by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The crystalline kinetics of PPS changes significantly during melt processing, which further corroborates the thermal degradation mechanism of PPS.