A continuous-flow exposure method to determine degradation of polyphenylene sulfide non-woven bag-filter media by NO₂ gas at high temperature

The degradation behavior of polyphenylene sulfide (PPS) fabric filter media by NO₂ gas at high temperatures was investigated in detail with a continuous-flow type exposure method, as specified in ISO16891:2016. An increase in the exposure time to NO₂ gas lessened the tensile strength and elongation of the PPS filter media in both machine and transverse directions. These reductions were observed in the transverse direction (TD) more markedly than in the machine direction (MD). Exposure to NO₂ gas enhanced the oxidation of sulfur, and introduced new oxygen-containing functional groups (e.g., [sbnd]SO[sbnd] and O[dbnd]S[dbnd]O) into the PPS molecular structure, which reduced the atomic ratio of carbon in the PPS filter media with increasing exposure time. These chemical degradations severely damaged the PPS fiber through cracking, splitting, and formation of protrusions on the surface. Furthermore, assuming that the chemical reaction between PPS and NO₂ gas is diffusion-controlled by NO₂, a model to estimate the change in the conversion of PPS and the NO₂ concentration in the exhaust gas was proposed, based on an unreacted core model. It could successfully reproduce the experimental data. A model to evaluate the change in the tensile strength of the filter media was also proposed, which could express experimental data only in the MD.