Polyphenylene sulfide (PPS) non-woven fabrics are often used at high temperatures for bag filters in incinerating plants. Even though they degrade in the presence of acid gases, there has been not much information on the degradation of mechanical properties of PPS in nitric oxide (NO). At 200 degrees C, which is generally the highest operational temperature of bag filters, PPS fabrics gradually lose their elongation even if the modulus is barely unaffected. On the other hand, at 250 degrees C, which is near its melting temperature of 285 degrees C, the modulus increases while the elongation decreases. Contrary to our first guess, PPS does not soften near its melting temperature and becomes even more rigid. Our hypothesis then becomes that crosslinking and branching dominate around 250 degrees C, leading to the embrittlement of PPS bag-filter materials and severe strength loss. Therefore, it is our recommendation that the operational temperature of PPS bag filters should always be below 200 degrees C and the NO concentration should be far below 1000 p.p.m., at which point chemical degradation occurs severely.