Effect of polytetrafluoroethylene (PTFE) emulsion impregnation coating on filtration performance and thermal property of polyphenylene sulfide (PPS) needle felt

Abstract

Polytetrafluoroethylene (PTFE) emulsion is widely used as a coating material in the impregnation process for preparing polyphenylene sulfide (PPS) needle felts due to its excellent chemical stability and good mechanical properties. However, the effect of emulsion impregnation coating on the filtration performance of needle felts is still under debate. Moreover, in industrial applications with high temperatures, the service life of needle felts is directly affected by their thermal stability, but the pyrolysis and kinetic properties of PPS needle felt after PTFE emulsion impregnation post-processing have rarely been quantitatively investigated. In this study, the PPS fiber/PTFE emulsion (PPS/PTFE) composite needle felt was fabricated by a direct impregnation process. The pressure drop characteristic and mechanical collection efficiency of PPS needle felt and PPS/PTFE composite needle felt were comprehensively evaluated. It was found that the PTFE emulsion impregnation coating not only increases the pressure drop, but also decreases the collection efficiency. More specifically, for particles having a size below 2.5 μm, the decrement of collection efficiency further increases with the decrease of particle size, but the mechanical collection efficiency of PPS/PTFE composite needle felt for particles having larger size is almost the same as that of PPS needle felt. Three emulsion impregnation coating distribution models were inferred to systematically explain this experimental phenomenon. Additionally, the thermal degradation process of PPS needle felt and PPS/PTFE composite needle felt was analyzed, and several typical pyrolysis kinetic parameters were also determined theoretically. It was confirmed that the PTFE emulsion impregnation coatings can enhance the thermal stability of PPS needle felts. This work provides new insight into the rational application of the direct impregnation process as well as emulsion impregnation coating in the industrial filtration field.