Chemical Recycling of Used PI/PTFE Sandwich Composite Filter Bags

ABSTRACT Recycling is a major approach to addressing resource waste and environmental pollution issues, but it remains a challenge to recycling of the polyimide/polytetrafluoroethylene (PI/PTFE) sandwich composites. In this work, an efficient process for recycling PI/PTFE composite filter bags was proposed, which mainly included pretreatment, pre‐hydrolysis, separation, recovery, and reuse. First, the effect of washing pretreatment of used composite needle felt was evaluated by SEM and EDS characterization. Then the strength of the PI fibers was decreased by pre‐hydrolysis so that the PI could be easily separated with PTFE. The effect of hydrolysis time on the mass loss rate of PI, peel strength of PI with PTFE, and tensile strength of PTFE was systematically investigated. Finally, the PI was depolymerized into monomers in an alkaline solution. This method successfully realizes the recycling of used PI/PTFE composite filter bags, and the waste liquid generated can be recycled and reused. Moreover, the recycled ODA and PMA were used to prepare PI films by thermal imidization. The tensile strength and elongation at break of the PI recycled films were 107.6 MPa and 7.8%, respectively, and the films had excellent thermal stability. The recycling of used PI/PTFE composite filter bags avoids wasting resources.