Solid-state modification of poly(butylene terephthalate): Design of process from calorimetric methods for catalyst investigation to reactive extrusion

Abstract

The production of plastics has been increasing for more than half a century and the problem with significant growth is the waste associated with this activity. At this time, polymers are mainly recycled by classical pathway (e.g., mechanical or chemical recycling) but at the moment these techniques still present several issues (e.g., obtaining unclean material, etc.). In this study, it is proposed to reuse the materials to give them a second life by solid-state modification (SSM). This paper reports the design of a new process based on SSM technique of polyesters from batch into a continuous process. Poly(butylene terephthalate) (PBT) and 1,12-dodecanediol (DDO) are used as model compounds. At first, a calorimetric method is developed to investigate the main features of the reaction at small scale and make the proper choice of catalyst with the help of differential scanning calorimetry (DSC). At the second step, a qualitative kinetic discussion confirms our calorimetric results and the influence of the reaction time on the molecular and thermal characteristics of the copolymers obtained. The optimized conditions are then transferred to a gram-scale batch reactor and finally tested in reactive extrusion (REx) continuous process allowing to decrease the reaction time as much as possible and to test the shear forces in the SSM framework. This study therefore encompasses the design of a new process for recycling polymeric materials and offers the possibility of making polymers more sustainable.