Recycling Polyethylene Terephthalate (PET) into fiber-reinforced tapes through a capillarity-based method

Abstract

In the context of circular economy strategies and low-energy processing routes, this work proposes an original method for recycling polyethylene terephthalate (PET) into fiber-reinforced thermoplastic tapes via solution impregnation of carbon fibers at ambient temperature. PET is dissolved in hexafluoroisopropanol (HFIP), enabling impregnation without the high temperatures typically required for conventional thermoplastic processing. The objective is to achieve homogeneous fiber wetting while limiting porosity in the final composite material. PET/HFIP solutions containing 0 to 15 wt% PET were systematically characterized in terms of density, viscosity, surface tension, and capillary rise behavior within carbon tows. The solution density decreases linearly, surface tension increases linearly also with increasing PET concentration, whereas viscosity increases quasi-logarithmically. All solutions exhibit Newtonian behavior, allowing spontaneous impregnation to be described using the Washburn model. Analysis of wicking experiments enables determination of apparent contact angles, which decrease and stabilize above 10 wt% PET. Impregnation speed are calculated through analytical calculation. Although impregnation velocities remain low, they provide a relevant basis for comparing solution formulations. A transition in solution structure is observed upon PET addition, as the pure solvent deviates from linear trends. This work paves the way toward low-energy, recyclable, scalable PET-based thermoplastic composite manufacturing routes globally.