Bio-based solvents for polyolefin dissolution and membrane fabrication: from plastic waste to value-added materials

Abstract

Membrane technology is a low-footprint and highly efficient industrial separation process. While more stable membranes could substantially contribute to modernizing the chemical industry, sustainability must be seen holistically. Polymer sources, solvents, and recycling strategies that adhere to the strategic concepts of the circular economy should be considered at the membrane design stage. Recycling plastic waste into separation membranes can help remediate the environmental impact of the current plastic pollution. Polyolefins are the most manufactured and used polymer family, and their high chemical resistance and low price are attractive for membrane preparation. However, their limited solubility in mainly non-renewable solvents at high temperatures restricts their processability and recycling. In this work, we present the use of polypropylene (PP) and low-density polyethylene (LDPE) as the source of membrane preparation by their dissolution in two bio-based and renewable solvents (α-pinene and D-limonene). The thermal properties and phase separation behavior were studied and phase diagrams were obtained. Liquid–liquid phase separation and spherulitic morphology were observed for the three studied systems. PP membranes were obtained by a thermally induced phase separation (TIPS) process employing α-pinene as a solvent, and food packaging plastic waste or commercially available PP pellets in the polymer dope solution. The obtained membranes were tested for water-in-oil emulsion separations. The influence of the polymer content and the quenching media on the morphology, mechanical and thermal properties, and water contact angle was investigated. PP membranes were fabricated with 20–30 wt% polymer contents using water at 4 °C and 20 °C as quenching media. The contact angles were higher than 150° under oil enabled efficient water-in-toluene emulsion separation, where approx. 95% water rejection and an average of 99.97% toluene purity were achieved.