Reactive modification of PET with 1,5–pentanediol: Polymer properties and porous membrane formation via wet phase inversion

Pressure-driven membrane processes such as microfiltration, ultrafiltration, nanofiltration, and reverse osmosis are essential in water treatment, food, pharmaceutical, and wastewater applications. Poly(ethylene terephthalate) (PET) offers high mechanical strength, chemical resistance, and thermal stability, making it a promising alternative to conventional polymers used in membrane preparation. However, its poor solubility in environmentally benign solvents limits its application in wet phase inversion technology. This study proposes a reactive modification of PET via glycolysis with 1,5–pentanediol to enhance solubility in less toxic solvents. The two-step process – PET depolymerisation and subsequent polycondensation – yields poly(pentamethylene terephthalate), characterised by 1H NMR, gel permeation chromatography (GPC) and contact angle measurements. The modification reduces crystallinity, improves chain flexibility, and significantly increases solubility in solvents such as THF, Cyrener, and DMF at 40 ◦C. Membranes prepared from Cyrener solutions via wet phase inversion exhibit a porous, finger-like morphology confirmed by SEM. The hydrophilicity of the modified PET surface increased markedly (contact angle reduction from 110◦ to 65◦). Combining chemical modification with a bio-based solvent provides a practical, sustainable pathway for producing PET-based membranes. The results demonstrate strong potential for developing environmentally friendly, durable membrane materials for advanced separation processes.