Sustainable upcycling of waste polyglycol ethers into high-performance ethoxylated citrate plasticizers for PVC: Enhanced thermal stability and low migration

The urgent demand for safer, bio-based alternatives to phthalate plasticizers has driven the development of sustainable plasticization strategies. In this study, industrial distillation residual waste polyglycol butyl ether (PGBE) was repurposed as a renewable feedstock for synthesizing high-performance citrate-based plasticizers. A novel class of bio-derived plasticizers—citrate poly (ethylene glycol) butyl ether ester (CA-PGBE) and its acetylated derivative (ACA-PGBE) was successfully synthesized via a two-step esterification process catalyzed by an acidic ionic liquid. Using citric acid and waste PGBE as starting materials, the process achieved a high yield of 92.6% under an optimized molar ratio of CA: PGBE: butanol = 1:2:1.25. Poly(vinyl chloride) (PVC) films plasticized with CA-PGBE and ACA-PGBE exhibited markedly superior performance compared to those using conventional citrate plasticizers, such as tributyl citrate (TBC) and acetyl tributyl citrate (ATBC). Notably, the PVC containing 40 per hundred resin (phr) ACA-PGBE demonstrated outstanding flexibility (elongation at break: 567.9%) and a significantly reduced glass transition temperature (14.0 °C), along with improved thermal stability (T 5 up to 247.4 °C), low volatility, and suppressed migration. These enhancements are attributed to hydrogen bonding between ethoxy groups and PVC chains, increased molecular weight, and superior compatibility. Density functional theory (DFT) calculations revealed that CA-PGBE and ACA-PGBE form stronger binding interactions with PVC (−17.0 to −20.4 kcal/mol) than TBC (−8.8 kcal/mol), primarily through favorable intermolecular interactions involving carbonyl and ether functionalities. This work not only introduces a promising alternative to conventional plasticizers but also provides a viable route for waste valorization, promoting circularity in the plastics sector.