Circular poly(ethylene terephthalate) with lignin-based toughening additives

Preparation of benzoate ethyl lignin derivatives and their application for upcycling PET. • An environmentally friendly method to convert technical lignin toward versatile and uniform building blocks. • These benzoate ethyl groups (BELignin) were thoroughly characterized, showing enhanced uniformity and thermal stability. • Blending BEignin with PET can attain toughness (+91 %) and strength (+ 56 %), simultaneously. • Renewable lignin toughening additives can reduce PET greenhouse gas emissions by 17% and prompt its circularity. Creating sustainable plastics demands an efficient strategy to reduce the carbon footprint and enhance the circularity of widely used materials. Inspired by the structure of plant cell wall, renewable lignin macromolecules are modified with benzoate ethyl functional groups and combined with semi-crystalline poly(ethylene terephthalate) (PET) at a 10 % weight ratio. This process significantly improves the toughness (+97 %) and strength (+ 56 %) of PET while also reducing greenhouse gas emissions (−17 %) and promoting circularity, outperforming traditional toughening agents. Our in-depth analysis indicates that benzoate ethyl lignin derivatives exhibit improved thermal stability and controllable physical structure. The newly added benzoate ethyl groups are similar to fundamental units in PET, facilitating the formation of micro-scale particles within the PET matrix and improving their crystallinity and mechanical performance. The resulting composite can be reprocessed at least three times, representing a significant breakthrough in mechanical processing thermoplastics. Therefore, this study presents a promising approach to utilizing lignin biopolymer and waste PET for advanced materials with positive environmental footprints.