Toward sustainable, flame-retardant, antimicrobial, and cross-linked waterborne polyurethane via intrinsic modification with a fully biobased chain extender

Abstract

The development of high-performance bio-based flame retardants is crucial yet challenging for polymers. This study designed and synthesized a fully bio-based multifunctional flame retardant (PLV) composed of phytic acid (PA), vanillin (Van), and l-lysine (L-lys). This flame retardant contains abundant phenolic hydroxyl groups, enabling covalent incorporation into the polyurethane backbone at low temperatures (55 °C). Through crosslinking chains, it ultimately forms a three-dimensional network structure, successfully creating a sustainable polyurethane material (PLWPU) that integrates flame retardancy, mechanical properties, and antimicrobial functionality. This system overcomes the limitations of traditional additive flame retardants, such as migration loss and reliance on fossil-based raw materials, while also avoiding the high energy consumption associated with high-temperature polymerization processes. Performance test results indicate that when the PLV content is 20%, the limiting oxygen index (LOI) of PLWPU-4 is 32.7%, achieving a UL-94 rating of V-0. It also reveals significant reductions in total heat release (THR), total smoke production (TSP), and peak smoke production rate (pSPR) by 34.27%, 63.41%, and 50.79%, respectively, compared to unmodified waterborne polyurethane (WPU). PLWPU-3 also exhibits a 36% antibacterial rate against Escherichia coli (E. coli). This work provides innovative insights for developing high-performance, multifunctional, and sustainable polymer materials, expanding the application potential of water-based polyurethanes in high-end coatings, biomedicine, and other fields.