<scp>UHMWPE</scp> composites: Effect of flame retardant tannic acid as coating agent and hardener for epoxy resin systems

Abstract This study investigates the dual functionality of Tannic Acid (TA), a bio‐derived polyphenol, as a surface modifier for ultra‐high molecular weight polyethylene (UHMWPE) fibers and as a hardener for diglycidyl ether of bisphenol A (DGEBA) epoxy resin, aimed at enhancing composite laminate performance and sustainability. The surface characteristics of UHMWPE fibers were investigated by Fourier transform infrared spectroscopy and scanning electron microscopy. The TA‐modified fibers exhibited functional groups that enhanced their polarity and improved their compatibility with the epoxy matrix. Furthermore, thermogravimetric analysis revealed an increase in thermal degradation onset from 336°C to 357°C after TA treatment. The hand lay‐up method was used to manufacture composite UHMWPE laminates impregnated with TA‐hardened resins at different TA concentrations. Cone calorimetry results revealed improved fire resistance for TA‐loaded composites, with a 44% reduction in peak heat release rate (PHRR) respect to the control sample, as well as a better fire performance index. Composite laminates manufactured with TA‐modified fibers and TA‐hardened resin demonstrated up to 45% improvement in tensile strength. Highlights Tannic acid (TA) proves to be a sustainable alternative to petroleum‐based hardeners. TA enhances UHMWPE fibers' thermal stability and adhesion to epoxy. TA‐modified fibers show an increase in thermal degradation onset. TA‐hardening of epoxy improves fire resistance, reducing PHRR by 44%. Composite laminates with TA show a 45% increase in tensile strength.