Styrene-free unsaturated polyesters for hemp fibre composites

N-vinyl-2-pyrrolidone (NVP) and tri(ethylene glycol) divinyl ether (TDE) are utilized as reactive diluents to replace carcinogenic styrene (St) during the formulation of unsaturated polyester (UPE) resins. The processability and thermomechanical properties of the UPE resin-containing hemp fibre composites are evaluated. Both NVP-UPE and TDE-UPE resins exhibit better miscibility than the St-UPE resin. Rheological and curing measurements reveal that the St-free resins have much lower viscosity and curing temperatures than the St-UPE resin, indicating their superior processability. Furthermore, hemp fibre composites with NVP-UPE resin show comparable mechanical properties to the St-UPE composites. Composites of TDE-UPE have comparable tensile and impact strengths to the St-UPE composites. However, the flexural strength and modulus, storage modulus, and glass transition temperature of TDE-UPE composites are all lower than those of the St-UPE composites.