Modified hemp fiber combined with melamine cyanurate for enhancing fire safety and mechanical properties of unsaturated polyester resins for automobile parts

The application of flame retardants in automobiles is extensive, and the existing flame retardants will cause some pollution to the environment. Therefore, environmentally friendly flame retardants need wide exploration. Natural fibers have been used in various fields for their environmentally friendly features. Thus, in this paper, hemp fiber (HF) was modified with phytic acid and then combined with melamine cyanurate to improve the fire safety of unsaturated polyester resins (UPRs). The fire behavior and thermal stability of UPR composites were evaluated using the limiting oxygen index (LOI), cone calorimeter test, and thermo-gravimetric analysis (TGA). With 3 wt. % modified HF (HF-P) incorporation, the LOI value of UPR/HF-P-3 composites increased from 18.9% of pure UPR to 22.1%, and the average heat release rate (AHRR) and total heat release were reduced to 401.9 kW/m2 and 150.6 MJ/m2, respectively. TGA revealed that UPR/HF-P-3 composites led to the increased amount of residual char and better thermal stability compared to UPR/HF composites. In addition, HF-P endowed a better enhancement on the flexural strength of UPR composites.