Effects of melamine pyrophosphate on mechanical and flame retardant properties of bamboo fiber/polypropylene composites

The melamine pyrophosphate (MPP) was introduced into bamboo fiber/polypropylene (BF/PP) mats as flame retardant to prepare a series of MPP-BF/PP composites. The effects of MPP mass fractions on mechanical properties, microstructures of MPP-BF/PP composites were investigated by mechanical test and SEM. The flame retardancy, thermal stability and water resistance of MPP-BF/PP composites were studied using limiting oxygen index (LOI), thermal gavimetric (TG) and water absorption as index. The results show that the bending strength and impact strength of the MPP-BF/PP composites increase firstly and then show a decreased trend when the mass fraction of MPP is less than 30wt%. As the mass fraction of MPP increases up to 5wt%, the bending strength and impact strength of MPP-BF/PP composites reach the optimal values. MPP distributes evenly in the MPP-BF/PP composites, but the surface roughness of cross section increases with the mass fraction of MPP increasing, which means the interface compatibility between MPP and PP becomes worse, reducing the mechanical properties of MPP-BF/PP composites. The results of LOI indicate that the flame retardancy of MPP-BF/PP composites is enhanced with the mass fraction of MPP increasing. When the mass fraction of MPP reaches to 30wt%, the LOI is 24.3%. TG test reveals that the addition of MPP enhances the thermal decomposition temperature and char residues of MPP-BF/PP composites, contributing to the flame retardancy. The test of water resistance of MPP-BF/PP composites indicates that the water absorption and thickness swelling values are almost not affected by the mass fraction of MPP when less than 20wt%. According to fuzzy comprehensive evaluation, the MPP-BF/PP composites will achieve the optimal properties when the mass fraction of MPP is 10wt%.