Hierarchical hybrid glass fibers modified by hyperbranched polyphosphoramide and graphene oxide sheets to improve flame retardancy and suppress candlewick effect of poly(lactic acid)/glass fibers composites

Abstract Glass fibers (GFs) reinforced polymer composites display high mechanical performance but deteriorated flame retardancy due to the “candlewick effect” caused by fibers. To solve this problem, novel hierarchal hybrid glass fibers (GF@HBPPA@GO) were prepared by multistep coating of 3‐aminopropyltriethoxysilane (APTES), hyperbranched polyphosphoramide (HBPPA) and graphene oxide (GO) in sequence. Several GFs reinforced poly(lactic acid) (PLA) composites were fabricated with the same GFs loading. PLA/GF@HBPPA@GO composite showed the highest limited oxygen index (LOI) value of 25.2% and much decreased peak heat release rate, total heat release and mass loss rate, corresponding to a drop of 23.2%, 16.6%, and 53.8% respectively compared with PLA/GF‐APTES composite. Meanwhile, it maintained similar tensile and impact strength values. The improved flame retardancy was mainly attributed to the good synergistic effect of HBPPA and GO on generating high‐yield char residues encapsulating GFs perfectly in the condensed phase, which effectively reduced the interface energy and increased the surface roughness of GFs to suppress the wetting and spreading of PLA melt toward the flame zone, and consequently weakened the candlewick effect of GFs and achieved better flame retardancy. This provides new ideas for preparing fiber reinforced polymer composites with encouraging mechanical properties and outstanding fire safety simultaneously.