Synthesis of phenylphosphorylated microcrystal cellulose biobased flame retardants and its flame-retardant modification on PLA biomaterials

Highly-efficient biodegradable cellulose-based flame retardants have great potential to be developed as new generation of sustainable flame retardants. In this study, phenylphosphorylated microcrystal cellulose (PhPMCC) and phenylphosphorylaminated MCC (PhPNMCC) as novel biobased flame retardants were successfully synthesized by phosphorylation and phosphoryl amination modification, respectively. The limited oxygen index (LOI) of Poly(lactide) (PLA) biocomposite with a loading of 4 wt% PhPMCC increased to 27.0%, and PLA/4wt%PhPMCC passed UL-94 V-0 rating. The PhPMCC and PhPNMCC exhibited good flame retardancy and melt-dripping suppression on PLA, and the proposed flame-retardant mechanism of the PLA/PhPMCC biocomposites was mainly attributed to that the phosphorus-oxygen radicals inhibited the decomposition rate of macromolecular chains of PLA, and a stable residue containing polyphosphate and polyaromatic ring had a synergistic barrier effect on the condensed phase. The tensile and bending strengths of PLA/PhPNMCC biocomposites were superior to those of PLA/PhPMCC composites because the interfacial reaction between the amino groups of PhPNMCC and PLA matrix provided them good interfacial compatibility. The preparation of highly efficient cellulose-based flame retardants and fully biobased PLA composite promote the utilization of renewable biomaterials.