Chitosan Oligosaccharide@Melamine Polyphosphate Modified Polylactic Acid with Enhanced Flame Retardancy

A novel material, chitosan oligosaccharide@melamine polyphosphate (CMP), with enhanced flame-retardant and hydrophobic properties, was synthesized by cross-linking melamine polyphosphate (MPP) with chitosan oligosaccharide. Compared with MPP, the CMP overcomes its inherent drawbacks when used as a flame retardant in polylactic acid (PLA) composites, namely the high loading demand and unsatisfactory interfacial compatibility with the polymer matrix. The results demonstrated that the peak heat release rate (p-HRR) dropped significantly in comparison to pure PLA, from 304.69 kW·m−2 to 210.39 kW·m−2, while the fire performance index (FPI) increased from 0.1 to 0.48 s·m−2·kW−1. Furthermore, the fire growth index (FGI) decreased from 1.51 kW·m−2·s−1 to 1.03 kW·m−2·s−1. Additionally, the CMP demonstrated enhanced thermal stability, making the pyrolysis activation energy Eα increase from 135.04 to 191.97 kJ/mol during 308~416 °C by pyrolysis kinetics. Compared to composite PLA incorporating pristine MPP, the CMP-modified counterpart exhibits superior mechanical properties and significantly enhanced hydrophobicity, evidenced by a maximum water contact angle reaching 93.96°. It provides a strategy for adapting phosphorus-based flame retardants for PLA, thereby broadening their applicability across diverse scenarios.