Expanding the application range of flame-retardant polymer biocomposites remains a huge challenge for a sustainable society. Despite largely enhanced flame retardancy, until now the resultant poly(lactic acid) (PLA) composites still suffer reduced tensile strength and impact toughness due to improper material design strategies. We, herein, demonstrate the design of a green flame retardant additive (ammonium polyphosphate (APP)@cellulose nanofiber (CNF)) via using the cellulose nanofibers (CNFs) as the green multifunctional additives hybridized with ammonium polyphosphate (APP). The results show that PLA composite with 5 wt % loading of APP@CNF can pass the UL-94 V-0 rating, besides a high limited oxygen index of 27.5%, indicative of a significantly enhanced flame retardancy. Moreover, the 5 wt % of APP@CNF enables the impact strength (σ_i) of the PVA matrix to significantly improve from 7.63 to 11.8 kJ/m² (increase by 54%), in addition to a high tensile strength of 50.3 MPa for the resultant flame-retardant PLA composite. The enhanced flame retardancy and mechanical strength performances are attributed to the improved dispersion of APP@CNF and its smaller phase size within the PLA matrix along with their synergistic effect between APP and CNF. This work opens up a facile innovative methodology for the design of high-performance ecofriendly flame retardants and their advanced polymeric composites.

The design of fully biological flame retardants is vital for environment-friendly and sustainability development. Herein, a fully biological hyperbranched flame retardant named PA-DAD was synthesized successfully through a simple neutralization reaction between 1,10-Diaminodecane (DAD) and phytic acid (PA). PA-DAD as a kind of reactive flame retardant was subsequently employed to composite with epoxy resin (EP). The obtained EP composite, comprising 25 wt% PA-DAD, exhibited excellent flame resistance with an appreciative limiting oxygen index (LOI) of 28.0%, and a desired V-0 rating of UL-94. The favorable attributes stem from the evident flame-retardant characteristics of PA-DAD, manifesting particularly within the gaseous and condensed phases of combustion. Benefitting from the PA-DAD with the synergetic effect of smoke suppression and flame resistance, the EP/25% PA-DAD composite displayed highlighted reductions both in smoke production and heat release rate. In contrast with neat EP, total smoke production (TSP), peak smoke production release (pSPR), the peak heat release rate (pHRR), and the rate of fire growth (FIGRA) of the EP/25% PA-DAD composite were decreased by 49.5%, 57.0%, 72.2% and 77.8%, respectively. Moreover, the EP/25% PA-DAD composite resulted in well-preserved mechanical properties, especially enhanced toughness, compared with the neat EP. The strategies in our work provided a facile, green, and highly efficient way for fabricating high fire-retardant EP composites.