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An intumescent flame retardant, poly(diaminodiphenyl methane spirocyclic pentaerythritol bisphosphonate) (PDSPB) has been covalently grafted onto the surfaces of multiwalled carbon nanotubes (MWNTs) to obtain MWNT‐PDSPB and according nanocomposites were prepared via melt blending. After high density PDSPB (65 wt %) were attached to the MWNTs, core‐shell nanostructures with MWNTs as the hard core and PDSPB as the soft shell were formed. The resultant MWNT‐PDSPB was soluble and stable in polar solvents, such as DMF. The optical microscopy and TEM results showed that the functionalized MWNTs can achieve better dispersion in ABS matrix. The linear viscoelastic behavior indicated that MWNT‐PDSPB can form network structure at very low nanotube loading than un‐functionalized MWNTs. The results of flammability showed that better flame retardancy was obtained for ABS/MWNT‐PDSPB nanocomposites due to the better dispersion of MWNT‐PDSPB in ABS matrix. The flammability of the composites is strongly dependent on the network structure of nanotubes which reduces the diffusion of volatile combustible fragments generated by polymer degradation which diffuse towards the surface of the burning polymer to evaporate to feed the flame. The grafting of intumescent flame retardant of PDSPB can improve both the dispersion of nanotubes in polymer matrix and flame retardancy of the nanocomposites.

The design of flame-retardant biocomposites based on biobased flame retardants (FRs) represents a promising direction for creating a sustainable world. To date, it remains a major challenge to explore a green and scalable strategy for the design of highly effective, biobased FRs for bioplastics, such as polylactic acid (PLA). Herein, we have demonstrated a green, facile fabrication approach for a core–shell-structured biobased flame retardant (APP@CS@PA-Na) via layer-by-layer assembly using water as the assembly media. With electrostatic interactions, APP@CS@PA-Na was prepared by sequential assembly of ammonium polyphosphate (APP) with positively charged chitosan (CS) and then negatively charged phytic acid salt (PA-Na). The addition of APP@CS@PA-Na can enhance both the flame retardancy and the toughness of PLA. With the addition of 10 wt % APP@CS@PA-Na, the resultant PLA composite can pass an UL-94 V-0 rating and meanwhile shows an increased elongation at break by 28.4%, compared with that of neat PLA (8.1%). Through the analysis of the volatile gases and the residues, the flame retardant mechanism of APP@CS@PA-Na in PLA plays the key role in the condensed-phase. This work will broaden the practical application field of PLA, such as in electric and electronic and fibers fields.