The multi-walled carbon nanotubes (CNTs) were modified using phosphaphenanthrene compounds (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO)) and vinyl triethoxy silane (VTES) by covalent bond. The DOPO- and VTES-treated CNTs were named DVCNT, and the structure was characterized by Fourier transform infrared, thermogravimetric analysis, and transmission electron microscopy. Nanocomposites were prepared by adding CNTs or DVCNT to poly(lactic acid) (PLA), and the flame retardancy was examined by determination of limiting oxygen index (LOI), vertical burning (UL94), and cone calorimetry. Results reveal that the LOI of PLA/DVCNT_4% composites was increased to 26.6 and prevents dripping of PLA in some level, and DVCNT can significantly reduce heat release rate and mass loss rate during combustion, which indicate that DVCNT can improve the dispersibility of the CNTs in the polymer composites and hence enhance the flame retardancy simultaneously.

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To reduce the flammability of epoxy resin (EP), a flame retardant (designated as D‐POSS) containing diphenylphosphinyl and polyhedral oligomeric silsesquioxane (POSS) was constructed by aminopropyl‐isobutyl POSS and diphenylphosphinyl chloride. The chemical structure of D‐POSS was fully characterized, then it was used to enhance the flame retardancy of EP. When the flame‐retardant EP composite contained 4 wt% D‐POSS, its limiting oxygen index value was 29.0% and it achieved UL 94 V‐1 rating. Also, its peak of heat release rate (pk‐HRR), total heat release (THR) and total smoke production were decreased by 35.3%, 30.3%, and 38.3%, respectively. Moreover, the results from cone calorimeter disclosed that diphenylphosphinyl group and POSS group in D‐POSS showed a strong synergistic effect in inhibiting pk‐HRR, THR, and smoke production, promoting the charring formation of EP material, and forming an intumescent char layer. Additionally, the theoretical THR reduction of flame‐retardant EP composite was calculated by the equation deduced from the standard, and it was almost same with the practical THR reduction. Notably, some silicon oxide enriched on the residue's surface. The phenomenon led to form a double‐layer residue that consisted of white yarn‐like outer char and normal intumescent inner char. This double‐layer residue was contributed to enhance EP composite's flame retardancy.

The DOPO@ZIF-67 promoted the carbonization process of the EP flame retardant composites, and the rigidity and damping coefficient of EP composites are also improved compared with pure EP.