Imparting hydrophobicity and flame retardancy to wood using functionalized carbon nanotubes compounded with ammonium polyphosphate

Ammonium polyphosphate (APP) and hydrophobic multiwalled carbon nanotubes (M-MWCNT) were introduced into wood to impart flame-retardant properties and hydrophobic. First, the wood was partial delignification followed by TEMPO oxidation (denoted DW). APP and M-MWCNT were then sequentially vacuum impregnated to obtain the DW@APP@M-MWCNT composite. The resulting DW@APP@M-MWCNT exhibited a limiting oxygen index (LOI) of 39.5 %, passed the UL-94–0 vertical combustion test, and showed a 39.86 % reduction in total heat release (THR) in the MCC test compared to DW. Additionally, the graphitization degree (ID/IG) of DW@APP@M-MWCNT was 31.82 % lower than that of DW@APP. After combustion, the wood retained its original structure. The FT-IR, TG-IR, and XPS analyses reveal that the flame-retardant mechanism of APP and M-MWCNT in DW is primarily a combined effect of radical trapping, synergistic charring, and thermal inhibition. This study provides an effective method for fabricating wood with both flame-retardant and hydrophobic properties.