A bio-based intumescent flame retardant with biomolecules functionalized ammonium polyphosphate enables polylactic acid with excellent flame retardancy

•A core–shell flame retardant was prepared via the simple ionic interactions.•AG as biomass material was firstly applied in intumescent flame-retardant system.•The synergistic effect of APP@CS@ATMP and AG in flame-retardant PLA was explored.•PLA/APP@CS@ATMP/AG showed excellent flame-retardant and anti-dripping properties.