In　order　to　overcome　the　performance　barriers　of　polylactic　acid　(PLA),　a　multifunctional　layered　chitosan　derivative,　DAMC-Al,　is　synthesised　and　used　as　an　intumescent　flame　retardant.　The　acid　sources　used　in　this　work　are　9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide　and　amino　trimethylene　phosphonic　acid,　which　act　synergistically　to　facilitate　the　conversion　of　chitosan　to　carbon.　The　combustion　tests　demonstrate　that　the　PLA/5DAMC-Al　exhibits　excellent　flame-retardancy　with　a　limiting　oxygen　index　of　30.3　%　and　a　UL-94　flammability　rating　of　V-0.　The　heat　release　rate　and　total　heat　release　are　significantly　reduced　compared　to　pure　PLA,　and　the　residual　carbon　expands　rapidly.　In　addition,　the　composite　has　improved　toughness　while　maintaining　the　stiffness　of　the　PLA　substrate,　with　a　31.0　%　increase　in　elongation　at　break.　DAMC-Al　can　also　effectively　block　the　transmission　of　95　%　of　ultraviolet　lights,　protecting　the　PLA　macromolecular　chain　from　high-energy　ultraviolet　damage.　Actually,　the　ultraviolet　protection　factor　of　PLA/5DAMC-Al　is　determined　to　be　as　high　as　51.43.　Furthermore,　the　soil　degradation　tests　show　that　PLA/5DAMC-Al　has　the　same　excellent　natural　degradation　properties　as　PLA.　©　2025　Elsevier　Ltd