Fabrication Of Core-Shell Bio-based Flame Retardants And Study On Flame Retarding And Toughening Polylactic Acid

As a biomass polymer material with many advantages,polylactic acid(PLA)has been applied to a variety of industrial production fields,which is expected to replace traditional petroleum-based polymer materials.However,it is highly combustible,brittle,and not resistant to ultraviolet light and easy to age.Therefore,it is necessary to optimize the toughening,flame retardant and UV resistance of PLA to expand its application.In this paper,three different biobased flame retardants were synthesized with using ammonium polyphosphate(APP)as acid source,and their effects on the flame retardancy,mechanics and UV shielding properties of PLA were investigated.First,bio-based flame retardant APP@CS@Si was assembled in water phase with ammonium polyphosphates(APP)and chitosan(CS)and carboxylated silicone oil(Si-COOH/Si).The Si-COOH shell not only decreased the hydrophilicity of the flame retardant but also improved char formation ability.Only 2 wt%APP@CS@Si can endow PLA with satisfying flame retardancy such as UL-94 V-0 grade.The higher values of fire propagation index FPI(0.150)and flame retardancy index FRI(1.33)were also achieved by PLA with 4 wt%APP@CS@Si compared with those of PLA with the same loading of APP@CS.Interestingly,the total smoke release amount(TSR)of PLA/4APP@CS@Si is 60%lower than that of PLA/4APP@CS,exhibiting its excellent smoke suppression ability.Moreover,the flexible structure of Si-COOH could also improve the toughness of PLA with the increased impact strength and the elongation at break of PLA composite by 20%and 16%,respectively.Secondly,using APP as the core,polydopamine(PDA)as the shell material,and then assembled graphene oxide(GO)or oleic acid(OA)modified GO to prepare the flame retardant and toughening APP@PDA@GO and APP@PDA@GO-OA.The hydrophilicity of flame retardant is decreased.Loading 3 wt%APP@PDA@GO will enable PLA to pass the UL-94 V-0 rating.Compared with pure PLA,the pHRR of PLA/6APP@PDA@GO decreased by 30%,FPI and FRI increased to 0.234 and 1.45,FIGRA decreased from 1.99 to 1.22,showing the better flame retardant property than the first system.The loading of 3 wt%APP@PDA@GO and APP@PDA@GO-OA can increase the impact toughness of PLA composites by 31%and 43,showing that the mechanical properties were also better than the first system,and the flame retardant material has excellent UV shielding ability.Finally,a new intumescent flame retardant Lig-APP based on lignin was synthesized,which increased the biobase component to 50%.The data showed that the addition of Lig-APP could give PLA better flame retardant performance.The pHRR and THR of PLA/6Lig-APP composites decreased by 30%,8.7%,and FPI increased from 0.17 to 0.20 by adding 3wt%Lig-APP through UL-94 V-0 grade,and FRI rose to 1.27,which has also better flame retardant performance than the first system.In terms of mechanics properties,Lig-APP improves the rigidity and impact toughness of PLA materials.PLA/6Lig-APP composite also has excellent anti-UV shielding properties.