Fabrication Of Biobased Core-shell Flame Retardants Through Layer-by-Layer Self Assembly And Their Application In Poly(lactic Acid)

Poly(lactic acid)(PLA)prepared from biomass resources has shown great potential to replace petroleum-based polymer materials for its degradable and renewable properties.However,PLA is flammable.And it is an important factor for limiting its wide application.Therefore,the research on flame retardant modification of PLA is very necessary.Firstly,ammonium polyphosphate(APP),chitosan(CS)derived from biomass resources and phytic acid(PA-Na)adjusted to weak acidity with sodium hydroxide were used as raw materials to prepare the core-shell flame retardant APP@CS@PA-Na that intergrated all the three sources via layer-by-layer self-assembly method.APP,APP@CS coated with CS only,as well as APP@CS@PA-Na coated with both CS and PA-Na,with the addition of 10 wt%,were blended with PLA,respectively.Then,it was to study the influence of flame retardancy and mechanics for PLA.The results showed that APP@CS@PA-Na had the best flame retardant and toughening properties for PLA.With the addition of 10 wt%APP@CS@PA-Na,LOI of flame retardant PLA could reach 30.5%and obtain UL-94 VO grade.Whafs more,the elongation at break of PLA/10wt%APP@CS@PA-Na increased by 28.4%compared with pure PLA.Subsequently,the effect of different additions of APP@CS@PA-Na on the flame retardancy and mechanical properties of PLA were studied.And the flame retardant mechanism was researched,as well.The results showed that the more APP@CS@PA-Na was added,the better flame retardant property for PLA was obtained.The LOI of flame retardant PLA with 15 wt%APP@CS@PA-Na reached 34.7%.The less APP@CS@PA-Na was added,the better the tensile toughness for PLA was obtained.The elongation at break of flame retardant PLA with 5 wt%APP@CS@PA-Na increased by 59%compared with PLA.Through scanning electron microscopy-energy dispersive spectrometry(SEM-EDS)and Raman tests of carbon residue,combined with the analysis of gas phase products of flame retardant PLA when decomposed in nitrogen,it was found that APP@CS@PA-Na mainly worked with the mechanism of condensed phase flame retardant for PLA.Secondly,replacing PA-Na with alginic acid(AA),a new core-shell flame retardant APP@CS@AA was prepared.And it could be coated with several CS/AA shells(Bilayer,BL)via layer-by-layer self-assembly.Then,with 10 wt%addition,APP@CS@AA-1BL,APP@CS@AA-2BL and APP@CS@AA-3BL were blended with PLA,respectively.Then,it was to research the influence of flame retardancy for PLA.The results showed that APP@CS@AA-3BL had the best flame retardant property for PLA.Wlth the addition of 10 wt%APP@CS@AA-3BL,LOI of flame retardant PLA could reach 30.6%and obtain UL-94 VO grade.Subsequently,the effect of different additions of APP@CS@AA-3BL on the flame retardancy and mechanical properties of PLA were studied.The results showed that the more APP@CS@AA-3BL was added,the better flame retardant effect property for PLA was obtained.The LOI of flame retardant PLA with 15 wt%APP@CS@AA-3BL reached 34.5%.The less APP@CS@AA-3BL was added,the better the tensile toughness for PLA was obtained.The elongation at break of flame retardant PLA with 5 wt%APP@CS@AA-3BL increased by 91%compared with PLA.Through SEM-EDS and Raman tests of carbon residue,combined with the analysis of gas phase products of flane retardant PLA when decomposed in nitrogen,it was found that APP@CS@AA-3BL mainly worked with the mechanism of condensed phase flame retardant for PLA.