Preparation Of Phytate Based Flame Retardants And Study On The Flame-retarant Mechansims

Due to its low carbon,green,and safety,bio-based flame retardants have gradually become a research hotspot in the field of biodegradable flame-retardant materials.However,the bio-based flame retardants with high reserves（such as cellulose deritives or lignin）are usually not effient enough to be used alone.What’more,these flame retardants usually should be modified or compound with multi-aromatic compounds,nitrogen compounds or phosphorus-containing compounds,especially for the phosphorus-containing compounds with significant flame retardancy in the gas and condensed phases during the combustion.Phytic acid is a kind of biological phosphorous flame-retardant monomer,containing 28 wt%phosphorus content,with the advantages of non-toxicity and good modifiability.Therefore,in this paper,series flame retardants based on phytic acid were synthesized using environmentally friendly solvents（anhydrous ethanol or water）and blended with four bio-based degradable plastics.And the series bio-based biodegradable flame-retardant blends were prepared.The effects of four phytate based flame retardants on the flame retardancy,thermal,and mechanical properties of biodegradable blends were studied.By studying the molecular weight,carbon layer,and combustion gas of the blends after the combustion,the flame retardancy mechanism of phytate based flame retardants in biodegradable blends was further revealed.The main conclusions are as follows:1.Choline phyate（CPA）flame retardant was prepared by ion exchange and acid-base neutralization in ethanol using phytic acid and choline as raw materials.Then it was mixed with thermoplastic starch（SG）to prepare bio-based flame-retardant starch named SGCPA.The results showed that CPA had both plasticizing and flame retarding effects on SG.As the CPA loading was 30 phr,the crystallinity of thermoplastic starch decreased from 11.7%to7.6%,the limiting oxygen index（LOI）increased to 43.7%,and the SGCPA₃₀ film（1 mm）could pass UL-94 V0 rating.Compared with the SG film,the peak of heat release rate（PHRR）was decreased by 68.7%and the total heat release（THR）was decreased by 33.8%for the SGCPA film containing 20 phr CPA.According to the study of the char residues after cone test of SGCPA,after the addition of CPA,the volume of the carbon layer increased obviously,showing a typical intumescent flame-retardant characteristic.What’s more,the quality of the char residues was improved obviously,which meant the main mechanism was the condensed phase flame retardant.2.Phytic acid modified lignin（LMP）was successfully prepared by mannich and supramolecular self-assembly reaction in water using phytic acid,melamine,and alkaline lignin as raw materials.Moreover,the toughened and flame-retardant polylactic acid blends（PLAG/LMP）were prepared by blending PLA and LMP.The results showed that the mechanical properties of PLA blends were reduced by adding pure alkaline lignin without modification.However,the toughness of PLA blends was improved after adding the lignin modified by phytic acid.What’s more,elongation at break and impact strength of PLA blends containing 10 phr LMP were 23 times and 2 times that of the pure PLA,respectively,and the toughness of PLA blend was significantly improved.It was noting that the oxygen index of PLA/LMP₂₀ increased to 24%when the LMP dosage was 20 phr,and the flame retardancy of PLA was improved.It could be seen that phytic acid modified lignin can improve the toughness and flame retardancy of PLA.3.Melamine phytate（MPA）,melamine copper phytate（MPACu）,melamine zinc phytate（MPAZn）,and melamine magnesium phytate（MPAMg）were successfully prepared by the hydrothermal method using phytic acid,melamine,and divalent metal ion(Cu²⁺,Zn²⁺,and Mg²⁺)compounds as raw materials.Four flame-retardant PLA blends were prepared by blending PLA with them respectively.The results showed that the mechanical properties of the PLA blendswere less effected by MPAZn,and the flame-retardancy of PLA/MPAZn was better.The PHRR and THR of PLA/MPAZn₂₀ were reduced by 45.0%and 40.7%in cone test compared with pure PLA,respectively.In the PLA/MPAZn blends after cone test,Zn²⁺acted as the crosslinking points of the tight char layer,which made the char residues denser and more continous.In addition,MPAZn has a positive effect on the gas phase flame retardancy of PLA/MPAZn₂₀ blend during combustion by studying the gas composition and contents during the pyrolysis of the PLA blends.In conculusion,the flame-retardant mechanism of PLA/MPAZn₂₀ was the synergistic action of condensed and gas phases.4.Fufurylamine phyate（PAF）was prepared by the reaction of phytic acid and furfurylamine in anhyrous ethanol.PLA and PAF were blended to prepare the fully bio-based PLA blends（PLA/PAF）.The results showed that PAF is a highly effective bio-based flame retardant for PLA,which can effectively prevent the ignition of PLA.Compared with the pure PLA,the LOI of PLA/PAF_1.5contiainig 1.5 phr PAF was significantly increased from 20.5%to 30.6%.Meanwhile,the PLA/PAF_1.5 and PLA/PAF_2.0films（about 250μm）were self-extinguished without igniting cottons in the vertical burning test.Different from the traditional flame-retardant mechanism,PAF,as a heat stabilizer of PLA for the droplet-promoting mechanism of PLA/PAF,that is polymers with lower molecular weight are more likely to be generated in the combustion process of polymers rather than small molecules.In addition,the tensile strength of PLA/PAF_1.5 was 66.5 MPa,which still mantianed a high strength,and the blend film still maintained good transparency.It could be seen that flame-retardant PLA with excellent comprehensive performance can be prepared by fufurylamine phyate.