Synthesis Of Phosphaphenanthrene Structured Polymers Based On DOPO For Flame Retardant PLLA

Polylactic acid(PLLA),which is a biodegradable thermoplastic aliphatic polyester,has been widely applied in packaging and engineering plastics.However,the inherent flammability of PLLA seriously restricts its application in the field of high fire prevention level.In this paper,two new polymer flame retardants including polyphosphate(EDPP)and phosphorus-nitrogen polyurethane(PU)were synthesized by using DOPO and its derivative DDP as raw materials.They were blended with PLLA to prepare the flaming retarding materials,and their effects on the flaming retarding properties of PLLA were studied.1.A new flame retardant(EDPP)was synthesized from DOPO derivative 9,10-dihydro-10[2,3-bis(hydroxycarbonyl)propyl]-10-phosphate-10-oxide(DDP),ethylene glycol and phenylphosphonyl dichloride,and was compounded with PLLA in solution.The synthesis of EDPP was confirmed by FTIR and ~1HNMR.Scanning electron microscopy(SEM)and energy dispersive spectroscopy(EDS)tests showed that EDPP could be uniformly dispersed in PLLA matrix.When the blending ratio of EDPP flame retardant reaches 10wt%,the LOI and UL-94 vertical combustion grade are 36.4%and V-0,respectively.The flame retardancy of EDPP to PLLA can be achieved by the barrier of combustion carbon layer,free radical quenching and droplet effect.In addition,the addition of 10wt%EDPP has little effect on the tensile strength of PLLA,and the tensile strength remains at 50.07 MPa,and the toughness is improved.2.A novel phosphorus nitrogen containing polyurethane(PU)flame retardant was synthesized from p-phenylenediamine,p-hydroxybenzaldehyde,ethylene carbonate and DOPO.The structure and molecular weight of PU flame retardant were analyzed by ~1HNMR,FTIR and GPC.Then,PU/PLLA composites were prepared by solution blending of the synthesized PU flame retardant and PLLA.The effects of PU on the thermal stability,thermodynamic properties,mechanical properties and flame retardancy of PLLA were studied.When the blending proportion of PU flame retardant reaches 10wt%,the vertical combustion test grade and LOI value of PLLA/PU composites reach V-2(0.4mm)and 26.8%,respectively.The flame retardancy of PLLA can be improved by the barrier of burning carbon layer,free radical quenching and dilution of noncombustible gas.Compared with pure PLLA,the cold crystallization temperature of PLLA composites decreased significantly.Thermogravimetric analysis(TGA)shows that PU on the surface is helpful to the formation of combustion carbon layer.The addition of PU can reduce the mechanical strength of PLLA to a certain extent,but the tensile strength of PLLA composite can be maintained at 42.79MPa.