Study On Preparation And Properties Of UV Curable Flame Retardant Coatings Based On Fiber Composites

Natural fiber composites have the advantages of light weight,high specific modulus,non-toxic and degradable,and have been widely used in automobile,aircraft,home appliances,building decoration and other fields.However,the inherent flammability of fiber composites makes its application in these fields have huge potential safety hazards.The common flame retardant method of fiber composites is to introduce flame retardants in the processing process.However,the low thermal decomposition temperature of flame retardants and poor compatibility with polymers have bring great difficulties to the processing of composites.In view of the above shortcomings,this paper adopted a surface flame retardant method to prepare UV-curable flame retardant coatings containing phosphorus,nitrogen structure and phosphorus,nitrogen and benzene ring structure on the surface of fiber composites.The coating has good transparency,fast curing,high flame retardant efficiency and no harmful gas emissions.In this paper,polyurethane acrylate（PUA）,2-hydroxyethyl methacrylate phosphate（HEMAP）,bis[2-（methacryloxy）ethyl]phosphate（BMAOEP）and triallyl isocyanurate（TAIC）were used to prepare flame retardant coatings.The effect of different proportions of coatings on flame retardancy of fibre composites was investigated by adjusting the content of two phosphorus monomers HEMAP,BMAOEP and nitrogen monomer TAIC.The results showed that the limiting oxygen index（LOI）of fiber composites without flame retardant treatment was only（21.6%）,and the horizontal combustion rate was 14.63 mm/min.The LOI value of the coated fiber composite gradually increased with the increase of phosphorus monomer content.When the content of HEMAP and BMAOEP was 90wt.%,the maximum LOI value of the two series coatings could reach 26.9%and 26.5%,respectively.When the content of HEMAP and BMAOEP was 80wt.%and the content of TAIC was 10wt.%,the coated fibre composites self-extinguished within a short time in the horizontal combustion test and a continuous dense carbon layer was formed on the sample surface after combustion,raising the carbon residue rate of the fibre composites and effectively reducing the heat release rate and smoke release rate.The permeability of the coating was as high as 90%,and the adhesion could reach level 3.In addition,the mechanical properties of coated fiber composites gradually increased with the increase of TAIC content in the coating.The tensile strength of the sample increases by 41%compared to the sample without flame retardant treatment when the content of TAIC in the two series of coatings is 30wt.%.In order to further improve the flame retardancy of fiber composites,a single molecular flame retardant monomer PDHAA containing phosphorus,nitrogen and benzene ring structure was synthesized from phenyl phosphate dichloride（PDCP）and N-（2-hydroxyethyl）acrylamide（HEAA）.PDHAA monomer and HEMAP monomer were mixed with different mass ratios to prepare.The introduction of HEMAP reduced the curing shrinkage of the coating and improved the adhesion between the coating and the fiber composite.The research results showed that the surface flame-retardant fiber composite had a high LOI value,could quickly self-extinguish in the horizontal combustion test and passed the UL-94 V-0 test,a continuous dense carbon layer was formed on the surface of the sample after combustion,which effectively reduced the emission of CO and CO₂ and increased the carbon residue rate of the fiber composite.The coating and fiber composite also had good adhesion.With the increase of HEMAP monomer content in the coating,the adhesion was improved,up to level 2.The mechanical properties of the coated fiber composite increased by 58%compared with the samples without flame retardant treatment.To sum up,fiber composites coated with PDHAA monomers had better flame retardancy and had broad application prospects in the field of fire prevention.