Preparation And Study Of Flame Retardant Lignin-Based Polyurethane Coating Materials

Lignin is a biodegradable and renewable polymer with the second largest resources in nature world.It contains a large number of benzene rings and hydroxyl groups.It can be used as raw materials of environmental protection polymers,such as polyurethane,polyester,epoxy resin,phenolic resin and so on.In addition,lignin can be used as a carbon source for flame retardant polymer because of its high carbonization ability.In this study,the application of commercial organosolv lignin to prepare the flame retardant lignin based polyurethane coatings was explored.On the one hand,lignin-based flame retardants were synthesized through the reaction of isocyanate,lignin and flame retardant intermediate 9,10-dihydro-9-oxa-10-phosphatase-10-oxide(DOPO).This flame retardants has a high flame retardant phosphorus element and charring agent at the same time.On the other hand,lignin with a large number of hydroxyl groups could replace some petroleum-based polyols to prepare lignin-based polyurethane applied as coatings with excellent properties.In this study,the high efficiency and environmental friendly lignin-based flame retardants were synthesized by in situ reaction method.The flame retardants(LHDs)were synthesized by the reaction of hexamethylene diisocyanate(HDI),DOPO and lignin with different content(5%,10%,15%).Lignin-based polyurethane(LPU1)prepolymer was synthesized by the reaction between lignin,polyethylene glycol 200(PEG 200)and HDI.LHDs were then added in the LPU1 prepolymer and co-cured to prepare flame retardant lignin-based polyurethane.LPU1 had high flame retardant efficiency and environmentally friendly properties.Then the flame retardant properties,thermal stability,coating properties and flame retardant mechanism of LPU1 and FLPU1 were studied.The results showed that the hardness of FLPU1 can reach 3H,the flexibility is 2mm,the adhesion reaches 0 and the impact resistance reaches 100 cm/1000 g.For FLPU1,the hardness reached 4H when the content of L15 HD was 25% and other properties were well maintained.Meanwhile,the LOI value of FLPU1 was 30.2%.The properties of FLPU1 coatings obtained were shown to present excellent comprehensive performance.Considering the practicability and cost of the materials,the lignin-based flame retardants(LMDs)were synthesized via in situ reaction method by the reaction of lignin,DOPO and diphenylmethane diisocyanate(MDI)which is cheaper and more commonly applied in industy.Then,lignin was used to replace part of polyether polyol to react with MDI and PEG 2000 to prepare polyurethane(LPU2).The addition of PEG 2000 was to adjust the flexibility of LPU2.The LPU2 coatings had lower cost with good properties.The flame retardant LPU2 materials(FLPU2)were obtained with the adding of synthetic LMD.The flame retardancy,thermal stability and coating properties of FLPU2 were characterized.The results indicated that the coating performance reached a better balance when the content of lignin was 15%.The hardness of LPU2 was HB,flexibility was 2mm,the impact resistance was exceed 100cm/1000 g.The hardness of FLPU2 increased with the increased content of LMD.The flexibility and impact resistance of FLPU2 were decreased when the addition content of L20 MD was more than 20%.Therefore,the comprehensive performance of FLPU2 coatings was the best when the content of LMD was 20%.Its LOI value was 27.5% which can be inflammable.In conclusion,the lignin-based flam retardant and flam retardant lignin based polyurethane were prepared by in situ reaction with the directly application of commercial organosolv lignin.This method can enhance the comprehensive properties of flame retardant polyurethane with lesscosts and environmental pollution,which has great significance in terms of economical and social benefits.