Design Of Reactive Flame Retardant Based On Lignin And Its Application In Flame Retardant Phenolic Foam

With the development of the national construction industry,the market for building thermal insulation materials is huge.Compared with inorganic thermal insulation materials,organic thermal insulation materials are widely used due to their advantages in construction technology,thermal insulation performance,market maturity and cost performance.Compared with other organic thermal insulation materials,phenolic foam has the advantages of strong fire resistance,no dripping and no toxic gas produced in the combustion process,which can effectively reduce the harm of fire.On the basis of lignin substituted for phenol to prepare phenolic foam,the structures of 9,10-dihydro9-oxa-10-phosphoxanthine-10-oxide(DOPO)and pentaethylhexamide(PEHM)were introduced into primary lignin,oxidized lignin and aldehyde-modified lignin by Schiff base reaction and DOPO addition reaction.Thus,a reactive lignin-based flame retardant was prepared by nitrogen and phosphorus modification,which was used to substitute phenol for the preparation of modified phenolic foam.The effects of different substitution amounts on the flame retardancy and compressive strength of phenolic foam were studied.This paper focuses on the following three aspects:(1)Preparation of reactive flame retardants by functional modification of lignin and its application in phenolic foamEnzymolysis lignin has carbonyl group due to its extraction method,so enzymatic lignin can be directly modified with nitrogen and phosphorus to prepare reactive ligninbased flame retardants,and used for phenolic foam flame retardant modification.Elemental analysis and ICP-OES data showed that the nitrogen and phosphorus contents of modified lignin were increased to 2.95%and 3.55%,respectively.The mechanical properties,flame retardancy,thermal stability and morphology of phenolic foam modified with different substitutions were studied.It was found that the compressive strength and LOI of the modified phenolic foam were both increased when the replacement rate was 5%-15%,reaching the highest of 0.24 MPa and 55.8%.In addition,the total heat release and smoke release of modified phenolic foam are reduced by 40.8%and 56.2%respectively at 5%replacement rate.When the replacement rate is 5%,the compressive strength and LOI of the foam are the best,which are 0.24 MPa and 55.6%,respectively.(2)Preparation of reactive flame retardant by functional modification of oxidized lignin and its application in phenolic foamOn the basis of confirming that enzymolysis lignin can be used as phenolic foam flame retardant after nitrogen and phosphorus modification,we selected sulfate lignin as raw material and solved the problem of low carbonyl content in sulfate lignin through oxidation reaction,and the oxidation reaction conditions were optimized.Finally,the optimal conditions were determined.The reaction temperature was 70℃,the reaction time was 4 h,the amount of oxidant H2O2 was 15 mL,and the amount of catalyst MoO3 was 0.15 g.The carbonyl content increased from 1 mmol/g to 10 mmol/g.The content of nitrogen and phosphorus in oxidized lignin was increased successfully by nitrogen and phosphorus modification,which were 5.13%and 4.99%respectively,and then used for flame retardant modification of phenolic foam.The effects of different substitutions on mechanical properties,flame retardancy,thermal stability and morphology of modified phenolic foam were studied.When the replacement rate is 5%,the compressive strength of foam increases from 0.15 MPa to 0.16 MPa.When the replacement rate is greater than 5%,the compressive strength will be negatively affected.When the replacement rate is 5%-15%,the LOI of the foam is significantly increased,and the maximum is 58%.In addition,the total heat release rate and total smoke release of modified phenolic foam decreased by 55.2%and 57.3%respectively at 5%replacement rate.(3)Preparation of reactive flame retardant by functional modification of aldehyde modified lignin and its application in phenolic foamUsing sulfate lignin as raw material,the aldehyde group was introduced by acetal reaction,and the reactive lignin-based flame retardants were prepared by nitrogen and phosphorus modification.The nitrogen and phosphorus contents of lignin-based flame retardants were 4.81%and 3.97%,respectively.The mechanical properties,flame retardancy,thermal stability and morphology of phenolic foam with different substitutions were studied.It was found that the compressive strength and LOI of modified phenolic foam were improved effectively when the replacement rate was 5%20%.When the replacement rate is 10%,FLPF10 has excellent compressive strength and flame retardant properties of 0.34 MPa and 58%,respectively.In addition,when the replacement rate was 20%,the LOI of FLPF20 was 59.6%and the compressive strength was not negatively affected.Cone calorimetric data also showed that the total heat release and heat release rate of modified phenolic foam were significantly lower than that of pure phenolic foam.