Application Of Lignin-based Flame Retardant In Composite Materials

As the second largest reserves of biomass and natural material,lignin are degradable,renewable and environment-friendly.It contains abundant groups,such as hydroxyl group,and a large number of benzene rings,so that it can become a kind of raw biomaterial for a variety of polymers,such as polyurethane,epoxy resin,phenolic resin and other materials,to replace some petrochemical raw materials.In addition,lignin can be used as an excellent carbon forming agent in flame retardant system.The addition of lignin can not only reduce the cost of synthetic materials,but also improve their comprehensive performance.In this paper,the industrial enzymatic hydrolysis lignin was used as the reaction material.There are hydroxyl groups on the lignin,and there are the P-H bonds on the 9,10-dihydro-9-oxo-10-phosphophenanthroline-10-oxide（DOPO）.They were chemical bonded by Triallyl isocyanate（TAIC）through the reaction with its double bond to synthesize the halogen-free lignin-based flame retardant（LTD）containing phosphorus and nitrogen.The flame retardant polyurethane foam（FPUF）was prepared by the reaction of diphenylmethane diisocyanate（MDI）and polyether polyols,which was commonly used in industry.The flame retardancy and mechanical properties of FPUF without LTD were18.2%and 0.151MPa,respectively.The LTD was added to the foam.When L₁₅TD（lignin content was 15%）content was20%in FPUF,the limiting oxygen index（LOI）reached 28%,the tensile strength reached 0.180 MPa and the compression set reached2.87%.Furthermore,the epoxy group of Triglycidylisocyanurate（TGIC）was used to react with the hydroxyl group of lignin and the-P-OH group of ATMP.Finally,the benzoic acid was added to react with the hydroxyl group of ATMP to synthesize a halogen-free lignin-based flame retardant（LTAB）containing nitrogen and phosphorus.The MDI was applied to react with polyether polyols to prepare PU foam,and the prepared LTAB was added into the mixture of MDI and polyether polyols to in-situ reacted/compounded and obtain FPUF.Because the flame retardant LTAB contained hydroxyl groups and reacted with MDI,it was a reactive flame retardant.Adding 25%LTAB in PUF,the LOI of FPUF reached 27.8%.The tensile strength reached 0.165 MPa,and the compression set rate reduced to be 2.88%.Compared with those of PUF（18.2%and0.104 MPa）,the mechanical and flame retardant properties were significantly improved.The prepared LTAB were also applied to polyolefin.It was melt compounded with polypropylene（PP）.When LTAB content was 25%,and added in PP to obtain flame retardant polypropylene（FPP）,the tensile strength of PP increased from22.8 MPa to24.6 MPa,and the Yong’s modulus increased from 565.0 MPa to 910.5 MPa.The LOI was increased to be 29.5%.FPP reached the level of V-0 for the UL-94 test,and the melt drop of polypropylene was solved.The research results showed that the prepared lignin-based flame retardants via reacting with the monomers containing nitrogen and phosphorus elements through multi-step reaction are helpful to the flame retardant and mechanical properties of PU and PP with lower cost.The lignin was thus be high-value utilized,which is very economic and social meaningful.