Synthesis Of Phosphorus-containing Lignin-based Flame Retardants And Their Applications In Epoxy Resins

Epoxy resin(EP)is widely used in transportation,aerospace industry and electronic and electrical fields because of its excellent properties such as electrical insulation,sealing and dielectric properties.However,the flammability of epoxy resins has limited its development.Fabricating a high-performing thermoset using bio-based flame retardant containing phosphorus is critical for the sustainable development of epoxy resins with superior fire safety and robust mechanical properties.In this thesis,we use industrial waste lignin and DOPO as raw materials to synthesize green bio-based flame retardants,and prepare EP composites with excellent flame retardancy and mechanical properties.The influence of structure,elements and dosage of bio-based flame retardants on epoxy resin was also investigated to achieve the best dose-effect relationship.In this work,allyl methacrylate(AMA)and phosphate-containing monomer DOPO were grafted onto lignin in a two-step process to prepare a highly efficient bio-based flame retardant(DAL-x),and added to epoxy resin to prepare EP composite materials(DAL-x/EP).The experimental results show that DALx/EP has excellent flame retardancy,thermal stability and mechanical properties.For example,with the introduction of 10wt% DAL-x,the EP composites passed the V-0 level of the vertical combustion test(UL-94),and the maximum LOI reached 29.8%,meeting the requirements of industrial fire protection.In terms of mechanical properties,the tensile strength of DAL-x/EP is also improved,and the storage modulus and elastic modulus are increased by 25% and 21%,respectively,compared with pure EP.In addition,the PHRR and THR of DAL-x/EP were decreased by 24% and 22%,respectively,while the residual carbon(RW)was increased to 15.96wt%.In this work,diacetone acrylamide(DAAM)and phosphate-containing monomer DOPO were grafted onto lignin in a two-step process to prepare a highly efficient bio-based flame retardant(DDL-x),and added to epoxy resin to prepare EP composite materials(DDL-x/EP).AS expected,DDL-x/EP have excellent flame retardancy,thermal stability and mechanical properties.Compared with DAL-x/EP,the DAL-x/EP composite can achieve UL-94 V-0 grade with DDL of only 7.5wt%,and LOI can be increased to 30%.In terms of mechanical properties,the elastic modulus,notched impact strength and KIC of DDLx/EP were increased by 42%,42% and 60%,respectively,compared with pure EP.Compared with DALx/EP,DL-X /EP has better flame retardancy and mechanical properties.In addition,the PHRR,PSPR and TSP of DDL-x/EP were decreased by 38%,31% and 45.8%,respectively,while the residual carbon(RW)was increased to 16wt%.