Study On Preparation And Properties Of Intrinsic Flame Retardant Bio-Based Epoxy Resins

Epoxy resins have been widely applied in epoxy flooring,copper clad laminate,aerospace and other fields because of their excellent weather resistance,adhesive properties,and mechanical properties.The commercial epoxy resin is mainly petroleum-based bisphenol A epoxy resin,which accounts for over 85%of the production of general epoxy resins.Bisphenol A has the resemble structure to 17β-estradiol and has been proven to be an endocrine disrupting agent that can lead to endocrine disorders.Therefore,the research and development of green and safe bio-based epoxy resin is of great significance.In addition,traditional epoxy resins are flammable and have grave fire safety.In response to this situation,three types of bio-based epoxy resin precursors were synthesized by using renewable lignin derivatives and phloretin as raw materials.After curing with suitable curing agents,their flame retardancy and mechanical properties were superior to those of bisphenol A type epoxy resin under the same curing conditions.The main research contents are as follows:（1）A polyphenol mixture containing dense aromatic rings was synthesized by electrophilic substitution reaction of guaiacol and paraphthalaldehyde,and it was graded and structurally characterized.Then a phenolic guaiacol-based epoxy resin precursor（GTEP）was synthesized by epoxidation reaction.A phosphorus-containing aromatic dialdehyde was synthesized by nucleophilic substitution reaction of vanillin and phenyl dichlorophosphate.Then,a phosphorus-containing phenolic-type guaiacol-based epoxy resin precursor（GPEP）was synthesized by electrophilic substitution reaction with guaiacol and further epoxidation.And various characterization methods have been used to determine that the products at each stage meet the expected goals.（2）After curing the epoxy resin precursor with 4,4’-diaminodiphenylmethane（DDM）,they were named GTEP/DDM and GPEP/DDM,respectively.Both resins exhibit better mechanical properties and flame retardancy than DGEBA/DDM resins.GTEP/DDM resin has the highest crosslinking density（17.2×10³ mol/m³）,showing an excellent glass transition temperature（209.5℃）,which is 49.1℃higher than that of DGEBA/DDM resin.Due to the additional forces（hydrogen bonds andπ–πstacking）within the molecules of GPEP/DDM resin,its tensile strength and modulus are 21.9%and 175.9%higher than those of DGEBA/DDM resin,respectively.In addition,compared to DGEBA/DDM resins,which has the disadvantage of flammability,both resins exhibit intrinsic flame retardancy,with flame retardancy ratings of UL94 V-1 and V-0,respectively.（3）The bio-based epoxy resin precursor PGE was prepared using phloretin derived from biomass as raw material.When it is cured with 4,4’-diaminodiphenyl sulfone（DDS）,there is not only the ring-opening curing reaction of epoxy group and amino group,but also the in-situ formation of Schiff base structure,which provides additional crosslinking points and further improves the crosslinking density.Finally,PGE/DDS resin has excellent T_g（240.9℃）,storage modulus（3057 MPa,40℃）,and carbon residue rate（40.1%,800℃,N₂）,which is 39.8℃,50.6%and 1.6 times higher than DGEBA/DDS resin,respectively.Due to the thermal crosslinking effect of Schiff base,the cured resin has excellent intrinsic flame retardancy,showing a high limiting oxygen index of 33.5%,and its flame retardant grade reaches V-0.In addition,the lone electron on the N atom hybrid orbital of Schiff base makes the cured resin exhibit excellent antibacterial properties.The work of this thesis a simple and feasible method for the preparation of bio-based epoxy resins with excellent comprehensive properties,and provides a reference for the development of bio based materials that can replace bisphenol A type epoxy resins.