| Epoxy resins,as one of the three most important thermosetting resins,have been widely used as coatings,adhesives and molding materials in the fields of electronics,optical machinery,engineering technology,rail transit,and others,because of their excellent adhesion,chemical resistance and mechanical properties,etc.However,traditional epoxy resins are flammable and cannot be extinguished spontaneously after being removed from the fire,and their heat resistance needs to be improved,which are the key factors restricting their further development.In addition,the sustainable development goal of achieving peak carbon dioxide emissions and carbon neutral requires the feedstocks of epoxy resins to gradually reduce the dependence on non-renewable petroleum resources.In order to resolve the above problems,in this dissertation,from the view of designing molecular structure,four kinds of novel bio-based epoxy resins bearing N-containing aromatic heterocycles or rigid aromatic structures were synthesized from renewable biomass resources,and their heat-resistant properties and intrinsic flame retardancy were improved effectively through adjusting their rigid molecular structures and functionalities.The glass transition temperature(Tg)of the bio-based epoxy resins synthesized in this dissertation were all higher than the commonly used petroleum-based bisphenol A epoxy resins(DGEBA)under the same curing condition,and some of them even surpassed the aviation grade 4,4'-diaminodiphenylmethane epoxy resins(TGDDM).The work of this dissertation not only dissolves the key problem that the heat resistance,mechanical properties(strength/modulus)and flame retardancy are hardly to be improved at the same time,but also provides valuable references for the development of high-performance bio-based polymer materials and enhancement of their competitiveness to petroleum-based products.It is of guiding significance in realizing sustainable development of polymer materials.The main research contents of this dissertation are presented as follows:(1)A bio-based bisphenol-like compound bearing pyridazinone structure(GSPZ)with only biomass carbon was synthesized from the common bio-based compounds,guaiacol and succinic anhydride.The obtained bio-based bisphenol-like compound can be used to prqpare a bio-based difunctional epoxy resin(GSPZ-EP,epoxy value:0.58 mol/100g).4,4'Diaminodiphenylmethane(DDM)was chosen as the curing agent for this system.Thanks to the aromatic N-heterocycle structure in GSPZ-EP,the cured GSPZ-EP/DDM showed a high glass temperature(Tg)of 187?,which was 14? higher than that of DGEBA(E51,epoxy value:0.51 mol/100g)/DDM cured at the same condition.Meanwhile,the storage modulus(300C,3327 MPa),Young's modulus(2798 MPa),and the char yield at 700 ? under N2 atmosphere(Cy700=42.3%)of the former were 70.5%,92.7%and 1.4 times higher than those of the latter,respectively.Furthermore,in contrast to the highly flammable drawback of DGEBA/DDM,the GSPZ-EP/DDM system also showed good intrinsic flame retardancy,passing the V-1 rating in UL-94 test.(2)In order to further improve the Tg and flame retardancy of the bio-based epoxy resin,an aromatic s-triazine triphenol compound(THMT)with only biomass carbon was synthesized from the common bio-based compound,vanillin,and the obtained compound can be employed to construct a bio-based trifunctional epoxy resin(THMT-EP,epoxy value:0.47 mol/100g).With 4,4'-diaminodiphenyl sulfone(DDS)as curing agent,thanks to the highly rigid aromatic s-triazine structure and polyfunctional characteristic of THMT-EP,the resultant cured THMTEP/DDS showed a record Tg of 300?,which was 120? higher than that of DGEBA(E44,epoxy value:0.44 mol/100g)/DDS.Meanwhile,the storage modulus(30?,3085 MPa),flexural modulus and strength(4137 MPa and 134.2 MPa)as well as Cy700 under N2 atmosphere(47.6%)of the former were 59.1%,53.9%,14.3%and 2.2 times higher than those of the latter,respectively.Furthermore,the cured THMT-EP/DDS showed excellent intrinsic flame retardancy,passing the highest level in UL-94 test,V-0 rating.(3)A magnolol-based bifunctional groups and tetra-functional epoxy resin(DGEM,epoxy value:0.51 mol/100g)was synthesized from a bio-based compound magnolol through a highly efficient one step process.Two epoxy groups and two allyl groups symmetrically existed in the structure of DGEM.Among them,the allyl groups can undergo addition reaction during the curing process of epoxy groups,which enhanced the cross-linked density of DGEM/DDS systems effectively and further endowed it with ultra-high Tg(279?),storage modulus(30?,3678 MPa)and flexural modulus(3455 MPa),which were 48?,47.5%and 41.3%higher than those of DGEBA(E51,epoxy value:0.51 mol/100g)/DDS,respectively.The flexible allyls in DGEM also endowed it with good processability.The viscosity of DGEM at 25? was only 0.155 Pa·s,significantly lower than that of DGEBA(8.913 Pa·s).In addition,the processing temperature window of DGEM/DDS was as high as 196?,which was suitable for application in the field of fiber reinforced composites.Furthermore,the biphenyl moiety in the structure of DGEM is beneficial for enhancing the charring ability of the resin system,thus the cured DGEM/DDS system showed ultra-high Cy700(N2)of 42.8%,which was 2.9 times higher than that of DGEBA/DDS.The ultra-high char yield of DGEM/DDS also endowed it with excellent intrinsic flame retardancy,making it pass the V-O rating in the UL-94 test and exerting the condensed phase and gas phase synergy flame retardant mechanism.(4)A magnolol-based tetra-functional epoxy resin(MTEP,epoxy value:0.95 mol/100g)was synthesized through epoxidation of the allyls in DGEM mentioned above.MTEP is liquid at room temperature,and its viscosity at 25? was significantly lower than that of tetrafunctional epoxy resin,TGDDM(JD919,epoxy value:0.90 mol/100g),which was beneficial for the processing and molding of resin complex components.Compared with TGDDM,the epoxy groups in MTEP were far apart,which was beneficial for improving their curing reactivity and making them easy to form a highly cross-linked resin system.Thus the cured MTEP/DDS showed higher comprehensive properties than those of TGDDM/DDS.The Tg,5%mass loss temperature under N2(T5%)and Cy700(N2)of the fromer were 326?,377? and 52.1%,respectively,which were 83?,47? and 1.1 times higher than those of the latter,respectively.Furthermore,the biphenyl moiety in the structure of MTEP also endowed the MTEP/DDS system with excellent intrinsic flame retardancy.It passed the V-0 rating in the UL-94 test,exerting the condensed phase flame retardant mechanism. |
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