Renewable Lignin Derivatives-based Thermosetting Resins

Nowadays,the crisis of petrochemical resources has become an important factor affecting the sustainable development.Among three basic types of materials,polymers have the greatest dependence on the petrochemical resources and thus face the biggest challenge and urgency.Heat resistant thermosetting resins are increasingly required by many cutting-edge fields including aerospace,electric,information,new energy,and so on.Besides,as they cannot be melted and dissolved again after curing,thermosetting resins exacerbate more dependence on petrochemical resources than thermoplastic ones.Therefore,it is of great importance to develop renewable heat resistant thermosetting resins.Lignin is an important aromatic compound in biomass materials.It is a renewable aromatic monomer with the most abundant feedstock(6*1014 ton),and its derxvative,vanillin,has been commercialized in a big scale.The huge amount and the rigid aromatic structure of lignin not only mitigate the impact of the petrochemical resource crisis on thermosetting resins,but also impart good thermal and mechanical properties to them.How to introduce lignin into bismaleimide resin(BMI)and epoxy resin and obtain reprocessable thermosetting epoxy resin is what this thesis focuses on.Firstly,a new kind of allyl compound ABE was designed and synthesized from biobased lignin derivative creosol.ABE not only derives from biomass but also has an easy synthesis route.Then,BMI resins(BA-n,n is the molar rario of allyl groups and imide groups)were developed based on 4,4'-bismaleimidodiphenylmethane(BDM)and ABE.The processability,thermal resistance and mechanical properties of BA-n resins were systematically researched.BA-n resins have much better properties than their petroleum-based counterparts,2,2'-diallylbisphenol A(DBA)modified BDM(BD-n)resins.Among them,BA-0.86 obtains the best integrated properties.Compared with BD-0.86,the best bismaleimide resin available,BA resins have lower viscosity in a wide temperature range.BA-0.86 not only has a 6h longer process window at 130? and 13.7? higher glass transition temperature,but also owns the highest flexural strength and modulus among all biobased allyl compound modified bismaleimide resins reported.The excellent properties of BA resins come from the unique structure of ABE and the crosslinked structure of BA resins.Secondly,a new type of biobased epoxy monomer Elg was synthesized from creosol,based on this,the cured epoxy resin Elg/MHHPA was prepared by taking MHHPA as the curing agent.The thermal,mechanical properties as well as the relationships between properties and structure are integrallty studied.Tg of Elg/MHHPA resin is 131.6?,lower than that of DGEBA/MHHPA resin(156.6?).Both toughness and rigidity of Elg/MHHPA resin are higher than those of DGEBA/MHHPA resin.Above results are derived from the molecular structure of Elg and the cross-linked structure of Elg/MHHPA resin,specifically,the rigid molecular structure of Elg endows good rigidity;while the lower crosslinking density gives it good toughness;however,the combined effects of them make Elg/MHHPA resin have a lower Tg.Thirdly,DTDA with disulfide bond was used as the curing agent to form reprocessable Elg/DTDA epoxy resin,whose dynamic mechanical properties,relaxation behavior and reprocessability are studied compared with DGEBA/DTDA resin.Elg/DTDA has higher modulus but lower Tg.This is because Elg has a rigid structure but Elg/DTDA resin has a lower crosslinking density.Elg/DTDA resin has a faster stress relaxation process,and the trend of relaxation time decreases with the increasing of temperature meets the Arrhenius equation.This is due to the lower activation energy of S-S bond exchange in Elg/DTDA resin.Under the same condition(200?,1MPa,2h),Elg/DTDA resin can be reprocessed better.The mechanical properties of Elg/DTDA resin before and after reprocess are higher than those of virgin DGEBA/DTDA resin.