Synthesis And Properties Of Biomass-based Benzoxazine Resins

Benzoxazine resin is a new type of thermosetting resin developed on the basis of phenolic resin.Conventional benzoxazine resins are produced from petroleum-based materials.With the depletion of global oil resources and the rising of oil prices,the energy crisis and environmental problems have become an inescapable problem.In order to minimize pollution and resource waste,the development of biomass-based benzoxazine resin has become a hot research topic in academia under the background of "carbon peak and carbon neutral" and "green and sustainable development".In this paper,three kinds of biomass-based benzoxazine monomers and oligomers were synthesized by introducing biomass raw materials of phydroxyphenylpropionic acid,cardanol,octadecylamine,and oleylamine,respectively.Benzoxazine oligomers were used as the toughening agents of epoxy resin as well as the precursor for the synthesis of biomass-based epoxy resins.The toughening effect of benzoxazine oligomers was systematically investigated.The specific work is divided into three areas as follows:1.Carboxyl-functionalized and biomass-based benzoxazine oligomer toughening agentTo overcome the problems of high brittleness and poor impact resistance of epoxy resin,we proposed a new method to toughen epoxy resin with biomass benzoxazine oligomer.Using octadecylamine and p-hydroxyphenylpropionic acid as raw materials,carboxyl-functionalized and biomass-based benzoxazine monomer(BZ1)and its oligomer(OBZ1)were synthesized.A series of EP-OBZ1 copolymers were prepared by using OBZ1 as toughening agent of epoxy resin.The effects of OBZ1 dosage on the toughness and thermal properties of EP-OBZ1 copolymers were investigated and compared with those of BZ1.The results showed that the OBZ1 toughening effect was better than that of BZ1.When the content of OBZ1 was 10%,the elongation at break of EP-OBZ1-10 copolymer was 16.6%.When the content of OBZ1 was 7.5%,the impact strength of EP-OBZ1-7.5 copolymer was 72.6 KJ/m2.After observed by scanning electron microscope(SEM),it was found that the EP-OBZ1 copolymer experienced significant plastic deformation during the impact process.The glass transition temperature,thermal stability,and plastic deformation degree of EP-OBZ1 copolymer were higher than those of EP-OBZ1 copolymer for the same contents of the added toughening agents.The biomassbased benzoxazine oligomer synthesized in this work is a new biomass-based toughening agent that can combine environmental sustainability with high toughness.2.Liquid biomass-based benzoxazine oligomer toughening agentA liquid biomass-based benzoxazine monomer(BZ2)and its oligomer(OBZ2)with a large number of flexible chain segments was synthesized from industrial grade cashew nut shell oil and oleylamine.A series of EP-OBZ2 copolymers were prepared by using OBZ2 as epoxy resin toughening agent.The effects of OBZ2 dosage on the toughness and thermal properties of EPOBZ2 copolymers were investigated and compared with the toughening effect of BZ2.The results showed that the OBZ2 toughening effect was stronger than that of BZ2.When the content of OBZ1 was 5%,the elongation at break of EP-OBZ2-5 copolymers was 14.3%and the impact strength of EP-OBZ2-5 copolymers was 55.3 KJ/m2.It was observed by SEM that the EP-OBZ2 copolymers experienced significant plastic deformation during the tensile impact process.The glass transition temperature,thermal stability,and plastic deformation degree of EP-OBZ2 copolymer were higher than those of EP-OBZ2 copolymer for the same contents of the added toughening agents.The new biomass-based toughening agent synthesized is a lowcost and easily processed liquid biomass benzoxazine oligomer(OBZ2),which can be miscible with epoxy resins without using solvents.It is easier to operate and reduces environmental pollution.It combines environmental sustainability,operability,and high toughness.3.Biomass-derived epoxy resin based on benzoxazine oligomerIn order to improve the safety of epoxy resin and expand the applicability of epoxy resins,it is urgent to prepare biomass-derived epoxy resin.From the point of molecular design,cardanol,allylamine,and paraformaldehyde were used to synthesized a cardanol-based biomass-derived benzoxazine monomer(BZ3)and its oligomer(OBZ3).A biomass-derived epoxy resin(OBZ3EP)based on benzoxazine oligomer was synthesized by epoxidation of unsaturated double bonds with OBZ3 as precursor.The epoxy value of OBZ3EP was 0.36mol/100g.The OBZ3EP/DDM thermosets were prepared using DDM as curing agent.The curing mechanism,toughening mechanism,mechanical,and thermal properties of OBZ3EP/DDM thermosets were investigated.The results showed that OBZ3EP/DDM had higher toughness,and the elongation at break of OBZ3EP/DDM thermoset was 28.2%.The OBZ3EP/DDM thermoset experienced significant plastic deformation during the tensile impact process.It can be seen that the biomass-derived epoxy resin(OBZ3EP)has excellent toughness,and the source is green and sustainable,which has great potential in the material field with high toughness requirements.