| As a typical thermosetting resin,epoxy resin(EP)has many advantages,such as excellent mechanical properties,electrical insulation properties,chemical corrosion resistance and bonding properties.It is widely used in electronic and electrical materials,coatings,adhesives,engineering plastics and composite materials.However,the poor brittleness and aging resistance of epoxy resin seriously limit its wider application.Therefore,in order to broaden the application field of epoxy resin,it must be modified to improve its toughness and aging resistance.At present,the toughening methods of epoxy resins often sacrifice the strength of materials while toughening epoxy resins,and the modifiers used are often synthesized by chemical synthesis,which will seriously pollute the environment while accelerating the energy crisis.Natural macromolecule were favored due to their wide range of sources and green production process.The research of epoxy resin modified by natural rubber(NR)and lignin(L)has a long history.However,natural rubber and lignin were difficult to disperse in epoxy resin matrix because of their high molecular weight and less active groups,so the effect of modifying epoxy resin with natural rubber and lignin was not obvious.In this paper,natural rubber and lignin were degraded and liquefied into liquid products with active groups by degradation method.These liquid products with active groups were introduced into epoxy resin curing system to obtain modified epoxy resin with good toughness and aging properties.The modification mechanism of these liquid products with active groups on epoxy resin was also studied.The main research results are as follows:(1)Firstly,natural rubber was degraded and liquefied into liquefied natural rubber(LNR)with carboxyl group by degradation method.The viscous average molecular weight of liquefied natural rubber decreased gradually with the prolongation of degradation time.At the same time,liquefied natural rubber was introduced into the curing system of epoxy resin.The mechanical properties test showed that the impact and three-point bending properties of liquefied natural rubber modified epoxy resin(LNR/EP)were improved comprehensively,which indicated that liquefied natural rubber modified epoxy resin had good toughness.The aging property test shows that the liquefied natural rubber modified epoxy resin has excellent salt spray aging property,while its ultraviolet aging property was relatively poor,but it still has obvious improvement compared with the unmodified epoxy resin.The test of stone cultural relics restoration showed that liquefied natural rubber modified epoxy resin could meet the requirements of stone cultural relics restoration,and could greatly improve the efficiency of restoration,which was helpful to expand its application in the field of stone cultural relics restoration.(2)Lignin was degraded and liquefied in hot-pressed ethanol/water system.Adding ammonia additives to lignin could effectively promote lignin degradation and liquefaction.FTIR,GC-MS and GPC characterization analysis show that the main degradation product of lignin in hot-pressed ethanol/water system was lignin fragment structure.The mechanical properties test showed that the tensile,impact and three-point bending properties of liquefied lignin modified epoxy resin(LL/EP)were significantly improved co mpared with those of unmodified epoxy resin,indicating that the addition of liquefied lignin could improve the toughness and strength of epoxy resin.The thermal performance test showed that liquefied lignin modified epoxy resin has excellent thermal stability.Ultraviolet aging tests showed that the ultraviolet aging properties of liquefied lignin modified epoxy resin were significantly improved coMPared with those of unmodified epoxy resin. |
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