| In order to realize the high-value utilization of lignin and explore a new idea of synthesizing epoxy resin modified by lignin,this paper took lignosulfonate(LS)extracted from pulp and paper industry as raw material and modified it by carboxylation,and successfully prepared the well-homogeneity lignin-modified epoxy resin composite system.The chemical structure,curing reaction kinetics,thermal stability,mechanical properties,morphology and shape memory properties of were studied in depth and systematically.The main results are as follows:(1)Under the synergistic dissolution of ethylene glycol(EG),LS was successfully dispersed evenly into the epoxy resin matrix.Through the esterification reaction of hydroxyl groups in LS and EG with anhydride,the rigid LS and flexible EG chains were incorporated into the crosslinking network structure of epoxy resin,the structure and final properties of cured samples were effectively adjusted by changing the proportion of LS and EG components.The curing reaction and kinetics of lignin modified epoxy resin system were systematically analyzed,and the optimal curing process was determined as 120℃/5h+170℃/1h.(2)After the LS-EG modified epoxy resin system was cured via optimal curing process curing reaction,thermal stability,mechanical properties system,the cross section morphology and shape memory performance of cured samples were systematically studied by thermogravimetric analyzer,universal mechanical testing machine,pendulum impact tester,scanning electron microscope and U shape memory test respectively.The results show that when LS and EG were introduced into epoxy resin,the initial decomposition temperature and the carbon residue increased,the thermal weight loss decreased,it indicates that the thermal stability of epoxy resin cured by adding LS and EG is enhanced.Compared with pure epoxy resin,the bending strength,modulus,tensile strength and impact strength of epoxy resin(epoxy/LS0.5-EG0.5)increased by 23.1%,37.5%,18% and 15.1% respectively.In addition,LS and EG modified epoxy resin systems show excellent shape memory performance and mechanical stability.(3)Carboxylated LS(CLS)was obtained by carboxylate modification on LS.CLS modified epoxy resin was successfully prepared by uniformly distributing CLS into the epoxy resin matrix composed of bisphenol A diglycidyl ether(DGEBA)and polyethylene glycol diglycidyl ether(PEGDGE)with water as solvent.The effect of CLS content on curing kinetics,mechanical properties,morphology and shape memory properties of epoxy resin were systematically studied.The results show that the mechanical properties of CLS/epoxy composites are significantly improved by the introduction of CLS.Especially when CLS was 5phr(CLS5/epoxy),the tensile strength,modulus,elongation at break and toughness increased by 23.8%,18.2%,217% and 113%,respectively.SEM results show that when CLS content was low(1 phr),the morphology was homogeneous and no phase separation was observed.However,with the increase of CLS content,obvious phase separation structure appeared,an island structure of CLS particles dispersed in the epoxy resin was formed.CLS dispersived phase,as a physical crosslinking point in epoxy resin matrix,can inhibit the generation of cracks in stressed samples and change the direction of crack propagation,so the larger and stronger toughness was obtained for epoxy resin.At the same time,the introducted CLS rigid chain blocks the movement of epoxy resin chain segment,thus improving its mechanical stability,which slows down the shape memory recovery rate of epoxy resin network to a certain extent.Appropriate CLS can strengthen and toughen epoxy resin simultaneously,which is mainly attributed to the introduction of rigid lignin structure and the formation of phase separation structure in epoxy resin matrix. |
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