Study On The Modification Of Poplar Cell Wall And Its Mechanism By Hydrophilic Monomer

China has abundant plantation resources,and making full use of abundant plantation wood resources can effectively alleviate the contradiction between wood supply and demand in China.However,plantation wood generally has defects such as low density,soft material,low strength,and easy deformation,which limited its scope of application.Hydrophilic chemical small-molecular-weight polar monomers can easily penetrated into the cell wall,and can achieved chemical modification based on the wood cell wall,thereby improving wood performance under relatively low Weight Percent Gain.This study was aimed at planting poplar wood,using water-soluble monomers as the main modifier,to develop three kinds of polyhydroxyl hydrophilic modification systems with good compatibility with wood,using one-step vacuum pressure impregnation and curing treated wood,studied the properties and modification mechanism of wood before and after modification,and got the following main conclusions:(1)Hydroxyethyl methacrylate(HEMA)and N-isopropylacrylamide(NIPAM)two kinds of water-soluble small molecular weight propylene-based monomer composite impregnated in plantation poplar,the results showed that within a certain weight concentration range(10%～40%),can improved the dimensional stability and mechanical properties of wood:ASE of modified wood reached 67.6%,MOR increased by 8.1%,MOE increased by 9.4%,and compressive strength along grains increased by 23.2%;the modification research on the influence of process conditions on the properties of modified materials showed that the more suitable process conditions was HEMA/NIPAM=6:1(wt/wt),modifier concentration of 40%(wt%),and initiation temperature of 60°C;NIPAM participation in copolymerization can effectively reduced the loss rate of modified materials;research on the water resistance of polymers showed that the addition of NIPAM can effectively reduced the water absorption rate of polymers;scanning electron microscope observation showed that the modifier penetrated into the cell wall and filled the cell wall,the thickness of the cell wall increased;the mercury intrusion test and the nitrogen adsorption test showed that the modifier penetrated into the cell wall micropores with a pore size ranging from 2nm to 225.1nm;the results of the graft polymerization mechanism of monomer with wood showed that monomers can be grafted and polymerized with wood,cellulose and lignin respectively;the results of NMR analysis showed that the monomers could be grafted at the C1 hydroxyl group of the cellulose model compound D-cellobiose and the phenolic hydroxyl group of the lignin model compound2,6-dimethoxyphenol.(2)In this study,HEMA as the main monomer and added acrylorganosilaneγ-methacryloxypropyltrimethoxysilane(KH570)to modified wood,the results showed that within a certain weight concentration range(10%～30%),the dimensional stability and mechanical properties of modified materials are improved:ASE of modified materials reached69.1%,MOR increased by 10.7%,MOE increased by 16.3%,and compressive strength along grains increased by 22.5%;the research on the influence of the properties of modified materials showed that the more suitable process conditions was HEMA/KH570=3:1(wt/wt),the modifier concentration was 30%(wt%),and the initiation temperature was 75°C.In this condition,the loss rate of the modified material was 5.3%,indicated that the addition of KH570 can effectively reduced the loss rate of the modified material;research on the water resistance of the polymer showed that the addition of KH570 can effectively reduced the water absorption rate of the polymer;scanning electron microscope observation showed that the modifier penetrated into the cell wall and filled the cell wall gaps,the thickness of the cell wall increased;mercury intrusion test and nitrogen adsorption method test showed that the modifier penetrates into the micropores in the cell wall with a pore size ranging from 11.1nm to286.6nm;Raman spectroscopy and imaging analysis showed that the modifier penetrated into the cell wall and in-situ polymerization to form polymer.(3)Compound modified wood with methylhexahydrophthalic anhydride(MHHPA)and isophorone diamine(IPDA)composite curing agent and water-soluble epoxy monomer1,4-butanediol glycidyl ether(BDE).The results showed that at a modifier concentration of 40%(wt%)and a modifier ratio of MHHPA/IPDA/BDE=1:1.5:2(wt/wt/wt),the mechanical properties and dimensional stability of the wood can be significantly improved:the ASE of the modified wood reached 48.3%,the MOR increased by 28.8%,the MOE increased by 12.8%,and the compressive strength along the grain increased by 21.8%;the mercury intrusion test and the nitrogen adsorption test showed that the micropores of the wood due to the effect of the alkaline modification system became larger,the cumulative pore specific surface area of the modified wood reached 17.6m~2/g,which is beneficial to the penetration of the modifier into the micropores of the wood cell wall;according to the preliminary study of the mechanism,the epoxy system was combined with the wood through the anhydride.(4)In conclusion,the formation of a polyhydroxy modification system by hydrophilic small molecular weight monomers,the enhanced modification of wood cell walls can be achieved.Under relatively low Weight Percent Gain,the HEMA/NIPAM modification system and HEMA/KH570 modification that has a significant effect on improving the dimensional stability of poplar.The MHHPA/IPDA/BDE system has a significant effect on improving the mechanical properties of poplar.