Study On In-situ Enhancement Of Plantation Poplar Wood With Water Soluble Monomers

As one of the most abundant biomaterials in China,plantation wood is not used extensively due to its loose material,low density and strength,poor decay resistance and dimensional stability.The chemical modification can improve the physical and mechanical performance of wood,leading to the application fields of plantation wood more widely.However,some volatile and toxic modifiers must be used in this modification method that potentially may harm the environment and people’s health.A major challenge in this area is to improve the performance of the wood through an environmentally friendly method.Besides,the mechanism of reaction between modifiers and wood needs to be further studiedIn this paper,the basic characteristics of the poplar were studied.Three methods of modification（modification with maleic anhydride and glycerol,water soluble vinyl monomers and organic-inorganic hybrid,respectively）were used to modify wood.The dimensional stability,water absorption,leachability,mechanical properties and thermal stability of treated wood were determined.The distribution of modifiers in the cell wall of the wood and the reaction mechanism with the cell wall components were analyzed.The enhancement mechanism of poplar wood with water soluble monomers was clarified.The main research results were summarized as below:（1）The dimensional stability（ASE）of maleic anhydride（MA）and glycerol modified wood was evidently improved,but the modulus of rupture（MOR）and modulus of elasticity（MOE）of the treated wood were declined.The results showed that the dimensional stability sequence is as follows:esterification temperature>esterification time>pretreatment temperature>pretreatment time>MA concentration.The 91.05%ASE was achieved after the maleic anhydride and glycerol treatment under the optimized condition.The MOR and MOE were 62.53%and 22.56%lower than that of untreated one,respectively.The FT-IR and SEM analyses indicated that the modifiers were permeated and fixed into the wood.（2）In this study,the HEMA and NMA were used as modifiers,which could improve the dimensional stability and mechanical properties of the treated wood.The results indicated that the HEMA/NMA mass ratio,the modifier concentration and the initiator showed effects on the physical and mechanical properties of treated wood.The optimal reaction conditions were proposed.When the HEMA/NMA ratio was 80:20,the concentration of modifier was 40%and the calcium chloride/hydrogen peroxide as initiator,the ASE,MOR and MOE increased by60.77%,20.19%and 38%,respectively.SEM-EDS revealed that the thickness of the treated wood cell walls increased by 40.73%;the microcracks between the treated wood cell walls were filled with modifiers.CLSM revealed that the modifiers have been distributed in the whole cell walls;the concentrations of the modifiers in inner-surface of the cell wall and compound middle lamella were relatively high compared with that in wood cell walls.（3）In this study,the feasibility of improving the performance（physical and mechanical properties,thermal stability）of wood by SiO₂ was explored.The results showed that with the increase of SiO₂ sol content,the water absorption of the treated wood decreased.The water absorption of the treated wood without SiO2 sol was 79.25%.When 5 wt%of SiO2 sol was added,the water absorption of the treated wood was 61.84%.After adding 5 wt%of SiO₂,the MOE and MOR of the treated wood increased by 6.27%and 10.5%,respectively.TG analysis indicated that the thermal stability of treated wood without Si O₂ sol was obviously lower than the untreated one.With the increase of SiO₂ sol content,the mass lose rate was decrease and thermal stability of treated wood had improved.When 5 wt%of SiO2 sol was added,SEM-EDS revealed that the thickness of the treated wood cell walls increased by 46.77%;there were Si elements in the cell walls,which indicated that the modifiers were permeated and fixed into the wood cell walls.When 7 wt%of SiO₂ sol was added,the modifiers were precipitated and solidified in the lumen.（4）The model compounds were used to explain the mechanism of the graft reaction between water soluble vinyl monomers and wood cell wall components.The FT-IR and NMR confirmed that graft copolymer was successfully prepared.The hydrogen of OH(C_2’)in D-cellobiose could be captured by the chlorine atom provided by initiator system and a D-cellobiose free radical will be generated.The water soluble vinyl monomers was assaulted by the D-cellobiose free radical to initiate a graft copolymerization between them.In addition,the signals of water soluble vinyl monomers could also be observed in treated D-cellobiose.This result indicated that water soluble vinyl monomers has been grafted to EHL through the dehiscence of double bonds.The NMR analyses of EHL model compounds showed that the reaction sites were mainly at the position of phenol hydroxyl groups in EHL.