| Woody material is a kind of promising low price feedstock with renewable and carbon-neutral properties.Research of effective utilization of its different sizes has attracted much attention in the world.But its complex cell wall structure is the biggest obstacle.Ionic liquids(ILs)are molten salts with glass transition temperature or melting point below 100℃,which are suitable for dissolving cellulose,lignin and woody materials.In this project,fast-growing poplar wood flour,slices and veneers were biomass feedstocks of different sizes.They were impregnated with solvents of IL or IL/polyethylene glycol(PEG).Then hot pressing,coagulation bath and drying were combined to prepare the modified poplar.During the impregnation process,the solvent gradually diffused into the interior of raw material and made it swell.The amorphous zone was destructed,followed by the crystalline zone destructing and transforming into an amorphous zone.At that time more energy or longer time was required to unravel the segment.In order to achieve large-scale production,only mild short-time low-temperature impregnation was used.The synergistic effect of strong hydrogen bonding ability of IL and hot pressing was used to disintegrate lignin-carbohydrate complexes(LCCs)and destroy the hydrogen bond between the cellulose.Thus partial dissolution of woody raw material was achieved.The dissolved part was used as the matrix phase of the modified material,and the undissolved part was used as the reinforcing phase.The hot pressing was used to fuse the interface between the reinforcing phase and the matrix phase.The solvent was removed by the coagulation bath to regenerate and reconstitute the modified poplar which was superior over the original feedstock.The specific research conclusions are as follows:(1)Ionic liquid 1-allyl-3-methylimidazolium chloride([Amim]Cl)was used to impregnate poplar wood flour and partially dissolution was achieved accompaning by hot pressing.The dissolved fraction was fused with the undissolved part of the raw material to regenerate and reconstitute a new type of modified material.In order to improve the performance of the modified material,filter paper was introduced as cellulose source which was easily dissolved by IL.The ratio of the matrix phase and reinforcing phase could be adjusted to improve the interface bonding.The results showed that the differences in the quantitative,thickness,transparency,color and mechanical properties of each group were influenced by the solubility of raw materials.When the wood flour content was not more than 40%,raw materials were easily dissolved by IL.Crystallinity index(CrI)was decreased and the interface of wood fiber was relatively tight.The mechanical properties of Group A,which was made from pure filter paper,were the best.The interface was tightly bonded and the bonding state was the best.The tensile strength(TS)was 114 MPa.As the amount of wood flour contained in the raw material increased,the content of the reinforcing wood fiber was also obviously increased.At this time,the content of the matrix for bonding was too small,the interface bonding was poor.So the corresponding mechanical properties were not improved.Nevertheless,the TS of Group D which was prepared from the raw material containing 60%wood flour was larger than the TS of the original filter paper.This indicated that the addition of filter paper to the wood flour could greatly improve the mechanical properties of the modified material made from pure wood flour.And the mass ratio of wood flour and filter paper in the raw material directly affected the degree of dissolution,and the microstructure,physical and mechanical properties,crystallization properties,infrared absorption spectrum and thermal stability of the modified material.(2)Ionic liquid 1-butyl-3-methylimidazolium chloride[Bmim]Cl was used to immerse poplar slices at different temperatures.In-situ partial dissolution and interface fusion were obtained by hot pressing.The coagulation bath was used to withdraw the IL containing in the[Bmim]Cl/slice.Finally,a kind of new modified material with better performance than the original wood slices was regenerated and reconstituted.The properties and structures of the modified materials were tested and characterized by universal material testing machine,X-ray diffractometer and infrared spectrometer.The results showed that the impregnation temperature was an important factor affecting the physical properties of the modified slices.Their thickness and mass were lower than the original slices.However,the density did not increase linearly with the increase of the immersion temperature.This was mainly because the temperature was so high that the degradation and loss of the wood material components.The tensile properties would increase as the temperature which was within a certain range increased.However,the tensile properties were also lowered when the immersion temperature was too high.Similarly,the immersion temperature had a certain influence on the water immersion stability,microfibril angle,CrI and crystallization width of the modified slices.Thus the physical and mechanical properties of the modified slices were affected.Even though,the crystal form and composition of each group did not change,while the ratio of cellulose,hemicellulose and lignin changed.(3)Taking poplar veneer as the research object,[Bmim]Cl(Group C)was used to immerse it.Pure water(Group B)was also used to immerse the veneer,which was the contrast group.Then hot pressing,coagulation bath and drying process were used to prepare the modified veneers with better performance than the original ones.And the physical and mechanical properties and structures of the samples were tested and characterized.The results showed that the veneers of Group B and C showed good plasticity during the preparation process.Their ductilities were improved.Among them,the ductility and thickness change rate of Group C were significantly better than those of Group B.The rate of change of the width of Group C was 64%higher than that of the untreated group,and 50.4%higher than that of Group B.SEM analysis also showed that the plasticity and lateral connection of Group C were improved.The mechanical properties of Group B and C were significantly improved.And TS and elastic modulus(E0)of Group C were higher than that of Group B.The mechanical properties in longitudinal and transverse directions were also improved.Compared with the untreated group,CrI of Group B and C increased.CrI of Group C was the largest.Even though,the crystal form of each group remained unchanged,and the composition of the veneer did not change.(4)[Bmim]Cl was used to immerse poplar veneers.Three sets of preparation processes were designed to form modified materials after impregnation.The effects of preparation process on the properties of modified materials were investigated by testing and characterizing the tensile properties,X-ray diffraction and infrared spectra of each sample.The results showed that IL impregnation could make veneers swell.Hot pressing could promote partial dissolution and interface fusion,while it could also effectively reduce the thickness of the veneer and achieve densification.Compared with the untreated group,the TS of Group A,B and C were significantly increased.And the highest TS of Group C was 145.39 MPa.E0 of Group B was the largest,which was 4.88 GPa.E0 of Group C was the lowest,which was 1.12 GPa.This indicated that the molding process had a certain influence on the mechanical properties of the modified material.The fastest pyrolysis temperature of three groups increased by 31.98℃,31.43℃,and 33.39℃,respectively,which indicated that the thermal stability of the resulted modified material was improved.Even though,IL impregnation and preparation process did not cause derivatization,and the main components remained unchanged,except that the relative contents of cellulose,hemicellulose,and lignin were changed.(5)Due to the high viscosity of pure[Bmim]Cl solution,the cosolvent PEG was selected.At the same time,the dissolution and plasticizing ability of the poplar veneer by using IL and PEG were combined with hot pressing and coagulation bath to obtain a new type of modified materials.The effects of different solvent systems on the properties of modified materials were studied.The results showed that both the PEG and the IL had certain plasticity compared with Group A.Group D with IL/PEG treatment had the best ductility.Under the same process conditions,Group D of dimensional change rate of both the thickness and the width direction was about 60%.This was mainly because the percentage of the matrix phase was increased due to the synergistically dissolution of the components in the veneer by PEG and IL.Thus the interfacial bonding between the matrix phase and the reinforcing phase was also improved.In the same way,the comprehensive mechanical properties of Group D were also the best.Even though,no other derivatization reactions occurred in each group. |
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