Study On Preparation And Microcosmic Mechanism Of Transparent Wood

Lightweight,strong and low-cost transparent wood have great potentials in transparent buildings,solar cell windows,optoelectronic device,energy-saving application,home materials,etc,has attracted extensive attention.Transparent wood can be produced through impregnating polymer into the chemically modified wood template.During the preparation of transparent wood,the interfacial separation gap occurs between the wood cell wall and the impregnated resin will cause light scattering and so that affects the performance of the transparent wood.In addition,lignin is the main absorbing component and the light absorption can be drastically reduced by chemical bleaching of the wood.But the delignification process was time-consuming and the severity of such processes weakens the mechanical properties of the wood template due to excessive lignin removal.Therefore,during the preparation of transparent wood,the changes of wood cell wall structure and chemical composition have great influences on the properties of transparent wood.It is necessary to study systematically from the microscopic level,but there is still a knowledge gap on this aspect.Transparent wood materials were prepared from wood subjected to coupling agent modification or chemical bleaching treatment prior to its polymer impregnation.This paper focuses on the microscopic mechanism of transparent wood preparation.And the properties of transparent wood were characterized by uv spectrophotometer,electromechanical universal testing machine,optical contact angle tester,color difference meter,thermal analyzer,fourier transform infrared spectroscopy spectrometer,scanning electron microscope and nanoindentation instrument.The effects of coupling agent modification or degrees of chemical bleaching treatment together with polymer impregnation on the properties of transparent wood were investigated.At the same time,the relationship between the mechanism of components and microstructure changes of transparent wood and the properties of prepared transparent wood was expounded,so as to optimize the properties of transparent wood for the further development of its application field.The main results are as follows:?1?The impacts of coupling agent modification on transparent wood were studied.Experimental results showed the obtained transparent wood had the best optical performances and tensile strength when the mass fraction of coupling agent was 5%.And the maximum optical transmittance was 16.8%at 800 nm and maximum tensile strength up to 181.1 MPa.The contact angle test showed that the hydrophobicity of the wood surface was improved by the coupling agent KH570.FTIR and SEM measurements indicated that coupling agent KH570 reacted with wood template and PMMA.The wood bonded closely with PMMA after coupling agent modification,and the interfacial compatibility was better than that without coupling agent modification.?2?The impacts of H₂O₂ treatment on transparent wood were studied.Experimental results showed decreases in cellulose,hemicellulose,and lignin content with increasing bleaching time.And the lightness of transparent wood increased with delignification,while the redness and yellowness decreased.The transparent wood exhibited a maximum optical transmittance of 44%at 800 nm when the bleaching time was 150 min and also possessed enhanced visual optical haze at different levels of H₂O₂ bleaching.The transparent wood displayed a maximum tensile strength up to 165.1 MPa when the bleaching time was 90 min.The results of thermal performances showed that the thermal stability of the obtained transparent wood samples was slightly higher than pure PMMA polymer in the range of about 300-500?.And the thermal stability of the obtained transparent wood samples was better than untreated natural wood in the range of about 250-400?.FTIR and SEM measurements indicated that the wood structure was still well preserved even after H₂O₂ bleaching treatment.Meanwhile,experimental results also indicated that the MMA solution was successfully impregnated into the wood templates.The nanoindentation test results showed that the elastic modulus?E_r?and hardness?H?of the transparent wood samples were lowered along with the increasement of delignification.The elastic modulus?E_r?and hardness?H?of the transparent wood samples were lowered along with the increasement of H₂O₂bleaching treatment time.?3?The impacts of chlorite treatment on transparent wood were studied.Experimental results indicated that the lightness of transparent wood increased with delignification,while the redness and yellowness decreased.The transparent wood exhibited a maximum optical transmittance of 61%at 800 nm when the chlorite bleaching time was 150 min and also possessed enhanced visual optical haze at different levels of delignification.In addition,transparent wood displayed a maximum tensile strength up to 171.4 MPa?60 min chlorite bleaching time?.The results of thermal performances showed that the thermal stability of the obtained transparent wood samples was slightly higher than pure PMMA polymer in the range of about 300-500?.And the thermal stability of the obtained transparent wood samples was better than untreated natural wood in the range of about 250-350?.FTIR and SEM measurements indicated that the wood structure was still well preserved even after lignin was removed.Meanwhile,experimental results also indicated that the MMA solution was successfully impregnated into the wood templates.In addition,nanoindentation test results showed that the elastic modulus?E_r?and hardness?H?of the transparent wood samples were lowered along with the increasement of delignification.In summary,transparent wood materials could be prepared from wood subjected to coupling agent modification or chemical bleaching treatment prior to its polymer impregnation.And the properties of the prepared transparent wood were improved to some extent compared with the natural wood.