| The transformation of wood modification object from ‘dead’ wood to ‘living’ standing wood is the key to the breakthrough of wood modification research at present.Biomimetic mineralization is a very important modification method in the process of changing from traditional ‘post-treatment’ modification to ‘pre-treatment’ modification.Exploring the modification of standing wood has important reference and guiding significance for the improvement of wood from the source and the preparation of new composites.Taking the10-year-old poplar as the object,the formation process of biomineralized wood was studied systematically through the screening of biomimetic mineralization solution system,the test of poplar wood impregnation mineralization system and the bionic mineralization test in poplar standing wood.And the microstructure of biomineralized wood was observed by anatomical means combined with optical microscope and scanning electron microscope.The chemical composition of biomineralized wood was analyzed comprehensively by means of Fourier transform infrared spectroscopy,X-ray diffractometer and X-ray photoelectron spectroscopy.The thermal stability of biomineralized wood was analyzed by thermogravimetry and differential scanning calorimetry,and the mechanical properties of biomineralized wood were analyzed by micro-tensile test.The detailed conclusions are as follows:(1)Screening of biomimetic mineralization solution system: silica,titanium dioxide and calcium oxalate were successfully prepared at room temperature and pressure.Under the microscope,the silica prepared in low concentration solution system(1 mmol/L)is amorphous and agglomerated,while the silica prepared in high concentration solution system(100 mmol/L)is 25～30 nm particles.In low concentration solution system(1 mmol/L),the prepared titanium dioxide is spherical and linked to each other.With the increase of solution concentration,the connection becomes denser,and the particle size is 20～40 nm.In the preparation system of calcium oxalate,when the concentration of the solution is low(1 mmol/L),the product is mainly tetragonal calcium oxalate monohydrate with a particle size of 250～280 nm,and when the concentration is high,the product is hexagonal calcium oxalate dihydrate with a particle size of 85～175nm.According to the comprehensive analysis,the best solvent system was selected:the ethyl orthosilicate hydrolysis system of 100 mmol/L was selected to prepare silicon dioxide;the tetrabutyl titanate hydrolysis system of 1 mmol/L was selected to prepare titanium dioxide;the synthesis system of 1mmol/L dihydrate oxalic acid and 1mmol/L anhydrous calcium chloride was selected to prepare calcium oxalate.(2)Study on poplar wood impregnation and mineralization system: after poplar strips were impregnated with the optimized mineralization solvent system in chapter 2,silica / poplar composites,titanium dioxide / poplar composites and calcium oxalate / poplar composites were prepared respectively.Microscopically,the basic structure of the wood in silica / poplar composite wood remained unchanged,and granular sediments were attached to the fiber cell wall,which was determined by XRD to be amorphous silica.In titanium dioxide / poplar composite,the deposit is filled in the cell cavity or attached to the cell wall,which is anatase titanium dioxide determined by XRD.In calcium oxalate / poplar composites,flake deposits attached to the cell wall were identified as calcium oxalate monohydrate by XRD.Most minerals exist in composite materials in the form of hydrogen bonding or physical accumulation.The analysis of TG and DSC showed that the thermal stability of the three inorganic composites was higher than that of the materials,and the glass transition temperature decreased.(3)Biomimetic mineralization in poplar standing trees: in this study,by using sol-gel method,different kinds of biomimetic mineralization solvent systems were transported to xylem by drop slow-release technology in the peak growth period of poplar,and the biomineralized wood was obtained.Macroscopically,the color of poplar disc heartwood after biomimetic mineralization is yellowish brown to dark brown,which is irregular relative to the normal growing poplar disc.Microscopically,there was no deposit in the normal growing poplar cell cavity;in the silica biomimetic mineralized wood,the wood fiber cell cavity was filled with sediment,which was determined by XRD to be amorphous silica;in the titanium dioxide biomimetic mineralized wood,there were spherical deposits in the lumen of ducts and wood fibers,which were determined by XRD to be anatase titanium dioxide.In the biomimetic mineralized wood of calcium oxalate,there are massive deposits in the fiber lumen,which are identified as calcium oxalate monohydrate crystals by XRD.The comprehensive analysis of FTIR and XPS showed that the inorganic matter in the three kinds of biomineralized wood formed a chemical connection with the wood.The results of micro-tensile test showed that the elastic modulus of three kinds of biomineralized wood slices decreased and the tensile strength increased compared with the control group.The results of TG and DSC comprehensive analysis showed that the pyrolysis temperature,thermogravimetric residual weight and glass transition temperature of three kinds of biomineralized wood were higher than those of normal poplar,and the thermal stability of three kinds of biomineralized wood was higher than that of normal poplar.(4)Biomineralized wood with good thermal stability was successfully prepared by biomimetic mineralization on poplar standing wood,which provided a new idea for the modification of standing wood and the preparation of wood-inorganic composites under normal temperature and pressure. |
PDF Full Text Request