| Forests perform a vital role in carbon neutral action and wood is an eco-friendly natural material that is renewable,degradable and capable of sequestering carbon.In recent years,the shift in the function of forest resources from wood utilization to ecological conservation has inhibited wood supply and people have turned their attention to fast-growing forests.Fastgrowing forests exhibit inherent properties such as fluffy material,low strength and the tendency to decay and burn.Thus,it is of great concern to investigate high-value and efficient wood utilization techniques to promote a low-carbon revolution in wood and to ensure ecological security.This dissertation takes fast-growing poplar and balsa wood as raw materials,makes full exploitation of the natural structure and properties of wood,and carries out macroscopic to microscopic multi-scale composite functionalization of improved wood by means of hot-press densification,surface coating and vacuum impregnation,and characterizes its structure and properties by means of optical detection techniques and instruments.The main experimental elements of this paper are as follows:The fluffy and unique structure of fast-growing poplar wood is taken into account in the preparation of densified,high-performance wood materials.The mechanical and physicchemical properties of the wood are modified to a certain extent by removing lignin and hemicellulose from the wood cell walls and by combining the softened wood fibers with a hotpress densification process to compress and reorganize them.Based on the mechanical properties tests it can be confirmed that the ultrasound group outperformed the other methods in terms of mechanical properties,achieving a compression ratio of 68%,a reduction in compression recovery to 3% and an increase in modulus of elasticity of 77.2% compared to natural wood.Following the hot-pressing process,wood polymers are removed from the cell walls and the wood fibers are rearranged.A stable and self-cleaning superhydrophobic coating for wood protection was prepared by drop coating polyvinyl alcohol cross-linked hollow silica nanoparticles onto the wood surface and modified with polydimethylsiloxane modifications.The coating was stacked on the wood surface and cured rapidly with the assistance of UV light.The coating obtained by adding 0.5wt% nanoparticles have excellent superhydrophilicity and an optimum water contact angle of160.4 ± 0.2°.The water contact angle remains at 151.5±0.7° even in wear tests at a distance of300 cm.Meanwhile,the resulting coating exhibits not only mechanical durability and chemical stability,but also good self-cleaning properties,thus effectively resisting surface contamination.A wood composite with excellent mechanical and thermal stability was prepared by impregnating the cell cavities of wood with a polyvinyl alcohol aqueous(PVA)-silica nano-sol dispersion system.The dispersion system has no significant negative impact on the impregnated modified poplar wood,and the PVA and nano-silica sol can form a cross-linked system that can effectively enter the wood and react with the cell walls,thereby improving its mechanical strength.At the same time,the two react in situ or by self-condensation within the wood to form chemical bonds such as Si-O-C and Si-O-Si,increasing the compressive strength of modified poplar by 72.29% compared to natural poplar.In addition,although the thermal decomposition temperature of the modified poplar wood was advanced by 40°C,the residual mass fraction of the pure nano-silica sol modified group and the PVA-nano-silica sol modified group were 42.87% and 21.08% respectively,much higher than the 9.65% of the natural wood group and the 11.33% of the pure PVA modified group,and the thermal stability was improved. |
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