Design And Construction Of Wood-based Multi-functional Membrane

In recent years,there has been a growing interest in replacing petroleum-based polymers with renewable biomass to produce advanced functional materials.This research has become a hot topic in academia and industry due to its great significance in realizing the two-carbon strategy.However,the cumbersome process of component separation and purification has made biomass utilization challenging.To overcome this difficulty,researchers have turned their attention to the "top-down" strategy,such as using natural wood as a base to directly construct various optical and energy storage materials.Wood is abundant in nature,lightweight,and has excellent mechanical properties,making it an ideal structural material widely used in construction and other fields.Recent advancements in nanotechnology have made it possible to modify and functionalize wood structures at the nano and molecular levels,resulting in high-value wood-based hydrogels,aerogels,and membranes,among other functional materials.Wood-based membrane materials,in particular,exhibit good flexibility,low thermal conductivity,and ease of modulation,making them ideal for use in flexible electronic devices,intelligent sensing,and optical shielding.However,incorporating inorganic/organic functional fillers into wood membrane networks to build composite membranes with strong interface affinity and evenly dispersed fillers remains a significant challenge.To address this challenge,this paper selects natural wood(balsa wood)as the raw material and uses the "top-down" strategy to prepare a series of wood-based composite membranes,leveraging the structure and microstructure of wood.The paper focuses on three main areas of work: 1)Regulation of the hydrogen bond network of wood membranes and the filling process of inorganic particles: By optimizing the densification process of wood membranes,the paper discusses the aggregation structure and composition change process,leading to the production of transparent and high-strength wood membranes.The paper also introduces commercial titanium oxide(P25)as the filler,resulting in a composite membrane with better optical properties after densification.2)Construction of composite wood membranes with interface strengthening and the introduction process of organic fillers: The paper pre-disperses the packing(chitosan)into polyvinyl alcohol(PVA)solution,and utilizes the hydrogen bonding between PVA and wood cellulose to achieve tight binding and good dispersion of the packing,leading to the production of composite membranes with excellent mechanical properties and UV shielding properties.3)Preparation of wood membranes and filler introduction process of 3D network limited domain: The paper introduces the filler(inorganic MXene)into the delignification wood with a loose pore structure using the drop casting method.After densification,the filler is uniformly confined in the membrane network,resulting in a composite membrane with high filler load and good electromagnetic shielding performance.The membrane is then applied to the intelligent sensing process.The specific work carried out in this paper can be summarized as follows:1)The wood membrane with good light transmittivity and mechanical properties was obtained by delignification and densification of wood with a "top-down" strategy.The total light transmittivity in the visible region was 88.1% and the longitudinal tensile strength was 182.6 MPa.P25/wood composite membrane was prepared by vacuum impregnation and densification.By means of infrared and other means,the changes of cellulose aggregation structure in wood structure during loading of pure wood membrane and P25 were investigated.After optimizing the loading load,it was found that the composite membrane filled with P25 solution with concentration of 100 ppm had good mechanical properties,light transmission,and excellent UV shielding effect.The longitudinal tensile strength of film was 156.1 MPa,the total transmittance of visible light region was 81.5%,the shielding rate of UVA region was 63.48%,and the shielding rate of UVB region was 90.02%.2)In order to enhance the dispersion and binding of functional fillers,PVA,which is rich in surface active hydroxyl groups,was selected as the dispersion medium and cross-linking medium to prepare the composite films.It was found that the mechanical and optical properties of the wood composite membrane could be effectively improved by introducing PVA polymer.When the mass fraction of PVA solution was 5 wt%,the total transmittance of the composite membrane in the visible region was 92.0%,the haze was 59.6%,and the longitudinal tensile strength was 281.3 MPa.Fillers were then dispersed into the PVA solution to prepare chitosan-PVA/wood membrane.After load optimization,the CTS-5 wt%PVA/wood membrane had a visible light transmittance of 79.0%,a haze of 29.6%,a UVA band shielding rate of 62.72%,a UVB band shielding rate of 96.41%,and a longitudinal tensile strength of 228.3 MPa.The graphene and chitosan wood composite membranes exhibited excellent mechanical properties and UV shielding properties.3)The MXene/wood membranes were prepared to expand the application range of wood membranes,which can be used in electromagnetic shielding and physiological motion sensing.MXene was introduced into delignification wood with a loose pore structure by drop casting method.After densification,a conductive flexible wood membrane with high mechanical properties and excellent electromagnetic shielding and sensing properties was obtained.MXenes were encapsulated in a wood substrate and tightly attached to cellulose chains by hydrogen bonding.The maximum loading capacity of MXene was 32.5 wt%,the tensile strength of the MXene/wood membrane was 260.7 MPa,the electromagnetic interference shielding efficiency was 55.5 d B(Xband,8.2-12.4 GHz),and the specific shielding efficiency was 2673.4 d B cm2 g-1.In addition,the superior electrical conductivity and flexibility make the composite membrane have the characteristics of pressure/strain sensing,which has a high sensitivity to the monitoring of human physiological motion,and has a good application prospect in the detection of human motion.Overall,the studies in this paper demonstrate that the mechanical properties and functional properties of wood composite membranes prepared by "top-down" strategies,regulating wood structure,and changing composite strategies,have been significantly improved.These materials have broad application prospects in the fields of optical shielding,flexible electronic equipment,and intelligent sensing,further realizing the high-value utilization of wood.