Preparation And Property Manipulation Of Transparent Wood-based Composites

Wood is a renewable,recyclable and natural degradable material.However,the disadvantages including opaque,poor water resistance and poor mechanical properties restrict the use of wood.In order to make full use of abundant timber resources and explore new methods of high value-added utilization of wood cellulose resources,this study attempts to prepare transparent and water resistant wood-based composites which have good mechanical properties.The main research includes the preparation and optical properties manipulation of transparent wood-resin composites,the extraction of hydrophobic cellulose nanofibers,the preparation and mechanical properties manipulation of cellulose nanofibers-resin composites,the preparation and photoelectric properties manipulation of cellulose-silver nanowire composites.The main results are listed as follows:(1)According to the refraction principle of light,the transparent wood-resin composites with visible light transmittance of 86%was obtained by infiltrating the delignified wood template by a transparent resin with high refractive index of wood cellulose.The transparent wood-resin composites can be used to fabriacte daylighting windows because of its excellent mechanical properties(tensile strength is 70 MPa,bending strength is 120 MPa,and Young's modulus is 3 GPa).Furthermore,the CsxWO nanoparticles were selected as the infrared barrier functional units and the transparent wood-resin-CsxWO composites were prepared.The transparent wood-resin-CsxWO3 composites showed excellent near-infrared(NIR,ranging from 780 to 2500 nm)shielding ability and low thermal conductivity(1/5 of the thermal conductivity of glass).As a building daylighting window,it can effectively isolate heat transfer from inside and outside the house,and also can shield the near infrared light in the sunlight,thereby reducing the energy consumption of air conditioning.(2)The hydrophobic cellulose nanofibers were obtained through surface esterification modification of wood cellulose fibers.Furthermore,the cellulose nanopaper and cellulose-polymethyl methacrylate(PMMA)composites were obtained from the hydrophobic cellulose nanofibers.In particular,the cellulose-PMMA composites were prepared by infiltrating the the cellulose nanopaper template by PMMA,which showed high strength(the tensile strength up to 120 MPa)and high visible light transparency(92%at a wavelength of 550 nm).(3)In view of the wood cellulose fibers containing a large number of hydroxyl groups and easy to form hydrogen bonds,the silver nanowires were selected as the conductive functional units and the cellulose-silver nanowire composites were obtained.On the one hand,transparent conductive nanopaper was made by vacuum filtration of silver nanowires and hydrophobicity cellulose mixed dispersion,which showed high conductivity(20 ?./sq),high visible light transparency(87.3%at a wavelength of 550 nm)and foldability.On the other hand,cellulose-dopamine-silver nanowires composite was made by dip-coating.The cellulose-dopamine-silver nanowires composite not only highly reflects middle-to-far infrared radiation from the human body(the average reflectance is up to 86%,approximately 66 times higher than normal cloth),but it also allows Joule heating with a quick thermal response(1 min,from 22 ? to 40 ?).Additionally,the cellulose-dopamine-silver nanowires composite was durable and washable,making it suitable for a personal thermal management cloth.