| Ultra-low density wood fiber composite (ULD_WFC) is a kind of environmentally friendly materials with biodegradablity and reusablity. It can serve in some applications like building insulation material and packaging buffer material. There are many advantages, such as low thermal conductivity and high coefficient of sound absorption, but the low mechanical properties which limit their applications. So, to improve the mechanical properties of ULD_WFC, the inorganic fillers of aluminum sulfate and sodium silicate were used to prepare Si-Al/ultra-low density wood fiber composite which prepared by sol-gel. Comprehensive research was performed on the principle of technology to preparation, distribution and interface of Si-Al inorganic fillers in ULD_WFC, the performance of composites and the composite mechanism of wood fibers and Si-Al inorganic fillers.The contrastive analysis revealed that a combined sol-gel method was judged to be better for enhancement the mechanical properties of ULD_WFC than a separate deposition method. The optimal conditions of PASS for ULD_WFCs were Si/Al molar ratio of 2:1, pH value of 8, and temperature of 50℃. Under these conditions, the average particle size of PASS (7.52 μm) and internal bond strength of ULD_WFCs (10.23 kPa) were obtained.To improve the brittleness of Si-Al compounds, PVA as an organic filler was used in this study. Results showed that there were two bondings of chemical bonds and cross linking together between PVA and Si-Al compounds. The mechanical properties of ULD_WFCs were improved by PVA which has good properties of film-formation and cohesiveness; and it could result in much homogeneous distributions of inorganic fillers on the surface of the fibers.The optimization experiment of the preparation conditions for Si-Al/wood fibers composites revealed that Si sol played an important role in the mechanical properties and thermostability of ULD_WFCs. The optimal conditions for preparing ULD_WFCs were 30%PVA content, 4% Si sol, and 500mL Si-Al compounds. Under these conditions, the average IB of ULD_WFCs, noise reduction coefficient, contact angle, and thermal conductivity were 14.33 kPa,0.858,127.0°, and 0.042 W/m-K, respectively.Systematic researeh of the interface and complex mechanism of Si-Al/wood fibers composites were carried out by SEM-EDS, TEM, NMR, XRD, FTIR, XPS, and thermal analysis. Results showed that a small-scale Si-Al inorganic film with thickness of 300-400 nm and less than 100 nm were found on the surface of fibers and cell cavity wall, respectively. There are two kind of coalescent mode between wood fibers and Si-Al sol-gel. Firstly, Si-Al sol-gel absorbed on the wood fibers’ surface by hydrogen bonding, or filled in wood fiber cell cavity by condensing with homopolymer. Secondly, Si-Al sol-gel reacted to carbonyl group hemicelluloses and lignin in wood fibers by covalent bonds, making Si-Al inorganic fillers coalesced with wood fibers in ’molecular composite’. |
