Preparation And Properties Of Poplar Composite Strengthened By Silica Sol

Wood inorganic functional composite in their excellent fire-retardant, decay resistance, natural drug-free and low prices, has attracted increasing attention. However, except hardness and abrasion resistance, its mechanical properties, such as toughness, modulus of rupture (MOR), modulus of elasticity (MOE), have decreased in some degrees. Summing up the research progress and advanced research methods at home and abroad in this field, on the premise of no weakened porous structure of poplar wood, this study aimed to strengthen the cell wall to prepare wood-inorganic composite,which will make the plantation wood have high intensity and high performance, and will provide technical supports for widening the application field of plantations, also will open up new avenues for the efficient use of plantations. It will be of important scientific significance and practical value. In this paper, plantation of poplar wood is selected for study; silica sol as impregnating solution. Poplar-solica sol composite was prepared through vacuum-pressive process. The main research results are as follows:(1)Under the same process parameters, the properties of the composite wood prepared by the liquid pressure impregnating process are better than those of prepared by air pressure impregnation process. As for the weight percentage gain (WPG), the vacuum treatment before the un-pressure can effectively increase WPG of wood composite and vacuum treatment after un-pressure does not have obvious effect on WPG. However, the latter can effectively remove excess impregnating solution on wood surface and does not reduce WPG of wood composite.(2)Full-cell pressure method can maximize WPG, MOE and MOR of wood composite. The research also showed that there was a certain linear relationship between the MOE and WPG of wood composite, however, MOR of wood composite was related to the location and depth of the silica sol impregnated inside wood. The simple physical filling will not change MOR of wood composite.(3)The average value of MOR of poplar wood impregnated with silica sol was 87.70 MPa, the average value of MOE was 12.41 GPa, the hardness of the end surface, flat surface and edge surface increased by 34.62%, 49.15% and 53.45% respectively, but the compressive strength parallel to grain was nearly changed or declined slightly. After being impregnated with silica sol, polar wood had some expansion along three different directions. Dimension in tangential, radial and longitudinal direction increased by 1.64%, 0.55% and 0.80%, respectively. Although the extension of vacuum time before impregnating can effectively increase WPG and mechanical properties of wood composite, it had a strong negative impact on the stability of wood size. So, the vacuum time before impregnating should be shortened in order that the mechanical properties of wood composite can reach to the standards. The optimal impregnating process parameters for poplar wood, such a soft wood, were as follows: the vacuum time before impregnating was 20 min, impregnating pressure was 1 MPa, impregnating time was 30min and the vacuum time after impregnating was 20 min.(4)Bonding properties will not be affected after wood impregnated with silica sol. The bonding strength and wood failure was up to the JAS standards and was similar to that of untreated wood. Thermal analysis result showed that thermal stability of wood composite had improved, which made wood composite have a certain fire-retardant property. And with the increasing of WPG, the remnants weight was increased and burning and fire-retardant property was also improved. By impregnating silica sol into wood, the dimension stability of wood in tangential, radial and longitudinal direction had been improved. And the dimension stability was related to WPG, and the improvement degree was from 25% to 35%. The study of wettability indicated that the contact angle of the wood increased significantly by impregnating with silica sol, and the wood composite showed good surface hydrophobic performance.(5)By the optical microscope and scan electron microscopy, there was mass silica accumulated in wood composite, and the distribution is: cross section > radial section > tangential section. Thin layer of SiO2 was found to be closely linked to the cell walls in radial section and tangential section, and the porous structure of wood was basically kept. The results from fluorescent microscope showed that SiO2 in cross section existed as physical filling; and that in radial and tangential section SiO2 had a chemical bond with cell wall in different levels.(6)The distribution of silicon elements in timber was uneven detected by X-ray spectrometer. Silicon was mainly distributed in tracheid, wood fiber, wood ray and intercellular layers. In the process of impregnation, silica sol penetrated into the wood gap through physical infiltration. It was found that more silicon appeared in the cell wall of wood fibers and wood rays. Because the cell chambers of the wood fibers and ray cells were relatively small, during the vacuum and pressure process, the silica sol can easily soak into wood organization. Poplar wood has a large number of pits, which is the major channel to realize transverse infiltration. Therefore, the pits had high content of silicon. Cell wall of wood fibers has a large number of pits, so that silica sol can easily be impregnated into the wood fiber.(7)Unchanged XRD diffraction peak position indicated that the lattice parameters of wood composite has not changed. IR spectrum analysis showed that SiO2 gained from silica sol polymerization interacted with wood frame materials. According to composite spectrum and untreated wood spectrum, it was found that the main characteristic peak has not changed significantly, but just the Si-O-Si antisymmetric stretching vibration peak of composite moved to the high-frequency direction, and the Si-O-Si bending vibration peak also had small displacement, this's mainly related with the formation of hydrogen bonds.