Study On The Properties Of Heat-treated Rubber Wood Modified By Silica Impregnation

With the background of the shortage of per capita wood resources in China,it is important to improve the utilization rate of wood resources and achieve the use of inferior materials.Wood heat treatment is considered a non-toxic and environmentally-friendly physical modification method.The equilibrium moisture content of heat-treated wood decreased,and the dimensional stability and biological durability are enhanced.At the same time,the heat treatment also results in the loss of mechanical properties of wood.How to achieve the advantages of retaining heat-treated wood while reducing the mechanical loss of heat-treated wood gradually attracts people’s attention.In this study,rubber wood was treated with superheated steam.The treatment temperature was 180℃-230℃,and the holding time was 2 h.The mechanical properties and chemical composition of untreated rubber wood and heat-treated rubber wood under different heat treatment temperatures were analyzed.In order to alleviate the mechanical properties loss of the heat-treated rubber wood,the rubber wood was modified by the impregnation of silica precursor and heat treatment.The silica precursor solution was vacuum-impregnated before and after heat treatment,and the heat treatment temperature was 200“C,and the holding time was 2 h.Comparative analysis of the mechanical properties,dimensional stability and thermal stability of untreated(U),heat-treated(HT),impregnation SiO2 precursor before heat treated(ISB)and impregnation SiO2 precursor after heat treated rubber wood(ISA).In order to enhance the anti-weathering performance and the aging resistance of heat-treated rubber wood,the rubber wood is modified by the silica-doped titania sol combined with the heat treatment.The main research content are as follows:(1)Research on the effects of heat treatment technology on the rubber wood.With the heat treatment temperature increases,mass loss of the heat treatment rubber wood gradually increases from 2.17%to 22.21%;the equilibrium moisture content decreases gradually from 10.59%to 5.31%;the modulus of rupture(MOR),modulus of elasticity(MOE),compression strength,and impact bending showed a significant downward trend.The chemical composition analysis showed that the holocellulose content was reduced,and the a-cellulose content was basically unchanged,indicating that the degradation of hemicellulose mainly caused by the heat treatment was the mainly factor for the loss of the mechanical properties.The color analysis shows that the color of the heat-treated material is deepened with the increase of temperature,and the color difference with the untreated material is gradually increased.(2)Silica impregnation modified heat-treated rubber wood.The rubber wood was modified by the impregnation silica precursor combined with heat treatment.The modified rubber wood showed that the MOR of the ISB and the ISA wood specimens increased by 43.87%and 20.37%,respectively,compared with the heat treated rubber wood,and the compression strength increased 17.96%and 33.64%respectively.The water absorbing and the swelling and shrinkage of the HT,the ISB,and the ISA wood specimens were all lowered that of the untreated rubber wood.Thermo gravimetric analysis showed that the thennal degradation rate of the ISB wood specimens was lower than that of the heat-treated rubber wood,indicating that the combination of silica and wood hindered thermal decomposition and complete cracking of the wood matrix,and the thermal stability of the rubber wood was improved.The ISB wood specimens have enhanced decay resistance from decay resistance to strong decay resistance.Fourier transform infrared spectroscopy(FTIR)showed that Si-O-Si characteristic peak appeared on the ISB wood specimens,indicating that silica was formed inside the wood.The results of X-ray diffraction analysis showed that there was no change in the position of the cellulose diffraction peak of the wood,indicating that the impregnated silica treatment did not destroy the crystal structure of the cellulose.(3)Silica/titanium dioxide impregnated modified heat-treated rubber wood.After accelerated aging by ultraviolet light,the lightness of heat treated rubber wood is lower than the untreated material,the brightness value decreases,the color deepens,and the chromatic aberration gradually increases with the aging time prolonged.The color change of the silica heat treated material and the titanium dioxide doped heat treatment material is the same as that of the heat-treated rubber wood.Chromatic aberration before and after aging decreased by 11.70%and 35.78%compared with heat-treated rubber wood.After aging,the compression strength,MOR and MOE of the heat-treated rubber wood decreased significantly.After the impregnation heat treatment of silica and titania,the mechanical properties decline rate decreased,indicating that the immersion treatment of silica and titania enhanced the aging resistance of the heat-treated material.Thermogravimetric analysis showed that the final residual material of pyrolysis of silica-doped titanium dioxide impregnation heat treatment increased compared with silica-impregnated heat-treated rubber wood,and the maximum degradation temperature was delayed from 335℃ to 340℃,indicating that titanium dioxide doping further improved wood thermal stability.The contact angle of the heat-treated rubber wood is increased to 107.10compared with the untreated rubber wood,and the hydrophobicity of the wood itself becomes hydrophobic,and the contact angle of the silica-impregnated heat-treated material reaches 130.01°,which further enhances the hydrophobicity of the heat-treated material.