| As a fast-growing and economical natural polymer material,Chinese fir has been widely used in architecture,furniture and industry.However,the large number of hydrophilic groups in wood makes it susceptible to water absorption in humid environments,leading to deformation,cracking and aging,which seriously limits its application.Therefore,storage and protection of the wood is crucial.At present,a lot of researches have been conducted on hydrophobic treatment of wood,but traditional modification methods still have problems such as complicated process operation and poor durability of hydrophobic coatings.In recent years,silicone has been applied to wood hydrophobic modification because of their excellent high temperature resistance,UV aging resistance and hydrophobicity.Based on previous research,in this work,polymethylhydrosiloxane（PMHS）,tetramethyltetravinyl cyclotetrasiloxane（V4）and SiO2 nanoparticles（fumed silica）were used as the main raw materials to construct in situ silicone resin coatings with good water repellency,wear resistance and weather resistance on the surface of cedar wood.The main research contents and conclusions of the paper are as follows:（1）Preparation of hydrophobic coating of silicone resin on wood surfaces by solvent method.The silicone resin was formed by the addition reaction of PMHS and V4 by mixing them thoroughly by aid of Karstedt catalyst at room temperature and pressure.When the mass ratio of PMHS to V4 was 5:1,the hardness and compressive strength of the silicone resin were 89 HA and 16.7 MPa,respectively.PMHS and V4with a mass ratio of 5:1 and Karstedt catalyst were dispersed in hexane to form a hydrophobic modification solution;then the hydrophobic coating of PMHS/V4 silicone resin was constructed on the surface of wood by impregnation method.The effects of modifier concentration and impregnation reaction time on the hydrophobic properties and water absorption of wood were systematically investigated.It was shown that the optimum reaction conditions were:the mass ratio of PMHS to V4 was5:1,the modifier concentration was 5%,and the impregnation time was 5min.At this time,the silicone resin modified wood had the best performance:the water contact angle of the modified wood diameter cut surface was 128°,and the 24 h water absorption rate was reduced from108.5%to 31.3%.The SEM images showed that the coating thickness of the solvent-constructed silicone resin was thin;at the same time,no change in the color and gloss of the modified wood appearance was observed with the naked eye.（2）Preparation of hydrophobic coating of silicone resin on wood surfaces by solvent-free method.The hydrophobic modification solution was made by mixing PMHS with V4 and Karstedt catalyst,and the wood was hydrophobically modified by a simple painting method and cured at room temperature and pressure to obtain PMHS/V4 silicone resin modified wood.The effect of the mass ratio of PMHS to V4 on the water contact angle and wear resistance of wood surface coatings was investigated,as well as the effect of curing time and reaction temperature on the wear resistance of wood surface coatings.The research results show that PMHS and V4 form silicone resin rapidly on the wood surface under normal temperature and pressure conditions,and have good self-reinforcing effect.When the modified liquid was coated on the wood surface for about 30 minutes,the silicone resin coating was cured to obtain a sandpaper wear length of 540 cm（sandpaper mesh:1500 mesh;wood block wear area:6.25 cm2;weight of the weight:200 g）.The wear resistance of the coating increased significantly with increasing curing time;when the curing time was 30 days,the wear length was 2940 cm.The water contact angle of the wood surface was 123.1°after PMHS/V4silicone resin modification.At the same time,the wood modified by solvent-free method has good water and stain resistance.The 24 h water absorption of the modified wood decreased from 103.5%to 14.5%.When the samples were buried in moist soil for 90 days,the mass of unmodified wood increased significantly and large black spots appeared on the surface,while the modified wood showed no significant changes.The surface of the modified wood showed good resistance to stains from milk,coffee and cola,which are commonly found in household life.SEM images showed that the silicone resin coating constructed by the solvent-free method achieved better coverage of the wood surface,and the original structure of the wood was not visible after coating.（3）Preparation of organic/inorganic hybrid silicone hydrophobic coatings on wood surfaces.by solvent-free method.PMHS,V4,fumed silica（SiO2 nanoparticles）and Karstedt catalyst were dispersed at high speed to produce the modification solution.The SiO2/PMHS/V4hydrophobic coating was constructed on the surface of cedar wood by applying the modification solution on the surface of wood by a simple brushing method under normal temperature and pressure conditions.The effects of SiO2 addition on the mechanical properties of SiO2/PMHS/V4silicone resin and hydrophobicity of modified wood,as well as the wear resistance of the coating were investigated.The results showed that the addition amount of SiO2 nanoparticles was 2%,the hardness and compressive strength of SiO2/PMHS/V4 silicone resin increased by 16.9%and 49.0%,respectively.At this time,the water absorption rate of PMHS/V4 silicone resin hydrophobically modified wood was only 6.9%.After curing under normal temperature and pressure for 3 days,the wear length of PMHS/V4 silicone resin coating was 750 cm,while the wear length of 2%SiO2/PMHS/V4 silicone resin coating was up to 3000 cm. |
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