Formation Mechanism And Construction Of Organosilicon Hydrophobic/Superhydrophobic Coating On Chinese Fir Surface

Due to the strategic objectives of achieving"carbon peak"and"carbon neutrality,"the use of renewable biomass materials has became a promising avenue for development.Wood,as a significant biomass material,has remarkable physical and mechanical properties,low energy consumption,biodegradability,renewability,and environmental friendliness.It is widely used in construction,indoor and outdoor decoration,and other fields.Wood mainly consists of cellulose,hemicellulose,and lignin.Cellulose and hemicellulose contain a large number of hydroxyl groups,making wood higly hydrophilic.As a result,water absorption from the surrounding environment can cause discoloration,deformation,warping,decay,and other issues,significantly reducing the lifespan of wood products.To address these challenges,wood protection techniques have a long-standing history,primarily focused on introducing hydrophobic substances with low surface energy to wood or reducing the hydrophilic groups within the wood to enhance its waterproof performance.In recent years,researchers have shown increasin interest in the superhydrophobic properties observed in various animals and plants in nature.These properties have inspired the development of superhydrophobic coatings for wood surfaces,aiming to replicate the microstructure found in natural surfaces and exhibit self-cleaning characteristics similar to lotus leaves.The construction of such coatings requires simultaneously fulfilling two essential conditions:enhancing the surface micro-nano-roughness of the material and reducing its surface energy.This paper focuses on the fabrication of hydrophobic/superhydrophobic coatings on wood surfaces using organosilicon and organomodified silicon dioxide（ORMOSIL）materials.These materials are selected for their low surface energy,anti-high and low-temperature,excellent weather proof,and distinctive chemical reaction characteristics.The study investigates the underlying mechanism involved in the construction of these coatings.The primary research objectives are as follows:（1）Constructing superhydrophobic silica coatings on wood surfaces through the regulation of tetraethoxysilane（TEOS）hydrolyzation-polycondensation.The modified solution is prepared by simply stirring TEOS,ethanol,and ammonia.The superhydrophobic modification of wood is achieved through a straightforward impregnation method.By adjusting the amount of ammonia and the extent of ethoxy hydrolysis in TEOS,it is possible to obtain hydrophilic and superhydrophobic coatings.The chemical properties and microstructure of coatings are characterized using techniques such as FTIR,29Si NMR,XPS,and SEM.The results demonstrate that higher concentrations of ammonia（greater than 6%）yield coatings with superhydrophilic properties.Conversely,lower ammonia concentrations（3%～6%）result in superhydrophobic coatings,characterized by a water contact angle of up to 167.6°.FTIR analysis indicates the appearance of absorption peaks corresponding to-OCH₂CH₃when lower concentrations of ammonia are employed,signifying slower hydrolysis of the ethoxy group during the hydrolyzation-condensation process of tetraethoxysilane into silica particles under low ammonia conditions.Consequently,the surface of the resultant silica particles contains more hydrophobic ethoxy groups,leading to the acquisition of superhydrophobic properties by the modified cotton cloth.XPS test results corroborate these findings,with the carbon content of silica prepared under low ammonia concentration measuring 33.42%,significantly higher than that prepared under high ammonia concentration,consistent with the FTIR results.SEM analysis illustrates that the cotton fibers treated using this method are coated with a multitude of silica particles.The hydrophobic properties of the silica particles,influenced by the amount of ammonia,are elucidated based on their chemical structure and macroscopic properties.The preparation method described in this chapter offers the advantages of simplicity and low cost,but the superhydrophobic silica coating created using this method on wood surfaces exhibits non-uniformity and poor stability due to weak adhesion with the wood surface..（2）The second part of the study focuses on the synthesis of SiO₂/PMHOS superhydrophobic coatings on wood surfaces by leveraging the reaction characteristics of polymethylhydrosiloxane（PMHS）and tetraethoxysilane（TEOS）.The synthesis process involves several steps.Initially,PMHS undergoes dehydrogenation,condensation,and alcohololysis in a Na OH/ethanol system,resulting in the formation of PMHOS particles.Subsequently,PMHOS particles and TEOS are hydrolyzed and condensed in an ammonia/ethanol system,yielding a SiO₂/PMHOS suspension.Finally,a superhydrophobic coating of SiO₂/PMHOS is applied to the wood surface using a simple impregnation technique.The modified wood’s chemical properties and surface morphology are evaluated using scanning electron microscopy with energy-dispersive X-ray spectroscopy（SEM-EDS）and Fourier-transform infrared spectroscopy（FTIR）.The findings demonstrate that the contact angle between the modified wood and water increases as the SiO₂/PMHOS suspension ages,surpassing150°after more than 3 days of aging,thus achieving superhydrophobicity.FTIR analysis reveals the presence of absorption peaks associated with-Si-CH₃,Si-O-Si,and-Si-OH,which are attributed to PMHOS,indicating the presence of SiO₂/PMHOS particles on the wood surface.SEM results illustrate the presence of a rough SiO₂/PMHOS layer coating the wood surface.Moreover,wear resistance experiments confirm that the superhydrophobic wood surface retains its superhydrophobic properties even after continuous wear,including finger wiping,knife scraping,tape stripping,and sandpaper friction.（3）In the third part of this research,we focused on synthesizing superhydrophobic coatings on wood surfaces by utilizing the reaction characteristics of hydrofluorosilicone oil（HFSO）and tetramethyl tetravinyl cyclotetrasiloxane（V4）.The objective was to enhance the water-repellent properties of wood by applying modified liquid HFSO/V4/SiO₂.To prepare the modified liquid HFSO/V4/SiO₂,we used industrial fluorinated HFSO,V4,hydrophobic SiO₂,and n-hexane as a solvent.The wood samples were transformed into superhydrophobic surfaces by immersing them in the HFSO/V4/SiO₂ modifier solution.We investigated the influence of the mass ratio of HFSO to V4 on the water contact angle and water resistance.The results revealed that the highest water contact angle,measuring 160.8°,and a sliding angle of 3.6°were achieved when the mass ratio of HFSO to V4 was 2:1.Moreover,the 24 h water absorption of the modified wood is much lower than that of the unmodified wood,reducing from 78.6%to 29.2%.FTIR analysis demonstrated absorption peaks at 2966 cm^-1,1214 cm^-1,and 901 cm^-1 in the HFSO/V4/SiO₂ modified wood,which could be attributed to the presence of Si-CH₃ groups in HFSO or V4.These hydrophobic Si-CH₃ groups contributed to the low surface energy of the HFSO/V4/SiO₂ coatings.SEM observations displayed numerous HFSO/V4/SiO₂ aggregates on the surface of the wood modified with the HFSO/V4/SiO₂ resin coating.These aggregates formed micro-nano multi-level rough structures,imparting superhydrophobic properties.The superhydrophobic silicone resin coating remained stable even after finger touch,tape peeling,and sandpaper wear,maintaining its excellent hydrophobic characteristics.Lastly,the resulting superhydrophobic wood exhibited remarkable anti-fouling properties,further highlighting the effectiveness of the developed coating.（4）In the fourth part of this research,the focus is on developing a hydrophobic silicone coating with high hardness for wood surfaces.This is accomplished by utilizing the chemical structure and reaction characteristics of organosilazane（OPSZ）.The hydrolysis process of OPSZ involves the conversion of the main chain’s-NH-groups to-OH groups through the absorption of moisture from the surrounding air.Simultaneously,the Si-H bonds present in the side chain of OPSZ react with the-OH groups generated by the hydrolysis process,as well as the-OH groups naturally occurring on the wood surface.This reaction leads to the formation of a hydrophobic coating that exhibits exceptional hardness and resistance to wear on the wood surface.The chemical properties and microstructure of the modified wood are assessed through several characterization techniques,namely Fourier-transform infrared spectroscopy（FTIR）,X-ray photoelectron spectroscopy（XPS）,and scanning electron microscopy（SEM）.The experimental results demonstrate that the most favorable hydrophobic effect is achieved when the mass ratio of OPSZ to n-hexane is maintained at 1:7,resulting in a contact angle close to 120°.Furthermore,the modified wood exhibits a significantly reduced water absorption rate compared to unmodified wood,decreasing from 78.6%to 25.38%after 24 hours of immersion.FTIR analysis reveals distinct absorption peaks corresponding to Si-H,Si-CH₃,and Si-O-Si groups,which are indicative of successful grafting of OPSZ onto the wood surface through chemical bonding.XPS analysis confirms the presence of signal peaks associated with silicon（Si）and nitrogen（N）elements on the surface of the modified wood.The observed increase in O/C,Si/C,and N/C ratios further supports the successful application of OPSZ on the wood surface.The ratio of C1 to C4 aligns with the ratio of C-H and Si-C bonds present in the OPSZ structural formula,providing additional evidence of the successful overcoating of OPSZ on the wood surface.SEM analysis demonstrates that the modified wood surface is coated with a layer of silicone resin,effectively concealing the underlying wood ray structures.Additionally,the hardness of the modified wood surface reaches a pencil hardness rating of 6H following the coating pencil hardness test.Moreover,the modified wood surface exhibits excellent resistance to friction,with a friction resistance length reaching 1440 cm in the sandpaper friction test.（5）In the fifth section of the study,a silicone/organic hybrid resin coating is constructed in situ on wood surfaces through the addition click reaction and dehydrogenation click reaction.The addition click reaction involves the reaction between the Si-H bond of polymethylhydrosiloxane（PMHS）and the-CH=CH₂ of divinylbenzene（DVB）,while the dehydrogenation click reaction occurs between the Si-H bond of PMHS and the-OH groups on the wood surface.The coating process involves mixing PMHS,DVB,and Kastredt catalysts,which are then applied to the wood surface and cured under ambient conditions.The liquid PMHS,which possesses reactive properties,shows good compatibility with the liquid DVB.In the presence of the Kastredt catalyst,the reactive hybridization takes place,resulting in the formation of a uniform composite with both silicone and organic resin frameworks.The chemical properties and microstructure of the modified wood are characterized using FTIR and SEM.FTIR analysis identifies specific absorption peaks,such as the stretching vibration peak of Si-CH₃ in the PMHS chain at 2968 cm^-1,the absorption peak at 2164 cm^-1 corresponding to the stretching vibration of Si-H in the PMHS chain,and the stretching vibration peak of the benzene ring in DVB at 844 cm^-1.These findings confirm the occurrence of the desired reaction between PMHS and DVB in the presence of the catalyst,leading to the successful construction of an organic silicone/organic hybrid resin coating on the wood surface.Hardness testing reveals that the hybrid resin exhibits the highest hardness when the mass ratio of PMHS to DVB is 3:1.The hardness increases with longer curing times and higher curing temperatures.Water absorption testing shows a significant reduction in water absorption for the modified wood,decreasing from 97.54%to 13.89%after 24 hours of soaking.Abrasive paper friction testing demonstrates an improvement in the friction resistance length of the coating with longer curing times,reaching 4300 cm after 30 days of curing,surpassing the performance of silicone rubber and silicone resin coatings.The anti-ultraviolet aging test indicates that the hydrophobic effect of the modified wood is initially lost after 1.5 hours of ultraviolet irradiation but can be restored after 7.5 hours of irradiation,highlighting the coating’s good weather resistance and self-healing properties.Furthermore,the hybrid resin coating exhibits resistance to acid and alkali environments,maintaining its hydrophobicity even after 24 hours of exposure to acidic and alkaline solutions.SEM results demonstrate that in alkaline environments,the silicone resin skeleton is eroded by the alkali,while the dense organic resin skeleton remains intact,providing excellent alkaline resistance to the hybrid coating.