Preparation And Properties Of Superhydrophobic Wood Based On Fractal Theory

Wood is a renewable green resource that is widely used in construction,home decoration,furniture,transportation and other fields.However,wood is susceptible to deformation or warping due to moisture in wet or flooded environments,resulting in a significant reduction in dimensional stability,which affects its performance and longevity.To solve this problem,bionanotechnology research has revealed that surfaces with superhydrophobicity in nature can prevent water penetration,providing a new idea for functional improvement of wood.Applying superhydrophobic treatment systems to wood surfaces can transform their hydrophilic properties into superhydrophobic ones,effectively resisting water penetration and thus solving problems such as dimensional changes caused by water absorption in wood.（1）Construction and Application of Wettability Calculation Method for Superhydrophobic Surfaces Based on Fractal Theory.By deeply investigating the wetting theory of superhydrophobic surfaces,the physical and chemical mechanisms of their wetting behavior can be revealed and the wetting behavior of water droplets on superhydrophobic surfaces can be understood;in turn,the directional design and performance regulation of superhydrophobic wood can be guided.In this thesis,fractal theory is introduced to investigate the wettability behavior of superhydrophobic surfaces in depth and to quantify the roughness of superhydrophobic surfaces and its relationship with wettability.By introducing fractal parameters（fractal dimension and scale concept）,the roughness of the superhydrophobic surface is quantitatively characterized;meanwhile,the wettability of the superhydrophobic surface is jointly analyzed and the preparation of the superhydrophobic surface is directionally designed by combining the quantified relationship between roughness and wettability derived by previous work.Compared with previous studies,this paper writes MATLAB software code that can be verified by standard fractal graphs,and uses MATLAB software and its Frac Lab plug-in toolbox to accurately and quickly calculate the fractal parameters of hydrophobic and superhydrophobic surfaces,which provides data support for studying the quantitative relationship between roughness and wettability of superhydrophobic surfaces;and then provides data support for the targeted design and performance tuning of superhydrophobic coatings on wood surfaces.It provides a theoretical basis and computational analysis method for the directional design and performance control of superhydrophobic coatings on wood surfaces.（2）Study on the Properties of Superhydrophobic Wood Prepared by Two-Component Spraying MethodBased on the fractal theory,a"bottom-up"preparation strategy is used to design and prepare fractal rough structures on the wood surface to achieve superhydrophobization of wood.The"bottom-up"preparation strategy uses fluorocarbon resin as the base layer and fumed Si O₂ or micro-and nano-Si O₂ as the top layer to prepare superhydrophobic coatings on the wood substrate surface by a two-step spraying method.The fluorocarbon resin as the base layer has excellent weathering resistance,chemical resistance and adhesion;it can firmly adhere to the wood surface,while it can firmly adhere to the Si O₂ particles of the top layer.The superhydrophobic wood surface prepared from micron and nano coexisting Si O₂ particles was found to have better mechanical stability compared to pure nano-Si O₂ by falling sand impact and sand shock wear tests.This is because the micro-and nano-Si O₂ particles build a stable micro-and nano-scale rough structure through the mechanical interlocking mechanism between the micron and nano particles,which provides a good physical structure basis for the preparation of superhydrophobic wood.The superhydrophobic wood prepared by fluorocarbon resin and micro-nano-Si O₂ can withstand up to 168 h of acid and alkali resistance,resistance to various organic solvents and resistance to xenon lamp irradiation.More importantly,the water resistance and swelling resistance of the superhydrophobic wood were significantly improved;compared with the original wood,the water absorption of the prepared superhydrophobic wood was reduced by 26.2 times and the swelling resistance was improved by about 74.3%.Based on the study of superhydrophobic surface wettability based on fractal theory,it can be verified that the surface of the prepared superhydrophobic wood has significant fractal characteristics;it is also due to the presence of fractal rough structure that the water resistance and swelling resistance of the superhydrophobic wood are greatly improved.The superhydrophobic coating can effectively reduce the water damage of the wood and make the wood have better dimensional stability.（3）Preparation and Properties of Superhydrophobic Wood with Long-Term Icing ResistanceThe icing resistance of wood surfaces is an important aspect in the design and construction of wood structures,as untreated wood surfaces can accumulate snow and ice,leading to structural damage and degradation of the wood.Based on the previous study,two superhydrophobic coatings were prepared on wood substrates using fluorocarbon resins and micro-nano-Si O₂ by both"bottom-up"and"hybridization and blending"strategies.Both coatings were found to delay icing（260 s for both static icing and 20 min for both static icing）and reduce the de-icing force（1/8 and 1/27 of the original wood,respectively）.In particular,the fractal rough structure of the surface coating can be designed and reconstructed based on the fractal theory of superhydrophobic surface wettability to restore the superhydrophobic and anti-icing properties of the superhydrophobic wood after the surface anti-icing properties are lost by the"hybridization and blending"preparation strategy,with simple sandpaper abrasion.The fractal theory is used to analyze and explain the reasons for the recovery of hydrophobicity and anti-icing properties of superhydrophobic wood surface coatings during sandpaper abrasion.In addition,the superhydrophobic wood was tested for actual icing resistance and found to withstand up to 100+icing-de-icing cycles.This part of the work provides new insights into the design of long-lasting anti-icing coatings on wood surfaces,which can help to prepare more widely applicable,practical and durable anti-icing coatings on wood surfaces.（4）Preparation and Properties of Superhydrophobic Wood with Excellent Mechanical StabilityThe composite coatings with excellent mechanical properties（hardness up to 1.22 GPa,modulus of elasticity up to 2.53 GPa,and pull-off adhesion value up to 1.05 MPa）were prepared on the wood surface by scraping method through the strategy of"hybridization and blending";subsequently,the composite coatings on the wood surface were designed and constructed with fractal rough structure by"sandpaper abrasion Subsequently,the fractal rough structure of the composite coating on the wood surface was designed and constructed by using the"sandpaper abrasion"method;finally,a superhydrophobic composite coating with mechanical stability and durability was prepared on the wood surface.The raw material ratio of fluorocarbon resin and micro-nano Si O₂,as well as the amount of solvent,are the main influencing factors on the mechanical properties of the composite coating on wood surface.The number of sandpaper grit used in the"sandpaper abrasion"method is a key factor in the design and construction of the fractal rough structure of the composite coating surface,i.e.,the key to determine the wettability of the wood surface;this can be explained and analyzed by the study of the superhydrophobic surface wettability based on the fractal theory.In addition,the experimental results show that the superhydrophobic composite coating can be prepared and applied on the surface of wood substrates on a large scale,and its fractal rough structure can be restored quickly,simply and inexpensively by sandpaper abrasion after the loss of superhydrophobicity of the composite coating,which in turn restores the superhydrophobicity of the wood surface.The experimental results also show that the superhydrophobic composite coating can impart good acid and alkali resistance,solvent resistance and aging resistance to the wood substrate,and can effectively reduce water damage to the wood（40.67 times lower water absorption and about 77.56%higher swelling resistance）and improve the dimensional stability and service life of the wood.This study provides a useful exploration for the preparation of superhydrophobic wood and the improvement of its mechanical stability performance,and also provides new ideas and methods for the application of wood waterproofing and anti-swelling.This thesis introduces fractal theory to quantify the wettability of superhydrophobic surfaces,and uses fractal theory to design and prepare superhydrophobic coatings on wood surfaces by using"bottom-up"and"hybridization and blending"preparation strategies,combined with"sandpaper abrasion",to achieve water,swelling and icing resistance of wood,and to broaden the scope of applications of superhydrophobic wood in real life.