Wood surface treatment aims to improve or reduce the surface activity of wood by physical treatment, chemical treatment, biological activation treatment or other methods to achieve the purpose of surface modification. After wood surface modification, the paint film adhesion performance, gluing performance, surface wettability, surface free energy and surface visual properties would be affected. This article aims to explore the effects of different modification methods on the adhesion of wood coating films. Modification of the wood surface significantly improves the adhesion properties of the paint film, thereby extending the service life of the coating. Research showed that physical external force modification improved the hydrophilicity and wettability of wood by changing its surface structure and texture, thus enhancing the adhesion of the coating. Additionally, high-temperature heat treatment modification reduced the risk of coating cracking and peeling by eliminating stress and moisture within the wood. Chemical impregnation modification utilized the different properties of organic and inorganic substances to improve the stability and durability of wood. Organic impregnation effectively filled the wood cell wall and increased its density, while inorganic impregnation enhanced the adhesion of the coating by forming stable chemical bonds. Composite modification methods combined the advantages of the above technologies and significantly improved the comprehensive properties of wood through multiple modification treatments, showing superior adhesion and durability. Comprehensive analysis indicated that selecting the appropriate modification method was key for different wood types and application environments.

Nine sets of orthogonal experimental samples were prepared by examining four factors: shellac microcapsules, carbonyl iron powder (CIP) microcapsules, CIP/ carbon nanotube (CNT) microcapsules, and primer coating thickness. By testing the morphology and performance of the coating and using the fracture elongation of the coating as an orthogonal experimental analysis, the maximum factor affecting the fracture elongation of shellac, CIP, and CIP/CNT microcapsule coatings was determined. The first two factors that had a significant impact on the fracture elongation of the coating were the content of CIP/CNT microcapsules and shellac microcapsules. In order to further optimize the coating performance, important factor experiments were conducted, using the content of CIP/CNT microcapsules and shellac microcapsules as variables. It was found that the coating had the best performance when the content of CIP/CNT microcapsules was 7.0% and the content of shellac microcapsules was 4.0%. The optical properties of coatings with added shellac, CIP, and CIP/CNT microcapsules were tested, and the color difference and glossiness of the coatings showed little change. The mechanical properties of coatings with added shellac, CIP, and CIP/CNT microcapsules were tested. The blending of the three types of microcapsules enhanced the toughness of the coating to a certain extent, and suppressed the generation of micro-cracks, demonstrating a good self-healing effect. The electromagnetic-absorption performance of coatings with added shellac, CIP, and CIP/CNT microcapsules was tested. The blending of shellac, CIP, and CIP/CNT microcapsules exhibited two effective bands of electromagnetic absorption and a good absorption performance at a relatively wide frequency range. The combination of shellac, CIP, and CIP/CNT microcapsules endows the fiberboard surface with self-healing and electromagnetic-absorption functions, while maintaining the original performance of the water-based coating. The results can be used for application of surface coatings on wooden materials with dual functions of self-healing and electromagnetic absorption.

In order to investigate the effect of thermochromic microcapsules on the surface coating performance of basswood board, two types of microcapsules prepared with syringaldehyde and sodium tripolyphosphate crosslinking agents were added to a UV primer and coated on the surface of basswood board. The color-change effect of the surface coating on basswood board with microcapsules added with syringaldehyde as the crosslinking agent was better than that with microcapsules added with sodium tripolyphosphate as the crosslinking agent, and the color difference varied more significantly with temperature. The effect of the two types of microcapsules on the glossiness of the surface coating on basswood board was relatively weak. The glossiness of the surface coating on basswood board with microcapsules containing syringaldehyde as the crosslinking agent showed an overall increasing trend with the increase in microcapsules, and the change trend was relatively gentle. The glossiness of the surface coating on basswood board with microcapsules containing sodium tripolyphosphate as the crosslinking agent increased first and then decreased as the amount of microcapsules added increased. The addition of microcapsules with syringaldehyde as the crosslinking agent had no significant effect on the reflectance in the visible light band of the surface coating on basswood board. Among the two groups of samples, the hardness increase in the surface coating on basswood board with syringaldehyde as the crosslinking agent was more significant. The adhesion level of the coating on the surface of the basswood board with the two microcapsules did not change. Neither of the microcapsules had a significant effect on the impact resistance of the surface on basswood board. In the comprehensive analysis, the surface coating on basswood board with microcapsules added with syringaldehyde as the crosslinking agent at a content of 4.0% had better comprehensive performance, better surface morphology, better color-change effect, and moderate mechanical properties. The color difference was found to be 21.0 at 25 °C, the reflectivity was found to be 57.06%, the hardness was found to be 3H, the adhesion was found to be five, and the impact resistance was found to be three.

Microcapsules with self-healing properties were synthesized via emulsion polymerization, with melamine formaldehyde resin serving as the microcapsule wall and a mixture of shellac and rosin solutions encapsulated as the core. The core–wall ratio was tested as a variable, and two ratios of 0.59:1 and 0.68:1 were selected for the preparations. Microcapsules were added to the waterborne paint films at concentrations of 0%, 5.0%, 10.0%, 15.0%, 20.0%, and 25.0%, respectively, to obtain self-healing waterborne paint films with different microcapsule contents. The effects of microcapsules with different core–wall ratios and concentrations in the paint films on the optical, mechanical, and self-healing properties of the paint film were investigated. The results showed that an increase in microcapsule content led to a corresponding rise in the paint film ∆E. The coating-film glossiness exhibited a decreasing tendency with an increase in microcapsule concentration. When the content of microcapsules was below 15.0%, the coating maintained a high level of adhesion and hardness. However, once the concentration surpassed 20.0%, coating adhesion began to decline. The addition of microcapsules effectively enhanced the thermal-aging resistance of the paint film. At the core–wall ratio of 0.68:1 and a microcapsule content of 20.0%, the paint film exhibited the best aging resistance, and the repair rate reached 16.1%, indicating good self-healing performance.

In this study, poplar boards were bleached and treated with two types of urea–formaldehyde-coated ternary system thermochromic microcapsules (UF@TS), which were mixed with UV primer. The bleached poplar boards were manually painted with two layers of primer and topcoat. Coating samples with varying microcapsule contents were prepared and evaluated based on factors such as glossiness, reflectivity, and other surface properties. The experimental results showed that bleaching treatment significantly increased the whiteness of poplar wood, with an improvement rate of up to 17%. Among the two microcapsule types, the coating containing #2 microcapsules exhibited superior surface quality compared to #1 microcapsules. As the microcapsule content increased, the coating glossiness showed an overall decreasing trend and a certain degree of fluctuation, and the #2 microcapsule showed lower reflectivity values. The addition of UF@TS microcapsules negatively affected the coating adhesion but had little effect on hardness. The #2 microcapsule enhanced the impact resistance of the coating to a certain extent and increased surface roughness. Regarding thermochromic performance, the #1 microcapsule exhibited higher color-changing temperature and larger color difference, while the #2 microcapsule showed color-changing temperature closer to room temperature. Despite a decline in thermochromic performance and glossiness during aging, the 1# microcapsule showed slightly better stability. The coating containing 10% #2 microcapsules demonstrated the best comprehensive performance on bleached poplar wood, with glossiness of 2.1 GU, reflectivity of 67.95%, adhesion grade of 1, hardness of 6 H, impact resistance grade of 4, and surface roughness of 0.681 μm. The ΔE in the range of −20 °C to 50 °C was 7.434. After aging, ΔE was 5.846, and the light loss rate was 9%, with excellent comprehensive performance.

Thermochromic microcapsules were synthesized and optimized using crystal violet lactone, bisphenol A, and decanol as the core materials, a dispersible cationic red dye as the color-modifying additive, and urea-formaldehyde resin as the wall material, based on orthogonal and single-factor experiments. The effects of the proportion of cationic red dye in the core material, the mass ratio of formaldehyde to urea, the emulsifier HLB value, and the core–wall mass ratio on yield, encapsulation rate, thermochromic ΔE, and formaldehyde release of microcapsules were systematically investigated. The results showed that the core–wall ratio was the key factor affecting the comprehensive performance of the microcapsules. Through the comparison of orthogonal and single-factor tests, 11# microcapsule was identified as having the best overall performance in terms of ΔE, and encapsulation rate. The ΔE value was increased by about 165% compared with the lowest-performing sample, significantly enhancing the thermochromic response. The encapsulation rate was improved by nearly 40%, effectively enhancing the encapsulation quality and core stability, with overall performance standing out. The best preparation process was to add 0.5% of the core material mass of dispersible cationic red dye, the mass ratio of formaldehyde and urea was 1.2:1, the HLB value of emulsifier was 10, and the core–wall ratio was 1:1.1. The yield of 11# microcapsules prepared under this condition was 31.95%, the encapsulation rate was 68%, the thermochromic ΔE was 9.292, and the formaldehyde release concentration was 1.381 mg/m³. Furthermore, 11# microcapsules with different addition levels were introduced into the UV primer to evaluate their effects on the mechanical and optical properties of the coating. The results showed that the addition of microcapsules weakened the gloss and light transmittance of the coating, increased the surface roughness, and decreased the elongation at break. When the addition amount was 5%, the coating exhibited the best overall performance: UV-visible light transmittance reached 91.92%, 60° gloss was 42.2 GU, elongation at break was 9.3%, and surface roughness was 0.308 μm. This study developed a purple thermochromic microcapsule system by regulating the dispersible dye content and interfacial conditions. In coating applications, the system exhibited a strong ΔE response and excellent overall performance, offering great advantages over existing similar systems in terms of color-change efficiency, ΔE enhancement, and coating adaptability.