Effects of Syringaldehyde/Gum Arabic Composite Chitosan Thermochromic Microcapsules on the Coating Properties of Basswood Surface

Thermochromic wood coatings hold promising application prospects, yet conventional thermochromic microcapsules are limited by monotonous color transitions and non-environmentally friendly wall materials. In this study, two formaldehyde-free thermochromic microcapsules were prepared via spray drying using crystal violet lactone (CVL) and bisphenol A (BPA) as the core system, with chitosan–syringaldehyde (SA-MCs, decyl alcohol as solvent, Schiff base crosslinking) and chitosan–gum Arabic (GA-MCs, lauryl alcohol as solvent, electrostatic complex coacervation) as the wall materials, respectively. These microcapsules were incorporated into basswood ultraviolet (UV) coatings at mass fractions of 1%, 3%, 5%, 7%, and 9%. With increasing microcapsule content, the gloss of both coatings decreased progressively, roughness increased gradually, and the color-changing amplitude, expressed as the color difference (ΔE), was continuously enhanced. At 9% addition, the SA-MC coating exhibited a moderate transition from light yellow to yellow-green (ΔE = 7.2), while the GA-MC coating displayed a dramatic reversible change from deep blue to light gray (ΔE = 42.4), both with good reversibility. In terms of mechanical properties, SA-MCs exhibited higher hardness, both systems achieved an impact resistance grade of 3, and GA-MCs demonstrated superior adhesion. After 24 h of short-term UV accelerated aging, GA-MCs still maintained a higher thermochromic response, albeit with more severe gloss loss. In summary, GA-MCs are superior in color-changing amplitude and adhesion, while SA-MCs offer advantages in gloss retention and hardness, providing a reference for material selection in the application of smart wood finishing.