Innovative Synthesis of Waterborne Styrene–Acrylic Resin Tailored for Bamboo

Bamboo, a fast-growing biomass material with excellent mechanical properties, is widely used in furniture and construction. However, its susceptibility to moisture, cracking, and aging limits its durability. While acrylic resins offer good weather and water resistance, the relationship between resin formulation and the performance of bamboo remains unclear. This study developed a novel water-based styrene–acrylic resin tailored for bamboo, systematically investigating the relationships between resin formulation, coating structure, and performance. Results show that vinyltriethoxysilane-modified styrene–acrylic resin outperforms hydroxypropyl-acrylate-modified and unmodified styrene–acrylic. At a 10% dosage of vinyltriethoxysilane, the Zeta potential reached −24.2 mV, indicating enhanced emulsion stability. The coated bamboo exhibited a water contact angle of 100.56 ± 1.11°, a pencil hardness of 4H, and an adhesion grade of 1, significantly improving its waterproofing, hardness, and bonding strength. UV aging tests confirmed improved anti-aging performance, with optimal results at 10% dosage: color difference (ΔE) of 3.00 ± 1.81, dimensional change rate of 0.76 ± 0.22%, and gloss retention of 78%. This study also pioneers research on contact angle hysteresis for coated bamboo. The findings provide theoretical and technical support for developing high-performance bamboo coatings and durable outdoor bamboo products.