Optimizing polyurethane coating formulation for enhancing the aging resistance of bamboo timbers

Bamboo is a promising sustainable alternative to conventional materials, yet its outdoor application is limited by susceptibility to moisture absorption, deformation, and aging. While polyurethane (PU) coatings can enhance performance, the relationship between curing formulation and long-term protective efficacy remains unclear. This study investigates the influence of the curing agent-to-main agent mass ratio on the coating structure, mechanical properties, and aging resistance of coated bamboo. Results indicate that a mass ratio of 0.8 yields the optimal balance of properties, exhibiting superior light transmittance (60%), high adhesion (4B), and excellent mechanical hardness. Water immersion tests confirmed that the coating significantly improved the water resistance and dimensional stability compared to uncoated bamboo. Furthermore, across natural weathering, boiling-drying cycles, and UV-accelerated aging tests, the coated bamboo with a 0.8 mass ratio consistently demonstrated the best aging resistance, characterized by minimal mass loss, negligible dimensional change, and high gloss retention. Consequently, a mass ratio of 0.8 is identified as the optimal formulation for manufacturing high-performance, durable bamboo materials for outdoor engineering applications. • 1The PU film with a mass ratio of 0.8 exhibited the best comprehensive performance • 2Waterproof and dimension stability of coated bamboo increased by over 96% and 85% • 3The coated bamboo with a mass ratio of 0.8 possessed the best aging resistance