Novel formulated Chitosan copper complex as a green color protection agent of Moso bamboo and its reaction characteristics on bamboo epidermis

Moso bamboo culms have become preferred over other lignocellulosic materials for application in the timber industry, notably due to their excellent mechanical properties, rapid growth cycle and renewability. Moreover, its beautiful green culm contributes an added aesthetic value that attracts most users. However, this green color rapidly fades into a dull light brown color and loses its glossiness, making it unappealing to the eyes, thereby reducing its economic value and service life. In this study, a novel formulated chitosan copper complex (CCC) was evaluated for its ability to provide green color protection to the bamboo epidermis. The parameters of concentration, chitosan (CTS) to copper salt ratio (CuCl2), temperature, and time were investigated to determine the optimal conditions for retaining green color. Furthermore, the surface properties of CCC treated samples were examined to analyze the mechanism of attachment. An attractive green color (L*= 54.89, a*= −8.07 and b*= 21.41) was obtained when the bamboo culms were treated with a 6% CCC solution at 80 °C for 2 h, using a 1:3 CTS/ CuCl2 ratio in aqueous solution. The morphological analysis through SEM showed formation of a rough material layer over the treated bamboo epidermis and blocked stomata. FTIR and XPS revealed that chitosan not only reacted with copper to form a chitosan copper complex but also cling closely with bamboo epidermal composition via hydrogen bond. Moreover, reactions between copper ions and chlorophyll may have occurred due to the increase in relative copper content and a corresponding decrease in magnesium content, as shown by XPS and chlorophyll analysis. Therefore CCC, an environmental-friendly formulation, could provide green color protection for Moso bamboo culms.