Enzymatic biocatalysis of bamboo chemical constituents to impart antimold properties

Current antimold agents that capitalize on broad spectrum biocidal toxicity for their efficacy can create potential hazards in the environment, as in many cases these biocides are not chemically bonded to the wood. They can therefore leach into the ecosystem to jeopardize off-target organisms. In this study, “bio-catalysis” of potassium iodide (KI) was used to impart non-diffusible antimold properties to 4-year-old bamboo, and the mechanisms of how this system works against Aspergillus niger and Trichoderma viride fungi were also studied. In addition to the bamboo block material tested, powdered samples of lignin, cellulose and hemicellulose were studied to better understand binding of iodide to the chemical subcomponents of the bamboo cell walls. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses were used to investigate the sample chemistries and antimold mechanisms, respectively. The results revealed that a specific ratio of laccase enzyme with a laccase-mediator functioned best in binding KI to bamboo. Lignin samples showed the greatest changes in FTIR, especially relative to the methoxyl groups and aromatic skeleton. Additionally, enzyme activity on lignin moieties showed much more differences than on hemicellulose and cellulose after biocatalyzed KI modification. Moreover, the XPS binding energy readings of 621.1 and 632.7 eV (Aromatic region) for lignin were consistent with I–C binding associated with its phenolic structures. While the 620.7 eV (Aliphatic region) suggested I–C bonding that associated with residual lignin in hemicellulose, no peaks were observed for the iodine 3d XPS spectra of treated cellulose. XPS analyses of the O/C and C1/C2 ratios revealed that the formation of I–C bonds was likely due to the substitution of oxygen-contained groups which were formed from laccase-catalyzed oxidation. Thus, enzyme-catalyzed formation of I–C bonds with bamboo chemical constituents is a highly effectual, as well as an ecological method to protect bamboo against mold colonization in the present research.