Okara, an organic waste product obtained from soy milk production, was used with copper chloride or sodium borate to formulate new wood preservatives as a substitute for expensive wood preservatives, such as copper-azole-based preservatives and ammoniacal copper quaternary. Before formulating the preservatives, okara was hydrolyzed by enzymes (cellulase, pectinase, and protease) to augment penetration and fix the biocide salts of the preservatives into wood blocks. The preservatives were injected into wood blocks by vacuum pressure to measure the treatability of the preservatives. The treated wood blocks were placed in hot water for 3 d to measure leachability. The treatability and leachability of the preservatives were affected by the type and loading amount of enzymes and the addition of sodium borate into okara-based wood preservative formulations. The treatability and leachability of the preservatives formulated with copper chloride and okara hydrolysates were 63.38 and 3.15%, and those of the preservatives with copper chloride, okara hydrolysates, and sodium borate were 61.47 and 3.32%, respectively. Despite the hot water leaching, wood blocks treated with preservatives formulated with 2% cellulase, pectinase, and protease hydrolyzed okara, CuCl(2), and sodium borate showed only 1.98% average weight loss against Fomitopsis palustris over 12 weeks. Microscopic observation revealed how okara-based preservatives work in wood blocks. Okara has potential as a raw material for cost-effective and environmentally friendly wood preservatives.
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