Sustainable Starch-Extracted Amylose-Rich/Tannic Acid Adhesives with Robust Adhesion Properties on Wood Substrates

Presently, a wide range of commercial wood adhesives are formaldehyde-based and derived from petroleum resources, causing major environmental concerns. The urgent requirement to minimize the production of formaldehyde, which can have damaging consequences for living organisms, has necessitated the development of eco-friendly adhesives derived from biobased sources. This study presents a novel, eco-friendly wood adhesive using amylose (AM) extracted from biobased starch (ST). The isolation of starch yields two distinct components, AM and amylopectin (AP). The use of the isolated AM-rich component, in conjunction with tannic acid, a natural polyphenolic compound, results in the formation of a formaldehyde-free adhesive derived from natural products through simple blending, without the need for additional cross-linking agents. The adhesive forms as the AM-rich solution recrystallizes via hydrogen bonding, creating a double helix structure and resulting in a hydrogel with a three-dimensional network. TA infiltrates the AM matrix, reducing matrix crystallinity by lowering interchain hydrogen bonding, which enhances adhesion by decreasing viscosity and increasing penetration and spreadability into wood pores. In addition, the AM-rich/TA adhesive formed a robust hydrogen bond with the wood substrate by the polyphenol present in TA, showing higher bonding strength and adhesion strength than the wood itself, supporting a weight of up to 23 kg. The phenolic moieties of TA exhibit good antibacterial and antimildew properties. Therefore, the multifunctional AM-rich/TA hydrogel is a sustainable and environmentally friendly adhesive with superior adhesion properties. This sustainable material offers a practical substitute for petroleum-derived adhesives and addresses the environmental concerns associated with their use.