**2.2 Wood industry**

Wood is the inseparable part of the furniture and several important industries. Wood contains organic acids, tannins, and lignocellulosic material which are most susceptible to biological, chemical, and physical decaying agents. Therefore, wood requires a large number of synthetic adhesives, glues, antitermite chemicals, and other coating materials in order to protect it. However, these materials have tremendously benefitted the wood industry, but they adversely affect the environment conditions. Because synthetic phenolics, amino resins, and formaldehyde used in wood industries are generally carcinogenic in nature. To overcome this problem, scientists are investigating natural materials of herbal or animal origins, such as tannins, that can be the best option or alternative material to be used in the wood industries [27].

In recent years, a lot of attempts have been made to improve the bio-durability and commercial properties of wood and wood-based furniture by using tanninbased preservatives. Although both condensed and hydrolysable tannins are used as adhesive, but mimosa tannin is proved to be the most effective wood glue, which attributed to good cross-linking, auto-condensation, poly condensations reactions, and hyper activity. Tannin-based adhesive is proved to be harder than pure synthetic adhesive due to great level of bonding with other aldehydes or different non aldehyde hardeners (glyoxal, furfuryl alcohol, hexamine, etc.) and lignocellulosic materials. Several industries in South Africa and America are using the mimosa and quebracho-based tannins that could reduce the formaldehyde-based emission from the industries. A similar technology has been used to produce the interior and exterior grade particle board largely used in the furniture industry [28]. Apart from this, catechin and gallic acid-based epoxide adhesives and starch-based adhesives from tannins were also produced. Epoxy adhesives are produced by reactions between catechin and epichloridrin via alkylation in the presence of unsaturated halogenated compound that leads to the oxidation. Tannin-based adhesives have been used for grinding wheels, angle grinder disks, and automotive brake pads matrices also.

Coating material is extremely useful to prevent wood surface from biotic and abiotic adversities like, rain, winter, and summer, and insects and microorganisms. Generally, coating material comprises of polyurethane and isocyanates. The urethane-based coating material is prepared by using the lignin and lignosulfonate/hydroxypropylate. Recently, Pinus tannins and di-isocyanates were used to prepare more effective coating material by exploiting hydroxypropylation and hydroxybutylation reactions which enhanced the bonding patterns between hydroxyl groups provided by tannins (flavonoids) and isocyanates [29]. However, tannins and isocyanate-based adhesives are good and environmental friendly, but these should be replaced with more bio-based material like tannins because they are naturally designed to protect wood against fungal attacks and natural decaying process of wood.
