Natural adhesives shellac

Natural resins have been used as adhesives. Shellac is used in bonding mica splittings to form micaboard and used in abrasives. Gum arable is used in remoistenable adhesives. Copal gums are used in spirit-soluble lino cements. 

Natural resins are generally described as solid or semisolid amorphous, fusible, organic substances that are formed in plant secretions. They are usually transparent or translucent yeUow-to-brown colored, and are soluble in organic solvents but not in water. The principal uses for natural resins are in varnishes, printing inks, adhesives, paper size, and polymer compositions. The term natural resins includes tree and plant exudates, fossil resins, mined resins, and shellac. They often have been altered from their original state during isolation and processing. For some appHcations, the resins have been chemically modified to increase their industrial utiUty. 

Oxidized castor oils are excellent nonmigrating, nonvolatile plasticizers (qv) for ceUulosic resins, poly(vinyl butyral), polyamides, shellac, and natural and synthetic mbber (see Rubber, natural). The high viscosity products are also used as tackifiers in gasket compounds and adhesives (qv) because of good oil and solvent resistance. They also serve as excellent pigment grinding media and as a base for inks (qv), lubricating oils, and hydrauHc oils (62). 

Uses Solvent for cellulose acetate, crude rubber, natural resins, nitrocellulose, vinyl resins, waxes, fats, oils, shellac, rubber, DDT, and other pesticides preparation of adipic acid and caprolactum additive in wood stains, paint, PVC paints, lacquers (to prevent blushing or improve flow), and varnish removers degreasing of metals spot remover lube oil additive in PVC adhesives to control evaporation rate leveling agent in dyeing and delustering silk. 

Solvent-Soluble Natural Polymers. The exudate of the lac insect is dissolved in alcohol to yield shellac. This solution has adhesive properties and should be reversible by treatment with the appropriate alcohol or similar solvent, although it may present problems in other performance areas (8). Solvent-soluble plant gums, especially coniferous resins (e.g., from firs or pines) can be dissolved in organic solvents and used as adhesives. Solvent solutions of some plant waxes may also have limited utility in gluing. All such glues should be reversible by treatment with solvents similar to those they were dissolved in when applied. 

In nature the enzymes are able to convert cheap feedstocks such as sugars and amino acids into a large variety of functional and structural polymers with very high complexity. For many years, biopolymers such as starch, dextrose, cellulose, shellac, casein plastics, and proteins were used as polymers from renewable resources to formulate adhesives [9]. The life sciences effort is promoting the development of new processes based upon biotechnological routes to carbo-... 

Some of the other materials used by early human beings as adhesives are now called beeswax, rosin, rubber, shellac, sulfur, tar, and vegetable gums. Later, as people developed bows and arrows, it was found that feathers fastened to an arrow shaft helped to stabilize the arrow s flight. The same sticky or heat-softened materials soon supplemented the use of natural fibers to attach the feathers. 

Liquid anaerobic adhesives dissolve in most organic solvents and oils and, even when true solution is not possible, they normally disperse harmlessly. With certain exceptions, the liquid adhesives will dissolve or swell many thermoplastic materials such as Polyacrylates, Polyvinylchloride, Polystyrene and, after lengthy exposure, natural rubber and shellac. 

Fig. 8. Starch foam cup and tray coated with water-resistant PHBV. An adhesive layer of shellac, a natural resin, prevents delamination of PHBV from the starch. Courtesy of R. Shogren, U. S. D. A.

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