Natural adhesives may come from animal, vegetable or mineral sources. They may be hot-melt adhesives, which come in solid form, melt on heating and harden on cooling. They may be water-soluble: adhesives of this type may be in the form of liquids or powders which dissolve in water; either kind remains soluble even after it has dried, so they are not water resistant. The adhesive may also be dissolved in an organic solvent which evaporates faster than water, thus allowing it to set quickly. This type of adhesive is normally water resistant.
The name glue is widely used for any type of adhesive, but strictly speaking only applies to protein derivatives, that is, gelatin like adhesives made from animal or vegetable protein. Scotch glue and similar types of woodworking glue are made by the traditional method of boiling down bones. They are hot-melt adhesives. A newer type, soybean glue, is made of vegetable protein. Casein glue is a water-soluble woodworking adhesive made from milk.
Natural starches, cellulose and gums from various plants are used to make light, inexpensive water-soluble adhesives. These are much used in the paper industry, and also in the home as wallpaper paste and office paste and gum. The adhesive on stamps and envelopes is gum arabic.
Natural rubber, generally dissolved in air-drying organic solvents, makes adhesives that are used in industry for gluing rubber and leather, in building for attaching wall and floor coverings, and in drawing offices for gluing paper (because it does not make the paper wrinkle and can easily be removed without leaving a mark).
Natural resins and bitumens include black top, which is used to bind aggregate (gravel) in road making and similar applications. Marine glue is a natural resin in an organic solvent. It is not a true glue; true glues are not water resistant enough for marine use. Sealing wax is a hot-melt natural resin. All the previously mentioned adhesives are organic in origin. There is one inorganic natural adhesive: water-glass (sodium silicate) which is used in the paper industry.
Recent Comments