Adhesives

An adhesive is any substance applied to the surfaces of materials that binds them together and resists separation. The term “adhesive” may be used interchangeably with glue, cement, mucilage, or paste. Adjectives may be used in conjunction with the word “adhesive” to describe properties based on the substance’s physical or chemical form, the type of materials joined, or conditions under which it is applied.

The use of adhesives offers many advantages over binding techniques such as sewing, mechanical fastening, thermal bonding, etc. These include the ability to bind different materials together, to distribute stress more efficiently across the joint, the cost effectiveness of an easily mechanized process, an improvement in aesthetic design, and increased design flexibility. Disadvantages of adhesive use include decreased stability at high temperatures, relative weakness in bonding large objects with a small bonding surface area, and greater difficulty in separating objects during testing.

Adhesives may be found naturally or produced synthetically. The earliest human use of adhesive-like substances was approximately 200,000 years ago. From then until the 1900s increases in adhesive use and discovery were relatively gradual. Only since the last century has the development of synthetic adhesives accelerated rapidly, and innovation in the field continues to the present.

Types of adhesives

• Albumin glues – A glue of better quality, not attacked by water and is used to bind furniture.
• Animal protein glue – Obtained by boiling the remains of animals in water. Develops strong and tough joints and is easy to apply.
• Natural resins
• Synthetic resins – Thermo-setting or thermo-plastic glues. Water proof, fire proof and very strong and their setting times can be regulated.
  • Melamine resins
  • Phenolic resins
  • Resorcinol resins
  • Urea resins
• Nitro-cellulose glues – Prepared from pyroxilin which is nitrated with cellulose. Produces films that adhere strongly to glass.
• Rubber glues – Developed by dissolving rubber in benzene and is used to join rubbers, plastics and glass.
• Special glues – Used to join metals e.g. Araldite
• Starch glues – Prepared from vegetable starch and has fair strength in dry condition.
• Vegetable glues – Prepared from natural gums and starches. Used for paper board articles, labeling, etc.