Understanding the Bonding Mechanisms of Glues and Adhesives

Adhesives and glues have been in existence since the Stone Age era, when early man used naturally occurring materials from tree sap, tar and beeswax to create basic wooden tools and hunting weapons. Later, processed natural products were produced from resin, animal protein and natural latex. During the Industrial Revolution, chemical industries and synthetic polymers were introduced and various adhesives and glues were explored. This exploration resulted in the production of glues and adhesives for use in different aspects of life. Today, glues and adhesives are classified based on their usage in household repairs, construction projects, or medical application solutions, bonding mechanism, and chemistry type.

Classes of Adhesives and Glues

To understand how glues and adhesives work, it is important to consider the forces that create the bond between the adhesive and substrate surface to ensure the glue used has necessary cohesion forces to hold different parts together. In general practice of what to know about glues and adhesives, a combination of adhesion and cohesion forces are used to classify them into physically hardening, chemically curing, or pressure-sensitive adhesives.

Chemically Curing Adhesives

Chemically curing adhesives are reactive materials that require chemical reactions (curing) to convert them from their thermoplastic state into solids. Once cured, these glues provide flexible and high strength to rigid bonds, resistant to extreme temperatures, humidity, and many chemicals. Chemically curing adhesives exist as single or double component adhesives, where single component adhesives are pre-mixed in their final proportions but are chemically blocked. During application, the adhesives are exposed to high temperatures, light, or humidity to initiate the curing mechanism. Double component chemical adhesives are solid systems that obtain their storage stability by separating the reactive components (resin and hardener) in separate containers. The two components are mixed during timed applications since the chemical reactions begin immediately.

Physically Hardening Adhesives

Physically hardening glues have the base polymer already formed but in a dissolved state and require the use of physical effects including temperature and pressure to create the bond. They are made from polymers that can be liquefied including thermoplastics, polymer dispersions, and soluble elastomers. The process of bond formation occurs through the loss of solvents present in the polymers. When subjected to temperature and pressure, the binding agent molecules in the adhesives merge to form a film.

Pressure-Sensitive Adhesives (PSA)

Pressure-sensitive adhesives are made from natural rubbers, polyacrylates, and certain synthetic rubbers. They are viscous; hence they are supplied dissolved in organic solvents as hot melts, coated tapes, and aqueous dispersions. Bonds in these adhesives form by bringing the adhesive film in contact with the substrate and applying moderate pressure. Inadequate pressure leads to bonding faults through the formation of bubbles leading to detachment. PSAs require no activation by use of solvents, water, or heat to create a strong bond on plastics, metals, wood, and cement. They have enough cohesive bonds and elasticity that allows them to be removed from surfaces without leaving residue.

General Rules for Gluing

Below are helpful tips to remember when using glues and adhesives.

●       Read and follow the manufacturer’s application, storage, and safety instructions

●       Keep glue bottles covered when not being used to prevent them from losing solvents

●       Maximize contact between surfaces by removing oils, grease, dust, and roughness for maximum contact area

●       Do not mix glues on a single surface due to the different bonding compounds present in each type of adhesive

●       More is not better with glue since too much glue creates weak joints

Choosing the Right Adhesives and Glues

Before settling on any type of adhesive for a home construction or repair project, examine all the particulars, including the amount of moisture required for the adhesive to dry, surrounding environmental conditions due to reactivity, and susceptibility to scrutiny. Multipurpose glues are essential tools to have around in your home and workshop, as they will help you with home repair projects without the need to purchase new parts.

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