Types of Adhesive

Packaging materials when thought about is topped by pictures of corrugated boxes, tapes, plastic bags etc. Has it ever come to your mind about the bonding agent used in packaging materials called adhesive? 

The adhesive is like the mortar which binds the bricks in construction and thus is a building block in packaging. Adhesive sticks two objects together and these objects which stick together are called substrates. 

There are various types of adhesives available to bind two substrates in packaging and they can be characterized by how they form the bond between the two substrates. 

1. Drying adhesives- 

Drying adhesives bind the substrates when the solvent or the carrier dries and the adhesive hardens. A good example of a drying adhesive is rubber cement. 

2. Pressure-sensitive adhesives- 

A pressure-sensitive adhesive is solid enough to retain its shape and at the same time is soft enough to flow and press into the substrates on applying pressure. When pressed into the substrate, molecular interactions firm and strengthen the bond, the most common example of a pressure-sensitive adhesive is a Scotch tape, other common examples are Post-it notes and Band-aids. 

3. Holt Melt adhesive- 

A hot-melt adhesive is a thermoplastic which is melted to use and then it solidifies when cooled. Once the adhesive solidifies it forms strong bonds between the substrates. One of the most common examples of a hot melt adhesive is a glue gun and a glue stick. 

4. Reactive adhesive-

A reactive adhesive is an adhesive that creates bonds by reacting to the substrate materials. The most common example of a reactive adhesive is a moisture-activated adhesive such as an envelope. The moisture from the saliva activates the adhesive when applied to it. A reactive adhesive is typically made with potatoes or corn starch which allows it to stick to materials such as paper. 

Adhesives categorized on the basis of raw material 

Adhesives could also be characterized by the raw materials that are used to make them. Some adhesives are made from natural sources such as starches (of corn, potatoes, sugarcane, wheat). Some are made from natural resins (such as gum arabic), casein which is a milk protein, and a range of adhesives are made from animal sources such as beeswax, shellac, and gelatin rendered from animal hides, hooves, or bones.  

Adhesives are made from natural, but non-renewable resources as well such as amber, silica, and sulphur. Then there are synthetic adhesives which are derived from human-made polymers such as thermoplastics, thermosets, and elastomers. 

Synthetic adhesives are costlier than natural adhesives, and these types of adhesives offer greater bond strengths and durability.