Adhesives: How They Work and Why They Stick

by Joost Nusselder | Updated on:  June 22, 2022
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An adhesive is a substance that binds two or more objects together.  It’s often used in construction, bookbinding, and even in arts and crafts.  But what exactly is it?  Let’s look at the definition and history of adhesives.  Plus, I’ll share some fun facts about the sticky stuff.

There are many types of adhesives, but they all have one thing in common: they’re sticky.  But how sticky is sticky enough?  And how do you measure stickiness?  I’ll get into that in this guide.

So, what is an adhesive?  Let’s find out.

What is an adhesive

Stuck on Adhesive: A Comprehensive Guide

Adhesive, also known as glue, is a substance that is applied to one or both surfaces of two separate items to bind them together and resist their separation. It is a non-metallic material that comes in a variety of forms and types, and is widely used in modern design and construction techniques. Adhesives are available in hundreds of varieties, each with its own unique properties and uses. Some of the primary forms of adhesive include:

  • Natural adhesives: These are adhesives that are produced from natural materials such as starch, protein, and other plant and animal components. They are often referred to as “glue” and include products like animal hide glue, casein glue, and starch paste.
  • Synthetic adhesives: These are adhesives that are produced through processing and chemical reactions. They include products like polymer adhesives, hot melt adhesives, and water-based adhesives.
  • Solvent-based adhesives: These are adhesives that are supplied in a liquid form and require a solvent to be applied. They include products like contact cement and rubber cement.
  • Solid adhesives: These are adhesives that are supplied in a solid form and require heat, pressure, or water to activate. They include products like hot glue sticks and epoxy.

How is Adhesive Prepared?

The method of preparing adhesive varies depending on the type of adhesive being produced. However, some general steps include:

  • Mixing the constituent materials together in the correct proportions
  • Processing the mixture to create the desired consistency and colour
  • Allowing the adhesive to dry or cure to its initial degree of strength
  • Packaging the adhesive for sale

What are the Properties of Adhesive?

Adhesive has a number of important properties that make it a useful material for a wide range of applications. Some of these properties include:

  • Adhesion: The ability of the adhesive to stick to a surface
  • Cohesion: The ability of the adhesive to hold itself together
  • Tack: The ability of the adhesive to grab onto a surface quickly
  • Setting time: The amount of time it takes for the adhesive to become fully dry or cured
  • Shelf life: The length of time the adhesive can be stored before it begins to degrade
  • Sensitivity to water, heat, or other environmental factors: Some adhesives are more sensitive to these factors than others
  • Holding power: The ability of the adhesive to resist separation once it has been applied

The Evolution of Adhesives: A Sticky History

Humans have been using adhesives for thousands of years. Evidence of glue-like substances has been found in ancient sites dating back to the Pleistocene era, over 40,000 years ago. Archaeologists have uncovered evidence of adhesive materials used by humans in various forms, including:

  • Birch bark tar: The oldest known adhesive, dating back to around 200,000 years ago, was discovered in Italy. It was composed of birch bark and ash, mixed together and heated to produce a sticky compound.
  • Clay: Ancient people used clay to connect parts of their tools and weapons.
  • Beeswax: Greeks and Romans used beeswax to bond wooden segments of their bows.
  • Ochre: This natural pigment was mixed with animal fat to create a paste used for bonding artifacts in the Middle Stone Age.
  • Gum: The ancient Egyptians employed gum from acacia trees as an adhesive for construction.

Development of Adhesive Production

Over time, people extended their range of adhesive materials and improved the process of creating them. Some examples include:

  • Animal glue: This adhesive was made by boiling animal bones, skin, and tendons to produce a liquid that could be used as a glue. It was commonly used in woodworking and bookbinding.
  • Lime mortar: The Greeks and Romans used lime mortar to bond stone and brick in construction.
  • Liquid glues: In the 20th century, liquid glues were developed, which made it easier to apply adhesives to surfaces.

The Role of Science in Adhesive Development

As science advanced, so did the development of adhesives. Scientists began studying the chemical properties of adhesives and experimenting with new ingredients to produce stronger and more effective products. Some notable advancements include:

  • Synthetic adhesives: In the 20th century, synthetic adhesives were developed, which could be tailored to specific applications and had improved bonding abilities.
  • Hot melt adhesives: These adhesives are solid at room temperature but can be melted and applied to surfaces. They are commonly used in packaging and woodworking.
  • Epoxy adhesives: Epoxy adhesives are known for their ability to bond a wide range of materials, including metal, plastic, and wood.

Adhesion: The Sticky Science Behind Bonding

Adhesion is the ability of an adhesive to stick to a surface. It involves the formation of chemical and physical bonds between the adhesive and the adherend. The strength of the bond depends on the intermolecular forces between the two surfaces.

The Role of Interfacial Forces

Interfacial forces play a crucial role in adhesion. These forces include adsorption, mechanical, physical, and chemical forces. Adsorption involves the attraction of particles to a surface, while mechanical forces involve the physical contact between the adhesive and the adherend. Chemical forces involve the formation of covalent bonds between the adhesive and the adherend.

The Mechanisms of Adhesion

Adhesion involves several mechanisms, including:

  • Wetting: This involves the ability of the adhesive to spread over the surface of the adherend.
  • Surface energy: This refers to the energy required to separate the adhesive from the adherend.
  • Contact angle: This is the angle formed between the adhesive and the adherend at the point of contact.
  • Grain boundary: This is the area where two grains meet in a solid material.
  • Polymer structure: This refers to the arrangement of molecules in the adhesive.

The Importance of Adhesion in Bonding

Adhesion is an important factor in the bonding process. It determines the ability of the adhesive to perform its desired function. The degree of adhesion required depends on the type of materials being bonded, the design of the joint, and the performance required.

The Different Types of Adhesives

There are several types of adhesives, including:

  • Chemical adhesives: These are adhesives that form a chemical bond with the adherend.
  • Physical adhesives: These are adhesives that rely on intermolecular forces to bond with the adherend.
  • Mechanical adhesives: These are adhesives that rely on mechanical forces to bond with the adherend.

The Main Techniques Used in Adhesion

The main techniques used in adhesion include:

  • Surface preparation: This involves preparing the surface of the adherend to ensure good adhesion.
  • Adhesive application: This involves applying the adhesive to the surface of the adherend.
  • Joint design: This involves designing the joint to ensure good adhesion.

The Alternate Methods of Adhesion

There are alternate methods of adhesion, including:

  • Welding: This involves melting the metal to form a bond.
  • Soldering: This involves using a metal alloy to bond two metals together.
  • Mechanical fastening: This involves using screws, bolts, or other mechanical fasteners to join two components.

Adhesive Materials: The Sticky Truth

  • Adhesive materials can be divided into two primary types: natural and synthetic.
  • Natural adhesives are produced from organic materials, while synthetic adhesives are made from chemical compounds.
  • Examples of natural adhesives include glue made from animal protein, starch-based glue, and adhesives made from natural rubber.
  • Synthetic adhesives include polymer-based adhesives, hot melt adhesives, and solvent-based adhesives.

Storage and Shelf Life of Adhesive Materials

  • Adhesive materials should be stored in a cool, dry place to prevent them from drying out or becoming too sticky.
  • The shelf life of an adhesive material will depend on its composition and the way it was processed.
  • Some adhesive materials, such as hot melt adhesives, have a shorter shelf life than others and may need to be used within a certain amount of time after they are produced.
  • In general, adhesive materials that are stored for longer periods of time may require additional processing or mixing to ensure that they are still suitable for use.

Putting It All Together: Applying Adhesives

When it comes to choosing the right adhesive for a specific application, there are a number of factors to consider. These include:

  • The materials being bonded
  • The desired degree of bonding strength
  • The size and area of the bond
  • The dynamic forces that the bond will need to withstand
  • The desired shelf life of the bonded components

Different types of adhesives are designed to perform well under different conditions, so it’s important to choose the right one for the job. Some common types of adhesives include:

  • Solid adhesives, which are applied in a molten state and then solidify as they cool
  • Liquid adhesives, which are applied in a wet state and then set or cure to form a bond
  • Pressure-sensitive adhesives, which are designed to bond on contact with a surface
  • Contact adhesives, which are applied to both surfaces and then allowed to dry before being bonded together
  • Hot melt adhesives, which are melted and then applied to one surface before being bonded to the other

Applying Adhesives

Once you’ve chosen the right adhesive for your application, it’s time to apply it. The following steps are generally followed when applying adhesives:

1. Prepare the surfaces: The surfaces to be bonded should be clean, dry, and free of any contaminants that could prevent the adhesive from bonding properly.

2. Apply the adhesive: The adhesive should be applied according to the manufacturer’s instructions. This may involve spreading it evenly over one surface, applying it in a specific pattern, or applying it to both surfaces.

3. Join the surfaces: The two surfaces should be joined together while the adhesive is still wet. This may involve aligning them carefully or applying pressure to ensure a strong bond.

4. Allow the adhesive to set: The adhesive should be allowed to set or cure according to the manufacturer’s instructions. This may involve leaving it to dry naturally or applying heat or energy to speed up the process.

Testing Adhesive Performance

Once the adhesive has been applied and allowed to set, it’s important to test its performance. This may involve measuring the strength of the bond, testing its ability to withstand dynamic forces, or checking its ability to prevent filleting (the spreading of adhesive beyond the desired bond line).

There are a number of methods that can be used to test adhesive performance, including:

  • Tensile testing, which measures the force required to break the bond
  • Shear testing, which measures the force required to slide the bonded components apart
  • Peel testing, which measures the force required to peel the bonded components apart
  • Dynamic testing, which measures the ability of the bond to withstand repeated stresses and strains

How Long Can Your Adhesive Last? The Shelf Life of Adhesives

Several factors can affect the shelf life of adhesives, including:

  • Storage conditions: Adhesives should be stored in a cool, dry place to prevent changes in their chemical composition. Exposure to moisture, heat, or direct sunlight can cause adhesives to degrade more quickly.
  • Material composition: The composition of an adhesive can affect its shelf life. Some adhesives contain antioxidants or UV stabilizers to improve their stability over time.
  • Aging: Over time, adhesives can age and lose their physical properties, such as flexibility or strength. Aging can be accelerated by exposure to heat, moisture, or chemicals.
  • Temperature: Adhesives can be sensitive to temperature changes. Extreme temperatures can cause adhesives to become too thick or too thin, affecting their ability to bond.
  • Testing: Manufacturers conduct studies to determine the shelf life of their adhesives. These studies involve testing the adhesive’s bond strength over time to determine when it begins to degrade.

Expiration Date and Recommended Use

Manufacturers typically provide an expiration date for their adhesives, after which the adhesive should not be used. It is important to follow the recommended use and disposal guidelines to ensure that the adhesive remains stable and chemically safe. Using expired adhesives can result in a weaker bond or even failure of the bond altogether.


So, that’s what adhesives are and how they work. They’re a pretty useful thing to have around, and you should know a little more about them now. 

You can use adhesives for everything from construction to bookbinding, so don’t be afraid to use them. Just make sure you’re using the right kind for the job and you’ll be fine.

I'm Joost Nusselder, the founder of Tools Doctor, content marketer, and dad. I love trying out new equipment, and together with my team I've been creating in-depth blog articles since 2016 to help loyal readers with tools & crafting tips.