In order to explain what adhesive is made of, we must repeat two of your favourite subjects from school: physics and chemistry. But don't worry: afterwards, you will be very well informed about adhesives and their mixture. And you'll be rewarded by a plate of spaghetti on top of it.
What do spaghetti and adhesive have in common?
Technologies
Adhesives: how mixture and chemical structure determine properties and areas of application.
The balance between tack, cohesion, and adhesion determinates the application field
Lesson 1: Physics
From a physical point of view, three forces impact the properties of an adhesive. Besides the what is known as the tack of the adhesive (stickiness), there is the adhesion ("bond to surface") and the cohesion ("inner bond" of the adhesive). These forces ensure that two things can be firmly connected to each other – and determine how quickly, solidly and long it takes for things to adhere to each other. When it comes to the composition of an adhesive, the last force is the most interesting of all: cohesion. That is because this involves how firmly and stably an adhesive sticks to itself. And that leads us straight to our second favourite subject.
Lesson 2: Chemistry
What is the chemical composition of adhesives and adhesive tapes? The cohesion forces of an adhesive are based on molecular interactions between what are known as polymers. Polymers are large molecules (macromolecules) that are composed of many smaller molecules (monomers). "Poly" stands for "multiple", "mono" for "single". They are components of an adhesive.
Polymers in turn form long-drawn, moving chains of molecules. Above a certain length, these get tangled up in each other and produce the inner cohesion of the adhesive. Now it is time for your promised reward: if you look at these tangled-up chains of molecules under a microscope, the adhesive looks like a large pile of spaghetti.
Between the bonding points, these long chains of molecules are in motion. This lets the adhesive flow well over the surface and bond there. At the same time, it is possible to create other solid bonds between the chains by means of chemical processes. We call this "reacting" or "polymerization". By this the adhesive properties can be adjusted and precisely controlled. That's how it is with adhesive – a mixture that is worth taking a deeper look at.
Ingredients of natural rubber adhesives: rubber, resins, fillers.
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The chemical structure of synthetic rubber adhesive shows a Rubber Matrix (grey) that provides adhesion and elasticity. The long polymer chains are tangled up together like spaghetti on a plate. Polystyrene Domains (blue) provide additional cohesion and tear resistance.
