Why Adhesive is Sticky?

According to the record, Egyptians used natural glue made from animal collagen since 5000BC. In modern times, we use glue to stick things together. Have you ever wondered what is the secret inside?

Behind the Stickiness of An Adhesive

To put it briefly, Adhesive is sticky because of the interaction of adhesives and substrates.

Adsorption Theory

The adsorption theory explains the phenomenon of adhesion based on the Hydrogen bond and Van Der Waals forces that develop between molecules. This concept has relative to contact angle, wet ability, and surface tension.

One point is the hydrogen bonding, it is between water molecules, allow the liquid to resist low levels of external force. The other is Van Der Waals forces, all materials are composed of positively charged and negatively charged electrons. When the positive and negative electric distribution inside these materials is uneven, it will become the polar material. When two polar materials are close to each other, the phenomenon occurs, the glue molecules stick to the surface molecules like millions of microscopic magnets. On the opposite, Van der Waal’s forces are weak attractions between molecules that may not normally have positive or negative charges. Therefore, different purposes need different adhesives. Highly polar materials such as metal and paper (fiber) are easily to be adhesive, while relatively low polarity materials such as PE and PP must use the special adhesive.

Mechanical & Anchor Theory

The mechanical theory is an important element of adhesion. It is linked to the surface of substrate roughness or not and the porosity.
If you take the observation of every material at the microscopic level the surface will be composed of valleys and ridges, so it may allow the adhesive to fill the valley. And then it will become the “anchorage areas” between the adhesive and substrate.

Therefore, the adhesion method will be better on the rougher surface or the contact area is larger.
In sum, none of the adhesives is a cure-all to all materials. In Chemix Guru, our R&D team develops different adhesives to reach the best adhesion on each substrate. Our product line includes pressure-sensitive, polyurethane, PVAc, etc. For more information please contact our expert.