Ever wondered what exactly makes the sticker label on a product stick to a surface for so long without coming off? Or what exactly makes the adhesive tape sticky? The immediate answer is of course, adhesion. But like you are about to find out, there is a whole complex chemical and physical process that makes adhesives sticky. The concept has been studied for so long in a bid to come up with effective sticker labels that make use of eco-friendly and non-toxic adhesive properties. To better understand how the process works, one must first look at the chemical composition of adhesives.
The Chemical Aspect
When it comes to adhesion, polymers play a crucial role. They are simply pressure sensitive adhesives which are naturally sticky and tacky because they feature highly viscous liquids that have elastic characteristics. In other words, they are not only highly viscous, they are also viscoelastic. This means they wet the surface on which they are pressed on.
Adhesion And Cohesion
It is impossible to understand how adhesives work without taking into account adhesion and cohesion. These two components cannot be separated. Adhesion is simply the force that binds two different materials while cohesion is the force that binds two similar materials. Each time two materials come in contact with each other, surface molecules interact and react. This may give rise to attractive forces that can be chemical, physical or electro-plastic.
Tapes and Stickers
There is a separate chemical that makes tapes and stickers work. When molecules are dissimilar in structure and composition, adhesive force holds together substrates. In simple words, the sticky nature of a tape is caused by a combination of molecular forces of glue material that sticks itself as it holds on to a substrate.
This is where acrylic and pressure sensitive adhesives come into the picture. Experts refer to this type of adhesion as specific adhesion or mechanical adhesion. It occurs when an adhesive flows into a substrate’s texture. This type of specific adhesion includes van der Waal’s forces as well as acid-base interactions which quickly happen between the substrate and the adhesive. The intensity of the bond grows stronger with time. This continuous strengthening of bonds and the increasing degrees of stickiness occurs solely because of the amount of time it takes for an adhesive to flow onto ad into a surface texture. It also occurs because of the adhesive polymer needs time to align with the surface so as to create interactions.
Point To Note
There is no reaction or chemical bonding between pressure sensitive adhesives and substrates. This is because pressure sensitive adhesives are sticky, viscous and liquid like materials that adhere to surfaces through pressure. To stick to a surface well, they should feature good adhesion and cohesion and in some instances internal strength. For optimum adhesion, an adhesive should readily flow onto a surface. The freeness or degree of a flow will ultimately determine the intensity of adhesion. Note that the degree of flow wholly depends on the difference between surface energy of material and the surface energy of an adhesive.