Everyone probably knows natural rubber. 70 percent of all car tyres have natural rubber. It is also in condoms, gloves and air balloons. As well as in masking, packaging and other kinds of adhesive tape. That is because bonding using natural rubber really works. And really well, too.
Can I seal my parcel with milk?
The science behind tapes, Adhesive tape components
Sometimes adhesive grows on trees: Natural rubber and its properties are very special – so it is often used for adhesives.
You may at first be amazed to hear that you can even use natural rubber as glue. This possibility exists as a pure, natural product extracted from the milk (latex) of the rubber tree (Hevea brasiliensis). And although latex does not on the whole glue, it has very unique qualities: its special chemical structure gives it outstanding components for adhesives.
The reason: natural rubber consists in particular of long polymer chains. If it is mixed with resin (to make it sticky), you get an adhesive that is extremely flexible due to the length and mobility of these polymer chains. Adhesive tapes with natural rubber profit from these natural rubber properties: the adhesive remains mobile at low temperatures where other substances would become solid and brittle. And the entangling of the polymer chains produces a high inner solidity for the adhesive mass.
The type of rubber used, the compounded resins, and other ingredients determine the performance of the natural rubber adhesive. In general, natural rubber properties offer many advantages for adhesive tape applications. The first of these is its outstanding peel adhesion or “grab” – not only on polar surfaces but even on substrates with low surface tension ("non-polar substrates").
Peel adhesion is defined as the force needed to “peel” an adhesive tape from any given surface, whether flexible, smooth, or rigid. The attachment time required until it achieves its final tack is very short (low dwell time). Furthermore, adhesive tape with natural rubber adhesion can be removed easily and does not leave any trace, for example in the case of masking tape.
Finally there is the high tack, i.e. stickiness, of the adhesive: the adhesive tape glues with minimal pressure and minimal contact time. The rubber tree's latex makes the adhesive tape "faster". That explains why natural rubber adhesive tape and adhesives are often used and popular, and why they are found in and for a large number of applications – from cloth tape to packaging tape. And that is why many adhesive tapes that safely seal our packages contain milk from the rubber tree.
The special chemical structure also entails some disadvantages, however: the adhesive in natural rubber glue or adhesive tape has a limited amount of adhesion and cohesion at temperatures above 70° C, requires stabilizers to resist ageing and the environment in the event of UV and ozone exposure, and is not very resistant to chemicals and solvents.