As the name suggests, instant adhesives stick instantly, and to almost anything. Chemically, they are based on cyanoacrylate building blocks. The building blocks are in fact monomers – highly reactive single molecules that combine together in a process known as polymerization to form the cured (hardened) adhesive. The tiniest traces of moisture are all it takes to trigger this reaction at lightning speed. And the only way to prevent cyanoacrylate adhesives from reacting directly in the tube or bottle is to add special stabilizers. Although conventional instant adhesives are highly versatile, they do have their limitations. They tolerate very little moisture, and tend to be brittle and break easily on impact. This is why standard instant adhesives are best used for bonding rigid small parts.

Rubber-toughened
Rubber-like polymers, known as elastomers, have precisely the properties that cured cyanoacrylates lack: toughness and elasticity. Mixing with elastomers produces high-performance adhesives with outstanding mechanical properties such as high impact strength. Until now, however, such mixtures have not been possible for instant adhesives. “The big advantage of instant adhesives is their speed of reaction, but it is precisely this speed that presents the biggest challenge here,” explains a development expert at Henkel in Dublin, Ireland. There is hardly a substance that doesn’t either trigger polymerization or impair bonding properties. Searching for a suitable elastomer is like looking for a needle in a haystack. Nevertheless, working in cooperation with an elastomer manufacturer, Henkel researchers found a substance that is compatible with cyanoacrylates. This made it possible to develop the first flexible instant adhesive.

A rubber-toughened instant adhesive for all
Building on experiences with the flexible instant adhesive for industrial customers, the international team has been working intensely since September 2006 on the first rubber-toughened instant adhesive for household use. Compared with the industrial product Loctite 435, which is produced in relatively small quantities, this means roughly 40 times the product volume. It also calls for totally different production technologies. The pure elastomer is supplied in sticky 25-kilogram blocks – in a consistency similar to that of candied lemon peel. Cutting it is virtually impossible, as it sticks back together again just as fast.
To make it at all possible to mix the elastomer with the liquid adhesive, the researchers had to develop a new processing method.
The outcome is impressive: The product will be the first clear rubber-toughened instant adhesive gel with outstanding flexibility and impact and peel strength for DIY enthusiasts and home improvers. It also features exceptionally high moisture resistance for an instant adhesive.

Learn more here about an instant adhesive for the skin.

Overcoming limitations: Getting previously incompatible raw materials to blend with each other makes it possible to add completely new properties to such well-known products as instant adhesives.