Modularity means flexibility. Simply combining a small number of different elements in different ways can result in a huge variety of finished components. With its Flextec® prepolymers, Henkel has created a modular system that can be used to make many different kinds of products, ranging from sealants to adhesives. Flextec® is a high-performance, solvent- and isocyanate-free binder that is exempt from hazard labeling. Using this basic technology, the product developers design the building blocks for polymers, one of the main components among the 10 to 15 different constituents of adhesives and sealants.
The basic structure of the polymers is relatively simple. Highly reactive silicon groups, also known as silane compounds, are docked onto the ends of polyether chains of different lengths. By modifying the chain structure, the adhesives researchers obtain products with, in some cases, fundamentally different characteristics.
The longer the chains are, the more elastic the product will be. Technically, the elasticity of a material is expressed as a value called the modulus of elasticity. A high value means that the product is not very elastic at all. Such materials are suitable for making adhesives. Materials with a low elasticity modulus, i.e. the more elastic ones, are used in sealants. The number of chain branches, on the other hand, affects product strength. The more branched the chain, the stronger the product.
The scientists control the speed at which adhesives and sealants react and cure by varying the molecule types – methoxy groups, for instance – linked to the silane compounds at the ends of the chains. An assembly adhesive, for example, has to hold immediately if the user wants to do something like bonding a shelf to a wall. A parquet adhesive, on the other hand, is designed to allow the flooring specialist to make corrections for some time during the installation process.
Modular system with Henkel know-how
Further components, or additives, in adhesives and sealants include fillers, which determine the mechanical properties and consistency of the product. The addition of UV-stabilizers makes the products resistant to solar radiation. Working on the modular principle, the specialists put together the components as required to achieve the desired product characteristics. Henkel’s special expertise lies in selecting the relative quantities of these components and their particular chemical compositions.
Advantages over polyurethanes and silicones
Products based on Flextec® technology have properties that are much the same as those of polyurethanes and silicones – but without their drawbacks. For instance, the polymers also adhere to almost all substrates, but have a far greater UV stability compared to polyurethanes, making them suitable for outdoor applications, too. They also adhere extremely well to damp substrates, can be painted and bonded over, are compatible with paints and coatings, and are detachable. They do not become brittle at low temperatures, i.e. they exhibit what the experts call “cold flexibility.” The products contain neither solvents nor isocyanate and, as one-component systems, are extremely user-friendly.
Also suitable for problem applications
Moreover, these innovative products can be used wherever polyurethanes or silicones fall short – in particularly difficult bonding situations such as the underwater sealing of fire protection pond liners or swimming pools. Other possible applications for these products include sealing problems in cold storage units or liquefied gas tanks.