Wacker Presents Silane-Terminated Polymers for Flexible and Elastic Sealants and Adhesives

At the European Coatings Show 2017, Munich-based chemical group Wacker will be unveiling two new silane-terminated polymers: GENIOSIL XM 20 and GENIOSIL XM 25. They can be used as binders in adhesives and sealants, where they can modify the mechanical properties, in particular impacting modulus. This allows adhesives and sealants manufacturers to compound without the need of conventional plasticizers. In plasticizer-free adhesives, the new grades additionally enhance the bonding properties. In low-modulus sealants, they ensure high elastic recovery. As a result, GENIOSIL XM opens up applications in the adhesives and sealants sector that had previously been unaccessible to silane-crosslinking polymers. The European Coatings Show will be held in Nuremberg, Germany, from April 4 to 6, 2017.

The new grades complement the portfolio of silane-terminated polyethers that the Munich-based chemical group markets under its GENIOSIL brand. As all silane-terminated polymers, GENIOSIL XM cures at room temperature under the influence of atmospheric humidity via silane crosslinking. In contrast to the other polymers, GENIOSIL XM 20 and GENIOSIL XM 25 only have one silane group at one of their chain ends, meaning they are crosslinkable only at that end.

GENIOSIL XM can be blended with other silane-terminated polymers in the desired ratio. On curing, the new polymers are firmly integrated into the resulting three-dimensional polymer network, reducing the crosslink density. This leads to a relatively wide-meshed network.

GENIOSIL XM thereby modifies the elasticity of the cured material, resulting in a low modulus system with high elastic recovery. When stretched or compressed, it behaves like a soft spring. In formulations of silane-terminated polymers, the two new grades thus act as reactive plasticizers. Since they do not alter the mechanical strength of the cured material, they can replace conventional plasticizers. This affords manufacturers of sealants and adhesives the freedom to formulate plasticizer-free products.

The two GENIOSIL XM grades not only adhere to concrete, wood, aluminum and glass, but also to low-energy surfaces such as polyvinyl chloride (PVC), polystyrene (PS) and cured ethylene propylene diene monomer (EPDM) rubber without prior pretreatment of these substrates.

GENIOSIL XM 20 is an alpha-silane-terminated polyether. This grade opens the door to plasticizer-free adhesives with extremely high elasticity. At the same time, these possess high ultimate strength and also adhere well to difficult substrates. Furthermore, the product can extend skin-over time. This provides the user with sufficient adhesive tooling time. Typical applications include wood-flooring adhesives and all-round adhesive sealants.

GENIOSIL XM 25, a gamma-silane-terminated polyether, allows the formulation of low-modulus sealants with exceptionally high elastic recovery. Should sealant manufacturers use this grade as a co-binder, low-modulus construction sealants that exceed ISO 11600 specifications are possible. Potential applications include sealants for expansion joints in buildings made of industrially prefabricated concrete parts and for connection joints between window frames and walls.

Wacker offers various silane-terminated polyethers that have been designed as binders for adhesive and sealant manufacture. They can be blended with each other acting either as the main binder or as a co-binder. This allows formulators to use the product portfolio like a toolbox to adjust the desired final properties of given products. Both gamma- and alpha-silane-terminated polyethers are available.

Within this portfolio, the hybrid polymers of the GENIOSIL STP-E product line constitute the standard. They cover a wide range of demanding adhesive and sealant applications. GENIOSIL XB is ideal for the manufacture of powerful and tough adhesives which make strong bonds possible. If, on the other hand, exceptionally strong yet elastic adhesives need to be formulated, polymers of the GENIOSIL XT range are the binders of choice. GENIOSIL XM is suitable for low-modulus sealants or flexible, highly elastic adhesive sealants with virtually universal adhesion.