Silane Chemistry for Mineral Filled Plastics

Silanes are adhesion promoters that unite the different phases present in a composite material. These phases are typically organic resins (e.g. ethylene/ vinylacetate copolymer, EVA) and inorganic fillers (e.g. ATH) or fibrous reinforcements. Silanes form “molecular bridges” to create strong, stable, water-resistant and chemical-resistant bonds between two otherwise weak bonding surfaces.

The properties and effects of silanes are defined by their molecular structure. The silicon at the center is combined with the organofunctional group, Y, and the silicon-functional alkoxy groups, OR. The silicon-functional groups, OR, are hydrolyzed in the first stage of application,  liberating the corresponding alcohol.

The organofunctional group, Y, binds to the polymer by:

• chemical reactions such as grafting, addition, and substitution
• physico-chemical interactions such as hydrogen bonding, acid-base interaction, entanglement, or electrostatic attraction.

The fixation of the silanol on the filler surface is accomplished as a first step through hydrogen bonding with the surface OH group. Therefore, mineral substrates that provide a high OH group density show better reactivity towards silanes than others. Until the water molecule is split off and eliminated from the reaction site, this reaction is reversible. As long as there is only hydrogen bonding, the silane can still migrate on the filler surface. The covalent [silane-O-filler] bond finally fixes the silane on the filler surface. In theory, the silane forms a monolayer on the filler surface. In reality trialkoxysilanes condense with themselves to produce three-dimensional networks.

Mastering the Challenge

Dynasylan^® imparts unique, high-end properties to finished products. Reduced water up-take through hydrophobization and an improved melt flow ratio through better dispersion of the mineral in the polymer matrix can be achieved. Chemical coupling between the inorganic and the organic parts of a composite is the key and basis for improved dimensional stability, improved wet-out between the resin and the filler, and reduced viscosity through improved dispersion. Dynasylan^® keeps costs down by maximizing the throughput of high-value products.

• Improved viscosity
• Improved processing
• Increased output
• Improved dispersion
• Higher filler loading
• Improved cost efficiency

In many research and high-tech projects Dynasylan^® silanes are used. For example, the MAGLEV traction technology employed in the Transrapid uses cables manufactured with Dynasylan^® silanes to meet very specific requirements.