Wacker Using Pyrogenic Fumed Silica in Wind Turbine Adhesives for Easier Processing
WACKER reports that its pyrogenic silica, manufactured under the brand name HDK®, has pronounced thixotropy and shear-thinning effect provided by pyrogenic fumed silica, which allows easy processing of adhesive components even at high silica loading levels. The company attributes their success to its integrated production system, statistical process control, and highly efficient reactor dynamics. The pyrogenic silica through hydrolysis of chlorosilane in an oxygen-hydrogen flame. The process yields highly branched aggregates when, upon cooling, they form weakly bound agglomerates, which make up the basic structure of pyrogenic silica. Pyrogenic silica made in the flame reactor is hydrophilic in nature. By post-treatment in a second reactor, WACKER offers hydrophobic pyrogenic silica grades. Hydrophobic grades can be used to control rheology in polar systems. WACKER’s pyrogenic silica has an exceptionally high surface area-to-mass ratio, which facilitates multiple particle interactions in liquid formulations, thereby building a three-dimensional physical network. WACKER’s HDK® is the basis for the rheology control of pyrogenic silica. Obtaining the desired rheology for an adhesive depends on selecting the specific surface area based on the desired specifications and using the correct hydrophilic or hydrophobic pyrogenic silica grade. To create strong thixotropy it is typical to combine opposite polarities provided by pyrogenic silica and the formulation (resin and solvent).
Wind turbine bonding pastes are typically based on epoxy and vinyl ester resins that are applied in thick beads onto half-shells of the rotor blade. WACKER reports that by adding its pyrogenic silica to bonding paste formulas enables optimal rheology control to meet the demanding requirements for sag resistance. The pronounced thixotropy and shear-thinning effect provided by pyrogenic silica allows easy processing of adhesive components even at high silica loading levels (~5 – 10 wt% loadings). Moreover, pyrogenic silica increases the viscosity of adhesive components during storage and prevents settling. Pyrogenic silica is a versatile solution through various adhesive systems enabling high-level performance.
HDK® H18 is a pyrogenic silica grade that exhibits high hydrophobic properties and performs well in polar formulations such as vinyl ester or epoxy-based adhesives requiring high rheological impact. In addition, it also provides excellent storage formulation stability. This grade is recommended for first-pass evaluation. HDK® H17 is another excellent alternative to facilitate improved dispersion. HDK® H17 displays well-balanced features and is particularly easy to disperse. As shown below, the use of hydrophobic silica provides excellent rheology. Interactions of the polar HDK® N20 with the polar resin have a weak thixotropic effect on the formulation. Whereas the non-polar HDK® H17 particle exhibits a strong thixotropic effect up to 28 days at room temperature.
Source: WACKER