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Resin Modification

With its range of additives, co-catalysts and process auxiliaries for use in high- and low-temperature processes, WACKER is ideally placed to provide comprehensive advice and overarching formulation competence, as well as technical support for all the major resins used in thermoset composites, such as unsaturated polyesters (UP), vinyl esters (VE), phenolics, epoxies (EP), melamines or polyurethanes (PU).

Due to electrostatic interactions, HDK® dispersed in resin formulations creates a three-dimensional network, which can increase viscosity up to gel-like consistency. Under shear, e.g. in the application phase, the network collapses so that the viscosity decreases sharply (shear thinning). At rest (e.g. after application), the HDK® network rebuilds and the viscosity increases again (thixotropy).

HDK® pyrogenic silica is used to control the flow behavior of liquids. It imparts shear-thinning and thixotropic effects to resin formulations, ensuring good fiber-wetting and impregnation properties during application. As a component of gelcoats, HDK® provides optimum thixotropic characteristics, thereby preventing sagging.

With its broad, application-specific product portfolio of hydrophilic and hydrophobic HDK®, WACKER has a tailored solution for almost any composites formulation.


  • Adjustment of thixotropic properties
  • Easy processing of gel coats
  • No sagging of the wet film
  • Stable viscosity of formulations during storage
  • Prevention of separation effects
  • Prevention of settling of pigments and filler sedimentation


  • Infusion
  • Hand lay-up
  • Spray-up techniques
  • Filament winding
  • Manufacture of
    • Composite stone
    • Laminating resins
    • Gel coats
    • Topcoats

VINNAPAS® solid resins (polyvinyl acetate) reduce the customary shrinkage of unsaturated polyesters (UP) and vinyl ester (VE) resins from 5 % to less than 0.05% This leads to consistently high product quality and extremely smooth, homogeneous surfaces. VINNAPAS® resins are available as carboxylated and carboxyl-free grades and in a wide range of viscosities. They dissolve readily in styrene and (meth)acrylic monomers; solutions can even be produced at room temperature. VINNAPAS® can therefore be used in a wide variety of formulations and processes.


  • Reduction of shrinkage to less than 0.05% for Class-A surfaces
  • Excellent gloss and surface smoothness
  • Good mechanical properties
  • Thickening effect in SMC applications
  • Fast and complete dissolution in styrene and (meth)acrylic monomers
  • Ease of processing


Manufacture of composites by

  • SMC
  • BMC
  • RTM
  • Pultrusion
  • Infusion

GENIOSIL® silanes bond organic and inorganic parts of composite stone chemically thus increasing the mechanical properties.

Composite stone comprises a blend of unsaturated polyester resins and minerals. The addition of silanes of the GENIOSIL® line produces a chemical bond between the organic resin and the inorganic mineral. At the same time, the mechanical strength is efficiently increased: Only 1% of GENIOSIL® is enough to transfer the strength of the hard, inorganic system to the soft, organic system.


  • Chemical bond between resin and fillers
  • Improved mechanical properties
  • Greater flexural strength


  • Manufacture of Composites by Prepreg Process
  • Manufacture of Composite Stone