Silicone Defoamer for UPR / VER Systems
Key Features
- Rapid bubble collapse and air release in UPR/VER at 100–1000 ppm dosage
- PDMS mechanism: spreading on bubble surface, displacement of resin film
- Available in spray-up, casting, and infusion-optimized viscosity grades
- Low-migration grades prevent interlaminar adhesion problems in multiaxial laminates
- Reduces surface pinholes and internal void content in cured composite panels
Silicone Defoamer for UPR/VER Systems is a polydimethylsiloxane (PDMS)-based defoaming and air-release additive formulated for use in unsaturated polyester resin (UPR) and vinyl ester resin (VER) composite fabrication processes. Air entrainment during resin mixing, chopper gun spray-up, hand lamination, and RTM/VARTM infusion can cause surface defects and internal porosity in cured composites, reducing mechanical performance and cosmetic quality. Silicone defoamer at 0.01–0.1% (100–1000 ppm) loading rapidly breaks foam bubbles at the resin surface and promotes release of dissolved air from the resin mass before gelation.
PDMS-based defoamers work through a combination of mechanisms: low surface tension PDMS droplets spread onto bubble surfaces, displacing the stabilizing resin film and causing bubble collapse; simultaneously, the incompatible silicone phase acts as a defoam nucleant at the air-liquid interface. In UPR systems, silicone defoamers must be carefully balanced — too little provides inadequate defoaming, while excessive silicone can migrate to the composite surface during cure and cause interlaminar adhesion problems and fisheye defects in subsequent coats of paint or gelcoat.
Formulated grades are available for different UPR viscosity ranges (spray viscosity for chopper gun, infusion viscosity for VARTM) and cure temperatures. Some grades contain SiO₂ or silica hydrophobic particles to enhance defoaming efficiency in high-viscosity systems. For closed mold infusion processes (RTM, VARTM), low-migration grades are essential to prevent interlaminar delamination of multiaxial fiber preforms.
Specifications
| Parameter | Value |
|---|---|
| Appearance | Clear to slightly hazy liquid |
| Flash point | >61°C |
| Density (20°C) | 0.900–1.000 g/cm³ |
| Silicone content | 10–100% (depends on carrier) |
| Active ingredient | Polydimethylsiloxane (PDMS) with silica |
| Viscosity (25°C) | 100–2000 mPa·s (grade dependent) |
| Typical dosage in UPR | 0.01–0.1% by weight |
Applications
FAQ
Fisheye and cratering occur when PDMS migrates to the resin surface during cure and remains as silicone-rich patches that resist wetting by subsequent paint or gelcoat layers. When gelcoat or paint is applied over a silicone-contaminated surface, the high surface tension paint dewets from the low-surface-energy silicone, creating circular craters (fisheyes). Prevention requires: (1) using minimum effective dosage (start at 0.02%, increase only if needed); (2) using a silicone-compatible or low-migration grade; (3) post-cure surface preparation (light sanding) before painting over silicone-bearing composites.
Direct Contact
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