Silicone Sealant Formulation: RTV-1 and RTV-2 Systems
title: "Silicone Sealant Formulation: RTV-1 and RTV-2 Systems" description: "How one-part (RTV-1) and two-part (RTV-2) silicone sealants are formulated from base polymer, filler, crosslinker, and catalyst—and how formulation choices drive construction and automotive performance." section: "midstream"
RTV-1 vs. RTV-2 Architecture
Room-temperature-vulcanizing (RTV) silicone sealants cure without heat. The two system types differ in how cure is initiated:
RTV-1 (one-part, moisture-cure): The base, crosslinker, catalyst, and filler are pre-compounded in a sealed cartridge. Cure begins when the sealant contacts atmospheric moisture after application. The crosslinker hydrolyzes and releases a byproduct:
- Acetoxy-cure (acetic acid byproduct): Fast cure, strong adhesion to glass and metals; unsuitable for marble, copper, or electronics (acid attack)
- Alkoxy-cure (methanol or ethanol byproduct): Neutral, no corrosion risk; preferred for construction, electronics, and sensitive substrates
- Oxime-cure (methyl ethyl ketoxime byproduct): Intermediate reactivity; widely used in automotive glazing
RTV-2 (two-part): Base and crosslinker are stored separately and mixed immediately before use. Cure is either condensation (tin-catalyzed) or addition (platinum-catalyzed). RTV-2 addition-cure gives no byproduct, cures at controlled depth regardless of section thickness, and is preferred for mold-making and electronics potting.
Key Formulation Components
| Component | Function | Typical Material |
|---|---|---|
| Base polymer | Backbone; sets elongation and modulus | 107 gum (hydroxyl PDMS, 10,000–100,000 cSt) |
| Reinforcing filler | Tensile strength, tear resistance | Fumed silica (7–20 phr) |
| Extending filler | Reduce cost, adjust viscosity | Precipitated silica, CaCO₃ |
| Crosslinker | Cure architecture | TEOS, MTES (alkoxy); acetoxy silane |
| Catalyst | Cure rate control | Dibutyltin dilaurate (condensation); Pt complex (addition) |
| Plasticizer | Elongation, flow | Low-MW PDMS (50–500 cSt) |
| Adhesion promoter | Bond to substrate | Silane coupling agent (KH-560, A-1120) |
| Pigment | Color | TiO₂ (white), carbon black, inorganic oxides |
Construction and Performance Properties
Construction-grade RTV-1 alkoxy sealants must meet:
- Elongation at break: >400% (ISO 37)
- Shore A hardness: 15–35 (soft, flexible joint seal)
- Movement accommodation: ±25% of joint width
- UV stability: No yellowing after 1,000 h QUV exposure
Automotive FIPG (formed-in-place gaskets) use oxime-cure RTV-1 with higher adhesion to metals and resistance to engine fluids. Electronics-grade RTV-2 (addition-cure) requires halogen-free formulation and UL 94 V-0 flame rating.