Sikaflex-221 Black Multi-Purpose Polyurethane Adhesive/Sealant – 300 mL for Flexible Bonding
Sikaflex-221 is a multi-purpose, one-component polyurethane adhesive and sealant from Sika, providing flexible, paintable bonding and sealing on metal, plastic, glass, and painted surfaces in aerospace, automotive, and marine applications. Its one-component moisture-cure system eliminates mixing, providing immediate application from the cartridge with no preparation beyond clean surface handling.
As both an adhesive and a sealant, Sikaflex-221 delivers dual functionality — it bonds components while simultaneously sealing the joint against moisture, air, and dust ingress. This dual function simplifies assembly operations by eliminating the need for a separate sealant application step after structural adhesive bonding, reducing material usage and assembly labor in production and MRO operations.
The cured Sikaflex-221 polyurethane film is flexible, paintable, and resistant to UV degradation, making it suitable for exterior aerospace and automotive applications where the adhesive joint may be overcoated with topcoat paint as part of the final surface finish system. The 300 mL cartridge provides a practical volume for moderate-scale bonding and sealing operations using standard cartridge gun equipment.
| Attribute | Detail |
|---|---|
| Manufacturer Part Number (MPN) | 96893 |
| Brand | Sika |
| Product Name | Sikaflex-221 |
| Color | Black |
| Product Type | One-Component Polyurethane Adhesive/Sealant |
| Package Size | 300 mL Cartridge |
| Cure Type | Moisture Cure — Room Temperature |
| Substrate Compatibility | Metal, Plastic, Glass, Painted Surfaces |
| Application Method | Standard Cartridge Gun |
| Industry Use | Aerospace, Automotive, Marine, MRO |
Technical Information
Sikaflex-221 is based on a moisture-reactive prepolymer polyurethane chemistry that cures progressively from the exposed surfaces inward as atmospheric moisture penetrates the adhesive bead. The moisture-cure reaction converts the prepolymer into a fully crosslinked polyurethane elastomer with excellent flexibility, adhesion, and environmental resistance properties. Cure rate is temperature and humidity dependent — higher temperature and humidity accelerate cure, while low temperature and dry conditions slow it.
Polyurethane adhesives like Sikaflex-221 provide a fundamentally different performance profile from epoxy adhesives — polyurethane cures are flexible and remain elastic, accommodating joint movement, vibration, and thermal cycling without cracking or losing adhesion. This elastomeric behavior makes polyurethane adhesives the preferred choice for joints between dissimilar materials with different coefficients of thermal expansion, and for bonding components subject to dynamic loading during service.
The paintability of cured Sikaflex-221 is a significant advantage for aerospace and automotive exterior applications where the bonded joint is overcoated with primer and topcoat paint as part of the surface protection system. The cured polyurethane surface accepts paint adhesion without requiring special primers in most cases, enabling a smooth, continuous painted surface over the adhesive joint.
Why Choose Sikaflex-221?
- ✅ Dual Adhesive and Sealant — Bonds and seals simultaneously in one product
- ✅ Paintable — Topcoat compatible for exterior aircraft finish systems
- ✅ Flexible Cure — Accommodates joint movement, vibration, thermal cycling
- ✅ One-Component — No mixing required, immediate cartridge application
- ✅ Multi-Industry Trusted — Sika’s globally proven adhesive/sealant brand
Applications
Sikaflex-221 is used for aircraft fairing bonding, exterior panel edge sealing, access panel bonding, automotive body sealing, marine hull joint sealing, and general industrial bonding applications requiring a flexible, paintable polyurethane adhesive/sealant.
Frequently Asked Questions
Q: What is Sikaflex-221 used for?
A: Sikaflex-221 is a multi-purpose polyurethane adhesive/sealant used for flexible bonding and sealing of metal, plastic, and glass in aerospace, automotive, and marine applications. It bonds components while simultaneously sealing the joint.
Q: What is the MPN for Sikaflex-221 300mL black?
A: MPN is 96893.
Q: Can Sikaflex-221 be painted over?
A: Yes. Cured Sikaflex-221 is paintable and compatible with standard aerospace and automotive primer and topcoat systems, allowing the adhesive joint to be overcoated for a smooth, continuous painted surface.
Q: How long does Sikaflex-221 take to cure?
A: Sikaflex-221 cures by reaction with atmospheric moisture at room temperature. Cure rate depends on temperature and humidity — refer to the Sika TDS for tack-free time and full cure schedule at your specific conditions.
Q: Is Sikaflex-221 flexible after cure?
A: Yes. Sikaflex-221 cures to a flexible polyurethane elastomer that accommodates joint movement, vibration, and thermal cycling without cracking — unlike rigid epoxy adhesives.
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