Methyl Ethyl Ketone (MEK, 99.5% min)
CAS 78-93-3Methyl Ethyl Ketone (MEK, 2-butanone, CAS 78-93-3) is a medium-evaporation ketone solvent used in composite fabrication for equipment cleaning, surface preparation, and as a co-solvent in specialty resin formulations.
Key Features
- ✓Slower evaporation than acetone — longer contact time for dissolving thick resin deposits
- ✓Stronger solvency than acetone — effective on wider range of resins and adhesives
- ✓Specified in aerospace composite repair procedures (MIL-SPEC, CMM) as cleaning solvent
- ✓Blends with acetone for optimized tool cleaner: fast initial attack + extended solvency
- ✓California CARB VOC-exempt — favorable for compliance in regulated applications
Specifications
| Parameter | Value |
|---|---|
| Purity | ≥99.5% by GC |
| Appearance | Clear, colorless liquid |
| CAS Number | 78-93-3 |
| Flash point | −9°C (ASTM D93) |
| Boiling point | 79.6°C |
| Water content | < 0.3% (Karl Fischer) |
| Density (20°C) | 0.805 g/cm³ |
| Relative evaporation rate | ~3.5 (n-BuAc = 1.0) |
FAQ
MEK is preferred over acetone in several situations: (1) When cleaning heavily loaded resin deposits (thick resin buildup on rollers, spray guns, mixing paddles) where acetone evaporates before fully dissolving the resin; (2) In hot environments (>30°C ambient) where acetone evaporates too quickly for effective cleaning contact time; (3) When cleaning surfaces for aerospace composite repair where MEK is specified by the aircraft manufacturer's CMM or MIL-SPEC procedures; (4) When cleaning partially gelated or green-cured UPR/VER where the stronger solvency of MEK is needed; (5) When lower flammability hazard than acetone is required (flash point −9°C vs. −18°C for acetone). Acetone remains preferred for routine high-volume cleaning due to its faster evaporation and lower cost per litre.