Surface Blooming: Is that White Powder on your Rubber Part a Defect?
Problem Statement
A white powdery residue (blooming) appears on EPDM rubber seals after 72 hours of heat aging at 150°C. The customer suspects material degradation, but the root cause is likely unreacted curing agents migrating to the surface.
Material Science Analysis
- Primary Cause: Excess sulfur or stearic acid in the compound migrates to the surface during post-cure cooling.
- Molecular Mechanism: Low solubility of curatives in EPDM at room temperature forces phase separation. The issue worsens with high-temperature cycling.
- Solution: Reformulate with peroxide curing (no sulfur) or optimize accelerator-to-sulfur ratios. RubberQ’s in-house compounding adjusts curative dispersion at the 0.5-1.2 phr level.
Technical Specs
- Material: RubberQ EPDM-700 (Peroxide-Cured)
- Shore A Hardness: 70 ±5
- Tensile Strength: 12 MPa (ASTM D412)
- Elongation at Break: 350%
- Temperature Range: -40°C to +175°C continuous
- Compression Set: 22% (70h at 150°C, ASTM D395)
| Parameter | EPDM-700 (Peroxide) | EPDM-600 (Sulfur-Cured) | FKM-800 (Fluorocarbon) |
|---|---|---|---|
| Blooming Risk | None | High (Grade 3 per ASTM D2000) | Low |
| Chemical Resistance (ASTM Oil #3, 70h) | Volume Change +8% | Volume Change +12% | Volume Change +2% |
| Adhesion to Steel (ASTM D429) | 15 kN/m | 12 kN/m | 18 kN/m |
| Cost Index | 1.0x | 0.7x | 3.2x |
Standard Compliance
RubberQ’s IATF 16949-certified process prevents blooming through:
- Pre-dispersion of curatives in a masterbatch (A炼 stage)
- Rheometer testing (ASTM D5289) to confirm complete crosslinking
- 72-hour heat aging QA per ISO 188 before shipment
For custom material compound development or IATF 16949 documentation, consult RubberQ’s engineering department.
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