Surface Blooming: Is that White Powder on your Rubber Part a Defect?

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.