SEM-EDS
Examine particle morphology and elemental composition.
FindingIrregular surface particles contained zinc, sulphur and oxygen, linking the deposits to the zinc-containing cure system.
NBR Seal Bloom: White Powder Investigation
A multi-technique investigation linked white surface deposits on moulded NBR seals to zinc-bearing bloom rather than external contamination.
Project context
Background and technical challenge.
A rubber products manufacturer observed irregular white powder deposits on newly produced NBR seals. Cleaning improved appearance temporarily, but the deposits reappeared and affected product appearance and sealing performance.
The challenge
The team needed to distinguish external contamination from additive migration, unreacted inorganic components, curing by-products or poor dispersion within the compound.
Analytical approach
Each method answered a different technical question.
XRD
Identify the crystalline phases behind the elemental signals.
FindingThe deposit was identified as a mixture of zinc sulphide (ZnS) and zinc oxide (ZnO).
TGA & process review
Relate inorganic residue to the NBR compound and curing conditions.
FindingThe residue pattern aligned with zinc oxide in the formulation and pointed to a combined formulation, dispersion and curing-control issue.
Root-cause conclusion
The evidence supported rubber bloom: excess or insufficiently dispersed zinc oxide interacted with the sulphur cure system, while process conditions increased the likelihood of zinc-bearing material accumulating at the surface.
Recommended next steps
- Reduce ZnO dosage through controlled formulation trials.
- Improve ZnO dispersion and review surface-treated nano-ZnO as an evaluation option.
- Rebalance the zinc oxide and stearic acid activation system.
- Use a more controlled two-stage curing approach and strengthen mixing and degassing.
Documented project outcome
- The customer adjusted zinc oxide level, dispersion practice, curing-system balance and process controls.
- The white-powder issue was resolved in the completed NBR seals.
- The finished parts showed cleaner, more uniform surfaces and improved production stability.
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