Outgassing

Most rubber compounds contain small quantities of oil and other ingredients that will become volatile under vacuum conditions. Evidence of this "outgassing" is apparent as a thin film deposited on surrounding surfaces. Optical and electrical contact applications are of special concern in this situation as they incorporate sensitive surfaces that must remain uncontaminated.

Post-Curing
To maintain purity and tight contamination control, a bake-out or post-cure process with elastomeric compounds such as Fluoroelastomer (Viton®), Fluorosilicone, and Silicone prior to service is necessary. Post-curing induces both physical and chemical changes and achieves two crucial objectives:

  • Removal of unwanted and residual volatiles
  • Stabilization of the physical properties by increasing the degree of crosslinking

Best Choice of Applications
The following are examples of applications for post-cured elastomeric compounds:

  • Vacuum seals for the aerospace industry
  • O-rings for optical sights used for application down to -40°C
  • Housing seals in electronics

Note: One big issue with electronic components is corrosion derived by sulfurous compounds outgassed from sulfur cured rubber compounds. Peroxide cured EPDM can be used to prevent the release of sulfur for seals used in electronics.

ASTM E595 Outgas Testing

We have completed outgas testing for three (3) compounds: Fluorosilicone, standard Fluoroelastomer, and an ultra low temp Fluoroelastomer with standard post-cure and vacuum post-cure.

In compliance with ASTM E595-07 testing, each sample was heated to 1°C at a vacuum of 5 x 10-5 torr for 24 hours. Industry standards for acceptable outgassing levels are: a total mass loss (TML) cannot exceed 1.00% and collected volatile condensable material (CVCM) cannot exceed 0.10% of the original specimen mass.

Note: Screening levels of 1.00% TML and 0.10% CVCM are also used by the space industry to select materials for space flight.

Results
All three compounds performed well with standard post-curing or with a vacuum post-cure. All three compounds were within the industry standards.

Download our Outgas Testing Laboratory Report.
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