What is the proper procedure for evacuation of trapped air from mixed material?
De-airing (vacuum degassing) is the process used to remove air bubbles that have been entrained in the liquid polymer because of mixing. Different formulations can be easier or harder to de-air, depending on the inherent surface tension and the amount of remaining pot life. Small amounts of additives can be employed to reduce the surface tension. The most important aspect of de-airing is a good, leak free apparatus and high quality vacuum pump (example Welch 1397, 17 cfm). Attempting to de-air a polymer with a leaky system or poor quality vacuum pump is frustrating and un-productive. Mixed material should be placed in a container with about five times the volume of the contents. After the material is placed in the vacuum chamber and a vacuum is generated, the material will begin to rise. Pressure must be added to the chamber to drop the material back down to the original level and then vacuum re-applied. After several cycles the rising material will “break” and the level will dramatically drop and stay down, even under vacuum. After this point, the vast majority of the trapped air has been evacuated. Several minutes of exposure at vacuum, continues to evacuate smaller bubbles. A vacuum gauge is highly useful, when attempting to troubleshoot a vaccum apparatus. No less than 29+ inches of mercury is required to properly de-air a polymer system.