TECHSiL’s Guide to Degassing Polyurethanes

What is Degassing and Why is it Important?

Degassing is a technique used to remove trapped air and moisture before moulding or casting. This ultimately improves the products finish as well as optimising its mechanical specification.

Read on for our essential housekeeping steps and considerations for the degassing of polyurethanes.

Degassing Good Practice

Prevent air introduction during mixing as much as possible, using a flat paddle is advised.

If the material has been warmed, this will affect the pot life and can reduce degas time depending on the volume of material.

Vacuum Degassing

The mixed polyurethane resin needs to be in a container 3-4 times the headspace as the resin will rise during the degassing process.

The vacuum needs to be pulled slowly. You need to keep the resin long enough for the trapped air to escape; the bubbling will typically slow dramatically after 30-120 seconds.

After the first crest has fallen, degassing for another 3-5 minutes is often enough to ensure air free results.

Release the vacuum slowly as to avoid re-entering air into the resin. A few small air bubbles may still be seen; however, this could be some of the ingredients producing these and not necessarily air being withdrawn. Don’t exceed the pot life whilst degassing.

Storage and Usage

It is important to ensure the material is protected from moisture ingress as much as possible, as moisture will react with the PU and create air bubbles. Opening and closing of the containers too often is normally discouraged.

We do not normally have issues with air entrapment when twin packs or cartridges are used as the material is degassed during manufacture. Most issues arise when people hand mix the material, which is when we recommend that they should investigate machine mixing & dispensing. Speak with your TECHSiL contact to assist or reach out to our Technical Team.