Vulcanization of Siloxanes
For additional flexibility when selecting silicone tubing, we now offer two types of silicone tubing, platimum and peroxide vulcanized (cured). Both silicone types are USP Class VI approved and FDA compliant and they have similar physical properties such as temperature ratings and chemical compatibility. The major differences are that the platinum-cured tubing has fewer potential leachables and is preferred in biological applications. The peroxide-cured tubing has a longer service life. There is absolutely no difference between the 06411-series and its direct replacement which is highlighted in the chart below. Additional catalog numbers have been added so all of the tubing sizes are offered in both platinum- and peroxide-cured formulations.
Silicone tubing is derived from the siloxane polymer polydimethyl siloxane. This polymer is an amorphous flowable substance which does not have useful tubing properties. By adding a catalyst which causes the siloxane polymer to cross-link, and adding a silica filler for strength, the elastomer silicone is formed. The processes by which siloxane is converted to silicone are known as vulcanization or curing. There are two commercially significant curing processes, peroxide-curing and platinum-curing.
This curing process occurs at room temperature, hence it is also known as Room Temperature Vulcanization (RTV). A platinum salt is added to siloxane as it is being extruded, exposure to air causes cross-linking to begin and silicone to be formed. The by-product of this reaction is ethanol which is easily removed. The silicone material formed by platinum-curing is generally not as strong as that formed by peroxide-curing.
In this curing process, the siloxane polymer is blended with an organic peroxide. The tubing is extruded and then heated. Heat initiates the cross-linking, forming silicone. Catalytic by-products (peroxides and ketones) are volatile and evaporate during the cure process. If not properly cured, or over long periods of time, outgassing of peroxides and ketones may occur. The major symptom of outgassing is blooming, or a fine white crystalline powder forming on the inside of the tubing. This may be removed by heating the tubing and then rinsing it.
Platinum-cured tubing Peroxide-cured tubing
Fewer potential leachables - Longer service life
Smoother surface, less protein binding - Greater compression strength
Slightly better clarity - More economical
Shorter tubing life - Potential outgassing of peroxides