Tech Talk Blog

What is the best process for removing silicone oil from a catheter made of Pebax® tubing prior to a bonding operation?  Would you use plasma or corona?

Your question is one that we are seeing more frequently. And the short answer is that it all depends on the amount of oil.

If you can see a significant oil collection, then you need to wash the tubing in an ultrasonic bath with an emulsifier. Then, you may simply wipe the tubing with an alcohol wipe to remove any excess. It really depends on the level of contamination. Generally speaking, I’ve found that catheters have a superficial level of oil.

If the amount of oil is superficial, plasma can carry away the excess oil via a specific oxygen treatment. We do not advise corona treatment for this application, since it can make the silicone hydrophilic and give a false impression of being clean. Plasma is a more elegant solution and will “superclean” the surface to promote better adhesion.  Learn how we recently solved this challenge.

Blocking - The greater the level of treatment, the higher the degree of oxidation of the surface. The polar groups formed by the corona have an attraction for the molecular layer on the other side of the web, and when the two sides come into contact when they are on the roll, a self-adhering condition exists.  Sometimes this attraction can be greater than the internal bonds of the substrate so that delamination of the substrate can occur when the product is unrolled.  The tighter the roll is wound and the longer it is in storage the more severe the problem becomes.  Blocking is worse in the film at the center of the roll.

Heat Sealing – Excessive treatment also leads to problems when attempting to heat seal the product.

Additives – If the polypropylene or polyethylene contain additional components, such as slip additives or some processing aids, the initial treatment is reduced over time as these additives bloom to the surface and partially mask the polar groups formed during treatment. For this reason, it is better to treat these films at the point of use rather than the point of manufacture.

Check out the Video Learning Center to explore even more topics!