Plasma treatment of polymers
Henniker have a fantastic editorial in this month’s Medical Plastic News magazine print edition. The editorial features information on plasma treatment of polymers widely used in medical device manufacture but equally applicable to a wide range of other technical challenges.
Look out for the digital version available online soon at www.medicalplasticsnews.com, or download the free app to read this months issue for free here MPN app, or read our full article on the plasma treatment of polymers below:
plasma treatment of polymers: peek and ptfe
Engineering polymers, such as PEEK, POM, polyamides and PTFE have witnessed a remarkable growth in their use in recent years in medical product manufacturing, such as catheters, micro-catheters, nasogastric feeding tubes and endotracheal tubes to name but a few. They are typically chosen for unique properties which include resistance to chemicals, high strength to weight ratio and of course relatively low cost. However, there are fundamental differences between polymers and other engineering materials which create unique technical challenges in a production environment.
One important property is the characteristic low surface energy of polymers (see Table 1) and the resulting intrinsically poor adhesion characteristics. This is an important obstacle in achieving reliable glue joints and PAD printing steps, where various types of markings must be permanent. Various methods of improving adhesion are available but often don’t lend themselves to production settings and frequently involve the use of harsh and environmentally unfriendly chemicals to physically attack and etch the surface of the material. Plasma treatment of polymers offers a reliable and environmentally friendly alternative surface preparation for a wide range of materials.
Plasma treatments can be a vacuum types (batch) or atmospheric types (in-line) and contain reactive gas species which, by careful choice of gas type and process parameters, can be used to increase the surface energy of a wide range of engineering polymers, and in doing so significantly improve wetting characteristics and therefore adhesion characteristics.
In-line atmospheric plasma treatment has been successfully demonstrated to increase the surface energy of PEEK from 35mN/m to >72mN/m, ensuring permanent PAD print adhesion. The treatment is active on PEEK for several weeks and so parts can be stored until needed.
For PTFE catheters, air is ineffective due to the strength of the C-F bond. Batch processes are preferred which allow different plasma gases to be used and which are more effective in fluorine extraction from the surface. This process also increases the effective surface area which in turn improves ink adhesion as shown in the SEM images below for untreated and plasma-treated PTFE. The surface energy of PTFE is raised from 18mN/m to >72mN/m in this case also.
Untreated PTFE surface Plasma treated PTFE surface
Table 1: Typical surface energies of different materials
Does plasma treatment improve the adhesion of engineering polymers?
Yes, both batch and in-line plasma treatments offer a reliable and repeatable surface preparation method for improving adhesion to a wide range of engineering polymers used in medical device manufacture. Applications include gluing and PAD printing of catheter tubes for example.
Contact us for more information on the plasma treatment of polymers
Read our case study on how we provided a complete solution for our customers involved in PEEK device manufacturing. Or read our technology page on improving adhesion using plasma activation prior to printing/painting.