What’s a good adhesive for PET-Pebax bonding, and are there FDA required or recommended adhesives for constructing non-DEHP or non-phthalate PVC medical devices? This week’s Ask The Engineer answers these questions and more.
What is the best adhesive for bonding a polyethylene terephthalate (PET) balloon to a polyether block amide (Pebax) substrate? What is the recommended surface preparation? Are other catheter-shaft substrate materials more suitable than Pebax for bonding to a PET balloon?
You should select a medium-flexibility light-curable adhesive with the viscosity to achieve the level of wetting and gap filling appropriate to your design. In addition, it is important to choose an adhesive that fluoresces under a black light, enabling operators to detect and fix voids or air bubbles before the assembly is cured. This feature results in a better-quality bond and greater yields during production.
You can perform a surface treatment using plasma together with oxygen gas. While a plasma treatment with air gas—which has a lower O2 content than oxygen—is also effective, it is not as advantageous as using an oxygen plasma treatment. The oxygen deposits onto the surface of the material and increases the number of bond sites to which the adhesive can stick.
You ask whether other catheter-shaft substrate materials are more suitable than Pebax for bonding to a PET balloon. Pebax is commonly used for manufacturing catheter shafts because adhesives bond well to it. A polyether/nylon copolymer, the material can be mixed with higher proportions of nylon (polyamide) to create higher-durometer materials (72D), or it can be mixed with lower proportions of nylon to create lower-durometer materials (35D). The greater the amount of nylon in the Pebax, the farther apart are the bond sites and the more difficult it is to bond. For example, bonding PET to 35D Pebax is easier than bonding it to 72D Pebax. If you can incorporate a small layer of 35D Pebax at the bond location while retaining 72D Pebax underneath to achieve greater material stiffness, the bonding application will be improved.
Are there FDA required or recommended adhesives for constructing non-DEHP or non-phthalate PVC medical devices?
That’s a good question and one we are seeing a lot these days. The good news from an adhesive manufacturing standpoint is that many of the adhesives used in medical-device assembly don’t need a plasticizer like DEHP or phthalate-based materials. Most light-curable acrylated urethanes, cyanoacrylates, epoxies, silicones, and polyurethanes do not contain these materials. These adhesive products bond readily to the polymers that are replacing DEHP plasticized PVC, even if they are alternative grades of PVC, extruded silicone, latex, urethane, or other polymer families. Most companies, Dymax included, are usually asked to provide a letter at the beginning of a project stating that these adhesives do not contain DEHP or BPA.