Solvent Bonding Polycarbonate to Polycarbonate - Update

It didn't work well. Unfortunately, it seems the bond created was very porous (see image below). After curing in a fume hood for 18 hours, the surface was still a bit tacky (after pulling the two pieces apart). The bond surface was abot 1/4" square and held roughly 20 lbf before seperating. It may have been stronger had it cured all the way, hard to know for sure. I only tried a few samples, so perhaps there are process tweaks I could make that would improve the efficacy of the cyclohexanone bond, but at this point it seems a less than ideal solvent for bonding polycarbonate to itself.

Solvent Bonding Polycarbonate to Polycarbonate

I encountered the need to solvent bond Polycarbonate to itself for one of the projects we're currently working on. After speaking with several vendors and reading various snippets online, I discovered that Methylene Chloride is the solvent of choice for bonding polycarbonate. Great, right? Except not so great. This is why: the method of sterilization we've chosen for our product is EtO (and we can't change it for technical reasons), and apparently EtO sterilization does not react well to anything with chlorine in it. So, the chloride part of methylene chloride presents a challenge. After further digging, a technician at Masterbond recommended a chemical called Cyclohexanone (which, I confirmed, has no chlorine in it). I've got some on order and plan on doing a test this week. I'll fill you in on the results when I have them.

Moral of the story - methylene chloride is the solvent of choice for bonding polycarbonate to itself; however, if you'll be EtO sterilizing your parts, using methylene chloride won't work and you should consider an alternative, possibly cyclohexanone.

Shape Setting Nitinol for a Medical Device Prototype

This week I enjoyed the excitement and frustration of shape setting Nitinol tubing for a prototype medical device used for a demonstration. I obtained samples from NDC and Memry . Both provided free samples within days. Nitinol is commonly used in medical devices because of its superelastic or shape-memory characteristics. In my application, I am taking advantage of the superelastic properties.

Shape setting Nitinol is a quick and easy process provided you have the appropriate equipment. To shape set the Nitinol, I created a fixture to securely hold the Nitinol to the desired shape. I then pre-heated an oven to 500-550°C. Next, I placed the part in the oven for 1 minute. I then removed the part and immediately quenched it in water. If you overheat the part it will reduce its superelastic properties.

The key to designing parts with Nitinol is to obtain material and start testing as soon as possible. Nitinol is NOT an easy material to design with because it does not have a linear stress-strain curve like stainless steels. Hence, most design formulas are not applicable. This week I learned that even though think-walled Nitinol tubes are flexible, they will splinter when compressed axially.

By Margaret Koga