“I am looking for an adhesive that can be used to bond tubes made of flurorocarbons (PVDF and FEP) to a titanium connector. This connection needs to withstand repeated autoclave sterilization at 134° celsius. Do you have any recommendations?”
Fluoropolymers such as PVDF, FEP, and PTFE (Teflon) are very difficult to adhere to. The only way to overcome this is by using a chemical etch solution. Two possible suppliers are www.actontech.com or www.fluorocarbon.co.uk. Both web sites also offer a variety of information regarding this topic.
The etching process removes a layer of fluorine atoms from the surface and allows oxygen and hydrogen from the atmosphere to attach, which enables adhesives to bond to it. The next challenge is the required resistance to repeated autoclave cycles. We recommend trying a two-part or heat-curable epoxy from Masterbond or Epoxy Technology.
“We use glass capillary coated with polyamide and insert the glass capillary into a FEP tube. What is the best adhesive that would hold both capillary and FEP tubes?”
In general, FEP (Fluorinated ethylene propylene) is very difficult to adhere to. It has very similar properties to Teflon (PTFE), which is known for its anti-sticking surface. Due to the design of your part, you may achieve sufficient bond strength, especially if the capillary is inserted deep into the FEP tube and the adhesive can flow deep inside the bond gap. If you prefer a light-curable adhesive, I would start trials with DYMAX 1180-M (medical grade) or 3013 (industrial grade).
Before making a final adhesive recommendation, however, a few more aspects need to be considered:
- Length of the bonding area
- Bond gap size (OD capillary versus ID FEP tube)
- Forces / temperature the part will see when in use
- Medical-grade adhesive needed
- Optical properties
If you need higher bond strength, there is an option to chemically etch FEP. By using a Sodium Naphthanate solution, the surface of FEP can be modified so that most common adhesives can be used. This etch, however, creates a darker layer on the surface, so that the clear properties of FEP are no longer given.
“Our application requires a watertight seal between FEP tubing (0.8 mm OD, 0.2 mm ID) and a borosilicate glass capillary (0.17 mm OD, 0.10 mm ID) with an overlap of 1-3 mm. This is part of a one-time use, disposable cartridge. We are currently using a 5 minute epoxy because the zero shrinkage is advantageous. The cure time, however, is not. We have tried UV-cure epoxy in the past for this joint but found that the epoxy did not cure inside the FEP tubing. Any suggestions?”
UV light-curable epoxies typically cure with the UV spectrum from 300-390 nm and do not make use of visible light to cure. With the semi-hidden bond described in the application above, switching to a visible-light-curable, acrylated-urethane adhesive would be worth trying. A visible-light-curable adhesive will allow more of the available light to hit the adhesive and cure deep within the FEP tubing.
An important issue with this application is that the borosilicate glass capillary will act like a light fiber. It will take the light, carry it like a fiber-optic cable, not allow it to get to the adhesive (as it is bouncing the light internally within the glass), and move it past the bond area. The visible-light-curable adhesive should be exposed with high-intensity light. The adhesive should allow the light to penetrate into the gap.
One alternative to a visible-light-curable adhesive is a cyanoacrylate adhesive that could cure deep within the FEP tubing without light. Due to the deep overlap area in this application, only the top surface would be exposed to water and could provide enough protection to create a water-tight seal. Another alternative is a new product, DYMAX 9440 A/B, which is a light-curable silicone adhesive. This material is unique in that you can expose the adhesive to light during dispensing and assembly and still have enough time to assemble the part before the material starts to set up. DYMAX Applications Engineers can work with you one-on-one to discuss exact options and materials.