Why Would I Need to Etch Tubing?
Fluoropolymers such as PTFE, FEP, and PFA are very lubricious (slippery). This lubricity reduces bonding ability of the material. Etching alter the surface properties of the polymer allowing it to be bonded to other materials.
How Does it Work?
Etching is performed by placing the fluoropolymer tubing in a sodium solution. The resulting chemical reaction removes fluorine molecules from the carbon-fluorine backbone of the fluoropolymer leaving carbon atoms that are deficient in electrons. When the etched surface of the material is exposed to air, oxygen molecules, water vapor, and hydrogen allow restoration of the electrons. This restoration process results in a group of organic molecules that enables adhesion.
Will Etching Change the Properties of My Tubing?
The etching process penetrates only to a depth of a few angstroms (10-10 meters), thus the properties of the tubing remain mostly unaffected. However, the etching process will darken the surface of the material, usually to a brown or tan tint. Surface lubricity is also reduced by the etching process. After the material is etched and dries, a white crust may form on the surface. This crust will impede the bonding process. This residue can be removed by dipping the material in isopropyl alcohol, acetone, or ethyl alcohol.
How Should I Store Etched Tubing?
Etched fluoropolymers will "grab" molecules from the air to repair their electron deficiency. This results in a weakening of the surface etching. For this reason, all etched materials should be stored in their original sealed bags. Zeus ships all etched tubing orders in sealed black protective bags.
Does a Darker Color Mean a Better Etch?
Not necessarily. In the picture below, both tubes have been etched and have nearly the same contact angle. However, as apparent from the picture, their colors are quite different. Color is not a reliable indicator of etch quality. For this reason Zeus includes etch certifications with each order shipped.
How is the Etch Tested?
The etched material is tested via the contact angle method: This technique uses a goniometer and microscope to measure the angle of a sessile drop resting on a flat portion of the etched surface. Contact angle measurements of liquid droplets on substrate surfaces are used to characterize surface wettability. Chemical etching results in greater contact with droplets placed on the etched surface. The greater the contact with the droplet, the lower the contact angle between the droplet and the surface of the material and the greater the bondability of the surface. Contact angle measurements provide a means to assess the degree of etching and the potential for bondability of the etched surface to other materials.
Chemical etching and contact angle:
Surfaces that have been more thoroughly etched have increased wettability. Droplets placed upon etched surfaces show a reduced contact angle with the surface compared to less well etched or un-etched surfaces.
Zeus performs contact angle tests on all etched tubing orders and includes a Certificate of Compliance with the material. Test results are available by request. Or call 1-800-526-3842 to discuss how etching can be a solution for you.