FAQ and Information

Q. Will TETRA-ETCH etchant react with other plastics?

A. TETRA-ETCH etchant will etch the reactive polymers listed below at different rates, dependingupon the molecular structure and the relative amount of carbon to fluorine bonds in the molecule.In general, TETRA-ETCH etchant will strip fluorine atoms from carbon selectively. It will notstrip chlorine from carbon. A molecule containing lots of fluorine (eg. Kel-F® or Viton®) will bestripped more rapidly than a molecule containing a larger proportion of chlorine atoms (eg. Kynar® orhydrogen eg. Tefzel®). 

Q. Is it necessary to ship TETRA-ETCH etchant under refrigeration?

 A. No. Normal surface shipment does not impair guaranteed shelf life. 

Q. How long should the PTFE piece be left in the TETRA-ETCH etchant?

 A. Generally 10 seconds is ample time for strong etchant to react with Teflon® and Fluon® grades of PTFEand give a tan to brownish finish. Longer etching times will darken the colour of the PTFE but thesubsequent adhesive bond will not be any stronger. Precise timing is unnecessary since the reaction tendsto be self-limiting. When the etchant has penetrated the PTFE surface to about 5 microns, thecarbonaceous backbone already formed acts as a barrier to further penetration of the etchant. However,with extended etching times, bonding stresses may cause the carbonaceous film to detach itself from thevirgin PTFE. 

Q. Why does PTFE turn brown when etched with TETRA-ETCH etchant?

 A. The PTFE molecule is a long chain of carbon atoms to which fluorine atoms are bonded. TETRA-ETCHetchant strips the fluorine atoms from the chain, leaving the carbon atoms with a temporary deficiency ofelectrons. When the etched surface is withdrawn from the etchant bath and exposed to air, molecules ofoxygen, hydrogen and water vapor restore the missing electrons. The resulting carbonaceous backbonecontains functional groups (eg. hydroxl (OH), carbonyl (C=O), carboxyl (COOH), etc) which are the organicspecies responsible for adhesion. Fluorinated ethylene propylene (FEP) and perfluoroalkoxy (PFA) resin,on the other hand, are long chains of carbon and fluorine atoms with many side chains. The branchedchains interfere with the attack of etchant on the main backbone, causing a time delay. Hence, thesematerials require a longer etching time. 

Q. Does TETRA-ETCH etchant lay down a film of adhesive on PTFE?

 A. No. A chemical reaction alters the PTFE surface. 

Storage of tetra-etch

Q. Can TETRA-ETCH be saved and stored after opening?

 A. Yes. The airspace above the etchant left in the bottle should be flushed with an inert gas (such asdry nitrogen or argon) and capped securely. It should then be stored in a cold environment (refrigerator,cold box, freezer etc). Any air left in the bottle (or any other container) will destroy the remaining etchant ina short period of time.If only a small quantity of etchant is required for each application, it is sometimes beneficial todecant the whole bottle on receipt into smaller containers. Polypropylene or glass containersshould be used. They should be clean and dry. The TETRA-ETCH etchant should be allowed tototally defrost, the bottle shaken well to disperse all particles, then decanted. The smallercontainers should be filled as far as possible to exclude air space, then they can be frozen. The sixmonth shelf life guarantee will not be valid if this process is undertaken but the TETRA-ETCHetchant would be expected to remain active for at least 6 months.  CAUTION : NEVER USE CARBON DIOXIDE TO DISPLACE THE AIR IN A CAN OFTETRA-ETCH ETCHANT 

Q. How can you tell if TETRA-ETCH etchant is still viable?

 A. The colour of the etchant is a good indicator. If it is a dark green to black, it has etching capability. If thecolour is brown, tan, yellow or white, the etchant is no longer viable. 

Q. What is the shelf life of TETRA-ETCH etchant at room temperature?

 A. If covered and protected from air moisture about 7 days at 20-25°C (unexposed) or about 3 weeks at 2-15°C after receipt of shipment. A blanket of inert gas (dry nitrogen or argon) is a great help if the containerhas been opened.