looking for tubing with at least fair resistance to Acetone vapor. need tubing with ID ~ 1/32 " should be as soft as possible (must be able to slip over a glass pipette and seal to gas at low pressure)
Comment by Composite Agency on 31 Aug 2009 at 22:34:24
Probably Polytetrafluoroethylene (PTFE) based flexible is suitable. The permeability of 100% Acetone vapour in PTFE in ambient condtions is in the order of 1E-8 gram/m x s. Divide this figure by the wall thickness and multiply this figure with the total wall square to obtain the total mass flux per second.
Polyethylenes (PE's) could also be used but they have short life time expectation due to potential for stress cracks (the grades with higher crystallinity). Moreover, their permeation is a factor 10 - 20 higher than the PTFE based polymers. Fluoro treated PE's have a slight better performance, but the same drawback on the long term (although permeation appoaches the virgin PTFE performance).
Concluding: for long term service life the PTFE based solution with a crystallinity in the order of 50 to 60 percent should be really appropriate.
Regards, Composite Agency
Comment by shalom on 01 Sep 2009 at 09:47:58
Is there flexible PTFE tubing ? flexible enough to create a seal for gas over a glass pipette ? Do PTFE shrink tubes preserve the permeation charactaristics of ordinary PTFE tubing ?
Comment by Composite Agency on 01 Sep 2009 at 11:11:40
Since heat shrink tubing is often cross-linked through the use of electron beams, peroxides or moisture - the cross-linking helps to make the tubing maintain its shape, both before and after shrinking - the permeation characteristics will be less than virgin material. However permeation in itself is in most tubing application not of major concern, usually the degree of swelling and/or stress cracking causes mechanical problems on the relative short term. With this regard, a PTFE based solution remains a good option. At least as long as the material is not strained for long times and exposed to impact loads.
Below a link with some suggestions for manufacturers for heat shrink tubing (includes well-established companies like 3M, etc.):