Aged polyurethane

Thread Starter

cmartinez

Joined Jan 17, 2007
8,220
Now that I think of it, I've been using polyurethane tubing for all my pneumatic projects (which have been many) and not a single hose has ever aged the way those chains did... perhaps their production process is of a far higher quality, or is the material being used substantially different?
Another thing I noticed, is that when I built my etching tank (more on that on a future thread) I once tried to use that same tubing to blow bubbles in the ferric chloride solution and the thing cracked and disintegrated in the course of a few days! why is that? The tank itself is made of acrylic and is unaffected by FeCl3 but what part of the polyurethane is it attacking? It wasn't until I used vinyl tubing that the thing more or less resisted the FeCl3, but it's not immune to it like acrylic... it's also attacked by it and cracks after a couple of years.
 

GopherT

Joined Nov 23, 2012
8,009
Now that I think of it, I've been using polyurethane tubing for all my pneumatic projects (which have been many) and not a single hose has ever aged the way those chains did... perhaps their production process is of a far higher quality, or is the material being used substantially different?
Another thing I noticed, is that when I built my etching tank (more on that on a future thread) I once tried to use that same tubing to blow bubbles in the ferric chloride solution and the thing cracked and disintegrated in the course of a few days! why is that? The tank itself is made of acrylic and is unaffected by FeCl3 but what part of the polyurethane is it attacking? It wasn't until I used vinyl tubing that the thing more or less resisted the FeCl3, but it's not immune to it like acrylic... it's also attacked by it and cracks after a couple of years.
There is way to much chemistry and materials science needed to explain chemical-based answers to all of those questions. Soooo.... I will say, all those things happened because you did not consult a chemical compatibility chart available from a high-quality tubing supplier. The chart should indicate what concentration of ferric chloride was tested when finding compatible vs. incompatible, how long the contact was made (hours, days, months, years).
 

Thread Starter

cmartinez

Joined Jan 17, 2007
8,220
There is way to much chemistry and materials science needed to explain chemical-based answers to all of those questions. Soooo.... I will say, all those things happened because you did not consult a chemical compatibility chart available from a high-quality tubing supplier. The chart should indicate what concentration of ferric chloride was tested when finding compatible vs. incompatible, how long the contact was made (hours, days, months, years).
Yeah... I figured the question was a rather broad one... but one thing, if you have the time, of course, how come acrylic is the only plastic I've found that seems to be completely unaffected by it? All else, including polyurethane, vinyl and even nylon is attacked by it... what is it that's present in those components that makes them susceptible to chlorine? (I'm guessing it's the chlorine in the FeCl3 that's acting on them) ... pardon my ignorance, but maybe I shouldn't have called acrylic a plastic?
 

GopherT

Joined Nov 23, 2012
8,009
Yeah... I figured the question was a rather broad one... but one thing, if you have the time, of course, how come acrylic is the only plastic I've found that seems to be completely unaffected by it? All else, including polyurethane, vinyl and even nylon is attacked by it... what is it that's present in those components that makes them susceptible to chlorine? (I'm guessing it's the chlorine in the FeCl3 that's acting on them) ... pardon my ignorance, but maybe I shouldn't have called acrylic a plastic?
Acrylic is a thermoplastic. Ferric caloric is essentially HCl with iron oxide. It is a fairly acidic salt. Condensation polymers can be hydrolyzed by acids (amorphous nylon) if the acid can swell into the polymer chains.

Acryllic is low polarity polymer and only solvents like methylene chloride will swell/dissolve the polymer and allow solvent welding to other acrylate pieces. Water and acid just will not get into acrylate.

Polyurethane can be damaged by acid. Especially if it is a foam and easily penetrated (open cell vs closed cell). There is another category of poly urethane - TPU - thermoplastic poly urethane and this is very different (see earlier posts on variety of PU). TPU is commonly used for hoses, shoe soles, or anything that requires abrasion resistance, some flexibility and processible by injection molding or extrusion. Not a foam and, therefore slower penetration by water/acid but can still eventually be damaged by acid.

Acrylic is a chain of carbon bonds, the others that you mentioned are alternating with some carbon chains of the monomer and some hetero-atoms (oxygen, nitrogen) that form the linkages of the monomer units through condensation reaction or a urethane linkage. All of these heteroatom linkages are more easily damaged by acid than C-C linkages of vinyls, acrylics, etc

I think I have rambled on enough and my gin and tonic needs a refill.
 
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