Sciencemadness Discussion Board

Nylon and Acid

Curious George - 8-3-2012 at 10:22

I can dissolve Ny 6 or Ny 66 in concentrated (30%) HCl.

When this happens, is there a REACTION -- i.e. does the polymer decompose into the components from which nylon is made?

If I pour the concentrated nylon / HCl solution into a bucket of fresh water (thereby diluting the acid), I form fine white threads.

Are these threads nylon re-formed from the starting materials?

OR, has the nylon just become soluble in strong acid, and then precipitates when the acid is diluted?

With strong acid, have I just broken the POLY-MER into nylon "mers", or have I broken up the nylon "mers" into smaller chemical species?


Thanks!

marko - 8-3-2012 at 12:34

Looks like it is soluble in HCl. If you broke the chain, it wouldn't continue to behave like nylon once removed.

('monomer' is the word you're looking for)

Curious George - 8-3-2012 at 13:56

Any way to tell is what precipitated out of the acid solution upon dilution is really NYLON and not some other chemical?

And thank you for monomer -- I had a brain cramp!

Hexavalent - 8-3-2012 at 14:00

Why not research some literature for yourself before asking?

This thread should be in beginnings.

Curious George - 9-3-2012 at 06:02

Have not found a DEFINITIVE source that states that nylon "dissolved" in concentrated HCl is nylon MONOMER.

Also interested in understanding more of HOW this happens.

Does the acid REACT with the nylon polymer to cause depolymerization?

When I add water and dilute, why does a white solid precipitate? If the nylon has dissolved and formed nylon monomer, why would dilution of the acid cause a polymer (presumably nylon?) to re-form.

Thanks!

PHILOU Zrealone - 9-3-2012 at 14:38

If it is Nylon 6 it would give under acidic media:
(-NH-CH2-CH2-CH2-CH2-CH2-CO-)n -H2O/H(+)-> n HO2C-CH2-CH2-CH2-CH2-CH2-NH3(+)
Thus something moderately soluble to unsoluble in the media and displaying zwiterionic behaviour or tensioactive properties as a function of the pH.

If it is Nylon 66 it would give under acidic media:
(-NH-CH2-CH2-CH2-CH2-CH2-CH2-NH-CO-CH2-CH2-CH2-CH2-CO-)n -H2O/H(+)-> n HO2C-CH2-CH2-CH2-CO2H + n H3N(+)-CH2-CH2-CH2-CH2-CH2-CH2-NH3(+)
Thus one part will be little soluble (adipic acid or 1,6-hexandioic acid) and another part will be soluble as hexamethylendiamonium salt.

It would be easier to work with medium concentrated NaOH and some heating... but read first the safety rules concerning those reactants and keep in mind that in basic media, the free diamine will result and that such alkanic diamines usually stink like dead meat (the common names of the lower (or other) members of the familly gives you a hint...putrescine, cadaverine, spermine, ...).

[Edited on 9-3-2012 by PHILOU Zrealone]

Curious George - 11-3-2012 at 19:27


Thanks, Philou! Appreciate the equations.

I can understand that after dissolving nylon in ACID and then NEUTRALIZING, I would be reducing the concentration of available protons, and the soluble organic ions would join together and become insoluble.

SO, why does just DILUTION with pH7 water have the same effect?

In the beaker, there are the same number of organic "fragments" and H+'s. The CONCENTRATION is lower, but the number hasn't changed. By adding several volumes of water, the pH is still very low -- certainly less than 1.

Why the precipitation, please?

Thanks!

Vikascoder - 13-3-2012 at 20:41

Not sure about nylon in hcl but nylon does not react or dissolve in HNO3 or H2SO4 mix because i filtered my nitro starch from nylon filter only . I think it dissolves in hcl .

Curious George - 14-3-2012 at 05:26

I agree. It seems much more soluble in HCl than in sulfuric. Have not tried nitric.

The question, though, is: AFTER it dissolves in concentrated (30 - 35%) HCl, why does DILUTION cause it to precipitate?

watson.fawkes - 14-3-2012 at 09:59

Quote: Originally posted by Curious George  
I can understand that after dissolving nylon in ACID and then NEUTRALIZING, I would be reducing the concentration of available protons, and the soluble organic ions would join together and become insoluble.

SO, why does just DILUTION with pH7 water have the same effect?
What is the pH of an acidic solution after dilution? Does it stay the same?

Lambda-Eyde - 14-3-2012 at 10:50

Quote: Originally posted by PHILOU Zrealone  
but read first the safety rules concerning those reactants and keep in mind that in basic media, the free diamine will result and that such alkanic diamines usually stink like dead meat (the common names of the lower (or other) members of the familly gives you a hint...putrescine, cadaverine, spermine, ...).

If it is nylon-6,6, it won't stink. I have 250 g of 1,6-hexanediamine which smells pepper-ish, nothing stinky or foul. In fact, the label even describes the smell as "Like piperidine" (like that would help someone...).

Edit: Also, the lower nylons are hydrolyzed by strong acids, and even by water alone (although at higher temperatures).

[Edited on 14-3-2012 by Lambda-Eyde]

Curious George - 14-3-2012 at 13:09

Since pH is the CONCENTRATION of "free" hydrogen ions, dilution will reduce the CONCENTRATION of "free" hydrogen ions in a strong acid.

HOWEVER, once nylon is dissolved, and the hydrogen ions are associated with the dissolved nylon monomer, would CONCENTRATION still matter? The NUMBER of hydrogen ions in the beaker is still the same....

As far as a pH change: Concentrated (~ 30%) HCl has a pH less than 1. So does somewhat diluted HCl solution (say 15%). With the beaker still containing such a HUGE excess of hydrogen ions compared to the small number of nylon monomers, why would precipitation occur??

PHILOU Zrealone - 14-3-2012 at 16:58

Just a comment ...
Nylon does dissolve very wel in HOClO3 (69%) ... my samsonite school bag has had that experience when I was in first year university in chem sciences!

For the rest Curious George,
30% HCl is roughly 300gr HCl per kilogram water...
thus about 8,5 mol/L or about pH= -1 ...
diluting with 10 volumes of water will lead to a pH of arround 0
a further thenfold dilution will give a pH of approximatively 1...

The solubility of organic stuffs in water depends on many factors:
-type of molecule and number of functionnal groups
-molecular lenght and weight
-presence of H bonding
-presence of double, triple or aromatic linkage

Typically for alkanic molecules, the solubility in water drops down above 3-4 carbon atoms... see solubilities of propanoic acid, vs butanoic and pentanoic acid (or of the parent alcohols or amines)...
In this case you may consider you have 6 carbon atom chains with some kind of soap / tensio active / detergent structure that displays both properties of cationic, anionic and non-ionic detergents ...
You get precipitation if you mix cationic and anionic detergents together.
You also have critical miscellar concentration playing in the game. Thus everything looks dissolved and transparent, but when dilluted it turns cloudy with lumps.

[Edited on 15-3-2012 by PHILOU Zrealone]

watson.fawkes - 14-3-2012 at 17:51

Quote: Originally posted by Curious George  
[...] would CONCENTRATION still matter? The NUMBER of hydrogen ions in the beaker is still the same.
Chemistry is, to use a bit of mathematical jargon, a local affair, which means that molecules have to come into contact with each other to react. The total number of anything basically never matters itself; it's how many things are nearby that's what matters. So concentration is indeed what matters, and the number itself doesn't.

How much are they re-assembing?

jacobin - 20-1-2016 at 10:25


"If I pour the concentrated nylon / HCl solution into a bucket of fresh water (thereby diluting the acid), I form fine white threads."

Objects larger than light scatter. Is the original 30% HCl clear? Then the nylon has broken down into pieces smaller than light.

Are there really filaments? That would be great, but I suspect they may be nylon precipitate dust.

Try diluting very slowly, to try and grow larger crystals. Start with just a drop at a time, for safety's sake as well. Then more later, with a peristaltic pump, and maybe some NaOH to keep diluting water high. Nylon snowflakes, wow!

fusso - 5-4-2018 at 16:23

Interesting observation. Coincidentally I also have some nylon fishing line that someone gave me a few years ago. I will try with H2SO4 after going back to my home country.

mayko - 5-4-2018 at 17:27

When I was in middle school (about the time I discovered this series actually) I started collecting a few chemicals and such in my room, stuff like mothballs and baking soda. I was pretty pumped because I'd just discovered the big jug of muriatic acid in the garage and I really liked watching it smoke with ammonia. Anyway, that's how I got a bunch of dime-sized holes in my decent nylon soccer bag :(

unionised - 6-4-2018 at 05:06

A couple of things first stop CAPITALISING random words- it's distracting.
The second is this: is the solution of nylon in acid noticeably more viscous than the acid was?
Solutions of long-chain molecules tend to be sticky and thick because the polymer chains get tangled up. A solution of the monomer(s) would be less sticky.

There's another issue "nylon" covers a whole group of polymers.
Some are made by polymerising a single component- often caprolactam. Others are made from 2 different components, a dicarboxylic acid and a diamine.

If I recall correctly most of them dissolve quite well in formic acid.

DavidJR - 6-4-2018 at 18:25

Quote: Originally posted by unionised  

The second is this: is the solution of nylon in acid noticeably more viscous than the acid was?
Solutions of long-chain molecules tend to be sticky and thick because the polymer chains get tangled up. A solution of the monomer(s) would be less sticky.


I just tried this by dissolving some nylon zip ties (I don't know exactly which type of nylon though) in 36% HCl, and yes, the solution is pretty viscous.

fusso - 8-4-2018 at 08:19

Quote: Originally posted by DavidJR  
Quote: Originally posted by unionised  

The second is this: is the solution of nylon in acid noticeably more viscous than the acid was?
Solutions of long-chain molecules tend to be sticky and thick because the polymer chains get tangled up. A solution of the monomer(s) would be less sticky.


I just tried this by dissolving some nylon zip ties (I don't know exactly which type of nylon though) in 36% HCl, and yes, the solution is pretty viscous.


My H2SO4 soln is also definitely more viscous