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Topic: Kevlar synthesis  (Read 573 times)

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Offline Synthol

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Kevlar synthesis
« on: May 17, 2020, 11:19:41 AM »
Hello dear chemists

I wanted to synthesise kevlar from terephtalic Acid and p-phenylenediamine. But i couldnt find any reasonable publications on the exact conditions at which this polymerization may occur. does anyone Have any ideas? I guess high temperature is surely needed would you reccomend any other specific conditions?

Offline AWK

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Re: Kevlar synthesis
« Reply #1 on: May 17, 2020, 11:45:12 AM »
Search patents.
AWK


Offline Synthol

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Re: Kevlar synthesis
« Reply #3 on: May 17, 2020, 05:04:37 PM »
Thank you very much

Online hollytara

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Re: Kevlar synthesis
« Reply #4 on: May 17, 2020, 11:57:34 PM »
Not easy stuff to process.

Offline Enthalpy

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Re: Kevlar synthesis
« Reply #5 on: May 18, 2020, 04:45:15 AM »
Must it be para-aramide? It's perfect for ropes, but we have ropes already.

We need fibres that elongate elastically a lot but resist traction enough so σ/ρ > v2 with good margin like 3, where c=342m/s is the speed of sound in air. This would be necessary for the strings of musical instruments and of tennis rackets. Nylon is inferior, we still use sheep gut.

Possibly, yarn of meta-aramide is good - I have no data. Or some fibre where both the diacid and the diamine or diol are in meta position. Or anything you want. We are stuck.

But if the strong and stretchable fibre dampens much, it will have other uses.

Offline wildfyr

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Re: Kevlar synthesis
« Reply #6 on: May 18, 2020, 07:52:13 AM »
Meta aramid is already in use, thats what Nomex is.

Offline Synthol

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Re: Kevlar synthesis
« Reply #7 on: May 18, 2020, 06:02:51 PM »
I do not exclude trying m-aramides and, or some substituted variations  however for now i wanted to choose simplest and well known example to know whether im going in the right direction, if everything goes fine i Have lot of informations to confirm succes or failure.
Im currently working on high heat oven (up to 1300dg definitely enough)  controlled by PID so i know exact temperature as i Have No access to l propper academy lab during pandemy.. And also its just my own little project not really any scientific studies, I do not require any great strength of material. I’d just be happy to see little chunk of kevlar over my desk, I will probably also publish route on yt starting with aniline and PET bottles.

Even though I will stick to my plan, Im glad you responsed and thanks for advice.

Offline Enthalpy

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Re: Kevlar synthesis
« Reply #8 on: May 19, 2020, 09:01:16 AM »
Meta aramid is already in use, that's what Nomex is.

And sometimes available as a yarn, not only a felt. But I didn't find elastic properties for Nomex yarn. Someone must try whether it sounds tiiiing-tiiiing or poc-poc, when properly overspun with metal wire.

And if Nomex isn't good, find other fibres.

We really need better string materials, sorry to labour the point. Drifting and fragile sheep gut pleases no-one, but all replacements sound badly.

Offline Enthalpy

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Re: Kevlar synthesis
« Reply #9 on: May 19, 2020, 09:14:24 AM »
[...] starting with aniline and PET bottles [...]

That's seducing! Have you thought how to purify the recovered terephtalic acid? I just fear PET bottles contain too much dirt and plasticizers, so the impure acid would make too short macromolecules.

The same PET as bottles makes high-tech ropes too. Besides strong extrusion and the lack of plasticizers, there may be constraints on the composition.

Offline wildfyr

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Re: Kevlar synthesis
« Reply #10 on: May 19, 2020, 09:32:51 AM »
Very pure monomers are necessary to generate high molecular weight of any condensation polymerization.

Molecular weights that give good mechanical properties typically require greater than 99.9% conversion based on the Flory-Schultz distribution. Essentially, low molecular weight species vastly outnumber high MW species until monomer conversion is nearly complete, then oligomers have a chance to start condensing with one another.

 It's why diacyl chlorides and amines make great polymerizations, the amide bond is hard to break (less back reaction) and HCl is more easily pulled out of the system than water is during a carboxylic acid-based condensation, which drives the reaction forward. Kevlar is typically made this way. Also I've heard the processing of the strands is very nasty, done in neat sulfuric acid or something like that.

Perhaps you could get terepthlatic functionality back by converting to acid chloride and distilling it, provided no plasticizers are volatile. I'm sure someone has thought of this for recycling.

Just curious, you need a diamine, do you plan to nitrate and reduce aniline?

Offline Synthol

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Re: Kevlar synthesis
« Reply #11 on: May 19, 2020, 03:54:20 PM »
Very pure monomers are necessary to generate high molecular weight of any condensation polymerization.

Molecular weights that give good mechanical properties typically require greater than 99.9% conversion based on the Flory-Schultz distribution. Essentially, low molecular weight species vastly outnumber high MW species until monomer conversion is nearly complete, then oligomers have a chance to start condensing with one another.

 It's why diacyl chlorides and amines make great polymerizations, the amide bond is hard to break (less back reaction) and HCl is more easily pulled out of the system than water is during a carboxylic acid-based condensation, which drives the reaction forward. Kevlar is typically made this way. Also I've heard the processing of the strands is very nasty, done in neat sulfuric acid or something like that.

Perhaps you could get terepthlatic functionality back by converting to acid chloride and distilling it, provided no plasticizers are volatile. I'm sure someone has thought of this for recycling.

Just curious, you need a diamine, do you plan to nitrate and reduce aniline?

I thought of synthesising acetanilide first and then nitrating it becouse o-nitroacetanilide is far more soluble in chloroform than para isomer and so it can be extracted fearly easilly.
Then hydrolyse it with use of sulfuric Acid back to  -p nitrosubstituted aniline next reduce with Fe, HCl

- yes i already worried about PET which might be highly contaminated when i was cutting into pieces blue died bottles and so decided to throw them away and take most colourless bottles i could find.. but you are right there’s probably still ton of plasticisers in it ..
the only purification i came up with is just multiple Acid base extractions but i’m pretty sure that acid will remain highly impure..

I also Thought of
Converting it to Acid halogens but not as a purification manner however it is a great idea!!
Maybe using S2Cl2.. Its another week of work especially that S2Cl2 needs to be created in situ due to decomposition, but maybe worth trying ..

Offline Synthol

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Re: Kevlar synthesis
« Reply #12 on: May 19, 2020, 04:08:56 PM »
I think you are guys right my both monomers probably will be far too impure for making high quality if any kevlar however im so upbeat to this project that i still consider trying it. It might be a complete failure and huge mess but even if - diamine and terephtalic Acid seems to be usefull reactants on its own, and also route i found seems to be high yielding so it won’t be wasted time.

Offline Enthalpy

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Re: Kevlar synthesis
« Reply #13 on: May 21, 2020, 05:49:09 AM »
Trying is the condition of success.

I had imagined plasticizers in PET, but to hold drinks, bottle have probably none. Or at least, I hope so.

Less nice: I read here
https://en.wikipedia.org/wiki/Isophthalic_acid
that PET bottles use a mix of para- and meta- diacid, possibly for shock resilience. This is undesired at Kevlar.

Offline Synthol

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Re: Kevlar synthesis
« Reply #14 on: May 21, 2020, 05:37:39 PM »
Trying is the condition of success.

I had imagined plasticizers in PET, but to hold drinks, bottle have probably none. Or at least, I hope so.

Less nice: I read here
https://en.wikipedia.org/wiki/Isophthalic_acid
that PET bottles use a mix of para- and meta- diacid, possibly for shock resilience. This is undesired at Kevlar.

Ohhhh.. less nice information Kind of broke my plan of including green chemistry to the project, tho I guess it saved me so much time and effort as
separation of this 2 isomers might be a hard task.. Thanks !!
 But  I thought of treating p-xylene with some strong oxidizing agent i guess  alkaline KMnO4 + Heat will do a job + overall rxn is much cleaner, byproducts easier to get rid of and Risk of having isomers mixture reduced down to 0. What do you think of this ? 

Update;
  there’s No point in synthesising Terephtalic Acid from p-toluene as i found it being pricier and much harder to get than the product itself. So i just found terephtalic Acid in pure form shipped by legit company with propper purity documentation so i guess i Can skip that step.

Btw
You are right i just found MSDS of plastic bottles produced by some brasil company it contains 2-5 % of isophtalic Acid, however it has No additives nor impurities.
« Last Edit: May 21, 2020, 07:20:25 PM by Synthol »

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