Dear Sir. Concerning your issue about the method that dissolve lyocell fibres. The dissolution of cellulose, lyocell fibres, can be carried out in NaOH/ urea solution has strong dependence on the temperature of reaction. There is a critical temperature for reaction to take place in the studied solution system. The optimum NaOH concentration in this study is at 6% for high molecular weight cotton linter. Or can be dissolve in N-methylmorpholine N-oxide, to give a solution called "dope." I think the following below links may help you in your analysis:

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.465.6848&rep=rep1&type=pdf

https://en.wikipedia.org/wiki/Lyocell

http://www.ingentaconnect.com/contentone/aatcc/jor/2017/00000004/00000002/art00002?crawler=true&mimetype=application/pdf

Thanks

Dear Isam Eldin Hussein Elgailani,

Thanks for your elaborated reply and the links. We have experienced difficulties to dissolve lyocell fabrics. I guess the hornification is significant. We have used standard methods for DP determination developed for dissolving pulp. I've ordered your third tip and I'm excited to read it. Once again thank you.

The NaOH/urea, NaOH/thiourea and related systems are indeed great to dissolve cellulose fibers in general. However, it is inevitable that depolymerization will also occur. If decreasing DP is not a problem, you could try to pre-treat your fibers in an ethanol/HCl system before dissolution. See this paper

Article Enhancement of cellulose dissolution in water-based solvent ...

This route has helped me a lot to dissolve long cellulose fibers (from sisal plant), which showed to be tricky at first.

Anyway, a good way to go may be with DMAc/LiCl. Have you tried?

Dear Bruno Vinicius Manzolli Rodrigues,

Thanks for your advice. The reason we want to dissolve the lyocell fibres is to study their DP. Hence, NaOH based solvents may not be the optimum choice. We have received the advice to use DMAc/LiCl also from others who have not followed this thread.

Dear, Anders

In this case, I would go with the old aqueous solutions of metal complexes like cuproethylene diamine or cuprammonium hydroxide (Cuam)

They are simply great to dissolve cellulose for DP analysis. No derivatization and/or depolymerization usually take place.

Cheers.

Dear Bruno,

Thanks for the tip. Cuam is actually what has failed to dissolve our lyocell. We followed the standard ASTM D1795.

Dear Anders,

I wish you luck! Btw, do you have any idea about the DP value and crystallinity index?

Thank you Azadeh,

Are suggesting that the better solubility of cellulose a solvent system offers in the lyocell process - the better it will manage to dissolve the formed lyocell fibres?

Cheers,

Anders

Dear Marc Kostag

They have been dissolved using GPC solvents but not yet by conventional cellulose solvents.

Are you suggesting that it might be resin finish that needs to be removed in order to dissolve the lyocell fibres?