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Topic: Fiber reactive dyes and acid damage  (Read 168 times)

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Offline pcm81

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Fiber reactive dyes and acid damage
« on: September 18, 2020, 05:17:57 PM »
Greetings and salutations.
I bring today a puzzle from my observations today.
I have a set of pants that has some damage on them (discoloration) from muriatic acid. I tried to dye them with fiber reacive dye and stumbled on an interesting observation.

Normally fiber reactive dye is used on natural fibers at high-ish ph ~10 and it forms covalent bonds with cellulose in plant cell walls.
At low Ph values fiber reactive dyes can act like acid dyes and form ionic bond with proteins in wool or silk.

The pants in question are 100% cotton so i expected a reaction at high pH. It is interesting to note that fiber reactive dye took to the areas not damaged by muriatic acid, but for most part left the damaged areas untouched.
I then made a low ph solution with vinegar and the same fiber reactive dye (new batch from same jar). Interesting enough the acid bath colored the burnt areas better than high ph bath.

This makes me wonder if muriatic acid burn left the cellulose in a state unable to  bond covalently to fiber reactive dye, but low pH bath enabled the bonding like an acid dye? This further makes me wonder if for such acid burned fabric a chemical pre treatment can be used to enable covalent bonding in high pH bath, like fiber reactive dyes are supposed to work.

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