Re: glutaraldehyde

From: Katharine Thayer <kthayer@pacifier.com>
Subject: Re: glutaraldehyde
Date: Wed, 17 Mar 2004 16:13:15 +0000

> crosslinking, but questions whether there may be such a thing as too
> much crosslinking.

If you harden gelatin solution too much, it becomes too viscous to
coat, and eventually makes stiff gelly which won't melt at ordinary
melting/coating temperatures.

Note that much less quantity of glutaraldehyde is needed to harden
gelatin for sizing as well as other purposes compared to other
aldehyde hardeners.

> At the moment I'm experimenting with hardening gum arabic, for a
> purpose related not to gum printing but to painting; I'll explain
> after the glutaraldehyde comes and I have more complete results to
> report. But preliminary results are that at the strengths I've
> tried, chrome alum doesn't harden the gum enough and glyoxal hardens
> it perhaps too much, as it has a grainy, sugary appearance on the
> surface of the hardened gum. I'm already at the smallest amount of
> glyoxal that I can measure (1 drop) so next I will try 1 drop in
> more gum, to see if I can get the insolubility without the
> graininess.

Chrome alum's useful pH window is rather narrow. It requires carboxyl
ends to be dissociated (high pH) but at high pH chromium compounds
precipitates out and there won't be much active hardening agent left
in the solution.

Grainy appearance with hardening agent is typical if you use
concentrated hardener. You might want to dilute your glyoxal (or
glutaraldehyde for this matter) before use and use larger quantity of
it added very slowly while stirring the colloid solution.

--
Ryuji Suzuki
"All the truth in the world adds up to one big lie." (Bob Dylan 2000)