Re: adhesion

From: John Cremati <johnjohnc@core.com>
Subject: adhesion
Date: Fri, 04 Feb 2005 18:02:38 -0500

> I use a animal hide glue to glue chip glass.. The adhesion
> is so good that it will literally rip the surface of the glass of
> the glass plate creating a frost or fern like pattern as the glue
> dries............A property of the glue aside from the adhesion is
> that it shrinks when dried......How does this hide glue compare to
> your special gelatin?

I'm not sure about the comparison because I don't use that type of glue.

My chemically modified gelatin is made from regular lime treated
ossein gelatin. Dissolve the gelatin to make 1-10% solution and hold
it at 40C. To this solution, 10% (2.5M) NaOH is added to adjust the pH
to about 10. To this, 10% phthalic anhydride dissolved in dry acetone
is added in quantity about 1/10 of gelatin by weight (e.g. 1g PA
dissolved in 10ml acetone is added to 10g gelatin dissolved in 200 ml
water). The pH will slowly drop, but add necessary amount of NaOH to
maintain the pH at about 10 for 5 minutes or longer. All these should
be doen at 40C and with continual stirring. After that point, separate
gelatin from the water phase by lowering the pH to between 3.0 and 3.5
(gelatin will precipitate out and it will remain insoluble unless pH
is changed far above or below this range.) and use it as a part of
the sizing or emulsion.

Gelatin thus modified has increased carboxyl groups, thereby improving
the adhesion. Also as a consequence of this chemical modification, the
gelatin has little or no available amino group, because they are
almost completely sealed to provide extra carboxyl groups (called
acylation).

What it means is that, this type of gelatin cannot be crosslinked by
almost any hardener except chrome alum, unless some unmodified
gelatin is mixed in.

--
Ryuji Suzuki
"People seldom do what they believe in.  They do what is convenient,
then repent." (Bob Dylan, Brownsville Girl, 1986)