From: Gordon J. Holtslander (holtsg@duke.usask.ca)
Date: 07/10/03-10:15:42 AM Z
I've been googling around the net for info on gum arabic.
Some interesting things that people may find valuable, and some questions.
Since Christina has found some information indicating past users added a
variety of things to their gum solutions, these might be some of the
reasons.
The viscosity of gum changes with its pH
Gum arabic solutions exhibit Newtonian viscosity at concentrations up to
40%; but at higher concentrations, they acquire pseudoplastic character.
Normally, gum arabic solutions are of pH about 4.5-5.5, which is near pH
6, where maximum viscosity is displayed. Solution viscosity decreases with
age, following a zero rate order. This decrease is commonly due to
hydrolysis; but gum arabic solutions are affected, as are solutions of
other gums, by ultraviolet radiation and other glycosidic bond-breaking
phenomena. Viscosity rises with increases in pH to about 6 then gradually
falls to about pH 12 , where it again levels off. However, a more or less
broad maximum viscosity is displayed over the range pH 2-10. As expected,
when the pH is lowered to 3 or less, the ionization of the carboxyl groups
is repressed, and the polymer tends to gel and lose solubility.
^from http://www.jumbo.th.com/application.html
Is gum viscosity significant in gum printing?
Does viscosity influence gums hardening with a dichromate?
Gum Arabic consists of Arabic acid, C12H22O11, combined with calcium,
magnesium, and potassium, to the presence of which its solubility is due
^ from http://www.ibiblio.org/herbmed/eclectic/sayre/acacia-sene.html
If the viscosity of Gum is signifcant for gum printing would altering the
amount of calcium,magnesium, or potassium in a gum solution signifcantly
change its behaviour? If so how can this be done chemically?
Gum arabic is effective in preparation of oil-in-water emulsions. The
emulsions are stable in the presence of electrolytes; in fact, some
emulsions develop improved stable in the presence of electrolytes. Thus,
an emulsion produced by 10% gum arabic can be duplicated in stability by a
0.5% gum solution to which a sodium salt has been added. Stable emulsions
are produced by gum arabic over a range of pH values. Gum collects at the
emulsion interface in the form of a visible film that prevents coalescence
of the oil microspheres. The viscosity of the emulsion differs with the
type of oil and film thickness.
^ from http://www.jumbo.th.com/application.html
Gord
---------------------------------------------------------
Gordon J. Holtslander Dept. of Biology
holtsg@duke.usask.ca 112 Science Place
http://duke.usask.ca/~holtsg University of Saskatchewan
Tel (306) 966-4433 Saskatoon, Saskatchewan
Fax (306) 966-4461 Canada S7N 5E2
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