Re: gloy for tricolor on yupo?

From: Katharine Thayer <kthayer@pacifier.com>
Subject: Re: gloy for tricolor on yupo?
Date: Sun, 02 Apr 2006 09:01:18 -0700

> [...] gloy is PVA, a very simple and well-understood polymer, mixed
> with some other stuff,

Since you called gum arabic "extremely complex" and "not entirely
understood and somewhat indefinite structure," I would add that PVA is
also complex and somewhat indefinite structure.

If you read highschool textbook, PVA may be drawn like a straight
vinyl chain with alcohol hanging every other carbon (1,3-diol), but
that is not the entire picture, and PVA manufactured by current method
has some degree of branching. This is because PVA is made from
poly(vinyl esters) and this polyvinyl esters are already somewhat
branched. Then there are some places where two alcohols are hanging on
adjacent vinyl carbons (1,2-diol). Manufacturers try to minimize this
but they exist to a small percentage.

Furthermore, the alcohol groups in PVA is primary alcohol and so they
undergo usual alcohol reaction, such as oxidation. So alcohols can be
oxidized to aldehyde or carboxylic acid. Commercial PVA is likely a
copolymer with a small fraction of acrylic acids.

> while gum arabic is an extremely complex arabinogalactan protein,
> with an enormous, not entirely understood and somewhat indefinite
> structure.

Gum arabic is not a protein.

> Gloy and gum arabic may behave the same, and the crosslinking
> mechanism may well be the same (although this is only a hypothesis)

When the crosslinking of PVA is now reported to vary if moisture is
present, how can you make such a statement?

From: TERRYAKING@aol.com
Subject: Is PVA a 'Gum' ?
Date: Sun, 02 Apr 2006 04:50:32 -0400 (EDT)

> The reality is that PVA was developed after gum was defined as a
> colloidal substance of plant origin which dissolve or wells in
> water.

Gum is not defined that way. First of all, "colloidal substance" is
a semantically improper usage of the term colloidal. Colloid is a
special case of dispersion and therefore at lest two phases must be
involved. (Gum molecules can be one phase, of course, but unless there
is another phase, there can't be a colloid.)

Gum is not a scientific term. According to James BeMiller of Purdue
University, "the term gum is applied to a variety of substances that
produce sticky or slimy, viscous solutions or molecular dispersions or
gels in an qppropriate solvent or swelling agent." It has nothing to
do with what it is, how it works or what it's similar to.

As I said above, PVA is not a definite compound, but its nomenclature
has nothing to do with what people call gum.

Finally, for those who want to endlessly argue the detaied chemistry
of anything, I suggest not to post this kind of clearly incorrect and
easily rebuttable arguments, especially if you'll have to escape to
such a weak argument as "that is irrelevant to practice" or "pedantic
turn of mind" kind of nonesense. If thing's started with better
arguments, or better yet no such argument at all, we all spare
subsequent posts of rebuttal.
Received on Sun Apr 2 18:10:30 2006