Re: polivinyl alcohol vs. gelatin sizing

From: Katharine Thayer <kthayer@pacifier.com>
Subject: Re: polivinyl alcohol vs. gelatin sizing
Date: Sun, 31 Jul 2005 08:55:57 +0000

> Perhaps, but in practice, which is what I think we're talking about
> here, they behave very differently. You can use polyvinyl alcohol as the
> colloid in the gum process. You can't use polyvinyl acetate or acrylic
> to print gum with, as neither of them will dissolve once dry, and the
> polyvinyl acetate won't mix with the dichromate; it just precipitates
> into little clumps of gunk. (I found this out once when I bought
> something called PVA glue, assuming it was polyvinyl alcohol). So it
> doesn't make sense in terms of practice to talk about them as if they
> were interchangeable.

Oh please, you must be thinking that I am saying PVA and PVOH are same
or similar. No one said that!

If you look at molecular structure of alcohol (very hydrophillic) and
acetate (hydrophobic) any reasonable chemist can tell those vinyl
polymers behave very differently. Also, there is no point of making
effort to make copolymers of similar things. People make copolymers of
various ratios because they want a mix of two different
functionalities in each molecule.

I said in acrylic medium, poly(vinyl acetate-co-alcohol) is used as an
emulsifying agent. Emulsifying agent, by definition, is something that
stabilizes the interface between water phase and non-water
soluble/miscible phase. Acrylic, that is polyacrylates, are
hydrophobic and emulsifiers are used to hold them in water. Neither
PVA nor PVOH alone can serve this purpose. Their mixture cannot serve
this purpose. But their copolymers can.
Received on Sun Jul 31 11:45:11 2005