Re: polivinyl alcohol vs. gelatin sizing

Ryuji Suzuki wrote:
>
> From: Giovanni Di Mase <gdimase@hotmail.com>
> Subject: Re: polivinyl alcohol vs. gelatin sizing
> Date: Sat, 30 Jul 2005 16:28:30 -0400
>
> > Let's be very clear, which one is Elmer's glue made from?
>
> The main ingredient is poly(vinyl acetate) and water.
>
> > When you said PVA is acetate or alcohol?
>
> PVA is an ambiguous acronym. Some people use PVOH to indicate
> poly(vinyl alcohol) to avoid confusion.
>
> > Yes, there is a confusion between them.
>
> There is no confusion in terms of chemistry. The confusion is just in
> acronyms. It's also that vinyl acetate and vinyl alcohol are often
> used as copolymers and also as mixtures of multiple copolymers in
> practice to achieve desired properties. One example I gave was acrylic
> medium.

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.
Katharine Thayer
Received on Sun Jul 31 09:51:57 2005