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Re: [BKARTS] PVA: beware?



Jet:

Barrow conjectured superior performance was
attributed to both what was present and what was
not present.

His tests started with commercial products and
were extended with formulations comprised of
additions of various ingredients as he tried to
match the performance of his superior commercial
"Sample 7."

Quoting in parts (my comments in brackets []):

The test data for the commercial PVA emulsion
adhesives pointed to the probability that the five
less stable Samples 3, 4, 5, 6, and 8 (there were
none labeled Sample 1 or 2) were homopolymers
with relatively volatile plasticizers, while the sixth,
more stable Sample 7 was a copolymer or "internally
plasticized" polymer. These conjectures required
confirmation through tests on emulsion of known
composition, with the following results [by comparison
to the test emulsions he had made up for further
testing.]

Since the homopolymer formulations had exhibited
such inadequate stability, it was desirable to examine
some adhesives composed of internally plasticized
copolymers. Because acidity is a principal cause of
deterioration in many organic substances, and because
of the high acidity of the emulsions from which these
samples were compounded, calcium carbonate and
calcium acetate [magnesium acetate was noted in
passing] were added to render them near-neutral.

Calcium carbonate and calcium acetate were used
to buffer the undesirably low pH which is common
to nearly all PVA adhesives. Heat-aging tests indicated
that these additions increased the lasting qualities of
the unstable formulations but had almost no effect on
those of very high stability. However, these additions
have the advantage of producing a near-neutral
adhesive suitable for use with paper of good lasting
qualities.

Four copolymer ("internally plasticized") formulations
in an unusually sever heat-aging test showed little
diminution of strength after 90 days [of testing at
100º C]. These formulations may be expected to have
good lasting qualities.

---------

Lacking a simple table of "goods and bads, it appears
to me that the
-  keywords for good are copolymer and buffered;
-  keywords for bads are homopolymers and not buffered
    with calcium carbonate, or calcium or magnesium acetate.

One last observation about what may now be in commercial
PVA formulations -- Barrow reported that freezing a -30º F
was not found to result in measurable damage to the very
stable PVA's.

Contrast this with the usual supplier caveats about and
halt of shipping PVAs during the winter in the northern climes.

So far, I am unable to clearly identify what Barrow's commercial
Sample 7 was, but will continue to search for it.

Problem is, as motioned in prior discussions on this thread,
the composition of many PVAs is not revealed -- though
modifiers are sometimes noted.


Alan Shalette





----- Original Message ----- 
From: "J. J. Foncannon" <bolu.bolu@xxxxxxxxxxx>
To: <BOOK_ARTS-L@xxxxxxxxxxxxxxxx>
Sent: Wednesday, February 08, 2006 12:46 PM
Subject: Re: PVA: beware?


|
| What differentiated the "unstable formulations" of PVA from those of "very
| high stability"? Did he say?
| Interesting posting.
| Jet
|

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