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Re: [BKARTS] PVA: beware?

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

Alan Shalette wrote:
> During the 1960's, the W.J. Barrow Research Laboratory
> conducted a series of hallmark experiments starting with
> the causes of deterioration of book papers and continuing
> with the general study of other factors causing the deterioration
> of books.
> In 1965 he published the results of his studies of PVA in
> "Permanence/Durability of the Book-IV, Polyvinyl Acetate
> (PVA) Adhesives for use in Lbrary Bookbinding."
> In it, he described in meticulous, but intelligible detail,
> the procedures and equipment he devised to test
> six commercial PVAs and eleven special formulations,
> all intended to be used in hand bookbinding.
> He also discussed a procedure for testing the acidity
> of aged, dried products.
> Among his conclusions were that (quoting) :
> - 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 producing a near-
>   neutral adhesive, suitable for use with paper of good
>   lasting qualities.
> - Other tests indicated that the acidic volatile decompo-
>   sition products (acetic acid) resulting from the aging
>   of PVA adhesives escape quickly into the atmosphere
>   and that it is consequently doubtful whether damage
>   will result to books to which these adhesives are
>   applied.
> - The increased viscosity of PVA adhesive required
>   for certain binding operations can be achieved by
>   the addition of methyl cellulose without endangering
>   the stability of the adhesive. Since methyl cellulose
>   is of value only during application and since it
>   does not increase either the stability or strength
>   of the adhesive, it should be used sparingly,
>   especially in the areas (e.g., the spine) requiring
>   high flexibility for long periods of time.
> - While in the absence of more natural-aging experience
>   of PVA adhesives than is now (sic.) available it is
>   hazardous to equate heat-aging with natural-aging, yet
>   a conservative con?jecture suggests one day of heat-aging
>   at 100° C. as the equiva?lent of 5 years of natural-aging.
>   Presuming this to be the case, the very stable adhesives
>   identified by the study may be expect?ed to have a longevity
>   of not less than 450 years, which should qualify them, with
>   respect to the characteristic of stability, for library use.
> In his discussion of the aging characteristics of PVA
> adhesives, he noted four principal mechanisms:
> - Loss of plasticizer - causes embrittlement - can be
>   accelerated at high temperatures (a storage consideration)
> - Oxidation - causes embrittlement - typically accelerated by
>   tackifying resins (such as some rosin derivatives)
> - Polymerization - breaks down and causes embrittlement -
>   accelerated by high temperatures (a storage consideration)
> - Hydrolysis - occurs at moderately alkaline pH (even 8.0) and
>   in very acidic conditions, causing loss of strength - may be
>   an environmental concern.
> I also note that the materials Barrow noted for their
> "high degree of stability" and "remarkable performance"
> had pH measurements ranging from 4.48 to 6.48 all of
> which increased with heat aging.
> Alan Shalette
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J. J. Foncannon
Philadelphia, PA  19139

	The Belgian surrealist painter Renee Magritte entered a cheese store in Brussels to purchase a wheel of Swiss cheese. 
The owner pulled a wheel from the front window, but Magritte said he preferred the one on the back counter.
	?But they are identical,? the owner protested.
	?No,? Magritte insisted.  ?This one?s been stared at.?

Now Online - The Bonefolder, Vol. 2, No. 1 at <http://www.philobiblon.com/bonefolder>
             For all your subscription questions, go to the
                      Book_Arts-L FAQ and Archive.
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