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Re: [BKARTS] PVA: beware?

In all likelyhood the formulations he used back then are probably not around.  But the information and logic are probably still applicable and strong tools when thinking about PVA's.

> ----- Original Message -----
> From: "Alan Shalette" <AlShal@xxxxxxx>
> To: BOOK_ARTS-L@xxxxxxxxxxxxxxxx
> Subject: Re: [BKARTS] PVA: beware?
> Date:         Wed, 8 Feb 2006 11:34:55 -0500
> 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 con­jecture suggests one day of heat-aging
>    at 100° C. as the equiva­lent of 5 years of natural-aging.
>    Presuming this to be the case, the very stable adhesives
>    identified by the study may be expect­ed 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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