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Re: [BKARTS] PVA, internally plasticized



Now that's some very useful information.




> ----- Original Message -----
> From: "Audrey Hollinger" <audreyh@xxxxxxxxxxx>
> To: BOOK_ARTS-L@xxxxxxxxxxxxxxxx
> Subject: Re: [BKARTS] PVA, internally plasticized
> Date:         Tue, 7 Feb 2006 17:29:37 -0500
> 
> 
> Perhaps the term "internally plasticized" is poorly chosen since I would
> expect the alternative ("externally plasticized"???) would have no
> effect on the structure of the dried glue. If the plasticizer isn't *in*
> the vinyl resin I don't see how it could have any effect.
> 
> I think that all PVA is plasticized to varying extents; padding glue is
> essentially a PVA plasticized to the point that it is soft an rubbery.
> The plasticizers are added to the vinyl resin to control the flexibility
> and strength of the dried glue. The problem is that many plasticizers
> are volatile and gradually diffuse out of the hardened plastic (the
> dried glue is essentially a film of vinyl). This is one thing that
> contributes to that "new car smell" and why not all plastic containers
> are food-safe.
> 
> The loss of plasticizers is one reason why plastic objects tend to
> become brittle as they age. The other major reason is UV damage. Both
> these effects contribute to your shower curtain example, the diffusion
> being aided by the large amount of surface area.
> 
> As mentioned in another posting, the dried film does not have a pH per
> se (nor for that matter do dry paper, thread, or leather), but it does
> have an effect on the pH of any moisture that contacts it. Furthermore,
> because of the release of gases during aging (not only plasticizers, but
> also emulsifiers and stabilizers from the original liquid and breakdown
> products of the vinyl itself) these gases can affect the pH of moisture
> at a distance. Thus the glue used in a sealed (or semi-sealed) display
> case can also be a cause for concern.
> -Kevin Martin
>   the Papertrail
> 
> 
> 
> > -----Original Message-----
> > From: Book_Arts-L [mailto:BOOK_ARTS-L@xxxxxxxxxxxxxxxx] On Behalf Of
> Nancy Nitzberg
> > An issue which I don't believe has yet been mentioned in regard to the
> 
> > quality of PVAs is that of "plasticizers."   While this 
> > information may be somewhat dated, it was the case that the
> PVAs
> > sold by conservation suppliers were "internally plasticized," meaning
> that
> > their flexible qualities were molecularly locked in.
> 
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>

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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.
                                    
          See <http://www.philobiblon.com> for full information
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