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Re: Methyl cellulose

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Jake's clear exposition of the various uses of MC is most welcome.  Our
own observations bear this out.  We worked on a number of fronts in our
own studies.

An MC for:

*  PVA thickener
*  Surface resizing of paper
*  Immersion resizing of paper
*  A light adhesive for fine tissue

Each of these requires a somewhat different grade, and the Dow booklet
which Jake mentions, together with the accompanying graphs and tables of
viscosity for the different grades, needs careful study to determine
what is needed.  Excellent bedtime reading!

We worked particularly on an appropriate grade of MC for resizing.  If
an inappropriate grade is used, then, amongst other problems, the sizing
can cause the paper to become too hard and brittle.  Thus, if a double
leaf of a signature is resized, one must be sure that the resizing mix
will allow sufficient strength, yet remain flexible, so as not cause the
fold to break when refolding the signature, and its subsequent resewing.
Careful analysis of Dow's MCs led us to a mixture of two grades:  A4M
and A15L.  These give a balance between a short molecule, and a long
molecule, respectively, enabling strength with the long molecule, and
penetration into the paper fibres with the short molecule.

An important article in the Manchester Conference Papers of the
Institute of Paper Conservation (1992) also went into this matter:  "The
role viscosity grade plays when choosing methyl cellulose as a sizing
agent", by Cathleen Baker.

For what it's worth, a small offering of our experience.....

Peter Krantz

Book Restorations.

Established 1976

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