Cellulose nitrate

Paul Storch <paul.storch [at] mnhs__org> writes

>Has anyone ever found white, acicular crystals growing on the
>surface of a cellulose nitrate object?  We recently removed a chair
>upholstered in faux-leather from exhibit after 12 years and found
>the sides and part of the back fairly uniformly covered with the
>crystals. The crystals brush off easily and there is no visible
>damage to the surface.  I tested the coating of the upholstery and
>found it to be cellulose nitrate, which is common in faux-leathers.
>The chair was made in the 1950's.  There was no camphor smell, or
other odors, and none of the other objects in the case with the
chair underwent any changes, so we have ruled out VOC's from the
case materials. The crystals were soluble in water, ethanol and
acetone.

The white crystals may result from degradation of phthalate
plasticizers which have been the most frequently used plasticizers
since the 1950s.

As esters, phthalate plasticizers are susceptible to hydrolysis when
exposed to strongly acidic or alkaline conditions.  Phthalic acid
(in acidic conditions) or anhydride (in alkaline conditions) and
alcohol are the products of such reactions.  Acidic conditions are
likely to arise when the cellulose nitrate degrades to form nitrogen
oxides, resulting in the formation of needle-like, white crystals of
phthalic acid; these are highly soluble in water and alcohol.

Yvonne Shashoua
Senior Researcher in plastics and rubbers
National Museum of Denmark


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                  Conservation DistList Instance 18:23
                 Distributed: Monday, November 22, 2004
                       Message Id: cdl-18-23-003
                                  ***