Experimental Investigation of the Recovery of Soaked Paper Using Evaporative Freeze Drying

Abstract

The aim of this article is to develop an experiment and a procedure to investigate the restoration of water-damaged paper and archival materials using freeze drying in order to allow a reproducible test and comparison of the influence of different operating conditions on drying time and restored paper quality. Firstly, a reproducible method for the preparation of soaked samples simulating water-damaged paper has been developed. Then, the samples have been freeze-dried in a laboratory-scale apparatus that allowed monitoring the temperature as well as the weight of the samples. The technique of evaporative freezing, which reduces the drying time required, has been used in this case. An innovative procedure for the visualization of the progress of the drying process has been validated, thus allowing the validation of a simple phenomenological model of the time evolution of the ice core volume; in addition, data on the residual moisture of the dried paper sheets in different zones have been given. Finally, optimization of this particular drying process by using simple or more sophisticated approaches has been discussed.

Keywords:

• Archival materials restoration
• Evaporative drying
• Freeze drying
• Vacuum drying
• Water-damaged documents

ACKNOWLEDGEMENTS

The authors thank Dr. Francesca Bosco and Dr. Mauro Banchero (Dipartimento di Scienza dei Materiali e Ingegneria Chimica, Politecnico di Torino, Italy) for fruitful discussions and technical assistance.