The hygroexpansivity of cellulose papers

Cellulose papers expand and contract when the humidity of the atmosphere with which they are in equilibrium changes. This phenomenon - known as hygroexpansivity - plays a significant role in the manufacture of such electrical components as capacitors, cables and transformers due to the shrinkage and consequent mechanical instability which the units suffer on being dried before impregnation. While many investigations have been made of the phenomenon, most of the work has been hampered and made useless by the failure of the researchers to establish repeatable data. It was the purpose of this work to determine why the effect was not reproducible within close limits and from the results to understand the mechanism of hygroexpansivity.