19—THE RELAXATION SHRINKAGE OF WOVEN WOOL FABRICS DURING SOAKING IN WATER AND HOFFMAN PRESSING

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Abstract
The relaxation properties of a wide range of woven wool fabrics have been examined by soaking in water, in solutions of different pH value and by Hoffman pressing and steam treatment. Since considerable shrinkage occurs during the drying of these fabrics, the “wet” measurement method used for hosiery fabrics cannot be employed and it is necessary to condition the specimens in a standard atmosphere before measurement. It is shown that the extent of shrinkage by soaking depends on a number of factors of which the most important are (a) temperature and pH of the solution used; (b) the number of soaking treatments given; (c) the relative humidity of the atmosphere in which the specimens are measured and, (d) the size of the speciniens tested. The shrinkage obtained during pressing depends on the condition of the steam used, e.g., wet steam will generally give a greater shrinkage than dry. “London Shrinking” treatment does not always render a fabric stable to Hoffman pressing. In two appendices, the results of experiments on (a) the effect of sett on shrinkage, and (b) a comparison of a curved-bed and flat-bed Hoffman press, are given. It is shown that tightly woven fabrics are more stable than fabrics of an open weave and that the differences between the shrinkages obtained with the two types of press are small. The curved-bed press tends to give a higher shrinkage than a Hat-bed, whilst the application of the vacuum with the head unlocked tends to give a greater shrinkage than with the head locked.

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