Influence of pH on hygral expansion, relaxation shrinkage and extensibility of wool fabric

The standard tests for relaxation shrinkage and hygral expansion of wool fabric take no account of pH. It is shown in this work that the pH of the solution in which wool fabric is relaxed as part of the procedure for measuring dimensional properties has a significant influence on the results. At around pH 4.8, which is close to the isoelectric point of wool, the hygral expansion reaches its greatest value and drops at both lower and higher pHs. A similar relationship between pH and extensibility of wool fabric was observed. Values of relaxation shrinkage were found to be dependant on pH. The reasons for the pH dependence of dimensional properties are discussed and these include changes in wool fiber swelling, yarn crimp and polymer relaxation phenomena with changes in pH.