The Dimensional Properties of Knitted Wool Fabrics

Abstract

Tumble-drying from the wet fabric state is shown to be a reasonable means of fully-relaxing rib structures. By this technique, an approximate discrimination can be made between dimensional changes due to relaxation and felting of all- wool rib structures. Upon washing from the fully-relaxed state, untreated fabrics felt immediately due primarily to loop-length changes and not by changes in loop shape. Felting rates depend strongly on machine tightness factor (MTF) and to a lesser extent on fiber quality and yarn twist. To ensure machine washability of rib structures to within the limits of ± 8% area shrinkage and ± 5% linear shrinkage over 10 machine-wash and tumble-dry cycles, yarns must be treated against felting at a high level of treatment. Further dimensional changes in washing from the fully-relaxed state are due to residual relaxation and not felting. Occasional fabrics, particularly loosely knit structures, exceed these chosen shrinkage limits. To guarantee machine washability of rib structures, a fully-relaxing procedure of two cycles of wetting and tumble-drying is recommended. Under most conditions of relaxation and washing, the dimensional behavior of shrink-resist-treated rib structures is anisotropic, i.e., length shrinkages are generally associated with width expansion. A possible reason for this behavior is presented in this paper.