7—the Rôle of External Polymers in Improving the Wrinkle-Recovery of Wool Fabrics

Stress-relaxation curves of a worsted fabric in bending, obtained under changing humidity and temperature conditions, are compared with those obtained from the same fabric treated with an elastic silicone polymer used to impart improved wrinkle-resistance. From an analysis of these curves, it is shown that the strain levels occurring in the polymer when the treated fabric is bent are two orders of magnitude higher than the strain levels occurring in the wool. From these and other data, it is concluded that the polymer improved the wrinkle-recovery of wool fabrics by providing elastic connexions between fibres. These act firstly by considerably reducing the frictional restraint impeding recovery and secondly by providing an additional elastic restoring force, which does not stress-relax and is unaffected by temperature and humidity changes. This additional elastic restoring force arises from energy stored in shear deformations in the polymer.