Linear Viscoelasticity Applied to Wool Setting Treatments

Abstract

An account is given of setting experiments in hot water or urea/bisulfite solutions done on keratin fibers stretched up to 5% strain. The fibers are released in water at 20°C. A formula is derived to describe the setting process in viscoelastic terms. The formula correctly predicts the amount of set or contraction in wool subsequent to a setting treatment. The formula breaks up into separate observations the factors con trolling the set produced in a fiber. The formula holds because, after setting, the fiber can be regarded as being linearly viscoelastic about its set length. The dominant factor in producing the set in a fiber is the retractive force in the fiber prior to release; however, the stiffness of the fiber after release and its decay also are significant. The stiffness of a set fiber appears to age or increase with time after release in water. The initial stiffness of the fiber after release partly determines its set.

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