Physical Ageing and Annealing in Fibers and Textile Materials

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Abstract
The theory of viscoelasticity in textile assemblies reported in Part I of this series of papers is extended to blended textile materials. The complex effects of ageing or an nealing or both of these on the stress relaxation processes in a blended textile material are separated into several regions according to the demarcation provided by the glass transition temperature of the constituent fibers in the blend. The influence of ageing or annealing processes on the mechanical properties contributed by constituent fibers in the blend can be represented by horizontally shifting the stress relaxation curves of the fibers in the logarithmic time scale. The time shift factors for each individual group of fibers in the blend take into account the changes in temperature and ageing or annealing history. The sufficient condition to obtain a single effective time shift factor for the blend is that all viscoelastic component fibers must have only one identical time shift factor with respect to the same reference state. The theory predicts that, in most real situations, there should be no single time shift factor obtainable for textile blends owing to the differences between the shift factor of the component fibers. The interaction between the fiber components in a blended fabric represents an important aspect of its viscoelastic behavior. An experimental study reveals that the interaction between fiber blend components in wool/polyester fabrics is influenced by the differ ences in the stress relaxation behavior of the blend constituents, blend composition, and fabric weave construction. The study also indicates that the annealing process improves the viscoelastic properties of wool/polyester blended fabrics. Optimum an nealing conditions occur when these fabrics are heated in the vicinity of the glass transition temperaure of wool fibers at the equilibrium moisture regain corresponding to 20°C and 65% RH.