Effect of fiber swelling on the structure of lyocell fabrics

The effect of liquid swelling on the structural rearrangement of lyocell tw ill fabrics is studied using a variety of techniques, including optical mic roscopy, dimensional measurements, and water and hexadecane retention. Lyoc ell fibers swell predominately laterally in water by about 30% over the dry diameter. Fiber lateral swelling in NaOH solutions is greater than in wate r, with diameters increasing by over 200% at optimum concentrations. The la teral expansion in the fibers leads to fabric shrinkage (reduced planar dim ensions and increased fabric thickness), which explains most of the irrever sible constructional changes that occur during tensioned preparation from t he loomstate. Fabric structural changes during subsequent wetting and dryin g are also explained using swelling-shrinkage and hygral expansion-contract ion models. Irreversible swelling-shrinkage in NaOH is exaggerated, and sub sequent rewetting leads to reversible fabric growth rather than the reversi ble shrinkage experienced by fabrics prepared in water. NaOH treated fabric s also have lower wet state rigidity than fabrics prepared in water. Tensio ned NaOH treatment allow fabrics to be stabilized at larger dimensions and a permanent, flatter fabric construction with lower amplitude reversible be havior.