Effect of Fiber Swelling on the Structure of Lyocell Fabrics

Abstract

The effect of liquid swelling on the structural rearrangement of lyocell twill fabrics is studied using a variety of techniques, including optical microscopy, dimensional measurements, and water and hexadecane retention. Lyocell fibers swell predominately laterally in water by about 30% over the dry diameter. Fiber lateral swelling in NaOH solutions is greater than in water, with diameters increasing by over 200% at optimum concentrations. The lateral expansion in the fibers leads to fabric shrinkage (reduced planar dimensions and increased fabric thickness), which explains most of the irreversible constructional changes that occur during tensioned preparation from the loomstate. Fabric structural changes during subsequent wetting and drying are also explained using swelling-shrinkage and hygral expansion-contraction models. Irreversible swelling-shrinkage in NaOH is exaggerated, and subsequent rewetting leads to reversible fabric growth rather than the reversible shrinkage experienced by fabrics prepared in water. NaOH treated fabrics also have lower wet state rigidity than fabrics prepared in water. Tensioned NaOH treatment allow fabrics to be stabilized at larger dimensions and a permanent, flatter fabric construction with lower amplitude reversible behavior.