Stress-Strain and Recovery Properties of Cross-Linked Rayon Yarns in the Wet and Dry States

Abstract

Continuous-filament rayon yarns were subjected to an acid-catalyzed cross-linking treatment using dihydroxydi methylol ethyleneurea under pad-dry-cure conditions to two levels of add-on. The stress-strain curves of these yarns were measured at a constant 40%/min rate of extension in the dry (65% RH and 70°F) and wet states and in an "anhy drous" condition. In the dry state, cross-linking increases the elastic modulus, the stress at the yield point, and the stress at break, and decreases the extension at break and the energy to break. In the wet state, there is a disappearance of the primary yield point and the deformation process is plastic-like from the onset without an initial Hookean elastic region. Furthermore, in the wet state, the untreated yarns are weaker and more extensible than under dry conditions, but cross- linking again increases strength and decreases extensibility. Cross-linking brings about the reappearance of the primary yield point even in the wet state. This is interpreted to reflect a protective effect of the hydrogen-bond network in the cellulose structure. The recovery properties were measured as a function of load, strain, and energy of deformation over the entire possible range of values. In uncross-linked state, dry yarns are more resilient than wet yarns, when measured from given loads of deformation, whereas wet yarns are more resilient than dry yarns, when measured from given strains, except for strains below the primary yield point. At low energies of deformation, uncross-linked dry yarns are more resilient, whereas at higher energies of deformation the reverse is the case. These data clearly indicate that, in comparing the recovery prop erties of yarns with different stress-strain curves, an entirely different view of this important yarn characteristic is obtained, depending on whether recovery is measured from given loads, strains, or energies of deformation. Cross-linking significantly increases resilience both in the wet and dry states, particularly from higher levels of deformation.