Influence of Domain Orientation on the Mechanical Properties of Regenerated Cellulose Fibers

Abstract

The determination of the crystal orientation of regenerated cellulose fibers produced under different drawing regimes is presented. Orientation is determined by using wide-angle X-ray diffraction from a synchrotron source and by measuring the azimuthal width of equatorial reflections. The orientation parameter <sin2> theta is then determined to compare fiber samples. By using a 500 nm beam size, clear differences between the crystal orientations of the skin and the core of the fibers are reported for a range of differently processed fibers for the first time. These results are shown to have implications for the mechanical properties of regenerated cellulose fibers. By applying tensile deformation to fiber bundles it is shown that the most misoriented samples undergo rapid decreases in the orientation parameter, which is an indication of crystal reorientation. However, the more highly oriented fibers undergo little reorientation. An average shear modulus for these fibers is determined by placing the data on a master curve and fitting with a model equation. By using another model for the fibers of low orientation and the shear modulus from the master curve analysis, it is shown that the deformation of less oriented fibers is dominated by shear between crystals, whereas the more oriented filaments are likely to undergo more significant chain deformation. By using a new model for fibers of low orientation, a parameter ksigma is introduced that gives the proportion of the fiber stress that is due to crystal shear. Systematic differences between this parameter for fibers of increasing initial orientation are reported. Moreover it is shown that the fibers of initially lower average orientation are governed by uniform strain, in agreement with the new model, whereas more highly oriented fibers deform under uniform stress. Furthermore, the model that we propose for misoriented domains and the use of a new factor dictating the proportion of shear stress may have general applications in materials engineering.

All-cellulose composites by surface selective dissolution of aligned ligno-cellulosic fibres

“…Furthermore, the reduction in the sharpness of the reflections for the composites prepared with longer immersion time also indicates lower molecular orientations in these composites. This is caused by an increase in the fraction of the formed amorphous phase (no orientation) with immersion time [32]. Correspondingly, the scanning electron micrographs (SEM) of the cross-section of the composites ( Figure 5) show that longer immersion times lead to a reduction in fibre size and the formation of thicker matrix layers between the remaining fibre cores.…”

Reorientation of crystalline and noncrystalline regions in regenerated cellulose fibers and films tested in uniaxial tension

“…That is, flax,2, 3 coir,4 thin slices of wood,3, 5, 6 and single wood fibers5 using X‐ray diffraction (XRD) technique. Wide‐angle XRD experiments with strained regenerated cellulose fibers7–9 and cellulose composite films10 also demonstrated the reorientation of crystalline regions upon straining. In a recent study, it was shown that the mechanical performance of regenerated cellulose films can be greatly improved by stretching in wet condition and consecutive drying 11…”

Alkali Treatments of Woven Lyocell Fabrics

“…However, Gindl et al (2006) showed that only two different parts within lyocell fiber do exist, skin and core. They observed that studied fibers have uniform skin-core orientation, in contrast, Kong et al (2007) obtained non-uniform skin-core orientation by X-ray diffraction as claimed due to the differences of used beam size (5 × 5 µm vs. 500 nm). This non-uniformity resulted in the higher average orientation of the fiber skin than of the core.…”