Multiscale structure of cellulose microfibrils in regenerated cellulose fibers

Cellulose in solution can be assembled into textile fibers by wet-spinning (Viscose etc.) or dry-jet wet spinning (Lyocell, Ioncell etc.), which leads to significant differences in the mechanical properties of fibers. We use scanning X-ray microdiffraction (SXM) to reveal regenerated fibers having a "skin-core" morphology. The "core" region comprises microfibrils (MFs) with ~100 nm in diameter. The cellulose forms elementary fibrils having a ribbon-like cross sectional shape of about 6 × 2 nm, which are packed into MFs. Our SXM studies demonstrate that MFs within Ioncell fibers are composed of elementary fibrils with homogeneous morphologies. Furthermore, the stacking of cellulose molecular sheets within elementary fibrils of Viscose fibers is preferentially along the 010 direction, while those of Ioncell fibers preferably stack in the 1-10 direction. The better structural regularities and distinct morphologies of elementary fibrils give Ioncell fibers enhanced mechanical properties and a wet strength far superior to those of Viscose fibers.