Cross-sectional Distribution of Crystalline and Fibril Orientations of Typical Regenerated Cellulose Fibers in Relation to their Fibrillation Resistance

Abstract

The structural distributions and their formation mechanisms, on both the morphological and crystallographic scales of two types of regenerated cellulose fiber, cuprammonium rayon (Cupra) and solvent spun rayon (Lyocell), were studied in relation to fibrillar formation using transmission electron microscopy and electron micro-diffraction analysis. Cupra had a multilayer structure. The outer layer of the fiber had a network structure without distinct fibrils, but with high crystallinity (χ_c) and crystalline orientation ( F_c), whereas the center of the fiber had a well-developed fibrillar structure with an amorphous state. The high χ_c in the outer layer probably resulted from the release of both copper and ammonia from the fiber during coagulation. The fibrillar structures in the center could have been formed by the deformation of the network structure along the elongation direction before crystallization took place. Lyocell was crystallographically and morphologically uniform along the fiber radius, with a highly developed fibrillar structure with high χ_c and F_c. The type of fibrillar formation was closely correlated with the morphological distribution, that is, fibrillation started from layers with a well-developed fibrillar structure.