The Influence of the Multi-level Structure Under High Drawing on the Preparation of High Strength Lyocell Fiber

In order to research the multi-level structure of Lyocell fiber at different draw ratios and to reveal the limiting factors for preparing the high strength Lyocell fiber, the paper reports on the effect of draw ratio including low drawing (1–5), high drawing (6–11) and excessive drawing (12–20) on the multi-level structure and the mechanical properties of Lyocell fiber. The structure was determined by wide-angle X-ray diffraction, small-angle X-ray scattering and fibrillation test, and the result showed that, at low draw ratio stage, the breaking strength, yield strength and modulus of the fiber increased with the draw ratio owing to crystallinity as well as orientation increased while the micropore decreased, and there are almost no microfibrils on the fiber surface. At high draw ratio stage, the orientation of amorphous region increasing was the principal reason for the increase of fiber mechanical properties, and the micropores continued to decrease and a few short and thick microfibril was formed. At excessive draw ratio stage, the breaking strength remained constant mainly due to the basically unchanged crystallinity and orientation of the fibers, the yield strength and modulus decreased due to the slip of the highly crystallized and oriented elementary fibril. Meanwhile, the micropores still decreased and became much slenderer, the number of microfibrils increased and the microfibrils showed tenuous structure. It could be summarized that Lyocell fiber had the characteristics of multi-level structure, and the fundamental reason limiting the improvement of mechanical properties with draw ratio increase was the slip of elementary fibril.

APPLICATION OF LYOCELL FIBER STRUCTURE FORMATION MECHANISM IN FLAME-RETARDANT MODIFICATION OF LYOCELL FIBER

In order to overcome the disadvantage of Lyocell fiber flammability, two types of flame-retardant finishing liquids, 2-carboxyethyl phenylphosphic acid (CEPPA) and N-hydroxymethyl-3-dimethoxyphosphoacyl propanamide (MDPA), were used in this study to treat Lyocell fiber in two different states: never-dried and dry. The results showed that CEPPA and MDPA can react with the hydroxyl groups of the cellulose and graft onto the Lyocell fiber under appropriate conditions, resulting in increased flame-retardant performance of the fiber, a slight reduction in crystallinity, and a significant decline in mechanical properties. Compared with the dry fiber, the P content and LOI of the fiber obtained by treating the as-spun never-dried Lyocell fiber rose significantly: the P content was higher by 38.9% (for CEPPA) and 20.5% (for MDPA), respectively, while the LOI increased by 6.0% (for CPPA) and 4.0% (for MDPA), respectively, which means that the fiber had better flame-retardant performance. Although the breaking strength of the fiber decreased, it still met the requirements for textiles. In addition, direct flame-retardant treatment of never-dried wet fiber can reduce energy consumption by avoiding repeated drying. Furthermore, the results of this study also have guiding significance for other post-processing procedures for Lyocell fibers, such as dyeing, catalyst infiltration during carbon fiber preparation etc

Basic research about corncob residue as Lyocell spinning material

Using the corncob residue as a new cheaper source material for Lyocell spinning technology. Chemical properties of the corncob residue after extraction of hemicellulose and lignin were investigated in this paper. It was found that the main composition of corncob residue is cellulose, accompanied by slight hemicellulose and very tiny amount of spinning insoluble components. Compared to wood pulp, corncob residue has a similar number-average molecular weight, a slightly larger weight-average molecular weight, a lower peak-relative molecular weight, and a larger polydispersity. All those properties suggest that this kind of corncob residue has big potential to be used as spinning material for regenerated cellulose fiber. A new type corncob residue made fiber was produced, using the Lyocell spinning technology. Mechanical properties of the corncob residue fiber were analyzed. The corncob residue fiber has a tensile strength value between that of viscose fiber and Lyocell fiber, indicating its good application prospects. However, the corncob residue fiber has a high crystallinity and the orientation value with large fiber linear density, suggesting that the spinning technology needs to be further improved.