Objective A varity of Lyocell fibers in the market are different in the product quality and spinnability. In order to understand the performance and quality differences of different Lyocell fibers and the analysis of the causes, this research systematically studied the differences of Lyocell fibers in terms of morphological structure, mechanical properties, wear properties, crystallinity, orientation and filament ratio, and analyzed the reasons for the differences. This paper provided suggestions for the subsequent improvement and development direction of domestic Lyocell fibers.
Method Lyocell fibers from 9 different manufacturers were selected for characterization and comparative analysis on the apparent morphology, mechanical properties, frictional properties, crystallinity, orientation and filament ratio. Due to the differences in the process route and post-treatment technology, the quality of domestic Lyocell fibers has a certain gap compared with Lyocell fibers prepared by major international manufacturers. The characterization instruments used in this research includes SEM,XRD,microscope,fiber wet tribometer and fiber strength tester.
Results Except for domestic Lyocell fibers, filament cross sections are approximately circular with certain defects and creases on the surface and uneven fiber diameter thickness (Fig.2). The 1# and 3# fibers have a small amount of hollow structure, and the 7#fibers have a large amount of hollow structure. The mechanical properties of all Lyocell fibers from different manufacturers have little difference in dry breaking strength ranging from 3.6 to 4.0 cN/dtex, elongation at break ranging from 7% to 10%, and initial elastic modulus ranging from 60 to 70 cN/dtex (Tab.3). The polymerization degree of the 1# fiber is low (Tab.3). When the capacity of the spinneret component is the same, the cellulose concentration in the spinning stock solution of the 1# fiber is higher, which is more conducive to the increase of production line output and reduce the fiber production cost. The rotation time of friction axis of 1# Lyocell fiber is 8.76 s. The rotation time of friction of domestic Lyocell fiber is short and the degree of fibrillation is relatively high (Tab.4). There is no significant difference in the major diffraction peaks of all Lyocell fibers, and the diffraction peaks of 1# and 2# fibers are significantly lower than those of other fibers (Fig.3). Most of the domestic Lyocell fibers have (040) crystal planes near 2θ of 35.5°, indicating that there are a few quasicrystals in amorphous regions in the fibers. The crystallinity of domestic Lyocell fibers is higher than that of foreign countries on the whole, and the orientation of Lyocell fibers of different enterprises has little difference (Tab.5).
Conclusion The morphological structure, degree of polymerization, mechanical properties, wear properties, crystallinity, orientation and filament ratio of Lyocell fibers from sampling suppliers were characterized and compared, and the following conclusions were obtained. The Lyocell fiber prepared by major international manufacturers seems to have regular and smooth appearance and regular round cross section, with wet wear loss of 8.76 s, crystallinity of 78.8%, low degree of fibrination, low filament ratio (2.591%), fiber breaking strength of 3.91 cN/dtex, elongation at break of 9.79%. With high yarn strength and excellent fiber quality, Lyocell fiber downstream manufacturers have a high degree of recognition. Due to the difference in processing route and post-treatment technology, the quality of domestic Lyocell fiber is better than that of foreign Lyocell fiber. Domestic manufacturers should continue to optimize the fiber microstructure, gloss, spinnability and brand promotion to further improve the market share of domestic Lyocell fiber. In the future, the domestic manufacturers should continue to optimize the micro-morphology, filament ratio, gloss, spinnability and brand promotion, so as to further improve the market share of domestic Lyocell fiber.