Abstract:

Objective The research on the relationship between the condensed structure and the degree of fibrillation of Lyocell fiber at a higher spinning speed is relatively scarce. Selecting appropriate preparation conditions to change the condensed structure of fiber and regulate the degree of fibrillation can ease the main problems that restrict the industrial promotion and scale applications of Lyocell fiber. This research studied the influence of different preparation conditions on the condensed structure of Lyocell fiber and the degree of fibrillation, further established the relationship, which was then used to control the degree of fibrillation at high spinning speed.
Method In order to explore the relationship between the condensed structure and the degree of fibrillation of Lyocell fiber at high spinning speed, the fibers were spun with different N-methylmorpholine-N-oxide (NMMO) mass fractions, spinning speeds and blowing speeds. The degree of fibrillation was regulated by adjusting the structure. Using X-ray diffraction, wet friction tester and polarized microscope, the effects of NMMO concentration, spinning speed and blowing speed on the condensed structure and the degree of fibrillation were explored.
Results The condensed structure and fibrillation behavior of the fibers prepared under different conditions are obviously different. Increasing the concentration of the NMMO to a certain extent optimizes the fiber structure, leading to significant increase in the degree of orientation and transverse crystallite size as shown in Tab. 1, and in the degree of fibrillation of the fiber as illustrated in Fig. 2-3. The fiber with low crystal orientation and small crystal size has better antigen fibrillation properties. The coagulation bath with lower NMMO mass fraction is more suitable to prepare low fibrillation Lyocell fiber at high spinning speed. As the spinning speed increases, the crystallinity and the grain size of the fiber increases slightly as suggested in Tab. 2. However, the amorphous region is further oriented and the degree of fibrillation also increases(Fig. 4 and 5). To a certain extent, reducing the spinning speed can reduce the fibrillation of the fiber. Adjusting the air blowing speed has a significant impact on the structure of fiber as shown in Fig. 6, especially on the transverse grain size as shown in Tab. 3, which can control the degree of fibrillation as Fig. 7 reveals. In a certain range, the lower the blowing speed, the less the crystal orientation and the smaller the grain size, the more conducive to reducing the fiber fibrillation. Too low the blowing speed affects the forming of the fiber and the spinning stability.
Conclusion The condensed structure of Lyocell fiber directly affects the degree of fibrillation. The antigen fibrillation properties of the fiber prepared at high spinning speed is better in having low crystallization, low orientation and small crystallite size. To a certain extent, reducing the concentration of NMMO, spinning speed and blowing speed can reduce the degree of fibrillation. By comprehensively changing the degree of orienta-tion (especially the orientation of amorphous region) and the transverse grain size, the regulation of fibrillation is more obvious. Adjusting the concentration of NMMO is an easier way, among the above factors, to control the fibrillation behavior at high spinning speed. The Lyocell fiber prepared under mild spinning conditions demonstrates better antigenic fibrillation properties.

Key words: high spinning speed, condensed structure, fibrillation, Lyocell fiber, structure regulation