Identifying breach mechanism during air‐gap spinning of lignin–cellulose ionic‐liquid solutions

Abstract

To be able to produce highly oriented and strong fibers from polymer solutions, a high elongational rate during the fiber‐forming process is necessary. In the air‐gap spinning process, a high elongational rate is realized by employing a high draw ratio, the ratio between take‐up and extrusion velocity. Air‐gap spinning of lignin–cellulose ionic‐liquid solutions renders fibers that are promising to use as carbon fiber precursors. To further improve their mechanical properties, the polymer orientation should be maximized. However, achieving high draw ratios is limited by spinning instabilities that occur at high elongational rates. The aim of this experimental study is to understand the link between solution properties and the critical draw ratio during air‐gap spinning. A maximum critical draw ratio with respect to temperature is found. Two mechanisms that limit the critical draw ratio are proposed, cohesive breach and draw resonance, the latter identified from high‐speed videos. The two mechanisms clearly correlate with different temperature regions. The results from this work are not only of value for future work within the studied system but also for the design of air‐gap spinning processes in general. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47800.

The challenge of predicting spinnability: Investigating benefits of adding lignin to cellulose solutions in air‐gap spinning

“…In our previous publication we suggested that the reduction of critical draw ratio at higher temperatures is due to draw resonance, which causes the rupture of the filament 17 . Thus, if this is the case, the pure cellulose solutions suffer from draw resonance at higher viscosities compared to the solutions that contain lignin.…”

“…Such mechanism may be necking and/or draw resonance which causes a locally reduced cross section and thus stress amplification leading to filament break‐up. In our previous study it was concluded that for a solution with 50:50 lignin: cellulose, draw resonance was observed for temperatures above the temperature at the maximum critical draw ratio 17 . It can be assumed that a pure cellulose solution would suffer from a similar disturbance at warmer temperatures.…”

“…The different breach mechanisms during air‐gap spinning of a lignin‐cellulose solution were recently studied in our lab. The critical draw ratio was determined and optically analyzed at different temperatures, and two dominating mechanisms were found 17 . At colder temperatures, in this case below 60°C, the filaments were proposed to undergo a cohesive breach as the stored elastic stress in the filament exceeded the breaking stress, and at warmer temperatures, above 60°C, the break‐up was found to be caused by draw resonance, which induce diameter fluctuations in the filament.…”

Kraft Lignin: A Valuable, Sustainable Resource, Opportunities and Challenges

“…By dissolution in a common ionic liquid-based solvent, it is possible to dry-jet wet spin fibers into an aqueous coagulation bath where the fibers solidifies. Results based on ionic liquid solvents (e. g., 1,5diaza-bicyclo[4.3.0]non-5-enium acetate [DBNH][OAc] and 1ethyl-3-methylimidazolium acetate [EMIM][OAc]) have, e. g., been published by research groups in Finland, [250][251][252][253][254] Germany, [255] and Sweden [256][257][258][259][260][261]), where precursor fibers with up to 70 wt % lignin content become flexible and strong. The corresponding CFs show promising mechanical properties after conversion via industrially relevant stabilization and carbonization times.…”

Linear stability analysis of nonisothermal glass fiber drawing

“…Thermal drawing processes are involved in a large range of applications as diverse as the manufacture of glass [1,2] and polymer fibers [3][4][5][6], optical fibers [7,8], or more recently multimaterial fibers with advanced functionalities [9][10][11][12]. We note that filamentary structures can also be produced naturally during volcanic eruptions.…”