The production of sustainable and high-performance fabrics requires high mechanical strength of the individual (staple) fibers. Although Ioncell fibers already exhibit higher fiber strength than commercial man-made cellulose fibers or cotton fibers, we further aimed to increase both strength and toughness to gradually approach synthetic fibers in these properties. Decisive factors for the achievable mechanical properties of the fibers were the pulp purity, the cellulose concentration in the spinning solution and length-to-diameter (L/D) ratio of the cylindrical part of the spinneret. The absence of low molecular weight fractions in combination with an increased average molecular weight had the highest impact on the achievement of both high strength and toughness. Using a spinneret with a high L/D ratio, it was possible to spin Ioncell fibers with a tensile strength of 925 MPa (61.5 cN/tex) and a modulus of toughness of 83.3 MPa (55.5 J/g). According to a fluid dynamic simulation, uniformly longer molecular cellulose chains in combination with a longer cylindrical capillary promoted an effective alignment of the cellulose molecules inside the spinneret capillary before entering the airgap, thus creating the conditions for a simultaneous increase in tensile strength and elongation i.e. toughness of the fiber. Mechanistically, high fiber toughness is caused by the structural parameters in longitudinal direction, in particular by a higher tilt angle, a longer periodicity of the lamellar plane and lower micro void orientation. In summary, we have developed lyocell-type fibers with high strength and toughness, which can potentially be used as a surrogate for synthetic fibers. Graphic abstract

In this study, we propose a convenient method for testing the fibrillation tendency of man-made cellulosic fibres (MMCFs) and investigate the possibility to apply a commercial crosslinker for Tencel fibres on the ionic liquid-based regenerated cellulosic fibre (Ioncell fibre). The fibrillation tendency of various MMCFs including viscose, Modal, Tencel and Ioncell fibres were examined through wet abrasion by using ball bearing and blending methods. The fibrillation tests using a laboratory blender was found to be a superior method over the ball bearing method in terms of time and energy saving. The fibrillation tendency of the fibres highly depended on their cellulose molecular orientation and the treatment intensity (time, temperature and alkalinity) in the blender. This fibrillation method was also applied to discover the effect of the crosslinking on the fibrillation tendency of the fibres. The Ioncell fibre proved to be suitable for crosslinking treatment to reduce fibrillation using 1,3,5-triacryloyl-hexahydro-1,3,5-triazine (TAHT)—a commercial Tencel crosslinker.

A novel, small-volume vertically arranged spin bath was successfully developed for an air gap lyocell-type spinning process. A maximum regeneration bath length with a minimum free volume characterizes the concept of the new spin bath. Using the ionic liquid (IL) 1,5-diazabicyclo[4.3.0]non-5-enium acetate [DBNH][OAc], the spin bath showed very good spinning performances of IL-cellulose dopes at high draw ratios and spinning duration for single filament spinning experiments. Using this new device, it was possible to get a step further in the optimization of the Ioncell ® process and simulate a process closed loop operation by performing single filament spinning in IL/H 2 O mixtures. Good dope spinnability and preserved fibers mechanical properties were achieved in a coagulation bath containing up to 30 wt% IL. It is only at 45 wt% of IL in the bath that the spinnability and fibers mechanical properties started to deteriorate. The fibers fibrillar structure was less pronounced in ILcontaining spinning bath in comparison to a pure water bath. However, their crystallinity after washing was preserved regardless of the spinning bath composition. The results presented in this work have a high relevance to the upscaling of emerging IL-based cellulose dissolution and spinning processes.

The cellulosic fiber-based sustainable textile industry needs greener alternatives to the existing hydrophobization approacheswhich are essentially based on nonrenewable and expensive hydrophobizing agents and adversely impact the environment. Herein, we report the production of novel hydrophobic cellulose based fibers produced by incorporating nature-derived hydrophobic additivesbetulin (BE) and betulinic acid (BA) using the Ioncell technology. The incorporation process is simple and does not require any additional step during dry-jet wet spinning. Spinning dopes containing up to 10 wt % BE and BA were spinnable and the spun fibers (10BE and 10BA) maintained their mechanical properties. Compared to BE, BA-incorporated fiber showed homogeneous surface morphology suggesting the increased compatibility of BA with cellulose. Consequently, in contrast to BE-incorporated fibers, BA-incorporated fibers demonstrated higher yarn spinnability. Both 10BE and 10BA fibers showed hydrophobicity (water contact angle >90°) in the produced nonwovens and yarns. In summary, we developed a system for hydrophobizing man-made cellulose fiber via a simple eco-friendly and cost-effective way, which has potential for scalability and industrial applications.

Cellulose can be dissolved with another biopolymer in a protic ionic liquid and spun into a bicomponent hybrid cellulose fiber using the Ioncell® technology. Inside the hybrid fibers, the biopolymers are mixed at the nanoscale, and the second biopolymer provides the produced hybrid fiber new functional properties that can be fine-tuned by controlling its share in the fiber. In the present work, we present a fast and quantitative thermoanalytical method for the compositional analysis of man-made hybrid cellulose fibers by using thermogravimetric analysis (TGA) in combination with chemometrics. First, we incorporated 0–46 wt.% of lignin or chitosan in the hybrid fibers. Then, we analyzed their thermal decomposition behavior in a TGA device following a simple, one-hour thermal treatment protocol. With an analogy to spectroscopy, we show that the derivative thermogram can be used as a predictor in a multivariate regression model for determining the share of lignin or chitosan in the cellulose hybrid fibers. The method generated cross validation errors in the range 1.5–2.1 wt.% for lignin and chitosan. In addition, we discuss how the multivariate regression outperforms more common modeling methods such as those based on thermogram deconvolution or on linear superposition of reference thermograms. Moreover, we highlight the versatility of this thermoanalytical method—which could be applied to a wide range of composite materials, provided that their components can be thermally resolved—and illustrate it with an additional example on the measurement of polyester content in cellulose and polyester fiber blends. The method could predict the polyester content in the cellulose-polyester fiber blends with a cross validation error of 1.94 wt.% in the range of 0–100 wt.%. Finally, we give a list of recommendations on good experimental and modeling practices for the readers who want to extend the application of this thermoanalytical method to other composite materials.