Abstract
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
Highlights
Due to the high toughness coupled with good mechanical, chemical and physical properties, synthetic fibers are widely used in common and technical textiles such as sportswear and work wear
The tensile strength of the man-made cellulose fibers (MMCFs) depends on the raw material properties, such as the weight fraction of short-chain molecules, the non-cellulosic components, the average molar mass, molar mass distribution and the spinning parameters (Michud et al 2016)
The targeted improvement of the fiber strength of man-made cellulose fibers is crucial for their future use in applications where synthetic fibers currently predominate
Summary
Due to the high toughness coupled with good mechanical, chemical and physical properties, synthetic fibers are widely used in common and technical textiles such as sportswear and work wear. Another study reported that 8.2–93 billion microplastic particles and synthetic fibers are discharged per year from the wastewater treatment plant in Germany (Essel et al 2015). These microplastics contaminate land areas (Zubris and Richards 2005), impact various organisms (Huerta Lwanga et al 2016), affect the marine environment (Salvador Cesa et al 2017), enter the food chain (Abihssira-Garcıa et al 2020; Zhang et al 2021) and affect the human health (Ramsperger et al 2020; Sana et al 2020). Further improvements in MMCFs are needed to simultaneously increase the tenacity, and elongation—and increase toughness values
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