A new chemical recycling method for waste cotton is presented that allows the production of virgin textile fibers of substantially higher quality than that from the mechanical recycling methods that are used currently. Cotton postconsumer textile wastes were solubilized fully in the cellulose-dissolving ionic liquid 1,5-diazabicyclo[4.3.0]non-5-enium acetate ([DBNH]OAc) to be processed into continuous filaments. As a result of the heterogeneous raw material that had a different molar mass distribution and degree of polymerization, pretreatment to adjust the cellulose degree of polymerization by acid hydrolysis, enzyme hydrolysis, or blending the waste cotton with birch prehydrolyzed kraft pulp was necessary to ensure spinnability. The physical properties of the spun fibers and the effect of the processing parameters on the ultrastructural changes of the fibers were measured. Fibers with a tenacity (tensile strength) of up to 58 cN tex (870 MPa) were prepared, which exceeds that of native cotton and commercial man-made cellulosic fibers.

A simple and inexpensive method for producing water-stable pulp fibre yarns using a deep eutectic mixture composed of choline chloride and urea (ChCl/urea) was developed in this work. Deep eutectic solvents (DESs) are eutectic mixtures consisting of two or more components that together have a lower melting point than the individual components. DESs have been previously studied with respect to cellulose dissolution, functionalisation, and pre-treatment. This new method uses a mixture of choline chloride and urea, which is used as a swelling and dispersing agent for the pulp fibres in the yarn-forming process. Although the pulp seemed to form a gel when dispersed in ChCl/urea, the ultrastructure of the pulp was not affected. To enable water stability, pulp fibres were crosslinked by esterification using polyacrylic acid. ChCl/urea could be easily recycled and reused by distillation. The novel process described in this study enables utilisation of pulp fibres in textile production without modification or dissolution and shortening of the textile value chain. An interdisciplinary approach was used, where potential applications were explored simultaneously with material development from process development to the early phase prototyping.

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Flaxseed (Linum usitatissimum L.) fibers were modified by oxidoreductive and cellulolytic enzymes. The lignin amount and intrinsic plant peroxidase activity was evaluated by histochemical and spectrophotometric assays. Peroxidase activity was not found from bast fibers. The flaxseed fibers were further separated and treated with laccase to conjugate the model compounds, that is, the hydrophobic gallate molecules on fiber surfaces. Laccase was able to slowly oxidize fiber-conjugated phenolics, but no fundamental changes in fiber cell surface structure or notable coupling of the applied hydrophobic gallate molecules onto the fibers occurred, as revealed by Fourier transform infrared spectroscopy. The reactivity of the mature fibers was further investigated using cellulolytic enzymes. Cellobiohydrolase (CBH) and endoglucanase (EG)-rich enzyme preparations were applied to reach a hydrolysis degree of 1-6% (of the fiber dry matter) using a standard enzyme dosage. The CBH mixture altered the fiber surface morphology distinctly, and SEM images illustrated fibers in which the cellulose fibrils seemed to be loosened and partially hydrolyzed. In contrast, the effect of the EG-rich preparation without CBH activity was notable on the fiber surface, polishing the surfaces. The cellulolytic treatments were potentially interesting for specific enzymatic modifications of flax fiber surfaces, whereas the approach to use oxidoreductive enzyme treatments on mature linseed fibers offered little potential, obviously due to the low lignin content of the fibers.