This article elucidates the dissolution of cellulose from different raw materials in NaOH aqueous solution via the combination of synchrotron-radiation-based SAXS/WAXS characterization. The X-ray measurements probed the mesostructure of the cellulose samples during the freeze-thawing cycle allowing tracking the initial swelling of the structure, the kinetics of disintegration of the cellulose crystallites as well as controlling the final state of the cellulose solution, i.e. presence or absence of cellulose aggregates. The individual SAXS and WAXS measurements were fitted and modelled to enable visualisation and tracking of the changes in the structure in relation to temperature during cooling and warming phases. To further increase the understanding of the parameters affecting dissolution different cellulose samples and solution compositions were considered. For this purpose the effect of increasing the concentration of NaOH and adding Zn2+ has been carefully investigated as well as the importance of the cellulose origin. We found consistent development that the dissolution occurs faster at higher concentrations of NaOH and with Zn2+ regardless the origin. Nevertheless, SAXS data show that materials with a larger amount of cellulose I show more apparent swelling in mesoscopic structure than bleached agricultural containing cellulose II. Despite few crystalline residues after the complete cooling-heating cycle shown by WAXS, some cellulose was not completely dissolved as some network structure remained in the samples under the test condition as suggested by SAXS. © The Author(s) 2024.

The narrow dissolution window for cellulose in NaOH(aq) is a limiting factor in the production of regenerated cellulose materials, which is why understanding of the molecular interactions in this solvent system is of the highest importance. In this work, we highlight the interaction between cellulose and CO2 in NaOH(aq). The model compound methyl α-D-glycopyranoside (MeO-Glcp) was used to compare the difference of the dissolved state in NaCl(aq) and NaOH(aq), including both pre and post-dissolution addition of CO2. N MR a nd A TR-IR  spectroscopy as well as ocular observations were used in the evaluation.  1H and 13C NMR spectroscopy showed a clear change in chemical shift of the MeO-Glcp when dissolved in NaOH(aq) compared to NaCl(aq), which is a result of deprotonation. Interestingly, the addition of CO2 either pre or post-dissolution of MeO-Glcp in NaOH(aq) affected the chemical shifts differently (apart from the expected change in pH). With quantitative 13C NMR measurements, the uptake of CO2 was found to be more than twice as high when the CO2 was added post-dissolution of MeO-Glcp in NaOH(aq) compared to prior to dissolution. This suggests that specific interactions occur between CO2 and MeO-Glcp when the latter is dissolved prior to the addition of CO2, which could be attributed to the deprotonated state of MeO-Glcp. Furthermore, the dissolved state of cellulose in NaOH(aq) was visually shown to iffer in terms of pre or post-dissolution addition of CO2. Post-dissolution addition of CO2 resulted in the formation of a gelled structure when solutions was left to age in room temperature for two weeks. ATR-IR spectroscopy of materials regenerated from the aged solutions confirmed the introduction of a n ew waveband corresponding to CO2 out-of-phase stretching confirming the sorption of CO2 on cellulose when dissolved in NaOH(aq).

The chemical recycling of cellulosic fibres may represent a next-generation fibre–fibre recycling system for cotton textiles, though remaining challenges include how to accommodate fibre blends, dyes, wrinkle-free finishes, and other impurities from finishing. These challenges may disrupt the regeneration process steps and reduce the fibre quality. This study examines the impact on regenerated viscose fibre properties of a novel alkaline/acid bleaching sequence to strip reactive dyes and dimethyloldihydroxyethyleneureas (DMDHEU) wrinkle-free finish from cotton textiles. Potentially, such a bleaching sequence could advantageously be integrated into the viscose process, reducing the costs and environmental impact of the product. The study investigates the spinning performance and mechanical properties (e.g., tenacity and elongation) of the regenerated viscose fibres. The alkaline/acid bleaching sequence was found to strip the reactive dye and DMDHEU wrinkle-free finish from the cotton fabric, so the resulting pulp could successfully be spun into viscose fibres, though the mechanical properties of these fibres were worse than those of commercial viscose fibres. This study finds that reactive dyes and DMDHEU wrinkle-free finish affect the viscose dope quality and the regeneration performance. The results might lead to progress in overcoming quality challenges in cellulosic chemical recycling. 

Herein, we explore the intrinsic ability of cellulose dissolved in NaOH(aq) to reversibly capture CO2. The stability of cellulose solutions differed significantly when adding CO2 prior to or after the dissolution of cellulose. ATR-IR spectroscopy on cellulose regenerated from the solutions, using ethanol, revealed the formation of a new carbonate species likely to be cellulose carbonate. To elucidate the interaction of cellulose with CO2 at the molecular level, a 13C NMR spectrum was recorded on methyl α-d-glucopyranoside (MeO-Glcp), a model compound, dissolved in NaOH(aq), which showed a difference in chemical shift when CO2 was added prior to or after the dissolution of MeO-Glcp, without a change in pH. The uptake of CO2 was found to be more than twice as high when CO2 was added to a solution after the dissolution of MeO-Glcp. Altogether, a mechanism for the observed CO2 capture is proposed, involving the formation of an intermediate cellulose carbonate upon the reaction of a cellulose alkoxide with CO2. The intermediate was observed as a captured carbonate structure only in regenerated samples, while its corresponding NMR peak in solution was absent. The reason for this is plausibly a rather fast hydrolysis of the carbonate intermediate by water, leading to the formation of CO3 2-, and thus increased capture of CO2. The potential of using carbohydrates as CO2 capturing agents in NaOH(aq) is shown to be simple and resource-effective in terms of the capture and regeneration of CO2.

Textile-to-textile recycling from cotton textiles can be done either mechanically or chemically. In chemical textile recycling of cotton there are challenges to overcome in order to regenerate new fibres. Two of the challenges among others are reactive dyes and wrinkle-free finishes that could disturb the regeneration process steps since these finishes are covalently linked to the cellulose.

This poster discusses the impact of using a novel alkaline/acid bleaching sequence to strip reactive dyes and wrinkle-free finish (DMDHEU) from cotton textile for production of regenerated viscose fibre properties. The results might generate a promising step forward to overcome quality challenges for cellulosic chemical recycling.