Anisotropic Cryogels derived from textile-derived cellulose nanocrystals and xanthan gum blends Maria-Ximena Ruiz-Caldas, Varvara Apostolopoulou-Kalkavoura, Carina Schiele, Seyed Ehsan Hadi, Lennart Bergström, Aji P. Mathew Department of Materials and Environmental Chemistry, Stockholm University, Sweden New lightweight materials from renewable sources or alternate feedstock are gaining attention. Cryogels are a class of lightweight solid foams that feature a 3D network structure formed via freeze-drying of a gel. Polysaccharides such as pectin 1 and Xanthan gum 2 , and bio-based nanostructures such as chitin nanofibers 3 , cellulose nanocrystals (CNCs) 4 , and cellulose nanofibrils 5 have been used to prepare cryogels. The morphology of a cryogel can be tuned using different methods, such as directional freeze-casting. With this technique, the gel precursor is slowly frozen from a specific direction, causing the ice crystals to grow preferentially in that direction and guiding the arrangement of pores. This results in anisotropic cryogels, which have an oriented network with directional variation in their morphology and properties. In our recent work 6,7 , we obtained CNCs from cotton-based waste fabrics. The resulting CNCs had equivalent properties to those extracted from virgin sources and their surface chemistry could be tuned up via the extraction method. While cellulose nanocrystals (CNCs) have been employed as building blocks for anisotropic cryogels 4 , research exploring the impact of CNC surface chemistry and aspect ratio on the properties of CNC-based cryogels remains limited. Our array of CNCs extracted from alternative feedstocks provides an opportunity to investigate these chemical relationships while exploring uses for textile-derived CNCs To address this knowledge gap, we investigated the influence of CNC chemistry on the properties of anisotropic cryogels made from three types of CNCs extracted from post-consumer cotton-based textiles: CNCs with sulfate- half-ester groups (SCNCs), CNCs with carboxyl and citrate groups (CitCNCs); and CNCs with carboxyl groups (TCNCs). In preliminary experiments, foams exclusively prepared from CNCs exhibited limited robustness, possibly due to the shorter aspect ratio of these CNCs compared to other nanoparticles used to prepare cryogels. Therefore, to enhance the mechanical properties of these CNC-based foams, xanthan gum was introduced into the CNC suspensions before freeze-casting. Diverse CNC surface chemistries influenced the interactions between CNC and xanthan gum and the rheological properties of the CNC/xanthan gum gels. For instance, the zero shear viscosity of SCNC suspensions was lower than TCNC suspensions with and without Xanthan Gum. In turn, this impacted the final morphology and mechanical and thermal properties of the anisotropic CNC-based cryogels. By highlighting the potential utilization of CNCs extracted from discarded garments and exploring the applicability of these cryogels in various domains, we expect that our research will contribute to the advancement of the preparation of lightweight materials from renewable sources and alternative feedstock. References 1. F. Zou et al. Chemical Engineering Journal , 2023, 462 , 142236S. 2. Liu et al. Carbohydr Polym , 2017, 174 , 392–399. 3. A. Poskela et al. ACS Sustain Chem Eng , 2019, 7 , 10257–10265.
4. C. Darpentigny et al. Cellulose , 2020, 27 , 233–247. 5. F. Martoïa et al. Mater Des , 2016, 104 , 376–391.
6. M.-X. Ruiz-Caldas et al. ACS Sustain Chem Eng , 2022, 10 , 3787–3798 7. M.-X. Ruiz-Caldas et al. J Mater Chem A Mater , 2023, 11 , 6854–6868
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