2025 AIChE Annual Meeting

(488c) Lignin-Based Nanocomposite Films for Sustainable, Multifunctional Materials

Authors

Mika Sipponen, Stockholm University
Lignin is the second most abundant terrestrial natural polymer on Earth, and it is receiving increasing attention as an emerging renewable alternative for new sustainable advanced materials due to its structure, attractive properties, and low cost, as it is considered a byproduct of the pulp and paper industry. The chemical structure of this macromolecule is strongly influenced by the extraction process used to isolate it from biomass. Lignin obtained from the Kraft pulping process contains aliphatic and phenolic hydroxyl groups and carboxyl groups1. Notably, the last ones, deprotonate in neutral or even slightly acidic pH, creating negative charges2. These can be exploited for the production of composites through electrostatic interactions with positively charged polymers. Although not naturally cationic, cellulose, the most abundant polysaccharide in nature, is an attractive candidate, thanks to its high number of hydroxyl groups, which provide a platform for chemical modifications. The cationic modification of cellulose is a well-established reaction that introduces to the polymer positive charges, such as from quaternary ammonium groups. 2,3-Epoxypropyl trimethylammonium chloride (EPTMAC) is commonly used as a cationic reagent since it has a quaternary ammonium and, an epoxy group3. This modification was selected in this study to obtain cationic cellulose nanofibers (CNFs).

The CNF in this study is derived from cotton obtained from discarded textiles. Transforming post-consumer clothing waste into sustainable cellulose nanofibrils not only valorizes textile waste but also reduces the environmental impact of the textile industry. This approach supports a circular economy by diverting materials from landfills, lowering greenhouse gas emissions, and mitigating the overall footprint of textile production and disposal4. The cationically charged CNFs serve as nucleation substrates for the in-situ formation of lignin nanoparticles (LNPs) via solvent shifting. Kraft lignin, dissolved in a mixture of acetone/water, is added to the suspension of cationic CNFs. As lignin is not soluble in water, this dilute suspension acts as antisolvent, driving the formation of LNPs. Homogeneous thin films of the CNFs and LNPs were obtained through filtration of varying amounts of lignin. It was possible to increase the content of lignin up to 50 wt.%. The high charge density of cellulose achieved after the modification enhances the interfacial interactions between lignin and the nanofibers, resulting in a uniform particle distribution within the nanofiber network. At the same time, filtration prevents segregation during drying. Preliminary imaging results suggest that the composite's microstructure may include lignin particles distributed on the CNF surfaces, attracted by electrostatic interactions. Early observations hint that these particles are of a size comparable to measurements performed by DLS to LNPs in the absence of nanofibers. The mechanical properties of the cationic CNF- LNP composites reveal improved ductility as the lignin content increases, though this is accompanied by a reduction in tensile strength compared to films made solely from cationic CNFs.

Although the tensile strength decreased with increasing lignin content, the samples with 50 wt.% lignin exhibited enhanced toughness, demonstrated by their increased flexibility and energy absorption prior to failure, a property not previously reported in the literature. A high lignin content provides several benefits, including enhanced UV protection, strong antimicrobial activity, improved water barrier properties compared to cellulose films, and consequently increased hydrophobicity. Thus, the reduced strength of high-lignin content films is offset by these enhanced properties, making them a suitable bio-based alternative for multiple applications. In particular, the high capacity of Kraft lignin to adsorb oils has been previously reported 5,6 , thereby rendering our high-lignin films possible candidates for oil spill cleanup. Moreover, its entirely bio-based composition supports the principles of a circular economy.

References

    (1) Zevallos Torres, L. A.; Lorenci Woiciechowski, A.; de Andrade Tanobe, V. O.; Karp, S. G.; Guimarães Lorenci, L. C.; Faulds, C.; Soccol, C. R. Lignin as a Potential Source of High-Added Value Compounds: A Review. Journal of Cleaner Production 2020, 263, 121499. https://doi.org/10.1016/j.jclepro.2020.121499.

    (2) Lignin recovery from spent alkaline pulping liquors using acidification, membrane separation, and related processing steps: A Review :: BioResources. https://bioresources.cnr.ncsu.edu/.


    (3) Gao, Y.; Li, Q.; Shi, Y.; Cha, R. Preparation and Application of Cationic Modified Cellulose Fibrils as a Papermaking Additive. International Journal of Polymer Science 2016, 2016 (1), 6978434.
    https://doi.org/10.1155/2016/6978434.

    (4) Ruiz-Caldas, M.-X.; Apostolopoulou-Kalkavoura, V.; Pacoste, L.; Jaworski, A.; Mathew, A. P. Upcycling Textile Waste into Anionic and Cationic Cellulose Nanofibrils and Their Assembly into 2D and 3D Materials. ChemSusChem 2024, n/a (n/a), e202402103. https://doi.org/10.1002/cssc.202402103.

    (5) Adsorption of dietary oils onto lignin for promising pharameutical and nutritional applications :: BioResources. https://bioresources.cnr.ncsu.edu/.


    (6) Kraft lignin: a novel alternative to oil spill cleanup recycling industrial waste. ResearchGate.
    https://www.researchgate.net/publication/320826563_Kraft_lignin_a_novel_alternative_to_oil_spill_cleanup_recycling_industrial_waste.