Biomacromolecules in Functional Fiber Engineering: Valorizing Lignin Residues
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The simultaneous abundance of agricultural and industrial biowaste and the need for more sustainable alternatives to petroleum-derived fiber products have created a new research intersection. Lignin is a biomacromolecule that offers renewability and functional advantages, but its valorization faces challenges due to structural heterogeneity, high polydispersity, and variability across different botanical origins, conversion methods and post-treatments. Existing literature has largely neglected scalable pathways for pure or minimally modified lignin-based fibers, cross-origin comparisons inclusive of regionally-relevant agricultural residues, and development of inherently multifunctional lignin-based textile fibers beyond carbon-focused applications.This dissertation addresses above gap through implementation of simple, low-cost, circular spinning systems for biobased fiber synthesis, analysis of structure-property relationships for scaled lignin standardization, application-specific inherent multifunctionality engineering, and high-value biowaste utilization. Two spinning approaches, electrospinning and wet spinning, are addressed due to their adaptability for sustainable biopolymer-to-fiber systems, efficiency in processing, and tailoring potential for fiber physical properties. Chapter 1 highlights the current challenges and efforts in lignin valorization through a fiber lens, introducing relevant spinning technologies and lignin conversion methods for textile applications. Chapters 2 and 3 demonstrate benefits of electrospinning through cross-engineering of fiber scale with functional advantages of blended lignin-based dispersions and solutions. In Chapter 2, comparison of sustainable, flexible lignin/PLA micro/nanofiber membranes explores the impact of lignin structure on fiber spinnability and functionality across lignins from different botanical origins, pretreatment methods and fractions. Chapter 3 further narrows the scope to agricultural residue-derived CELF-extracted lignins, to investigate impact of structure across low and high molecular weight (Mw) lignin from regionally-significant corn stover and hemp hurd in lignin/nylon 6 composite nanofiber membranes for sustainable, durable, inherently multifunctional textile membranes. Chapter 4 transitions to greener, less volatile solvent systems through wet spinning, further enhancing biobased polymer compositions, while controlling fiber formation and morphology. In this chapter, dispersions containing different CELF corn stover lignin fractions and sodium alginate are wet-spun in water, resulting in lignin-rich biobased, biodegradable water-stable fibers with fraction-specific performance. All key findings are then outlined in Chapter 5 and concluded with recommendations for future work.