Doctoral Dissertations

Orcid ID

https://orcid.org/my-orcid?orcid=0009-0008-6881-9166

Date of Award

5-2025

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Natural Resources

Major Professor

Siqun Wang

Committee Members

Nicole Labbé, Mi Li, Tong Wang

Abstract

The extensive use of synthetic materials, particularly plastics and per- and polyfluoroalkyl substances (PFAS), has led to severe environmental issues, including microplastic contamination, and elevated PFAS levels in water resources. Additionally, plastic waste, such as sheets, ropes, and nets, poses significant threats to wildlife. These challenges underscore the urgent need for sustainable, degradable alternatives. Lignin, which is biodegradable, inherently hydrophobic due to its low hydroxyl content, and UV-resistant owing to its polyaromatic structure, presents a promising solution. However, the complex and non-uniform composition of industrial lignin limits its practical applications. Reducing lignin to the nanoscale through mechanical processes eliminates the need for solvent chemicals, facilitating scalable and sustainable production.

This study investigated the manufacturing of lignin micro- and nanoparticles (LMNP), focusing on the effects of temperature and solid content during ultrafine grinding (UFG), as well as the associated electricity consumption producing 1 kg LMNP. Additionally, the use of LMNP as functional agents in biomass-based food packaging and tableware applications was explored. The impact of processing temperature on nanoparticle formation was systematically examined. Results revealed that elevated temperatures (~70°C) accelerated particle size reduction, whereas lower temperatures (~0°C) resulted in smaller final particle sizes. Increasing the solid content significantly reduced energy consumption during processing.

The LMNP suspension was then applied to paper and hot-pressed to form a dense, smooth film. Under optimized conditions (160°C, 3 MPa, and 3 minutes), the lignin film exhibited water resistance for over an hour and oil resistance for 25 minutes. To address aesthetic concerns, a sandwich structure was introduced, embedding the lignin composite between two paper sheets. This design enhanced tensile strength by 50% while maintaining water- and oil-resistant properties. Furthermore, a dry processing method was developed by blending LMNP with dry fibers, followed by direct hot pressing. This approach demonstrated energy and water efficiency compared to wet molding method, offering a viable pathway for sustainable, high-performance applications in green packaging.

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