Doctoral Dissertations

Date of Award

5-2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Energy Science and Engineering

Major Professor

Amit K. Naskar

Committee Members

Roberto S. Benson, David P. Harper, Nicole Labbe

Abstract

Demand for plant-derived materials has increased in recent years not only to boost the economics in US Agricultural and Forestry sectors, but also to address environmental concerns. Lignin, an aromatic polymer, extracted from biomass has the potential to be used for preparing innovative materials. Developing high-performance polymers from lignin is attractive, but often requires additional lignin modification and cost-intensive functionalization that creates chemical wastes. The overarching goal of this study was the development of sustainable high-performance alloys from thermoplastic and lignin without chemical modification using melt-blending technique, which is technically the most convenient and inexpensive method. Thus, the approach aimed to find value for lignin, a low-cost byproduct of modern biorefineries and woody biomass pulping industry. More specifically, we conducted comprehensive study on thermal, rheological, morphological, and structural properties of the thermoplastic-lignin blends together with lignin’s chemistry and thermal behavior to understand and improve the materials’ performance.The first part of the study involved exploiting lignin’s miscibility with polyethylene oxide (PEO) to enhance the compatibility between lignin and acrylonitrile-butadiene-styrene (ABS) polymer under reactive mixing conditions and develop a recyclable renewable matrix for sustainable composite applications.The second part consisted on manipulating the melt behavior of polyethylene terephthalate (PET) polyester from pre-consumer wastes using a renewable plasticizer tall oil fatty acid (TOFA). To avoid lignin degradation and devolatilization during amalgamation with plasticized PET we devised thermal treatment of lignin that not only improved the stability but also reduced dispersed lignin domains in the matrix.The last part was based on understanding the effect of source-dependent lignin chemistry on its compatibility with a renewable polyester. Organosolv lignin from oak, methanol fractionated Kraft pine lignin, and methanol fractionated acetic acid extracted wheat straw lignin give equivalent melt processability. Blends of these lignins with polylactic acid (PLA) were studied to understand the relationship between the lignin chemistry and resulting blends’ thermal stability, mechanical properties, and melt-rheology.This study answered questions on the role of lignin chemistry that affects the properties of thermoplastic/lignin blends and developed methods to modify melting behavior of both thermoplastic matrices and lignin without thermal degradation.

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