Lignin can be an important source of synthetic commodity materials owing to its abundance in nature and low production cost. The current
main usage of lignin, however, is very limited to cheap and poorly defined nonfunctional materials, because of undefined chemical structure of
lignin and difficulties in chemical modification. This dissertation presents fundamental studies of chemical modifications for natural lignin,
leading to advanced functional lignin-based polymers that contains covalently linked natural lignin and synthetic polymers (or other natural
biopolymers). The presented graft copolymerization methods of lignin emphasis on 1) natural lignin modification to possess alkyne or alkene
groups, 2) synthesis of well-defined functional polymer grafts, 3) covalent bond linkages between lignin and polymers, and 4) mechanical and
thermal property studies for material applications. Based on the fundamental method to produce lignin-based polymers, a new lignin-based
self-healing polymer, lignin-graft-poly(5-acetylaminopentyl acrylate) (lignin-graft-PAA) was synthesized. The natural lignin and PAA was
covalently integrated by a copper catalyzed azide-alkyne cycloaddition using graft-onto method. Prior to the click reaction, lignin was modified
to convert abundant hydroxyl groups to alkyne groups. The PAA was synthesized by reversible addition fragmentation-chain transfer (RAFT)
polymerization that produces low molecular weight distribution polymers containing chemically active terminal, azide end groups. The synthesized
lignin-graft-PAA showed excellent automatic self-healing function which was achieved by hydrogen bonding from the acetylamino groups in PAA. In
this lignin-graft-PAA, lignin functioned to strengthen the mechanical strength. The mechanical properties of Young's modulus, energy, maximum
strength, and ultimate elongation were enhanced with more lignin content. After using click chemistry as a graft method, a visible light induced
thiol-ene reaction was applied to lignin polymeric modification. This is the first time that lignin is modified by Ru(bpy)3Cl2 photoredox
catalyzed reaction. Among photoredox catalysts and UV initiators for thiol-ene reaction, including Eosin Y, Ru(bpy)3Cl2, and
2,2-Dimethoxy-2-phenylacetophenone, Ru(bpy)3Cl2 was found to be the most efficient on lignin modification. This modification was efficient
between lignin and various thiol compounds, even with a polymer example, poly(ethylene glycol). This new modification method is an important
synthetic tool for the further materials applications because of its features of low energy consumption, high efficiency, temporal and spatial
control, and no need of special reaction facilities. Using this thiol-ene reaction, a new lignin-based shape memory polymer, crosslinked
lignin-polycaprolactone (PCL) was synthesized. Lignin was modified from abundant hydroxyl groups to alkene groups to prepare for the thiol-ene
reaction. PCL was synthesized by ring opening polymerization with a 4-arm architecture, which was designed for a dense crosslinking. The
hydroxyl end groups from PCL was easily modified to thiol group through an esterification reaction. The alkene groups functioned lignin and
thiol groups ended PCL were densely crosslinked by the thiol-ene reaction. The crosslinked lignin-PCL possessed an advanced shape memory
function by the crosslinking structure with lignin as netpoints and PCL as switching segments. During the shape memory process, lignin netpoints
hold the permanent structure and PCL switching segments allowed shape change. In this system, the role of lignin was a crosslinker additive.
Moreover, the content of lignin crosslinker provided adjustment to melting temperature of the crosslinked lignin-PCL. More lignin content
lowered the melting temperature by introducing defect to the PCL crystalline structure. Overall, lignin was integrated with polymers by
precisely synthesis in this dissertation. The role of lignin was used as an important base polymer that occupies large portion, as well as a
small amount additive. Both of the two roles can significantly change polymer properties to strengthen mechanical property and tune thermal
property. The overall lignin-based polymer research in the dissertation may be very useful for advanced levels of material applications such as
self-healing and shape memory polymers. / A Dissertation submitted to the Department of Chemical and Biomedical Engineering in partial fulfillment of the
requirements for the degree of Doctor of Philosophy. / Fall Semester 2018. / November 8, 2018. / Includes bibliographical references. / Hoyong Chung, Professor Directing Dissertation; Joseph B. Schlenoff, University Representative; Daniel T.
Hallinan, Jr., Committee Member; Jingjiao Guan, Committee Member.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_661227 |
| Contributors | Liu, Hailing (author), Chung, Hoyong (professor directing dissertation), Schlenoff, Joseph B. (university representative), Guan, Jingjiao (committee member), Florida State University (degree granting institution), FAMU-FSU College of Engineering (degree granting college), Department of Chemical and Biomedical Engineering (degree granting departmentdgg) |
| Publisher | Florida State University |
| Source Sets | Florida State University |
| Language | English, English |
| Detected Language | English |
| Type | Text, text, doctoral thesis |
| Format | 1 online resource (131 pages), computer, application/pdf |
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