The developments and characterizations of polyester with built-in properties from bio-based comonomers
Date
2022-08
Authors
Lee, Ting-Han
Major Professor
Advisor
Cochran, Eric
Li, Wenzhen
Kraus, George
Panthani, Matthew
Wang, Qun
Committee Member
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
The work disclosed in this thesis is a discussion of the properties and implementation of poly(ethylene terephthalate) (PET) that is partly or fully replaced by using the bio-derived chemicals as monomers. The first work focuses on the synthesis and characterization of bio-naphthalate-based polymers. In this work, we synthesize a family of engineering polyesters featuring bio-based naphthalate rigid segments through two-step polycondensation similar to that used in the industrial production of PET. The two chemicals we use as monomers are 2,7-naphthalate-based rigid segments of dimethyl 1,2,3,4-tetrahydronaphthalene-2,7- dicarboxylate (THN) or dimethyl 2,7-naphthalene dicarboxylate (2,7-N). Amongst these, 2,7-N is found to be especially promising. The results show that poly(ethylene 2,7-N) (27PEN) has superior performance in many aspects compared to those of PET, including higher service temperature, higher thermal stability, and better oxygen barrier property. However, it shows brittle performance due to its sluggish crystallization. Thus while 27PEN has many appealing properties, its prospects for use in applications where resilience to even modest mechanical distress appear to be limited without remediation.
This leads us to the second work in this thesis which is the study of a series of poly(ethylene terephthalate) (PET) copolymers with the incorporation of bioadvantaged 2,7-N as a comonomer since we anticipate that 2,7-N will reveal its true potential. The results show that the incorporation of 2,7-N allows for significant improvements in the melting point and thermal deformation/stability; moreover, the mechanical properties are tuned to show superior to those of PET homopolymer. In addition, the oxygen barrier analysis indicated that the barrier capability of 2,7-N is 2 times better than that of petroleum-based commercial analog dimethyl 2,6-naphthalene dicarboxylate (2,6-N). These results suggest that bioadvantaged comonomers like 2,7-N are capable of being used for modifying polymer properties, both in sustainability and performance compared with those of traditional PET. Moreover, the fundamental structure-property relationships connecting the bioadvantaged chemicals as hard-segment inside polymers to their performance is constructed as a guide for value-added renewable polymers in the future.
During the screening of bio-derived chemicals as monomers for polymer synthesis. We observed that the aromatic ring of the monomer containing methoxy groups shows some instability during high-temperature polycondensation. This leads us in another direction which the polymer containing this chemical inside the polymer chain can maintain its target performance but can proceed degradation easily under milder conditions, compared to those of normal PET. In this dissertation, we insert biobased diethyl 2,5-dihydroxy terephthalate (DHTE) as a degradation trigger, which we called trojan horse unit, into the polymer chain through copolymerizing these chemicals as comonomer unit during polycondensation. The improvement is shown in degradation conversion and rate constant of PET containing DHTE as degradation trigger. Composition-optimized copolymers showed a decrease of nearly 50% and 6 order of magnitude in activation energy and time needed for degradation, respectively, with the insertion of 5% DHTE loading. In addition, the service temperature and thermal stability of these modified PET remained at the same level as those of PET. These results suggest that comonomer like DHTE is not only capable of being used for modifying PET degradability, but also conserves the thermal performance of the materials. Furthermore, this study provides novel insight to the design of polymers toward upcycling while maintaining its target performance such as service temperature.
Series Number
Journal Issue
Is Version Of
Versions
Series
Academic or Administrative Unit
Type
dissertation