TRADE-OFF BETWEEN LIMONENE & GERANIOL-BASED REPROCESSABLE AND NON-REPROCESSABLE EPOXY THERMOSETS: ROLE OF ALIPHATIC DIAMINES IN POLYMER NETWORKS DESIGN

Author

• Priyankkumar Kanubhai Patel, Pittsburg State UniversityFollow

Date of Award

Spring 5-16-2025

Document Type

Thesis

Degree Name

Master of Science in Chemistry (MSChem)

Department

Chemistry

First Advisor

Dr. Ram K. Gupta, [email protected]

Second Advisor

Dr. Alessandro Martins, [email protected]

Third Advisor

Dr. Timothy Dawsey, [email protected]

Keywords

Sustainable, Terpene derived epoxy resins, Covalent adaptable network, Reprocessability, Hardener

Abstract

The growing demand for sustainable materials, driven by environmental concerns and the rapid depletion of fossil fuels, has garnered significant attention in the fabrication of bio-based epoxy thermosets as renewable alternatives to petroleum-derived thermosetting polymers. The present study focuses on the synthesis and characterization of epoxy prepolymer resins derived from limonene and geraniol via a two-step process, followed by the fabrication of thermally cross-linked flexible epoxy thermoset films using various traditional aliphatic diamine curing agents, namely 1,2-ethylenediamine (EDA), 1,4-butylenediamine (BDA), and 1,6-hexamethylenediamine (HDA). Additionally, the incorporation of cystamine, a disulfide-containing diamine, enabled the formation of a covalent adaptable network through disulfide metathesis that results in reprocessable thermoset with extended lifespan. As per thermal transition (DSC) all the limonene and geraniol-based epoxy thermosets exhibited glass transition temperatures (T_g) in the range of ~ 4 T_g30 °C and ~ 7 T_g32 °C, respectively. In addition, dynamic mechanical analysis (DMA) further determines the material's ability to store energy (storage modulus) and also the loss factor (tan δ) that corroborates with the viscoelastic behavior as well. Moreover, TGA showed that all the thermosets were quite thermally stable up to ~³ 250 °C, while their reprocessable counterparts retained good thermal stability up to ~220 °C. Furthermore, both limonene- and geraniol-based thermosets integrated with EDA cross-linker exhibit the highest tensile strengths of 11.62 MPa and 17.95 MPa, respectively, while increasing the diamine chain length led to a reduction in tensile strength that reached 1.96 MPa for LME_ECH_HDA and 3 MPa for GME_ECH_HDA. In contrast, limonene and geraniol-based reprocessable thermosets showed moderate tensile strengths of 3.1 MPa and 3.68 MPa, respectively, coupled with enhanced elongation at break, indicating a balance between flexibility and mechanical performance. Moreover, all the thermosets exhibit > 95% gel content, which further confirms the cross-linked polymer network of the fabricated thermosets. At a glance, this research highlights the immense potential of limonene and geraniol-derived epoxy thermosets as sustainable materials, demonstrating robust thermal and mechanical properties alongside dynamic capabilities like reprocessability, weldability, and high-performance networks. By leveraging dynamic covalent chemistry, this work paves the way for innovative bio-based materials and reinforces their critical role in advancing circular economy principles.

Recommended Citation

Patel, Priyankkumar Kanubhai, "TRADE-OFF BETWEEN LIMONENE & GERANIOL-BASED REPROCESSABLE AND NON-REPROCESSABLE EPOXY THERMOSETS: ROLE OF ALIPHATIC DIAMINES IN POLYMER NETWORKS DESIGN" (2025). Electronic Theses & Dissertations. 832.
https://digitalcommons.pittstate.edu/etd/832