PhD Dissertation Defense: Cuma Ali UCAR
ARBON FIBER-REINFORCED PREPREGS AND COMPOSITES OF ONE-COMPONENT EPOXY RESINS CONTAINING THERMAL LATENT CURING AGENTS
Cuma Ali UCAR
Materials Science and Nano Engineering, PhD Dissertation, 2025
Thesis Jury
Asst. Prof. Dr. Bekir DIZMAN (Thesis Advisor)
Prof. Dr. Yusuf MENCELOĞLU
Asst. Prof. Dr. Hatice Sinem ŞAŞ ÇAYCI
Prof. Dr. Engin BURGAZ
Asst. Prof. Çağatay YILMAZ
Date & Time: June 25th, 2025 – 10 AM
Place: FENS G015
Keywords : Thermal Latent Curing Agents, Epoxy Resin, Thermoset Prepregs, Curing Kinetics, Cure Rheology
Abstract
Carbon fiber-reinforced composites are increasingly replacing metals in aerospace and defense due to their low density, high specific strength, and corrosion resistance. While thermoset prepregs are widely used to fabricate these composites, their susceptibility to premature curing at ambient temperature necessitates cold storage, leading to increased energy consumption, reduced storage flexibility, and higher processing costs. One-component epoxy resins (OCERs) formulated with thermal latent curing agents (TLCs) offer a promising alternative by remaining stable at ambient temperature and initiating cure only upon heating. This thesis focuses on the design, synthesis, and application of TLCs in OCERs to improve prepreg processability and composite mechanical performance. The work encompasses four interconnected studies that span molecular design to macroscale fabrication. The first study examined an OCER formulated with phenylurea propyl imidazole (PUPI) and diglycidyl ether of bisphenol A (DGEBA), which showed high conversion at moderate temperatures, three-day ambient temperature stability, and synergistic cure acceleration with dicyandiamide (DICY), lowering onset and peak cure temperatures. In the second study, a novel sulfonyl urea-based TLC, PTSU-EDA, was synthesized from p-toluenesulfonyl isocyanate and ethylenediamine and incorporated into DGEBA. This system exhibited superior thermal latency over imidazole-based systems and reduced cure temperatures compared to conventional urea accelerators, though its low cross-link density indicated a need for structural or stoichiometric optimization. To address limitations of small-molecule TLCs, the third study developed a polymeric TLC, poly(2-phenyl-2-oxazoline)-Im (PPhOZ-Im), with a terminal imidazole group. Used alone or with DICY in DGEBA, PPhOZ-Im significantly improved composite tensile and compressive strengths by 31.3% and 4.5%, respectively. The fourth study investigated the relationship between prepreg processability-specifically drapeability and tackiness-and interlaminar shear strength (ILSS). Prepregs with varied degrees of cure were prepared using off-stoichiometric formulations and cured identically. A strong correlation between drapeability and ILSS underscored the critical role of process control in optimizing TLC-based prepregs. Collectively, these studies offer a comprehensive framework for designing ambient temperature-stable, high-performance OCERs, with future improvements enabled by predictive modeling, tailored TLCs, and in-line monitoring tools.div>