Dissertation/Thesis Abstract

Thermal Aging of Benzoxazine-Epoxy Systems and Their Composites
by Patel, Ruchi D., M.S., California State University, Long Beach, 2018, 98; 10979174
Abstract (Summary)

New applications of polymers and their composites are arising and replacing traditional materials in the sectors of aerospace, automotive, and civil industries. Polymers and their composites are susceptible to oxidative degradation at high temperatures, especially when approaching but not quite reaching the glass transition temperature (Tg). Although the carbon fibers in these composites are stable at such temperatures, the matrix and especially the fiber-matrix interface can undergo degradation that affects the physical, chemical, and mechanical properties of the structure over time. From an industry point of view, it is important to understand the mechanism of these changes to improve the product quality and lifetime.

This thesis was designed to study the thermal oxidation of the Benzoxazine (BZ) and epoxy-based copolymer system and its composites with differing additives. During the comparison studies, two types of BZ based systems were used. These systems were differentiated by commercially and laboratory formulated systems. The cured specimens were aged at 160 °C, 180 °C, and 200 °C in an air-circulating oven for 24 weeks. The changes in weight, shear strength, flexural strength, and dynamic mechanical properties were recorded for aged samples. Fourier Transform Infrared Spectroscopy (FTIR) analysis was used to observe the changes in the chemical properties of the material after aging. Light microscopy and Dynamic Mechanical Analyzer (DMA) were performed to monitor the initiation of the oxidation-induced surface cracking and the crack number density, and the effect of thermal aging on glass transition temperature ( Tg), respectively.

The aim was to determine the thermal aging mechanism, oxidation thickness growth and crack initiation (damage indicators), and effects of oxidation on the physical, chemical, and mechanical properties of the tested materials. The resulting effects on the thickness of the oxidized layer (TOL) for resin systems and its composites showed that, after prolonged thermal exposure, the degradation mechanism changed from thermal oxidation to thermal degradation. The simultaneous effects of post-curing and thermal degradation lead to the change in Tg during exposure, which was noted from DMA results. Given the addition of epoxy to BZ was shown to be required to adjust the process-required viscosity, this study provides adequate information on mechanical and thermal behaviors of the copolymer resin systems and their composites under prolong isothermal exposure.

Indexing (document details)
Advisor: Barjasteh, Ehsan
Commitee: Lo, Roger C., Moghtadernejad, Sara
School: California State University, Long Beach
Department: Chemical Engineering
School Location: United States -- California
Source: MAI 58/05M(E), Masters Abstracts International
Subjects: Engineering, Chemical engineering
Publication Number: 10979174
ISBN: 978-1-392-07402-2
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