Date of Award

12-2016

Degree Type

Thesis

Degree Name

Master of Science in Material Science Engineering (MSMatSE)

Department

Materials Engineering

First Advisor

John A. Howarter

Committee Chair

John A. Howarter

Committee Member 1

Kendra Erk

Committee Member 2

Carlos Martinez

Abstract

High performance fibers are characterized by properties such as high strength and resistance to chemicals and heat. Due to their outstanding properties, they are used on applications under harsh environments that can degrade and decrease their performance. Fiber degradation due to different chemical and mechanical factors, is a process that begins at a microstructural level. Changes in the polymer’s chemical or physical structure can alter their mechanical properties. Knowledge of the structure-properties relationship and the effects of environmental chemical and physical factors over time, is crucial for the improvement and development of high performance fibers.

In this study ballistic fibers of poly(p-phenylene terephthalamide) (PPTA) were studied. Methods of accelerated degradation were used to mimic the wearness of the fibers over long periods of time at a smaller time range. Fibers were subjected to ultrasonication in aqueous solution at pH 7 for up to six hours in order to produce surface damage. Once degraded, properties like the creep behavior of these fibers were studied under a humidity range of 0-80% and temperatures of 30°C and 60°C. Characterization of the chemical and mechanical properties of degraded PPTA fibers were characterized by thermogravimetrical analysis (TGA), dynamic mechanical analysis (DMA), scanning electron microscopy (SEM), and tensile testing to failure.

Sonication produces small but significant changes in the crystalline structure of the fibers that allows the formation of layers of water and consequently affecting mechanical properties like the elastic modulus and peak load. These small changes can be related to the early stages of degradation. Moreover, this study shows the efficiency of techniques such as the DMA for the detection of early signs of degradation by measuring the amount of creep the material undergoes as humidity changes.

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