Date

2018

Document Type

Dissertation

Degree

Doctor of Philosophy

Department

Mechanical Engineering

First Adviser

Krick, Brandon A.

Abstract

Fluoropolymers and fluoropolymer composite materials are commonly used solid lubricant materials. Over the past fifteen years, the addition of nanostructured alumina particles to polytetrafluoroethylene (PTFE) was shown to improve the wear rate of unfilled PTFE by nearly 10,000x. In this work, the hardnesses of both porous and dense micron sized metal-oxide particles (alumina and CoAl2O4) were independently measured using in-situ nanoindentation experiments that correlated directly with wear rate of the PTFE-metal-oxide composites. Framework for developing ultralow wear of PTFE-nanostructured alumina composites was extended to melt processable perfluoroalkoxy polymer (PFA)-nanostructured alumina composites. These composites also exhibited a nearly 10,000x improvement in wear rate compared to unfilled PFA through the development of robust tribofilms. Wear debris of unfilled PFA was found to have increased crystallinity compared to bulk unfilled PFA samples. Infrared spectra of the wear debris of unfilled PFA revealed the formation of new carboxylic acid endgroups which supports the hypothesis that shear stress during sliding causes chain scission of the PFA backbone. Wear of PFA -nanostructured alumina composites was determined to be 100x greater in dry nitrogen environments compared to humid lab air environments. Infrared spectroscopy revealed the formation of carboxylic salt groups on the surface of the PFA-alumina composites was minimal in samples tested in dry nitrogen compared to samples tested in humid laboratory air. The mechanism leading to the 10,000x improvement in wear rate of fluoropolymer-metal-oxide composites was attributed to the reaction of the broken fluoropolymer backbone with environmental (O2 and H2O) with friable, metal-oxide fillers that reinforced the surface of the fluoropolymer without wearing away the countersurface material.

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