Date of Award

1-1-2019

Document Type

Dissertation

Degree Name

Ph.D.

Organizational Unit

Daniel Felix Ritchie School of Engineering and Computer Science, Center for Advanced Materials and Structures

First Advisor

Maciej Kumosa, Ph.D.

Keywords

Environmental degradation, Glass reinforced polymers, Modeling, Particle removal, surface roughness effect, Synergistic aging

Abstract

Synergistic effects involved in the environmental degradation of Glass Reinforced Polymer (GRP) composites were examined and a novel synergistic aging model was proposed in this study. Six GRPs based on glass fibers with four different polymer resins and six pure polymer thermoplastic resins were exposed either individually or in combination to ultraviolet (UV) radiation, water condensation and elevated temperature for approximately 1000 h. The composites and polymers were monitored for weight changes as a function of time and their surfaces were examined after the tests using optical and scanning electron microscopes (SEM). Photodegradation of the polymer matrices was analyzed by Fourier Transform Infrared Spectroscopy (FTIR) techniques. A comparison of weight changes of polymer composites degraded by UVA and UVB was also presented.

It has been shown that the selected aging conditions created noticeable synergistic effects causing extensive erosion of the polymer matrices of the tested composites which appeared to be much stronger under the combined actions than under individual exposures. However, synergetic aging of pure polymers was not as obvious as in the tested GRPs with the exception of the PVC resin. Based on the synergistic aging mechanisms observed on the surfaces of the tested GRPs, a new model of synergistic aging of polymers under UV and water condensation was proposed. The model includes numerical simulations of UV radiation, numerical simulations of hydrodynamic effects, and complex particle removal analyses. In the UV radiation modeling part of the simulations, flat and sinusoidal polymer surfaces were numerically modeled for their UV damage as a function of UV intensity, surface topography, and exposure time. The results showed that UV damage on uneven polymer surfaces reduces their surface roughness making them planar and that the degradation rates are the largest at the tips of the local heights of the surfaces. This was subsequently verified experimentally by exposing neat epoxy specimens to UV and by precisely monitoring their surface topography as a function of time. In the hydrodynamic portion, viscous shear stresses generated by slowly moving water were determined on uneven polymer surfaces as a function of surface morphology, flow rates, and volumetric forces.

In the particle removal portion of the analysis, a new micro-particle removal mechanism was suggested by comparing the adhesion forces calculated using the Johnson-Kendall-Roberts (JKR) model and the Hamaker approach with the drag forces created by slow water flows. Subsequently, the particle removal mechanism was verified on an inclined unidirectional glass/epoxy surface with randomly distributed epoxy particles subjected to a gravitational flow of water. It has been shown that the movement of polymer particles on polymer/composite surfaces depends very strongly on particle sizes, water velocity, and surface morphology.

The analysis of adhesion forces between particles and polymer surfaces was further enhanced by introducing the surface roughness effects for both the polymer surfaces and the particles. The interactions were simulated by using the Rumpf, Rabinovich, Kumar, and the modified Rabinovich models as a function of nano roughness and micro roughness of substrate surfaces, nano roughness of micro roughness of particles, particle size and the number of contact points. Adhesion forces between irregular particles and irregular surfaces were also analyzed for their effects on the critical sizes of particle which could be removed from different rough surfaces by shear stresses generated by slowly moving water. It has been shown that the polymer surfaces with irregular nano/micro structure characteristics significantly reduced their interactions with deposited rough particles. The critical sizes of rough particles that could be removed by water flows were found to be significantly smaller than for smooth particles removed from flat surfaces.

Publication Statement

Copyright is held by the author. User is responsible for all copyright compliance.

Rights Holder

Tianyi Lu

Provenance

Received from ProQuest

File Format

application/pdf

Language

en

File Size

182 p.

Discipline

Materials science, Chemistry, Plastics

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