Electronic Theses and Dissertations

Date

2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Civil Engineering

Committee Chair

Maryam Salehi

Committee Member

Claudio Meier

Committee Member

Farhad Jazaei

Committee Member

Peyman Babakhani

Abstract

The growing public awareness of plastic pollution and its harmful environmental impacts on public health and ecological safety has raised multiple questions regarding the rate of its accumulation, long-term fate, and transport within the environment. However, the extent of plastic release into the terrestrial environment, such as farmlands, remains inadequately understood, though it is expected to exceed that of the ocean. Therefore, this dissertation focuses on investigating the mechanical degradation of plastics that leads to the generation of microplastics through fragmentation in agricultural farmlands. This dissertation addresses several knowledge gaps regarding the influence of environmental conditions on the mechanical degradation of plastics in the terrestrial environment. Chapter 1 provides an overview of the research background, identifies knowledge gaps, and outlines the structure of the dissertation. Chapter 2 investigates the surface wear of low-density polyethylene (LDPE) pellets and films by soil particles. It focuses on factors that affect such as normal loads and abrasion duration that affect their fragmentation behavior. Additionally, the impact of photodegradation on plastic fragmentation by surface wear is examined. The results indicate that microcutting was the dominant wear mechanism under low normal loads on plastic surfaces, while higher loads caused a combination of microploughing and microcutting. Furthermore, photodegradation led to oxidation of the plastic surface, increasing its brittleness and significantly enhancing fragmentation, as well as microplastic generation. vii Chapter 3 focuses on polymer-coated controlled-release fertilizers (PC-CRFs) and their contribution to microplastic pollution as they release nutrients. This study examines the physicochemical changes in PC-CRFs during 25 days at 45°C as they release nutrients into the water and soil. Also, for one of the target fertilizers, this study investigated the generation of microplastics during the nutrient-release process in both water and soil media. Polyethylene (PE) was identified as the polymer used in type A PC-CRFs, and alkyd resin and dicyclopentadiene were found in type B PC-CRFs. Surface morphology analysis revealed the development of microscopic pores and cracks, likely caused by osmotic pressure during nutrient release, which may have contributed to MP generation. MP release in soil was greater than in water, likely due to soil abrasion and the effects of wet-dry cycles. Chapter 4 investigates the mechanical degradation of PC-CRF microcapsules under surface wear and shear forces by analyzing their surface morphology and fragmentation changes. Laboratory experiments simulate abrasion by soil and shear forces from heavy agricultural machinery. Surface morphology analysis reveals that microploughing and microcutting are the dominant mechanisms, as the normal load increased to 4.0 N during the surface wear experiments. Our results showed that a longer duration of surface wear increased the number of generated MPs, while higher loading in surface wear experiments resulted in a larger median diameter of the MPs. Chapter 5 concludes the dissertation and proposes directions for future research.

Comments

Data is provided by the student.”

Library Comment

Dissertation or thesis originally submitted to ProQuest.

Notes

Open Access

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