PHYSIOCHEMICAL DEGRADATION OF PLASTIC FIBERS FROM SYNTHETIC FABRICS AND EFFECT OF NATURAL ORGANIC MATTER IN AQUATIC ENVIRONMENTS ON NANOPLASTICS’ BEHAVIOR

Author

Amin Asadollahi, Southern Illinois University CarbondaleFollow

Date of Award

5-1-2025

Degree Name

Master of Science

Department

Civil Engineering

First Advisor

Fakhraei, Habibollah

Abstract

Plastic pollution is one of the most pressing environmental challenges globally due to the extensive use of plastics across various industries. Large plastics in the environment break down into smaller pieces, forming microplastics (MPs) (less than 5 mm) and nanoplastics (NPs) (less than 100 nm). These tiny particles can easily disperse and enter the food chain, posing risks to ecosystems and human health. Microfibers (MFs) from textiles are a growing pollutant, with domestic laundry being a primary source of microplastic pollution. The main goals of this research were: first, to determine how different laundry conditions affect the release of MP from various synthetic fabrics and their degradation under UV irradiation and varying pH conditions; and second, to identify the behavior of polyethylene nanoplastics (PE NPs) in different ionic strengths and their interactions with natural organic matter (NOM). This will be achieved using advanced quartz crystal microbalance (QCM) technology. Although previous studies have examined individual effects of washing conditions, fabric types, and laundering additives on MFs release, the combined impact of these factors has not been comprehensively assessed. This research evaluates microfiber shedding from cotton, acrylic, polyester, and nylon fabrics under a range of washing parameters. Results indicate that detergent use and extended washing time significantly increase MFs release, with cotton shedding the most microfibers (617.34 ± 85.2 mg/kg per wash) and nylon the least (225.12 ± 30 mg/kg per wash). The use of a laundry ball during washing raised microfiber release by 10-60%, and when washing duration and temperature were both increased, duration emerged as the primary contributor to MFs release for cotton. However, nylon shows greater sensitivity to temperature than to exposure duration. In mixed washing conditions, maximum MF release was observed at 75 minutes and using laundry ball, with a shedding increase of approximately 30-40% across fabrics. In complementary research examining environmental degradation pathways, UV exposure and pH-mediated hydrolysis were shown to significantly impact microfiber breakdown. After 150 days of UV irradiation, nylon fibers demonstrated the most severe degradation with approximately 38 μm² of surface damage per fiber, while acrylic showed remarkable resistance with only 9 μm² of damage. Notably, seawater's complex composition dramatically reduced UV degradation efficacy compared to both surface water and DI water, with observed damage decreasing by 40-60% due to UV scattering by dissolved salts and radical quenching by halide ions. The study revealed pH as a critical driver of microfiber degradation, with alkaline conditions (pH 12) inducing the most severe damage. Polyester exhibited complete ester bond hydrolysis within 72 hours under high pH, evidenced by FTIR and TOC results. In contrast, acidic environments (pH 4) caused minimal degradation (<5% mass loss), highlighting alkaline hydrolysis as the dominant chemical degradation pathway. Additionally, this study investigates the behavior of PE NPs on silica surfaces in the presence of NOM using QCM. Findings reveal that, under unfavorable conditions (bare negatively charged silica), PE NPs deposition is minimal across various salt types and ionic strengths, diverging from the Derjaguin−Landau−Verwey−Overbeek (DLVO) theory. However, on NOM- and poly-L-lysine (PLL)-coated surfaces, both salt type and ionic strength (IS) significantly influence NPs deposition and release. NaCl promoted the highest NPs deposition, whereas MgCl₂ had less effect, with the trend in deposition following NaCl > MgCl₂. Increasing IS enhanced NPs deposition on NOM-coated surfaces. This research provides key insights into factors influencing NPs deposition and release dynamics, to inform future MPs pollution mitigation strategies.