Reconstructing the Environmental Degradation of Polystyrene by Accelerated Weathering

Abstract

The fragmentation of macro- into microplastics (MP) is the main source of MP in the environment. Nevertheless, knowledge about degradation mechanisms, changes in chemical composition, morphology, and residence times is still limited. Here, we present a long-term accelerated weathering study on polystyrene (PS) tensile bars and MP particles using simulated solar radiation and mechanical stress. The degradation process was monitored by gel permeation chromatography (GPC), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), 13C magic-angle spinning (MAS) NMR spectroscopy, tensile testing, and Monte Carlo simulations. We verified that degradation proceeds in two main stages. Stage I is dominated by photooxidation in a near-surface layer. During stage II, microcrack formation and particle rupturing accelerate the degradation. Depending on the ratio and intensity of the applied stress factors, MP degradation kinetics and lifetimes vary dramatically and an increasing amount of small MP fragments with high proportions of carboxyl, peroxide, and keto groups is continuously released into the environment. The enhanced surface area for adsorbing pollutants and forming biofilms modifies the uptake behavior and interaction with organisms together with potential ecological risks. We expect the proposed two-stage model to be valid for predicting the abiotic degradation of other commodity plastics with a carbon–carbon backbone.

Impact of Enzymatic Degradation on the Material Properties of Poly(Ethylene Terephthalate)

“…On a chemical level, abiotic factors are relatively well characterized: Photooxidation by UV radiation and oxygen leads to radical-induced chain scission and the formation of new polar functional end groups, e.g., carboxylic acids, aldehydes, hydroxides, or peroxides [15][16][17][18]. Hydrolytic degradation strongly depends on an interplay of humidity, temperature, pH, and the crystallinity of the material [17,[19][20][21].…”

Quantification of photooxidative defects in weathered microplastics using13C multiCP NMR spectroscopy

“…The accelerated weathering experiments were carried out under controlled laboratory conditions in a test chamber Q-SUN XE-3 (Q-LAB Corporation, Westlake, OH, USA) according to a protocol developed previously. 17 The weathering chamber is equipped with three xenon arc lamps and a Daylight-Q filter system. The latter filters radiation with wavelengths smaller than 295 nm.…”

“…As the defect types vary in polarity and the ability to form charges as a function of the pH, a prediction of MP physicochemical properties and subsequent model building is not possible without quantifying the defect proportions. 17 …”

Microplastic in Water and Sediments at the Confluence of the Elbe and Mulde Rivers in Germany

“…While primary microplastics are intentionally produced, for example as spheres for industrial purposes, secondary microplastics originate from fragmentation of macroplastic objects by exposure to light, heat, mechanical friction or organisms (Geyer et al, 2017;Kataoka et al, 2019;Meides et al, 2021;Petersen and Hubbart, 2021). So far, researchers studied mostly marine environments, while the contamination of freshwater and terrestrial systems gained far less attention (Dris et al, 2015;Wagner and Lambert, 2018;Scherer et al, 2020).…”