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.

No abstract

No abstract

We demonstrate an efficient strategy to characterise weathering-induced photooxidative defects in microplastics. The central 13C cross polarisation NMR spectra offer high resolution and are quantitative when combined with multiple excitation.

Polymers are omnipresent in our everyday lives. For specific applications, their properties can be extensively modified by various types of additives, e.g., processing stabilizers, antioxidants, UV-stabilizers, flame retardants, and plasticizers. While several additives are nowadays considered to be toxic or persistent in the environment, quantitative data characterizing plastic fragmentation and microplastic formation have not yet been discussed in detail. Here, we present a long-term, laboratory-controlled accelerated weathering study on polypropylene (PP) particles with and without processing stabilizers. We were able to identify the stabilizers as Irgafos® 168, and Irganox® 1010. For both PP sample sets, we monitored the degradation using a combination of various analytical methods, such as gel permeation chromatography, particle size distributions, scanning electron microscopy, solid-state 13C magic-angle spinning NMR and liquid-state 1H, 13C, 31P NMR spectroscopy, differential scanning calorimetry and matrix-assisted laser desorption ionization time of flight mass spectrometry. The stabilizers prevent degradation by simulated solar radiation for about 350 h. Then, degradation sets in rapidly, leading to an exponential decrease in molecular weight and particle size, accompanied by an increase in crystallinity and the formation of oxygen-containing functional groups. After 3200 h, representing approximately 2 years of outdoor weathering, both PP samples exhibit comparable characteristics and sizes, regardless if a stabilizer was initially present. During degradation, an extremely large number of 100,000 daughter particles (4 µm) are formed and released from one MP particle of 192 µm diameter. Their physical properties and chemical composition have largely changed, resulting in a very low molecular weight and a hydrophilic character. These particles no longer resemble pristine PP. We thus expect them to be more prone to biodegradation compared to the starting material.