Assessment of Four Artificial Methods for Aging Plastic Mulch Films According to Efficiency, Rate, and Similarity to Natural Field-Aged Plastics

Artificial degradation is often used to recreate and accelerate the natural aging of plastic for small-scaled simulation experiments assessing their environmental impact. However, current artificial aging methods are rarely compared against reference materials or validated using field-aged samples, creating uncertainties when extrapolating results to naturally aged plastics, making it difficult to place findings in an environmentally applicable context. Therefore, here we compared four accessible, cost-effective, and easily replicable methods (heat, UVA, and UVC irradiance at two intensities) to produce artificially degraded materials. The artificial aging methods were assessed over a duration of 5 months against degradation rate, efficiency, and similarity to field-aged samples of conventional and biodegradable plastic mulch film over a 6-month field exposure period. We utilised attenuated total reflectance-Fourier transform infrared spectroscopy to calculate the carbonyl index and measure chemical changes of the mulch film surface, as well as differential scanning calorimetry and thermogravimetric analysis. Physical changes were assessed by thickness and surface roughness measurements. We found that UVA was the most suitable and realistic artificial degradation method at a medium rate, whilst UVC is recommended for rapid degradation without the need to simulate realistic changes, and heat for processing large volumes of samples without a requirement for realistic degradation over a prolonged time period. However, the methods compared in this study yielded differential results depending on polymer type and parameter of interest. We therefore recommend establishing the degradation aim, identifying the spectral region of interest, and accounting for different polymer types to select the most appropriate method.