Biale Greta, La Nasa Jacopo, Mattonai Marco, Corti Andrea, Vinciguerra Virginia, Castelvetro Valter, Modugno Francesca
Department of Chemistry and Industrial Chemistry, University of Pisa, 56124 Pisa, Italy.
National Interuniversity Consortium of Materials Science and Technology, 50121 Florence, Italy.
Polymers (Basel). 2021 Jun 18;13(12):1997. doi: 10.3390/polym13121997.
Most of the analytical studies focused on microplastics (MPs) are based on the detection and identification of the polymers constituting the particles. On the other hand, plastic debris in the environment undergoes chemical and physical degradation processes leading not only to mechanical but also to molecular fragmentation quickly resulting in the formation of leachable, soluble and/or volatile degradation products that are released in the environment. We performed the analysis of reference MPs-polymer micropowders obtained by grinding a set of five polymer types down to final size in the 857-509 μm range, namely high- and low-density polyethylene, polystyrene (PS), polypropylene (PP), and polyethylene terephthalate (PET). The reference MPs were artificially aged in a solar-box to investigate their degradation processes by characterizing the aged (photo-oxidized) MPs and their low molecular weight and/or highly oxidized fraction. For this purpose, the artificially aged MPs were subjected to extraction in polar organic solvents, targeting selective recovery of the low molecular weight fractions generated during the artificial aging. Analysis of the extractable fractions and of the residues was carried out by a multi-technique approach combining evolved gas analysis-mass spectrometry (EGA-MS), pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS), and size exclusion chromatography (SEC). The results provided information on the degradation products formed during accelerated aging. Up to 18 wt% of extractable, low molecular weight fraction was recovered from the photo-aged MPs, depending on the polymer type. The photo-degradation products of polyolefins (PE and PP) included a wide range of long chain alcohols, aldehydes, ketones, carboxylic acids, and hydroxy acids, as detected in the soluble fractions of aged samples. SEC analyses also showed a marked decrease in the average molecular weight of PP polymer chains, whereas cross-linking was observed in the case of PS. The most abundant low molecular weight photo-degradation products of PS were benzoic acid and 1,4-benzenedicarboxylic acid, while PET had the highest stability towards aging, as indicated by the modest generation of low molecular weight species.
大多数聚焦于微塑料（MPs）的分析研究是基于对构成颗粒的聚合物的检测与识别。另一方面，环境中的塑料碎片会经历化学和物理降解过程，这不仅会导致机械破碎，还会导致分子碎片化，迅速产生可浸出、可溶解和/或挥发性的降解产物并释放到环境中。我们对通过将五种聚合物类型研磨至857 - 509μm范围内的最终尺寸而获得的参考MPs - 聚合物微粉进行了分析，这五种聚合物分别是高密度和低密度聚乙烯、聚苯乙烯（PS）、聚丙烯（PP）以及聚对苯二甲酸乙二酯（PET）。将参考MPs在太阳能箱中进行人工老化，通过对老化（光氧化）的MPs及其低分子量和/或高度氧化部分进行表征来研究其降解过程。为此，将人工老化的MPs在极性有机溶剂中进行萃取，目标是选择性回收人工老化过程中产生的低分子量部分。通过结合热重 - 质谱联用（EGA - MS）、热解 - 气相色谱 - 质谱联用（Py - GC - MS）和尺寸排阻色谱（SEC）的多技术方法对可萃取部分和残留物进行分析。结果提供了关于加速老化过程中形成的降解产物的信息。根据聚合物类型的不同，从光老化的MPs中回收了高达18 wt%的可萃取低分子量部分。在老化样品的可溶部分中检测到，聚烯烃（PE和PP）的光降解产物包括多种长链醇、醛、酮、羧酸和羟基酸。SEC分析还表明PP聚合物链的平均分子量显著降低，而在PS的情况下观察到了交联现象。PS最丰富的低分子量光降解产物是苯甲酸和1,4 - 苯二甲酸，而PET对老化具有最高的稳定性，这表现为低分子量物质的生成量较少。
