Department of Chemical & Biomolecular Engineering, North Carolina State University, Raleigh, NC, United States of America.
Sea Education Association, Woods Hole, MA, United States of America.
Sci Total Environ. 2022 Mar 10;811:151368. doi: 10.1016/j.scitotenv.2021.151368. Epub 2021 Oct 31.
Accelerated weathering of LDPE laminates, with samples exposed to ultraviolet radiation (UVR) in air and while floating in seawater at the same temperature, was investigated in this study. The depth profiles of the concentrations of oxidation products in the two sets of samples was assessed by FTIR (Fourier Transform Infrared Spectroscopy) and suggest the oxidation on weathering to be diffusion-controlled in both air and in seawater, localizing the reaction to a thin surface layer. While the thickness of this layer is several hundred microns in air-weathered samples it is too small to be discernible by FTIR spectroscopy in sea water-weathered samples. A naturally weathered polyethylene microplastic pellet from floating ocean debris was also similarly studied by FTIR and the depth profile compared with that from accelerated weathering of LDPE laminates. Tensile properties of the LDPE weathered in air and in sea water were also compared to better understand the impact of diffusion-controlled oxidation on their mechanical integrity. How the origin of apparent retardation of the rate of weathering degradation of LDPE in seawater relative to that in air, is related diffusion-controlled oxidation due to the low concentrations of dissolved oxygen in seawater, is also discussed.
本研究考察了在空气中和在相同温度下漂浮于海水中时，LDPE 层压板的加速风化情况。通过傅里叶变换红外光谱（FTIR）评估了两组样品中氧化产物浓度的深度分布，结果表明在空气和海水中的风化过程均为扩散控制，将反应局限于一个薄的表面层。在空气中风化的样品中，这个层的厚度为几百微米，但在海水中风化的样品中，由于 FTIR 光谱无法识别，因此这个层的厚度太小而无法识别。还通过 FTIR 对来自漂浮海洋碎片的自然风化的聚乙烯微塑料颗粒进行了类似的研究，并将深度分布与 LDPE 层压板加速风化的深度分布进行了比较。还比较了在空气和海水中风化的 LDPE 的拉伸性能，以更好地理解扩散控制氧化对其机械完整性的影响。还讨论了与在海水中的风化降解速率相对于在空气中的明显延缓有关的问题，即由于海水中溶解氧的浓度低，扩散控制氧化的原因。
