Mundhenke Thomas F, Li Sonia C, Maurer-Jones Melissa A
Department of Chemistry and Biochemistry, University of Minnesota Duluth, 1038 University Dr., Duluth, Minnesota 55812, USA.
Environ Sci Process Impacts. 2022 Dec 14;24(12):2284-2293. doi: 10.1039/d2em00359g.
Polypropylene (PP) and polyethylene (PE) are commonly used polyolefins in a variety of applications, which have resulted in their accumulation in the environment. Once in the environment, these polymers undergo various chemical and physical transformations as the result of environmental stressors such as sunlight. While photodegradation has been studied for decades, there are key gaps in knowledge on the phototransformations of polyolefins that occur under aqueous conditions. Therefore, the goal of this study is to characterize the phototransformations of PP and PE in simulated freshwater conditions. Polymer thin films were irradiated with 254 nm and 350 nm UV light in air, ultra-pure water, and solutions of dissolved organic matter (DOM) to simulate natural systems. Irradiated plastics were evaluated for oxidation and chain scission. It was observed using Fourier transform infrared spectroscopy (FTIR) that oxidation in aqueous environments happened at a slower rate compared to oxidations in air. However, photo-oxidation was accelerated in the presence of DOM compared to ultrapure water, with singlet oxygen and hydroxyl radical causing varied amounts of degradation depending on the polymer. The vinyl characteristic, a chain scission product, revealed an increased yield but the reaction rate showed that these photoproducts were more likely to occur when oxidation is less favorable. Compared to naturally weathered samples, lab observed transformations were on par with naturally degraded samples and support the importance of the in-lab measurements. This work quantifies the extent and rate of photodegradation pathways in PP and PE to demonstrate the importance of photodegradation in aquatic systems.
聚丙烯（PP）和聚乙烯（PE）是在各种应用中常用的聚烯烃，这导致它们在环境中积累。一旦进入环境，这些聚合物会因阳光等环境压力因素而经历各种化学和物理转变。虽然光降解已经研究了几十年，但在水相条件下聚烯烃的光转变方面仍存在关键的知识空白。因此，本研究的目的是表征PP和PE在模拟淡水条件下的光转变。在空气中、超纯水和溶解有机物（DOM）溶液中，用254nm和350nm的紫外光照射聚合物薄膜，以模拟自然系统。对辐照后的塑料进行氧化和断链评估。使用傅里叶变换红外光谱（FTIR）观察到，与在空气中的氧化相比，水环境中的氧化发生得较慢。然而，与超纯水相比，在DOM存在的情况下光氧化加速，单线态氧和羟基自由基根据聚合物的不同导致不同程度的降解。作为断链产物的乙烯基特征显示产率增加，但反应速率表明，当氧化不太有利时，这些光产物更有可能出现。与自然风化的样品相比，实验室观察到的转变与自然降解的样品相当，并支持实验室测量的重要性。这项工作量化了PP和PE中光降解途径的程度和速率，以证明光降解在水生系统中的重要性。
