Many coating properties such as mechanical, electrical, and ultraviolet (UV) resistance are greatly enhanced by the addition of nanoparticles, which can potentially increase the use of nanocoatings for many outdoor applications. However, because polymers used in all coatings are susceptible to degradation by weathering, nanoparticles in a coating may be brought to the surface and released into the environment during the life cycle of a nanocoating. Therefore, the goal of this study is to investigate the process and mechanism of surface degradation and potential particle release from a commercial nanosilica/polyurethane coating under accelerated UV exposure. Recent research at the National Institute of Standards and Technology (NIST) has shown that the matrix in an epoxy nanocomposite undergoes photodegradation during exposure to UV radiation, resulting in surface accumulation of nanoparticles and subsequent release from the composite. In this study, specimens of a commercial polyurethane (PU) coating, to which a 5 mass% surface-treated silica nanoparticle solution was added, were exposed to well-controlled, accelerated UV environments. The nanocoating surface morphological changes and surface accumulation of nanoparticles as a function of UV exposure were measured, along with chemical change and mass loss using a variety of techniques. Particles from the surface of the coating were collected using a simulated rain process developed at NIST, and the collected runoff specimens were measured using inductively coupled plasma optical emission spectroscopy to determine the amount of silicon released from the nanocoatings. The results demonstrated that the added silica nanoparticle solution decreased the photodegradation rate (i.e., stabilization) of the commercial PU nanocoating. Although the degradation was slower than the previous nanosilica epoxy model system, the degradation of the PU matrix resulted in accumulation of silica nanoparticles on the nanocoating surface and release to the environment by simulated rain. These experimental data are valuable for developing models to predict the long-term release of nanosilica from commercial PU nanocoatings used outdoors and, therefore, are essential for assessing the health and environmental risks during the service life of exterior PU nanocoatings.

中文翻译：

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商业纳米二氧化硅/聚氨酯涂料在紫外线下的表面降解和纳米颗粒释放。

通过添加纳米颗粒，大大提高了许多涂层的性能，例如机械，电气和紫外线（UV）耐受性，这可能会增加纳米涂层在许多户外应用中的使用。但是，由于用于所有涂层的聚合物容易因风化而降解，因此在纳米涂层的生命周期中，涂层中的纳米颗粒可能会被带到表面并释放到环境中。因此，这项研究的目的是研究在加速的紫外线照射下，从商用纳米二氧化硅/聚氨酯涂料中表面降解和潜在的颗粒释放的过程和机理。美国国家标准技术研究院（NIST）的最新研究表明，环氧纳米复合材料中的基质在暴露于紫外线辐射期间会发生光降解，导致纳米颗粒表面积聚并随后从复合材料中释放出来。在这项研究中，将添加了5质量％表面处理过的二氧化硅纳米粒子溶液的商用聚氨酯（PU）涂层的标本暴露于受控良好的加速UV环境中。使用多种技术，测量了纳米涂层的表面形态变化和纳米颗粒表面积累随紫外线暴露的变化，以及化学变化和质量损失。使用NIST开发的模拟雨水工艺收集涂层表面的颗粒，并使用感应耦合等离子体发射光谱法测量收集的径流样品，以确定从纳米涂层中释放的硅量。结果表明，添加的二氧化硅纳米颗粒溶液降低了商业PU纳米涂层的光降解速率（即，稳定性）。尽管降解速度比以前的纳米二氧化硅环氧模型系统慢，但PU基体的降解导致二氧化硅纳米粒子在纳米涂层表面积聚并通过模拟雨水释放到环境中。这些实验数据对于开发模型以预测从室外使用的商用PU纳米涂料中长期释放的纳米二氧化硅是有价值的，因此，对于评估外部PU纳米涂料使用寿命期间的健康和环境风险至关重要。尽管降解速度比以前的纳米二氧化硅环氧模型系统慢，但PU基体的降解导致二氧化硅纳米粒子在纳米涂层表面积聚并通过模拟雨水释放到环境中。这些实验数据对于开发模型以预测从室外使用的商用PU纳米涂料中长期释放的纳米二氧化硅是有价值的，因此，对于评估外部PU纳米涂料使用寿命期间的健康和环境风险至关重要。尽管降解速度比以前的纳米二氧化硅环氧模型系统慢，但PU基体的降解导致二氧化硅纳米粒子在纳米涂层表面积聚并通过模拟雨水释放到环境中。这些实验数据对于开发模型以预测从室外使用的商用PU纳米涂料中长期释放的纳米二氧化硅是有价值的，因此，对于评估外部PU纳米涂料使用寿命期间的健康和环境风险至关重要。