Han Changseok, Sahle-Demessie E, Varughese Eunice, Shi Honglan
Department of Environmental Engineering, INHA University, Incheon 22212, Korea.
Oak Ridge Institute for Science and Education, Oak Ridge TN, 37831, USA.
Environ Sci Nano. 2019 Jun 1;6:1876-1894. doi: 10.1039/c9en00153k.
Nanomaterials (NM) are incorporated into polymers to enhance their properties. However, there are a limited number of studies on the aging of these nanocomposites and the resulting potential release of NM. To characterize NM at critical points in their life cycles, polypropylene (PP) and multiwall carbon nanotube filled PP (PP-MWCNT) plates with different thicknesses (from 0.25 mm to 2 mm) underwent accelerated weathering in a chamber that simulates solar irradiation and rainfall. The physicochemical changes of the plates depended on the radiation exposure, the plate thickness, and the presence of CNT fillers. Photodegradation increased with aging time, making the exposed surface more hydrophilic, decreasing the surface hardness and creating surface stress-cracks. Aged surface and cross-section showed crazing due to the polymer bond scission and the formation of carbonyls. The degradation was higher near the UV-exposed surface as the intensity of the radiation and oxygen diffusion decreased with increasing depth of the plates, resulting in an oxidation layer directly proportional to oxygen diffusion. Thus, sample thickness determines the kinetics of the degradation reaction and the transport of reactive species. Plastic fragments, which are less than 1 mm, and free CNTs were released from weathered MWCNT-PP. The concentrations of released NM that were estimated using ICP-MS, increased with prolonged aging time. Various toxicity tests, including reactive oxygen species generation and cell activity/viability, were performed on the released CNTs. The toxicity of the released fragments and CNTs to A594 adenocarcinomic human alveolar basal epithelial cells was observed. The released polymer fragments and CNTs did not show significant toxicity under the experimental conditions in this study. This study will help manufacturers, users of consumer products with nanocomposites and policymakers in the development of testing guidelines, predictive models, and risk assessments and risk based-formulations of NM exposure.
纳米材料（NM）被掺入聚合物中以增强其性能。然而，关于这些纳米复合材料的老化以及由此产生的NM潜在释放的研究数量有限。为了在纳米材料生命周期的关键节点对其进行表征，不同厚度（从0.25毫米到2毫米）的聚丙烯（PP）和多壁碳纳米管填充的PP（PP-MWCNT）板在模拟太阳辐射和降雨的试验箱中进行加速老化。板材的物理化学变化取决于辐射暴露、板材厚度以及碳纳米管填料的存在。光降解随老化时间增加，使暴露表面更具亲水性，降低表面硬度并产生表面应力裂纹。老化的表面和横截面由于聚合物键断裂和羰基的形成而出现裂纹。由于辐射强度和氧气扩散随板材深度增加而降低，在紫外线暴露表面附近降解程度更高，从而形成与氧气扩散成正比的氧化层。因此，样品厚度决定了降解反应的动力学以及活性物种的传输。小于1毫米的塑料碎片和游离碳纳米管从老化的MWCNT-PP中释放出来。使用电感耦合等离子体质谱法（ICP-MS）估算的释放NM浓度随老化时间延长而增加。对释放的碳纳米管进行了各种毒性测试，包括活性氧生成和细胞活性/活力测试。观察了释放的碎片和碳纳米管对A594人肺泡基底上皮腺癌细胞的毒性。在本研究的实验条件下，释放的聚合物碎片和碳纳米管未显示出明显毒性。这项研究将有助于纳米复合材料消费品的制造商、用户以及政策制定者制定测试指南、预测模型、风险评估以及基于风险的NM暴露配方。
