Fairbrother Andrew, Hsueh Hsiang-Chun, Kim Jae Hyun, Jacobs Deborah, Perry Lakesha, Goodwin David, White Christopher, Watson Stephanie, Sung Li-Piin
Polymeric Materials Group, National Institute of Standards and Technology (NIST), 100 Bureau Dr., Gaithersburg, MD, 20899, USA.
Polym Degrad Stab. 2019 Jul;165. doi: 10.1016/j.polymdegradstab.2019.05.002.
The photodegradation of polymers poses a serious challenge to their outdoor application, and results in significant financial loss due to early or unexpected system failure. A better understanding of their degradation kinetics aids the improvement of materials and systems. However, most work to date on many polymeric materials focuses on only one or a few exposure conditions which are pertinent to typical environmental ambients. Here the model polyolefin system of high-density polyethylene (HDPE) was exposed under controlled laboratory conditions to a range of temperatures (30 °C, 40 °C, 50 °C) and ultraviolet (UV) light intensities (153 W m, 61 W m, 38 W m, 15 W m, 8 W m, and 0 W m). Changes to the mechanical, chemical, and structural properties were monitored by uniaxial tensile testing and Fourier-transform infrared spectroscopy (FTIR), which showed that the rapid embrittlement of HDPE was concurrent with increases in yield strength, stiffness, oxidation, and crystallinity. The rates of change tended to increase under more aggressive exposure conditions, and the photothermal activation energies and UV dose-damage relationships for these properties were determined. A comparison to HDPE under outdoor exposure in southern Florida shows a similar magnitude of material change up to the point of embrittlement, despite the differences in spectral irradiance and the constantly changing outdoor conditions. These results quantify the effect of temperature and UV light intensity on the photodegradation of HDPE and can be utilized to develop stabilization strategies for these and related thermoplastic materials.
聚合物的光降解对其户外应用构成了严峻挑战，并因早期或意外的系统故障导致重大经济损失。更好地了解其降解动力学有助于改进材料和系统。然而，迄今为止，许多聚合物材料的研究工作仅关注与典型环境条件相关的一种或几种暴露条件。在此，高密度聚乙烯（HDPE）的模型聚烯烃体系在可控的实验室条件下暴露于一系列温度（30℃、40℃、50℃）和紫外线（UV）光强度（153W/m、61W/m、38W/m、15W/m、8W/m和0W/m）下。通过单轴拉伸试验和傅里叶变换红外光谱（FTIR）监测其力学、化学和结构性能的变化，结果表明HDPE的快速脆化与屈服强度、刚度、氧化和结晶度的增加同时发生。在更苛刻的暴露条件下，变化速率往往会增加，并确定了这些性能的光热活化能和紫外线剂量-损伤关系。与佛罗里达州南部户外暴露条件下的HDPE相比，尽管光谱辐照度不同且户外条件不断变化，但在脆化点之前材料变化的幅度相似。这些结果量化了温度和紫外线光强度对HDPE光降解的影响，可用于为这些及相关热塑性材料制定稳定化策略。
