Physics and chemistry-based constitutive modeling of photo-oxidative aging in semi-crystalline polymers
Physics and chemistry-based constitutive modeling of photo-oxidative aging in semi-crystalline polymers
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DOI：
10.1016/j.ijsolstr.2022.111427
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发表时间：
2022-02-01
影响因子：
3.6
通讯作者：
Shakiba, Maryam
中科院分区：
文献类型：
--
作者：
Najmeddine, Aimane;Xu, Zhen;Shakiba, Maryam
本文提出了一种基于物理化学的本构框架来预测严重光氧化老化的半结晶聚合物的响应。由紫外光和氧气引起的光氧化是影响聚合物寿命的主要降解机制之一。在这项工作中，我们首先表征了低密度聚乙烯(LDPE)的物理化学变化，以了解和绘制光氧化降解过程。分别用差示扫描量热法(DSC)和耗散监测石英晶体微天平(QCM-D)实验表征了结晶度和质量损失的变化。结晶度和相对于原始胶片的质量损失随曝光时间的变化被认为是材料退化的指标。在这些测试的基础上，我们提出了聚合物本构方程中材料性质的演化函数，以包含光氧化对力学响应的影响。将影响聚合物网络演化的物理化学过程与LDPE的机械响应联系起来，就不需要定义没有物理意义的额外拟合参数。所开发的本构框架通过对不同紫外线曝光时间老化的LDPE进行的一系列内部单轴拉伸测试来验证。对所提出的本构框架的验证证实了DSC和QCM-D作为表征LDPE薄膜降解的严谨技术的准确性，并证实了所开发的框架在预测光氧化老化LDPE的力学响应方面的稳健性。
This paper proposes a physio-chemically-based constitutive framework to predict the response of severely photo-oxidatively aged semi-crystalline polymers. Photo-oxidation induced by the exposure to Ultra-Violet (UV) light and oxygen is one of the main and dominant degradation mechanisms affecting the lifespan of polymers. In this work, we first characterize the physio-chemical changes of low-density polyethylene (LDPE) to understand and map the photo-oxidation degradation process. Changes in crystallinity and mass loss are characterized by Differential Scanning Calorimetry (DSC) and Quartz Crystal Microbalance with Dissipation Monitoring (QCM-D) experiments, respectively. The evolution of crystallinity and mass loss relative to the initial pristine films over exposure time are considered as indicators of material degradation. Based on these tests, we then propose evolution functions for the material properties in the polymer constitutive equations to incorporate the effects of photo-oxidation on the mechanical responses. Connecting the physio-chemical processes affecting polymer network evolution to the mechanical response of LDPE eliminates the need for defining extra fitting parameters that carry no physical meaning. The developed constitutive framework is validated with respect to a series of in-house uniaxial tensile tests performed on LDPE aged for different UV exposure times. Validation of the proposed constitutive framework confirms the accuracy of DSC and QCM-D as rigorous techniques in the characterization of degradation in LDPE films, and confirms the robustness of the developed framework in predicting the mechanical responses of photo-oxidatively aged LDPE.