Fundamental study on environmental stress cracking effects in polymer nanocomposites

环境应力开裂(ESC)是塑料构件寿命缩短的最常见原因之一。当产品受到机械应力和引发应力开裂的侵蚀性流体的同时作用时，总是会发生ESC风险。当产品用于例如医疗护理时，过早失效的后果通常是严重的，并且可能危及生命。因此，这被认为是一个巨大的挑战，要从根本上理解并在此基础上提高聚合物材料的耐ESC性能。一般而言，随着聚合物相对分子质量的增加和聚合物基质相对分子质量分布的扩大，耐ESC性能提高。此外，值得注意的初步结果表明，纳米填料的加入为提高聚合物的抗ESC性能提供了新的可能性，从而延长了聚合物的使用寿命。因此，本研究的目的是深入了解纳米填料参数和分子参数对非晶态聚合物在不同环境条件(应力破裂剂和常温)以及不同挑战力学条件(静态和动态加载)下ESC行为的影响。不同相对分子质量和相对分子质量分布的聚甲基丙烯酸甲酯(PMMA)将被用作聚合物基质。PMMA将与不同类型、大小和含量的纳米薄膜复合，这些纳米薄膜具有球形(纳米二氧化硅(SiO_2))、棒状(埃洛石纳米管(HNTs))以及片状几何结构(商业和特殊表面处理的层状硅酸盐)。通过利用力学、热、形态、光学、流变学和表面张力分析方法，将有可能关联纳米复合材料的结构-性能关系。这一分析所获得的见解将是理解聚合物纳米复合材料ESC行为的关键。

Environmental stress cracking (ESC) is one of the most common reasons of lifetime shortening for plastic components. The risk of ESC always occurs when the product is subject to the simultaneous effects of mechanical stresses and aggressive fluids that trigger stress cracking. The consequences of the premature failure are often serious and can be life-threatening when the product is used for instance in the medical care. Accordingly, this is considered to be a great challenge to understand fundamentally and based on this to improve the ESC resistance of polymeric materials. Generally, the ESC resistance improves with increasing molecular weight and a broad molecular weight distribution of the polymer matrix. Moreover, the notable preliminary results reveal that the incorporation of nanofillers provides new possibilities to improve the ESC resistance and consequently prolong the service lifetime of the polymers.Therefore, the objectives of this research proposal are to gain a deep understanding of the influence of nanofiller parameters and the molecular parameters on the ESC behavior of the amorphous polymer under various environment conditions (stress cracking agents and ambient temperatures) as well as different challenging mechanical conditions (static and dynamic loading). Polymethylmethacrylate (PMMA) with different molecular weights and molecular weight distributions will be used as polymer matrices. The PMMA will be compounded with different types, sizes, and contents of nanofillers which have spherical (nano-silicon dioxide (SiO2)), rod-like (halloysite nanotubes (HNTs)) as well as platelet-like geometries (commercial and special surface treated layered silicates). By utilizing mechanical, thermal, morphological, optical, rheological, and surface tension analysis methods, it will be possible to correlate the structure-properties relationship of the nanocomposites. The received insights of this analysis will be the key to understanding the ESC behavior of the polymer nanocomposites.