Fundamental investigations on the environmental stress cracking of vibration-welded thermoplastic-based nanocomposites

一旦热塑性产品同时受到机械应力（即外部和内部应力）和腐蚀性介质的影响，就会引发所谓的环境应力开裂（ESC），导致产品过早发生灾难性故障。这些产品在使用中的过早失效通常是严重的，特别是在可能危及患者生命的医疗技术中。对ESC行为的基本理解和改善ESC抗性被认为是热塑性材料的巨大挑战。已经确定的是，增加分子量和掺入纳米尺寸的无机颗粒可以改善热塑性塑料的ESC耐受性，并且因此延长其寿命。这种热塑性产品通常设计有焊接部件，这些部件也容易受到ESC的影响。到目前为止，对焊接产品的ESC行为的研究相当稀少。本研究的主要目的是调查纳米填料与不同的几何形状，球形纳米二氧化硅和棒状碳纳米管，在不同的ESC代理和环境温度的影响下，对振动焊接的PP和PC基纳米复合材料的ESC电阻的影响。更重要的是，应特别考虑焊接区域内碳纳米管取向对ESC行为的影响。预计该项目的成果将有助于深入了解焊接部件的ESC行为，并最终合理开发具有更长寿命和更高应用安全性的高耐ESC复合材料。

Once thermoplastic products are under simultaneous effects of mechanical stress, i.e. external and internal stress, and an aggressive medium, the so-called environmental stress cracking (ESC) can be initiated, which leads to a premature catastrophic failure of the products. Premature failure of such products in service are often serious especially in the medical technology that can be life-threatening for the patients. Fundamental understanding of ESC behavior and improvement of ESC resistance are considered as great challenges for thermoplastic materials. It has been well established that increasing molecular weight and incorporation of nano-sized inorganic particles can both improve the ESC resistance of thermoplastics, and as a result, prolong their lifetime. Such thermoplastic products are often designed with welded parts, which are also susceptible to ESC. Till now, studies on the ESC behavior of welded products are quite sparse. The key objective of this research proposal is to investigate the effects of nanofillers with different geometries, spherical nanosilica and rod-like carbon nanotubes, on the ESC resistance of vibration-welded PP- and PC-based nanocomposites under influence of different ESC agents and ambient temperatures. More importantly, the effect of carbon nanotubes orientation within the weld region on the ESC behavior should be particularly considered. It is expected that the project outcome can contribute to a deep understanding of ESC behavior of the welded parts, and finally, a rational development of high ESC-resistant composite materials that exhibit longer lifetime and higher application safety.