CAS-MNP: Origins of Secondary Nanoplastics and Mitigating Their Creation

非技术总结众所周知，塑料会降解成微型和纳米塑料。这些环境污染物在海洋表面(例如，大西洋垃圾带)被发现，现在在深海(最深)。虽然人们普遍认为这些物质会对海洋生物产生有害影响，但人们对它们是如何形成的，它们的最终命运，以及最重要的是如何减轻它们的发生，知之甚少。这项研究正是围绕这一主题展开的，特别是占目前使用的所有塑料的70%以上的半晶性聚合物。这项工作将结合实验和理论工具来阐明它们在机械力、水、空气和/或紫外线下的降解机制。因此，这项研究将带来成熟的聚合物表征工具，以描绘支撑纳米塑料形成的关键机制。除了这些方面，这项工作还预期了减少这些环境污染物产生的机制--找到并优化它们是该项目的第二个方面。从更广泛的影响角度来看，这项研究启发的设计问题将在工程设计课程等跨学科项目中展示。该项目还将促进哥伦比亚大学本科生的研究机会和对不同的初级和高级学生的培训。了解减少纳米塑料产生的途径，并将这一知识传达给外部世界，是拟议工作的最终重点，因此，这项工作深深植根于对全球可持续发展的贡献。技术摘要塑料降解成微塑料和纳米塑料现在是众所周知的。这些环境污染物在海洋表面和深海中都有发现。这项研究特别关注半晶聚合物，它占目前使用的所有塑料的70%以上。当这些聚合物在水环境中(即在海洋中)环境降解时，实验一致地表明，非晶相中的链段首先断裂，而晶态粒子实际上增长。这项工作提出，半结晶聚合物形成纳米塑料(100 nm或更小)是由于非晶相连接链的优先断裂，而非晶相连接链最初提供了相邻晶片之间的连接。类似于环境应力破裂现象，这些分子连接体的断裂会导致材料的局部失效，形成纳米塑料。拟议的工作将结合实验和理论工具来阐明不同化学成分的半晶聚合物在机械应力、水、氧气和/或紫外光下的降解机理。在实验上，它将纳米粒子的产生与最初的聚合物化学和形态相关联。这些变量如何影响由此产生的环境污染物的大小、结构和性质是这项研究应认真解决的开放问题。平行的理论研究将预测相邻晶体之间连通性的时间演变，降解塑料的机械性能，从而预测从本体聚合物临时产生的纳米塑料对象的大小和数量。因此，这项工作将带来成熟的聚合物表征工具，以描绘支撑纳米塑料形成的关键物理。超越这些方面，有人提出，使用共聚物或挤压材料可以增加晶体之间的连接性，从而作为一种有效的策略来减少它们的产生。受这项研究启发的设计问题将在工程设计课程等跨学科项目中展示。该项目还将促进哥伦比亚大学本科生的研究机会和对不同的初级和高级学生的培训。国际和平研究所将为本科生和K-12学生开发与本提案主题相关的在线学习模块。这位PI已经在哥伦比亚大学举办了一个为期三天的虚拟研讨会，内容是机器学习在材料科学中的应用。实现减少纳米塑料创造的目标是拟议工作的最终重点，因此该工作集中于全球可持续发展。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

NON-TECHNICAL SUMMARYIt is well-established that plastics degrade into micro and nanoplastics. These environmental pollutants have been found at the ocean surface (e.g., the Atlantic garbage patch) and now in the deep(est) ocean. While it is commonly believed that these materials can have deleterious effects on marine life, there is little understanding of how they form, their ultimate fate and most importantly how their occurrence can be mitigated. This research focuses on exactly this topic, in particular on semicrystalline polymers, which constitute over 70% of all plastics used currently. The work will combine experimental and theoretical tools to elucidate their degradation mechanisms when exposed to mechanical forces, water, air and/or UV light. The research will thus bring the well-established tools of polymer characterization towards delineating the critical mechanisms underpinning the formation of nanoplastics. Going beyond these aspects, this work anticipates mechanisms to mitigate the creation of these environmental pollutants -- finding and optimizing them is the second prong of the project. From a broader impacts viewpoint, design problems inspired by this research will be showcased in interdisciplinary programs such as the Engineering Design curriculum. The project will also facilitate undergraduate research opportunities and the training of a diverse cohort of junior and senior students at Columbia University. Understanding the routes to achieving decreased nanoplastic creation, and communicating this knowledge to the outside world, are the ultimate foci of the proposed work, which is thus deeply rooted in contributing to global sustainability.TECHNICAL SUMMARYIt is now well-established that plastics degrade into micro and nanoplastics. These environmental pollutants have been found on the ocean surface and in the deep ocean. This research focuses in particular on semicrystalline polymers, which constitute over 70% of all plastics used currently. When these polymers environmentally degrade in the aqueous milieu (i.e., in oceans) experiments consistently show that the chain segments in the amorphous phase break first, while the crystalline population actually grows. This work proposes that semicrystalline polymers form nanoplastics (100 nm and smaller) due to the preferential fragmentation of amorphous-phase tie chains which originally provided the connectivity between adjacent crystalline lamellae. By analogy to the phenomenon of environmental stress cracking, breaking of these molecular connectors leads to local material failure and the formation of nanoplastics. The proposed work will combine experimental and theoretical tools to elucidate the proposed degradation mechanisms of semicrystalline polymers of varying chemistries when exposed to mechanical stresses, water, O2 and/or UV light. Experimentally, it shall correlate nanoparticle creation with the initial polymer chemistry and morphology. How these variables affect the size, structure and properties of the resulting environmental pollutants are open questions that this research shall critically address. Parallel theoretical studies will predict the temporal evolution of the connectivity between adjacent crystals, the mechanical properties of the degrading plastics, and hence the size and number of nanoplastic objects that are temporally generated from a bulk polymer. The work will thus bring the well-established tools of polymer characterization towards delineating the critical physics underpinning the formation of nanoplastics. Going beyond these aspects, it is proposed that the use of copolymers or extruding the material can increase connectivity between crystals and thus serve as an efficient strategy to mitigate their creation. Design problems inspired by this research will be showcased in interdisciplinary programs such as the Engineering Design curriculum. The project will also facilitate undergraduate research opportunities and the training of a diverse cohort of junior and senior students at Columbia University. The PI will develop online learning modules related to the theme of this proposal for undergraduate and K-12 students. This PI has already run a three-day virtual workshop at Columbia University on the application of Machine Learning to materials science. Achieving the goal of decreasing nanoplastic creation is the ultimate focus of the proposed work, which is thus centrally focused on global sustainability..This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.