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

众所周知，塑料可降解为微塑料和纳米塑料。这些环境污染物已经在海洋表面（例如大西洋垃圾带）被发现，现在在深海（最深处）。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少它们的发生，却知之甚少。这项研究的重点正是这个主题，特别是半结晶聚合物，它构成了目前使用的所有塑料的70%以上。这项工作将结合实验和理论工具来阐明它们在暴露于机械力、水、空气和/或紫外线下的降解机制。因此，这项研究将带来完善的聚合物表征工具，以描绘支撑纳米塑料形成的关键机制。除了这些方面，这项工作还预测了减轻这些环境污染物产生的机制——寻找和优化它们是该项目的第二个重点。从更广泛的影响角度来看，由这项研究启发的设计问题将在跨学科课程中展示，如工程设计课程。该项目还将为哥伦比亚大学的本科生提供研究机会，并培养不同类型的大三和大四学生。了解减少纳米塑料产生的途径，并将这些知识与外界交流，是拟议工作的最终焦点，因此，这项工作深深植根于对全球可持续性的贡献。技术概述：塑料可降解为微塑料和纳米塑料，这一点现已得到证实。这些环境污染物已经在海洋表面和深海中被发现。这项研究特别关注半结晶聚合物，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（即海洋中）进行环境降解时，实验一致表明，非晶相中的链段首先断裂，而晶体数量实际上在增长。这项工作提出，由于非晶相链的优先断裂，半结晶聚合物形成纳米塑料（100纳米或更小），非晶相链最初提供相邻晶片之间的连通性。与环境应力开裂现象类似，这些分子连接件的断裂导致材料局部失效，形成纳米塑料。这项工作将结合实验和理论工具来阐明暴露在机械应力、水、O2和/或紫外线下不同化学性质的半晶聚合物的降解机制。实验上，它应该将纳米粒子的产生与最初的聚合物化学和形态联系起来。这些变量如何影响所产生的环境污染物的大小、结构和性质是本研究应严格解决的开放性问题。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，从而预测从大块聚合物中暂时产生的纳米塑料物体的大小和数量。因此，这项工作将带来完善的聚合物表征工具，以描绘支撑纳米塑料形成的关键物理。除了这些方面，有人建议使用共聚物或挤压材料可以增加晶体之间的连通性，从而作为一种有效的策略来减少它们的产生。受到这项研究启发的设计问题将在工程设计课程等跨学科课程中得到展示。该项目还将为哥伦比亚大学的本科生提供研究机会，并培养不同类型的大三和大四学生。PI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。该PI已经在哥伦比亚大学举办了为期三天的虚拟研讨会，主题是机器学习在材料科学中的应用。实现减少纳米塑料产生的目标是拟议工作的最终焦点，因此，该工作集中在全球可持续性上。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.