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

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.