Formation Mechanisms of Micro and Nanoplastics

Non-technical Description Polymers are widely used but may have unintended negative consequences, e.g., they form microplastics (sizes between 1μm and 3 mm) and nanoplastics (sizes between 10nm and 1μm), collectively termed MNPL. It is well-known that MNPL formation is triggered by (rare) bond-breaking events caused by exposure to air, water/solvent or to UV radiation, or by small external forces (e.g., polymers stretched for packaging). However, a thorough understanding of how such Å-scale bond-breaking events lead to much larger-sized fragments remains elusive. Filling the critical knowledge gap of the factors affecting MNPL formation, which could yield optimal pathways to their mitigation, is the focus of the PIs work in this area. An essential tool in this study will be the generation of data on MPNL formation and its analysis using AI and machine learning to look for hidden connections between polymer structure and ambient exposure. Such information will help to improve advanced manufacturing using these kinds of polymers. The PI will educate K-12 students, and in particular their teachers, on MNPL, and their formation mechanisms. The PI has already taught a group of 17 K-12 NYC teachers) who themselves will teach other teachers. Continuing these interactions, the PI now proposes to develop educational modules, in collaboration with K-12 teachers, to illustrate how MNPLs are created by ubiquitous processes such as shaking water in a plastic bottle, flowing water through PVC pipes, or through tire wear. Technical Description Based on available evidence, it is postulated that polymer morphology, i.e., amorphous, semicrystalline, or rubbers, is a critical variable in the creation of MNPL under quiescent conditions. Ambient exposure, e.g., oxygen, water, help to weaken and remove the amorphous polymer (mortar) – the crystalline portions (bricks) are then freed from each other and can go into the surroundings as MNPL. The PI hypothesizes that tailoring the mechanically key stress carriers in the mortar phase through a multipronged experimental and machine learning (ML) approach will provide several, complementary means to understand and hence mitigate MNPL release. Specifically, it is postulated that the length and number density of these stress carriers, and their ability to re-form, are central to polymer failure and hence MNPL creation. It is thus posited that increasing the number of stress carriers, reducing their lengths and/or in situ crosslinking them can result in slower MNPL release. The second key focus area is on polymers under (constant) stress, which will speed-up polymer failure and hence MNPL release. Critically delineating these two topics is the central emphasis. The experimental results from this work will be input into a ML formalism, coupled to a SHAP analysis, to enunciate the critical variables for MNPL formation; in parallel, the optimal conditions to minimize them will be determined by using the genetic algorithm. The PI has a strong track record of creating pipelines for students into STEM futures, and the PI will continue such career development for junior researchers. Finally, a center on Polymers at the end of life has been created in collaboration with NYU and other NY city schools. 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. NSF Award ID: 2609474 | Program: 01002627DB NSF RESEARCH & RELATED ACTIVIT | Principal Investigator: Sanat Kumar | Institution: Columbia University, NEW YORK, NY | Award Amount: $500,000 View on NSF Award Search: https://www.nsf.gov/awardsearch/show-award/?AWD_ID=2609474 View on Research.gov: https://www.research.gov/awardapi-service/v1/awards/2609474.html