Research Projects

Solid polymeric particulates with a size less than 5 mm are termed microplastics (size less than 5 mm), while nanoplastics have a size less than 1 micron. Secondary microplastics are particles produced by breakdown of polymeric objects during their use life. There is preliminary evidence pointing to the potentially adverse effects of micro/nanoplastic pollution on climate change and on human health. Microplastic pollution is one of the defining problems of our times due improper disposal of synthetic polymers into the environment. It is, therefore, of importance to understand the molecular mechanisms by which macroscopic polymeric objects fragment to form micro and nanoplastics. There are two aspects that are critical to developing this molecular understanding: (i) model polymer samples to systematically determine how molecular characteristics govern fragmentation into particles and; (ii) accelerated wear protocols that mimic natural processes experienced by polymers during use. While there has been extensive work on identification of microplastic contamination and its effects on the biosphere, there are relatively few studies that investigate the fundamental molecular processes that lead to micro/nanoplastic formation. Here, we propose studies that combine well-defined polymer samples with accelerated wear protocols developed in our group to provide insights into the influence of molecular structure on micro/nanoplastic formation. In regular use, polymers wear due to exposure to chemical attack (due to oxidation, free radical processes, hydrolysis, enzymatic attack, etc.) and/or due to mechanical stresses. We employ an advanced oxidation process to simulate accelerated oxidative degradation and combine it with mechanical shear, to weather the samples. Weathered samples and emitted micro/nanoplastics will be characterized in detail using visible light (to determine the number density of particles emitted) and Xray scattering (to probe the shape and size distribution of the particles), microscopy (to characterize size distribution and shape), spectroscopy (to track chemical changes in the plastic on weathering) and thermal analysis (to examine the impact on semicrystalline morphology). In particular, our investigations will examine the variation of crystallinity, controlled molecular weight polydispersity and chain orientation on micro/nanoplastic formation. We will focus on four specific sub-problems: (i) Effect of backbone chemistry, specifically examining fragmentation of iPP versus HDPE ; (ii) Role of tie chains in micro/nanoparticle formation using model bimodal iPP blends; (iii) Effect of orientation and residual stress on micro/nanoplastic formation and (iv) Effect of semicrystalline morphology, systematically varied using LLDPE copolymers with varying density, on micro/nanoplastic formation. This information is unprecedented and will provide important insights into how polymer molecular structure, and in particular the “tie chains” that hold crystals together in semicrystalline polymers determine micro/nanoplastic formation. These studies represent the first systematic investigations into the role of polymer molecular architecture on micro/nanoplastic formation. As there are very few mechanistic studies, the proposed work on well defined model systems will play an important role in shaping the narrative in the global research community. We anticipate that our work will be published as impactful manuscripts, especially given the growing concern about micro/nanoplastics in the community. Importantly, our work could provide valuable insights into how polymers can be engineered to have molecular features that mitigate secondary micro/nanoplastic formation.