CHEME 7900 Seminar: Sanat Kumar (Columbia)

Mechanism of Quiescent Nanoplastic Formation from Semicrystalline Polymers

Polymers are known to spontaneously produce microplastics (sizes 1μm – 3mm) and nanoplastics (10nm – 1μm). Still, the mechanisms by which environmentally-triggered Å-level random bond breaking events lead to the formation of these relatively large fragments are unclear. Significantly, ≈70 % of commercial polymers are semicrystalline, with a morphology comprised of alternating crystalline and amorphous layers, each tens of nanometers thick. It is well-accepted that chain scission events accumulate in the amorphous phase. We show that this leads to mechanical failure and the concurrent release of particulate nanoplastics comprised of polydisperse stacks of lamellae even under quiescent conditions. Noncrystalline analogs, which do not have a well-defined microstructure, do not form nanoplastics. While the amorphous phase of the semicrystalline nanoplastics continues to degrade, crystal fragments do not, and hence, they temporally persist in the environment. These results stress the critical role of polymer microstructure and fracture mechanics on particulate nanoplastic creation.

Bio: Sanat Kumar is the Bykhovsky Professor of Chemical Engineering at Columbia University. His research interests are in the field of polymers (nanocomposites, advanced capacitor materials, scattering methods) and biopolymers (protein-surface interactions).

Kumar creates, analyzes, and models new classes of polymer-based materials with improved properties. A particular focus is on hybrid materials (polymer with inorganic filler) with relevance to biomimicry, and energy storage and conversion. His group has been the pioneer over the last decade in the practically relevant topic of Polymer Nanocomposites where inorganic nanoparticles are added to polymers to obtain materials with synergistic properties

Kumar received a B.Tech. in chemical engineering from the Indian Institute of Technology, Madras in 1981 and a Sc.D. in chemical engineering from the Massachusetts Institute of Technology in 1987.