Exploring Polymer Deconstruction Through the Lens of X-Ray Scattering

Plastics offer a range of appealing properties for today’s consumer products. However, their versatility comes with significant challenges, as they do not readily degrade and thus pose a worldwide pollution problem. One of the five most widely used polymers is poly(ethylene terephthalate) (PET), for which different chemical and biological deconstruction routes have been developed.
A biological deconstruction route for PET uses PET hydrolases, which have demonstrated effectiveness in facilitating PET deconstruction by catalyzing hydrolysis of the ester bonds in this ubiquitous synthetic polymer, but their activity is greatly dependent on the morphology. Despite being able to measure product release from these enzymatic deconstruction reactions, our understanding of the interactions between the enzyme and the polymer during the interfacial biocatalytic reactions is limited. Current techniques for characterizing the enzyme-to-substrate interactions rely upon computational chemical modeling and x-ray crystallography, where model PET oligomers (i.e., dimers and trimers) are positioned within the enzyme active site. Yet these approaches do not account for the various morphologies of non-model PET substrates, or how the enzyme accesses the polymer chain. Thus, it remains challenging to understand the mechanism of digestion and why PET hydrolases preferentially digest the amorphous portion of PET while leaving behind the crystalline material.
This talk aims to explore how the morphology and crystallinity of specific PET substrates influence PET deconstruction. We have employed X-ray scattering techniques at the Stanford Synchrotron Radiation Lightsource to probe the nano (~1-100 nm) to atomic (<1 nm) length scales of polymers. Through the X-ray lens, we can analyze polymer conformation and morphology, allowing us to connect these factors to the deconstruction process. The tools developed herein can be applied to gain insight into other polymer systems and deconstruction pathways.