Topic Area: 6d. Biodegradation and Upcycling of Plastics

Formatted Title:

Effect of Nylon-6 Crystallinity on its Enzymatic Depolymerization

Background/Objectives:

Currently, little understanding exists on Polyamide-6 (“Nylon-6”; PA6) biological degradation and no direct enzymatic degradation pathway has been identified. With increased advancements in systems biology approaches, computational modeling, sequence-based homologue searching, and molecular docking allows us to elucidate PA6 biological basis of degradation using several target enzymes classes. The primary objective of this project is to elucidate the predominant structural characteristics of PA6 limiting sufficient access for the hydrolytic enzymes tested to date, coupled with a mechanistic investigation of enzyme amide cleavage at the polymer surface, which we expect will allow us to develop novel pathways that overcome or circumvent these structural hindrances.

Approach/Activities:

Several major enzyme classes have shown promising degradation of PA6. However, the molecular basis for the degradation mechanism is still not well understood, and enzyme interactions with varied polymer morphological domains are largely unknown. In this study commercially available or strain and consortia-derived cutinases, proteases, nylon hydrolases, and other esterases were investigated experimentally for activity on amide-containing model compounds and PA6 of varied morphologies. Enzymes were screened for amide activity spectrophotometrically with a model compound in a rapid plate-based liquid assay and were downselected before testing with condensed PA6 film. Commercial PA6 film was utilized, and its morphology was modified by heat pressing or rapid quenching to control crystallinity to high amorphous content, high crystallinity – alpha enriched, or high crystallinity – gamma enriched. Polymer morphology is characterized by x-ray diffraction analysis (XRD). Coupons of PA6 films are incubated with enzymes in buffer at 50 °C for 96 hours. The selected enzymes included 6 NylC variants and 2 NylB variants. XRD is performed after incubation to determine the effect of aqueous incubation and enzyme activity on crystallinity. Liquid chromatography-couple mass spectrometry (LC-MS) is used to determine liberation of PA6 monomer and related oligomers (dimer, trimers, tetramers, etc.).

Ashley Frank

Affiliation

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Effect of Nylon-6 Crystallinity on its Enzymatic Depolymerization