Biodegradable polyesters are being increasingly used to replace conventional, nondegradable polymers in agricultural applications such as plastic film for mulching. For many of these applications, poly(butylene adipate-co-terephthalate) (PBAT) is a promising biodegradable material. However, PBAT is also susceptible to photochemical transformations. To better understand how photochemistry affects the biodegradability of PBAT, we irradiated blown, nonstabilized, transparent PBAT films and studied their enzymatic hydrolysis, which is considered the rate-limiting step in polyester biodegradation. In parallel, we characterized the irradiated PBAT films by dynamic mechanical thermal analysis. The rate of enzymatic PBAT hydrolysis decreased when the density of light-induced cross-links within PBAT exceeded a certain threshold. Mass-spectrometric analysis of the enzymatic hydrolysis products of irradiated PBAT films provided evidence for radical-based cross-linking of two terephthalate units that resulted in the formation of benzophenone-like molecules. In a proof-of-principle experiment, we demonstrated that the addition of photostabilizers to PBAT films mitigated the negative effect of UV irradiation on the enzymatic hydrolyzability of PBAT. This work advances the understanding of light-induced changes on the enzyme-mediated hydrolysis of aliphatic-aromatic polyesters and will therefore have important implications for the development of biodegradable plastics.
Bibliographical noteFunding Information:
M.T.Z., M.M.J., H.P.K., M.S., and K.M. thank the Joint Research Network on Advanced Materials and Systems (JONAS) program of BASF SE and ETH Zurich for scientific and financial support. M.T.Z. thanks Björn Studer for access to the TOC analyzer, Peter Isler (IAC ETH Zurich) for access to illuminance data, Rachele Ossola for help with actinometry experiments, and Luise Fischer for help with gel fraction measurements. We acknowledge the funding from the Center for Sustainable Polymers at the University of Minnesota, which is a National Science Foundation supported Center for Chemical Innovation (CHE-1413862). G.X.D. gratefully acknowledges the help of David Giles, Kyungtae Kim, and Peter Schmidt for their helpful discussion of rheological and scattering analyses. Portions of this work were performed at the DuPont-Northwestern-Dow Collaborative Access Team (DND-CAT) located at sector 5 of the Advanced Photon Source (APS). DND-CAT is supported by Northwestern University, E.I. DuPont de Nemours & Co., and the Dow Chemical Company. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for by the DOE Office of Science by Argonne National Laboratory under contract DE-AC02-06CH11357.
© 2019 American Chemical Society.