Site-Specific Mineralization of a Polyester Hydrolysis Product in Natural Soil

Abstract

Poly(4-methylcaprolactone) (P4MCL) has been successfully incorporated into mechanically competitive materials with potential for biodegradability in engineered and natural systems. The mineralization of the hydrolysis product of P4MCL, 6-hydroxy-4-methylhexanoic acid (4MHA), was herein investigated by synthesizing tailor-made molecules with 13 C labels in the carboxylic acid group (4MHA-13 COOH) or the methyl group (4MHA-13 CH 3 ) and incubating each separately in a soil. Isotope-sensitive cavity ringdown spectroscopy on the efflux gas was then used to quantitatively monitor the mineralization of each isotopomer. These experiments clearly demonstrated that 4MHA was assimilated and utilized by the soil microorganisms and provided insight into position-specific mineralization. The 13 CO 2 evolution rate profiles and overall extents of mineralization to 13 CO 2 (∼85% and ∼46% for carboxyl-and methyl-labeled carbons, respectively) are consistent with the methyl carbon being preferentially incorporated into biomass rather than respired, whereas the carboxyl carbon is preferentially used for energy production and thus mineralized more rapidly (presumably by decarboxylation). These findings agree with previous reports regarding variations in the extents of mineralization of carbon atoms in different oxidation states. Moreover, this work demonstrates the value of systematically probing biodegradation of polymer hydrolysis products by the precise design of 13 C-labeled molecules.

Chemically Recyclable and Biodegradable Vulcanized Rubber

“…One likely receiving environment of rubber-derived micro- or nanoplastics is soil. The soil biodegradability of the polyester-based vulcanized rubber was elucidated via stable isotope-selective CO 2 tracking, a method previously established for quantitatively and unambiguously following mineralization of polymers. , A small-scale batch of polyester H1* was synthesized employing 13 C 2 –EG and subsequently vulcanized and manually cut into small particles (approximately 1 mm 3 ). Monitoring of biodegradation in agricultural soil at 25 °C showed substantial and continual conversion of the EG monomer to 13 CO 2 , with the mineralization extent reaching around 60% of the added EG– 13 C after 240 days (Figure ).…”

Polymers from Plant Oils Linked by Siloxane Bonds for Programmed Depolymerization

“… , The two variants of diester 2 carried 13 C-labels in different positionsdiester 2- 13 C-a on C-10 (C-1 = carboxylate) of the undecanoate chain and diester 2- 13 C-b on one of the methylsiloxane carbons. These two variants, which would presumably be formed upon enzymatic hydrolysis of the polymers, were chosen to assess the overall biodegradability of the entire molecule . From the soil incubation of 2- 13 C-a , with the 13 C label in the undecanoate chain, clear production of 13 CO 2 was observed during the 126 days testing period, reaching 64 ± 10% ( n = 3) of the 13 CO 2 level resulting from incubations of the biodegradable reference compound 13 C-glucose in the same soil (note that the nonmineralized fraction of glucose 13 C is ascribed to incorporation of that carbon into microbial biomass).…”

Biodegradation of Biodegradable Polymers in Mesophilic Aerobic Environments

“…This is one of the absolute tests to determine biodegradation and involves tracking carbon from biodegradable polymers into CO 2 and biomass. The approach is based on labeling the carbon atoms in the polymer backbone with carbon isotopes: 13 C (stable in nature) and 14 C (radioactive) [ 292 , 293 ].…”