Understanding Marine Biodegradation of Bio-Based Oligoesters and Plasticizers

Abstract

The study reports the enzymatic synthesis of bio-based oligoesters and chemo-enzymatic processes for obtaining epoxidized bioplasticizers and biolubricants starting from cardoon seed oil. All of the molecules had M_W below 1000 g mol^-1 and were analyzed in terms of marine biodegradation. The data shed light on the effects of the chemical structure, chemical bond lability, thermal behavior, and water solubility on biodegradation. Moreover, the analysis of the biodegradation of the building blocks that constituted the different bio-based products allowed us to distinguish between different chemical and physicochemical factors. These hints are of major importance for the rational eco-design of new benign bio-based products. Overall, the high lability of ester bonds was confirmed, along with the negligible effect of the presence of epoxy rings on triglyceride structures. The biodegradation data clearly indicated that the monomers/building blocks undergo a much slower process of abiotic or biotic transformations, potentially leading to accumulation. Therefore, the simple analysis of the erosion, hydrolysis, or visual/chemical disappearance of the chemical products or plastic is not sufficient, but ecotoxicity studies on the effects of such small molecules are of major importance. The use of natural feedstocks, such as vegetable seed oils and their derivatives, allows the minimization of these risks, because microorganisms have evolved enzymes and metabolic pathways for processing such natural molecules.

Keywords: bio-based polyesters; biocatalysis; bioplasticizers; cardoon oil; epoxidized fatty acids; epoxidized oil; marine biodegradation.

Figure 1

Structure of the bio-based monomers and the corresponding bio-based oligoesters obtained by enzymatic polycondensation. Codes refer to marine biodegradation tests.

Figure 2

A schematic representation of the structure of an unsaturated triglyceride (triolein) and the corresponding epoxidized products. The cardoon seed oil is actually composed of a variety of saturated and unsaturated fatty acids, as reported above. The figure aims at illustrating the transformation of a triglyceride in a simplified way. Codes refer to marine biodegradation tests.

Figure 3

Schematic representation of products obtainable from the ring opening of the epoxidized triolein. As in the case of Figure 2, the structure does not represent the actual chemical complexity of the composition of cardoon seed oil; rather, it aims at simplifying the illustration of the concept. Codes refer to marine biodegradation tests.

Figure 4

Structures of the products obtained from the enzymatically catalyzed epoxidation of oleic, linoleic, and linolenic acids. Codes refer to marine biodegradation tests.

Figure 5

DSC thermograms of the samples (a) (BDO-AA)n, (b) (Gly-AZA)n, (c) ESO-BDO, (d) ECO-SORB, and (e) EPX-OIL.

Figure 6

Degree of degradation of the oligoesters after 21 days of incubation in a marine environment; the data were normalized by subtracting the values of the control samples.

Figure 7

Degree of degradation of the epoxy cardoon oils and their derivatives after 21 days of incubation in a marine environment; the data were normalized by subtracting the values of the control samples.