Unveiling the Enzymatic Degradation Process of Biobased Thiophene Polyesters

Abstract

In the past 20 years, scientific research focused on the identification of valid alternatives to materials of fossil origin, in particular, related to biobased polymers. Recently, the efforts led to the synthesis of thiophene-based polymers (TBPs), a new class of polyesters based on 2,5-thiophenedicarboxylic acid (TPCA) that can be industrially produced using biomass-derived molecules. In this study, TBPs were synthesized using diols with different chain length (from C4 to C6) leading to poly(butylene 2,5-thiophenedicarboxylate) (PBTF), poly(pentamethylene 2,5-thiophenedicarboxylate) (PPeTF), and poly(hexamethylene 2,5-thiophenedicarboxylate) (PHTF), respectively, that were processed to thin films. To investigate enzymatic hydrolysis of these polymer films, cutinase 1 (Thc_cut1) and cutinase 2 (Thc_cut2) from Thermobifida cellulosilytica were recombinantly expressed in the host E. coli and purified. After 72 h of incubation at 65°C with 5 µM Thc_cut1, weight loss and HPLC analysis indicated 9, 100, and 80% degradation of PBTF, PPeTF, and PHTG with a concomitant release of 0.12, 2.70, and 0.67 mM of TPCA. The SEM analysis showed that tiny holes were formed on the surface of the films and after 72 h PPeTF was completely degraded. The LC-TOF/MS analysis indicated that Thc_cut2 in particular released various oligomers from the polymer during the reaction. In addition, the FTIR analysis showed the formation of novel acid and hydroxyl groups on the polymer surfaces. The results showed that the two used thermostable cutinases are promising biocatalysts for the environmentally friendly degradation of TPCA-based polyesters, in view of a possible sustainable recycling of plastic waste through resynthesis processes.

On the Selective Enzymatic Recycling of Poly(pentamethylene 2,5-furanoate)/Poly(lactic acid) Blends and Multiblock Copolymers

“…30 The choice of the above-mentioned cutinase relied on its excellent performance on other FDCA-based polymers and alternative 2,5-thiophenedicarboxylic acid-based polyesters, since 50 to 100% weight loss had been achieved for all tested films within 72 h of incubation. 31 A first visual evaluation of the films hydrolyzed with Thc_Cut1 displayed different hydrolysis trends, clearly dependent on the PLA/PPeF ratio. Films with higher content of PLA (95−99% in PP5, PP3, and PP1) were more resistant to the enzymatic treatment, preserving their original aspect and transparency.…”

“…Optimal temperature and buffer composition were adopted according to previous work . The choice of the above-mentioned cutinase relied on its excellent performance on other FDCA-based polymers and alternative 2,5-thiophenedicarboxylic acid-based polyesters, since 50 to 100% weight loss had been achieved for all tested films within 72 h of incubation …”

Recyclable and (Bio)degradable Polyesters in a Circular Plastics Economy

“…In subsequent work, Bertolini et al described the enzymatic hydrolysis of a series of TFDCA-derived polyesters (PBTF, PPeTF, PHTF) with varied aliphatic chain lengths (Scheme ). These polyesters displayed lower thermal transitions than PBTF ( T g = 8 (PPeTF) and 1 °C (PHTF); T m = 65 (PPeTF) and 95 °C (PHTF)) but maintained good thermal stability ( T onset = 380 (PpeTF) and 379 °C (PHTF)). Thc_Cut1 and Thc_Cut2 were trialed, utilizing the same conditions previously reported (temperature, buffer), for the polyester series.…”