Enzymatic Degradation of the Most Common Aliphatic Bio-Polyesters and Evaluation of the Mechanisms Involved: An Extended Study

Abstract

Commercial hydrolytic enzymes belonging to different subclasses (several lipases, proteinase k, cutinase) were investigated for their ability to degrade different aliphatic polyesters, i.e., poly(butylene succinate) (PBS), poly(butylene succinate-co-adipate) (PBSA), two poly(caprolactone), having two different molecular weights, poly(lactic acid) (PLA) and poly(propylene carbonate) (PPC). The enzyme screening was first carried out by investigating the capacity of fully degrading the target polymers in 24 h, then weight loss measurements of selected polyesters and target enzymes were performed. Solid residues after enzyme degradation were characterized by proton nuclear magnetic resonance (1H NMR), gel permeation chromatography (GPC), infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC) and thermogravimetry (TGA). Liquid fractions were studied via GPC, 1H NMR and high-performance liquid chromatography (HPLC). PCL and PBSA were found to be the most biodegradable polyesters, under the conditions used in this study. PBS was fully degraded only by cutinase, whereas none of the tested enzymes were able to completely degrade PLA and PPC, in the conditions assessed here. Cutinase exhibited the highest hydrolytic activity on PBSA, while lipase from Candida sp. (CALB) on low molecular weight PCL. Chemical analyses on residual solids showed that the enzymatic degradation occurred homogeneously from the surface through an erosion mechanism and did not significantly affect the macromolecular structure and thermal stability. Cleaving action mode for each enzyme (endo- and/or exo-type) on the different polyesters were also proposed based on the evaluation of the degradation products in the liquid fraction.

Bio-Based Degradable Poly(ether-ester)s from Melt-Polymerization of Aromatic Ester and Ether Diols

“…Polymer degradation involves different processes such as physical, chemical, and biological routes or a combination thereof, under the influence of several factors such as temperature (thermal degradation), air (oxidative degradation), water (hydrolytic degradation), microbial (biodegradation), light (photo-degradation), high-energy radiation (UV, γ-irradiation), chemical agents (corrosion), and mechanical stress [ 86 , 87 , 88 ]. These factors lead to irreversible changes in the materials and play a major role in the colonization by microbes and biofilm formation.…”

Triggering of Polymer-Degrading Enzymes from Layered Double Hydroxides for Recycling Strategies

“…Phosphate buffer was chosen since it is the optimal medium for the activity of cutinase toward the degradation of polyesters commonly used as tie-layers [1], and phosphate anion is reported to have a high affinity for the LDH structure [24]. Moreover, the pH 8 of the buffer is near the isoelectric point of cutinase (i.e., 7.8), thus no charges should be present, favoring the detachment of the enzyme [19].…”

“…A critical issue, however, is their thermal lability: the protection of enzymes is a necessary step to implement their use during polymer processing where high temperatures, which cause the denaturation of enzymes and the loss of their catalytic activity, are commonly employed. Among several enzymes, cutinase is a highly degrading polyester hydrolytic enzyme: biopolymers such as poly(butylene succinate) (PBS), poly(butylene succinate-co-adipate) (PBSA), and poly(caprolactone) are successfully degraded by cutinase [1][2][3]. The immobilization of cutinase in inorganic host structures such as layered double hydroxides (LDH) has been demonstrated as an effective approach to thermally protect the enzyme [4].…”

“…In view of the above considerations, phosphate and citrate-phosphate buffers, potassium carbonate, sodium sulfate, and sodium chloride were chosen as release media. Besides the already mentioned affinity of phosphate for the LDH structure, the phosphate buffer is also the optimal medium for the activity of cutinase toward the degradation of polyesters [1]. Its basic pH (8) is near the isoelectric point of cutinase (i.e., 7.8), thus no charges should be present, and the detachment of the enzyme is facilitated [19].…”

Triblock Copolymer Compatibilizers for Enhancing the Mechanical Properties of a Renewable Bio-Polymer

“…Priselac et al [32] proposed a biodegradable blend of poly(ε-caprolactone) (PCL) and poly(lactic acid) (PLA) for the production of relief printing plates for special applications in packaging materials. Other polymers such as poly(butylene succinate) [33,34], poly(ethylene oxide) [35,36], and poly(ethylene glycol) [37,38] have also been applied. Blending resulted in the superior performance of the corresponding reinforced composites.…”