What is the mechanism behind enzymatic degradation of biodegradable polymers?

Enzymatic degradation of biodegradable polymers involves the breakdown of the polymer chains through the catalytic action of enzymes. Enzymes are biological catalysts that accelerate chemical reactions. In the context of polymer degradation, enzymes, typically produced by microorganisms, recognize and bind to specific chemical bonds within the polymer structure. This binding forms an enzyme-substrate complex. The enzyme then catalyzes the hydrolysis, oxidation, or other chemical reactions that cleave the polymer chains into smaller fragments, such as oligomers, dimers, or monomers. These smaller fragments can then be further metabolized by microorganisms. The mechanism is highly specific, with different enzymes targeting different types of chemical bonds. For example, esterases and lipases are enzymes that hydrolyze ester bonds, which are common in polyesters like PLA and PHA. Cellulases are enzymes that hydrolyze glycosidic bonds, which are present in cellulose and cellulose derivatives. The rate of enzymatic degradation depends on several factors, including the type of enzyme, the concentration of the enzyme, the temperature, the pH, the crystallinity of the polymer, and the accessibility of the polymer chains to the enzyme. Surface erosion is a common phenomenon in enzymatic degradation, where the enzyme primarily attacks the surface of the polymer material. For example, the degradation of PLA in compost is primarily driven by enzymatic hydrolysis by microorganisms present in the compost.