Biodegradation in polymers refers to the natural process by which polymeric materials are broken down into simpler substances by the action of living organisms, mainly microorganisms such as bacteria, fungi, and algae, along with enzymes produced by them. In the context of the chemistry of materials, biodegradation is important because it determines how a polymer behaves after its useful life and how it interacts with the natural environment. Unlike ordinary degradation, which may occur because of heat, light, oxygen, mechanical stress, or chemicals, biodegradation specifically involves biological activity and biochemical reactions. Polymers are very large molecules made up of repeating structural units called monomers. Their high molecular mass, long chains, and often strong chemical bonds make many conventional polymers resistant to natural degradation. Materials such as polyethylene, polypropylene, polystyrene, and polyvinyl chloride can remain in the environment for a very long period because microorganisms generally cannot easily attack their carbon-carbon backbones. Biodegradable polymers, on the other hand, contain chemical structures that can be attacked or transformed by microorganisms and their enzymes. The biodegradation of a polymer generally takes place through several stages. First, the polymer may undergo physical and chemical changes that increase its surface area or reduce its molecular mass. Moisture, temperature, oxygen, ultraviolet radiation, and mechanical forces can assist this initial process. In some polymers, hydrolysis or oxidation breaks the long polymer chains into shorter chains and smaller molecules. These smaller molecules are more accessible to microorganisms. In the next stage, microorganisms attach themselves to the polymer surface and produce extracellular enzymes. These enzymes react with susceptible chemical bonds in the polymer. For example, polymers containing ester, amide, or other hydrolysable groups may be attacked more easily than polymers having a stable carbon-carbon backbone. Enzymatic hydrolysis can convert a polymer chain into oligomers, monomers, organic acids, alcohols, or other low-molecular-mass compounds. The resulting smaller molecules can then enter microbial cells and participate in normal metabolic pathways. Under aerobic conditions, where sufficient oxygen is available, microorganisms can ultimately convert biodegradable polymer components mainly into carbon dioxide, water, biomass, and mineral substances. Under anaerobic conditions, where oxygen is absent or very limited, the products may include methane, carbon dioxide, water, and biomass, depending on the polymer and the microorganisms involved. The chemical structure of a polymer has a major influence on its biodegradability. Polymers containing hydrolysable functional groups are generally more suitable for biodegradation. For example, aliphatic polyesters such as polylactic acid