Polymer Degradation :
Although such alterations are regularly undesirable, in some cases, such as biodegradation and recycling, they may be intended to avoid environmental pollution. Degradation could be useful in biomedical settings. For example, a copolymer of polylactic acid and polyglycolic acid is employed in hydrolysable stitches that slowly degrade after they are applied to a wound.
The susceptibility of a polymer to degradation depends on its structure. Epoxies and chains including aromatic functionalities are particularly susceptible to UV degradation while polyesters are susceptible to degradation by hydrolysis, while polymers containing an unsaturated backbone are mainly susceptible to ozone cracking. Carbon based polymers are more susceptible to thermal degradation than inorganic polymers such as polydimethylsiloxane and are therefore not perfect for most high-temperature applications. High-temperature matrices including bismaleimides (BMI), condensation polyimides (with an O-C-N bond), triazines (with a nitrogen (N) containing ring), and blends thereof are susceptible to polymer degradation in the form of galvanic corrosion when bare carbon fiber reinforced polymer CFRP is in contact with an active metal such as aluminum in salt water environments.
The degradation of polymers to form smaller molecules can proceed by random scission or specific scission. The degradation of polyethylene happen by random scission—a random breakage of the bonds that hold the atoms of the polymer together. After heating above 450 °C, polyethylene degrades to form a mixture of hydrocarbons. Other polymers, such as poly (alpha-methylstyrene), undergo specific chain scission with breakage happening only at the ends. They factually unzip or depolymerize back to the constituent monomer.
The organization of polymer waste for recycling process can be facilitated by the use of the Resin identification codes developed by the Society of the Plastics Industry to identify the kind of plastic.