Meaning
Exposure of diaryl ketones to ultraviolet radiation generates reactive triplet states that abstract hydrogen atoms from surrounding organic molecules. This benzophenone photolysis initiates crosslinking or degradation reactions in polymer matrices containing benzophenone additives. The process is widely exploited for modifying polymer surfaces and curing specialty resins.
Chemical Mechanism
Absorption of light at specific wavelengths excites the carbonyl group to a highly reactive state. Through benzophenone photolysis, the molecule transforms into a ketyl radical while generating a polymer radical on the plastic chain. These active sites rapidly combine to form permanent covalent bonds that alter the resin properties.
Polymer Modification
Surface treatment of moulded parts using UV irradiation improves adhesion and chemical resistance. Coating formulations often rely on benzophenone photolysis to create a dense network of linked chains at the outer boundary. This treatment creates a protective barrier without altering the bulk mechanical properties of the underlying thermoplastic, and it prevents the migration of internal additives to the surface.
Moulders use this technique to enhance the paintability of non-polar polymers like polypropylene.
Degradation Pathway
Unintended exposure to sunlight triggers the same radical reactions in untreated polymer materials. The resulting chain scission reduces the molecular weight, causing cracking and embrittlement in the field. Moulders incorporate UV stabilizers to block this pathway and extend the service life of outdoor plastic components.
