Degradation Chemistry
Chemical breakdown within polymer chains occurs when ultraviolet radiation strikes the molecular structure of substrates like paper coatings or plastic laminates. These photo oxidation products arise from the interaction between high energy light and polymer surfaces, resulting in free radicals that alter the physical properties of the material. Chain scission reduces the molecular weight of the substrate, while crosslinking increases brittleness in rigid packaging boards.
Reaction Mechanism
Energy transfer from light wavelengths initiates bond cleavage in the presence of atmospheric oxygen, creating hydroperoxides that propagate further decay. The speed of this conversion depends on the density of the protective coating and the presence of titanium dioxide or other stabilizing fillers meant to absorb harmful rays. Temperature shifts during shipping or storage accelerate the movement of these particles within the substrate matrix, leading to yellowing or surface cracks.
Performance Constraint
Precise monitoring of yellowing indices serves as an effective method for detecting accumulated byproduct levels during long term storage tests. High concentrations of these chemicals impair ink adhesion on recycled fibre surfaces and trigger the migration of volatile compounds into packaged goods. Substrates fail to maintain structural integrity under prolonged light exposure when the generation rate exceeds the protective capacity of added stabilizers.
