In practice, preventing the photo-oxidation of polymers by adding stabilizers is a convenient and effective approach. The basis for selecting a light stabilizer, besides its light stabilization efficiency, must also consider good compatibility with the resin, low volatility, and minimal antagonistic interaction with other additives during extraction. At present, the light stabilizer varieties commonly used in domestic agricultural films mainly fall into two categories: UV absorbers and free-radical scavengers. UV absorbers can be classified by chemical structure into salicylates, benzophenones, and benzotriazoles; free-radical scavengers are mainly hindered amines. During our development, we selected higher-efficiency hindered amine light stabilizers. From a chemical-structure perspective, hindered amine light stabilizers can be regarded as sterically hindered piperidine derivatives; one of their mechanisms is to capture free radicals. In this process, hindered amines function in the form of stable nitroxyl radicals. In addition, they also decompose hydroperoxides, quench singlet oxygen, and quench chromophores. The requirements for stabilizers in film products must consider not only protective efficiency but also their migration within the polymer, so they are not lost through volatilization, migration, or extraction. Under the same light stabilizer concentration and base resin, we screened several hindered amine light stabilizers based on xenon-arc weathering tests. Considering the anti-fog function actually required in greenhouse films, the same type and amount of anti-fog agent were added in this experiment. The xenon-arc aging tests were conducted in two groups: Group A used 0.2% light stabilizer at different film thicknesses; Group B used 0.22% light stabilizer at a film thickness of 0.08 mm. Quenchers, also known as energy-transfer agents, dissipate energy through intermolecular energy transfer. Ultraviolet light that is not shielded or absorbed is absorbed by the polymer, placing it in an unstable "excited state." To prevent further decomposition into free radicals, the quencher can remove the excitation energy from the excited polymer molecule, returning it to a lower-energy state. This type of stabilizer has a very good stabilizing effect on polymers and is mostly used in films and fibers; when used together with benzophenone- or benzotriazole-type UV absorbers, it shows a strong synergistic effect. Quenchers are mainly some divalent organic nickel chelates; their organic parts are substituted phenols and thiobisphenols. The main types are: (1) dithiocarbamate nickel salts, such as BC; (2) thiobisphenol types, such as AM-101; (3) phosphonate monoester nickel types, such as Light Stabilizer 2002. Organic nickel and organic cobalt light stabilizers applied in polyolefin agricultural films exhibit the advantages of low volatility, non-discoloration, good thermal stability and melt properties, and long service life. When used in fibers, they act as dyeing assistants, improving color lightfastness and brightness, and their addition level is also lower than that of absorbing-type light stabilizers. Because of their excellent performance, the development of new varieties was quite active in the 1990s. In recent years, due to the toxicity concerns of heavy-metal ions (fear that nickel salts may be carcinogenic), organic nickel complexes may gradually be replaced by other non-toxic or low-toxic quenchers.
