What is a light stabilizer?

　　Most organic compounds, including plastics, will change color, become brittle, and deteriorate in performance under long-term sunlight exposure. This is the result of a series of reactions that occur under the action of ultraviolet light and oxygen. This photo-oxygen aging process is also called Oxidative photodegradation. The obvious effect of photodegradation varies with the type of polymer. For example, the oxidative photodegradation of polystyrene will cause the product to turn yellow and the PVC will change from yellow to red and then to black. After the photochemical discoloration reaction occurs, the surface cracks, embrittlement and loss of strength are accompanied. At the same time, polar genes such as ketone groups, alcohol groups, hydroxyl groups, etc. are stored in the polymer, which reduces its electrical insulation performance. Adding various light stabilizers can delay the occurrence of this process, and achieve the purpose of prolonging the service life of the product.

　　According to the principle of light stabilization, it is best to contain the following components in the light stabilizer: First, the ultraviolet absorber, which can absorb the ultraviolet radiation energy before the polymer, through the rearrangement of the electronic structure in its own atoms The radiant energy is converted into heat energy and dissipated in the atmosphere. Once the heat energy is released, the atoms return to their original state; the second is a quencher (energy transfer agent), which has the function of making the released heat energy not damage the polymer. It does not directly absorb incident ultraviolet rays, but only absorbs excessive energy that will cause the polymer to degrade when a certain amount of energy is stored in the polymer, and transfers this part of energy to the surrounding atmosphere in the form of heat; the third is free radical capture Agent, it can capture the active radicals generated by ultraviolet rays acting on the polymer, thereby inhibiting the photo-oxidation process; fourth is the ultraviolet shielding agent, which can reduce the transmission effect of ultraviolet rays on the material. Therefore, it is often not enough to add UV absorbers in the process of improving the light stability of polymers.

　　In theory, a pure polymer will not absorb ultraviolet light. Only when the polymer contains certain "impurities" will it absorb ultraviolet light and transfer the absorbed energy to the surrounding polymer in the form of heat to promote Its molecular chain breaks and its performance deteriorates. Most of these "impurities" come from catalysts with metal ions remaining during the polymerization. Active groups such as hydroxyl groups, carboxyl groups, hydroperoxides, and processing aids such as heat stabilizers, antioxidants, and coloring caused by side reactions during the polymerization process Metal ions, etc. brought by agents, fillers, etc. It can be seen that, when choosing a light stabilizer, attention should be paid to the synergy with other additives.

　　Since the use of phenyl salicylate as the ultraviolet absorber of cellulose plastics in the late 1930s, the light stabilizer was not used in other polymers until the early 1950s. Later, due to the rapid development of polyolefin plastics, the pace of development of the light stabilizer industry also accelerated. At present, light stabilizers have great development in terms of variety and quantity.