How to choose antioxidant?
In the selection of antioxidants to pay attention to the cooperation between antioxidants, antioxidants and other heat, light stabilizers, etc.. Then it is necessary to think about the antioxidant with the most, most antioxidants have a most suitable concentration scale. Within this scale, followed by the amount of antioxidants, antioxidant effectiveness added to the maximum. Beyond this scale, it will bring adverse effects. The amount of antioxidant depends on the nature of the plastic, the power of the antioxidant, synergistic effect, the conditions of use of the product and the cost of the offer and many other factors. Usually amine antioxidant activity than phenolic antioxidants, so there should be greater antioxidant function, but the former in the air under the effect of oxygen and light will change color, itself is mostly colored, and toxic, so the use in plastics to be careful. Now the primary consideration of antioxidant cooperation.
(l) add and effect.
The use of a variety of antioxidants, can promote their respective characteristics and effects, increasing the total effect. For example, the different evaporation or spatial resistance of the hindered phenols and when used, can promote their antioxidant effect in a wide range of temperatures, the effect is enhanced. If in the formula, only one kind of antioxidant is used, it is inevitable to participate in a larger amount, which will cause intense oxidation reactions at high concentrations, which is not allowed. But the choice of several low concentration of antioxidants and use, not only to achieve the desired intention, and also to prevent intense oxidation, and carry forward its additive effect.
(2) Synergistic effect.
①When two different activities of the main antioxidant and use, the high activity of the antioxidant to give hydrogen atoms, so that the oxidation of the active chain to stop; and low activity of the antioxidant can give the high activity of the antioxidant to supply hydrogen atoms, so that it regenerates and develops a durable antioxidant effect, so the antioxidant effect is very good.
②When the main and auxiliary antioxidants are used, attention should be paid to the development of synergistic effects. Such as the main antioxidant simply give hydrogen atoms, hydrogen atoms can make peroxide free radicals into hydroperoxides, stop the chain reaction; and then hydroperoxides and auxiliary antioxidant peroxide splitting agent effect, generate inactive stabilization products. Thus greatly slow down the speed of oxidation reactions, adding the antioxidant effect. Such as in the polyolefin widely used in the antioxidant 264 and DLPT system is an example.
③An antioxidant molecule has two or more different stabilizing functions, said since the synergistic effect, such as sulfur-containing hindered phenolic antioxidant, it has a chain reaction stopper and peroxide differentiation agent of the two-layer effect, this antioxidant can strengthen the antioxidant effect, is a more desirable antioxidant.
④ antioxidant and heat, light stabilizer, should be selected to have a synergistic effect, and strive to prevent opposing effects. Such as most amine and phenolic antioxidants, in the presence of carbon black significantly reduced the effectiveness of the opposing effect, which may be due to carbon black directly catalyze the oxidation of antioxidants, depleted some of the antioxidant caused by. Thioether bonded antioxidant and carbon black but there is a synergistic effect. Therefore, the former should be abandoned, and the latter should be used.