Views:4 Author:Vera Publish Time: 2019-01-07 Origin:Site
Adding a small amount of antioxidant in plastic processing can prevent or delay the aging, thus prolonging the service life of plastic products.
When selecting antioxidant, it should be determined synthetically according to the kinds and types of plastic materials, the processing equipment and technological conditions, the varieties and quantity of other chemical additives, the environment and duration of the products' use, etc.
The following principles should be taken into account in selecting antioxidant for industrial use.
The compatibility between the antioxidant and the polymer is often poor, usually the antioxidant is combined with the polymer melt at high temperature, and the antioxidant molecule is compatible between the polymer molecules when the polymer is solidified. In the range of formula, antioxidant must be melted at processing temperature. Special attention should be paid to the melting point or upper melting range in selection of solid antioxidant, light stabilizer when designing the formula, which should not be lower than the processing temperature of the plastic polymer.
Oxidation occurs mainly on the surface of a plastic product, especially one with a smaller surface area to volume ratio (or mass ratio), this requires continuous migration of antioxidants from the interior of plastics to the surface of the product. However, if the migration to the surface of the product is too fast and the amount of migration is too large, the antioxidant will volatilize on the surface of the product. This loss is, in fact, inevitable and is taken into account in the design of the formula. When there is a choice of antioxidant, the varieties with relatively large molecular weight and proper melting point should be selected, and the amount of antioxidant should be determined on the premise of the harshest using environment.
Antioxidants should be kept stable in plastic materials, with little volatilization loss, no discoloration or coloration, no decomposition (except those used for processing thermal stability), and less volatilization loss in the working environment and in the process of high temperature processing. No adverse chemical reaction with other additives, no corrosion of mechanical equipment, and not easily extracted by other substances on the surface of the product.
When plastic products are processed, the viscosity of resin and screw torque may be changed by adding antioxidant. If the melting range of antioxidant to resin varies greatly, the antioxidant bias or screw suppression will occur. When the melting point of antioxidant is lower than 100 ℃, the antioxidant should be made into a certain masterbatch and then mixed with resin to process the product, in order to avoid uneven distribution of antioxidant and decrease of processing yield due to bias.
Environmental and healthy
Antioxidant should be non-toxic or low-toxic, no dust or low dust, no harmful effect on human body, no harm to animals and plants, no pollution to air, soil and water system in the processing and use of plastic products.
Plastic products that have indirect or direct contact with food, drugs and medical appliances, such as agricultural films, food packaging boxes, children's toys, disposable fluids, etc., should not only be selected and approved by the FDA (FDA), Or EC Commission decree allowed antioxidant varieties, and the amount should be strictly controlled within the maximum allowable limit.
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