Plastics usually age rapidly under the action of light, oxygen and heat, resulting in: a decrease in strength, stiffness and toughness; discoloration; scratches and surface Decreased gloss. Affect the performance of plastic products. It is necessary to add light stabilizers and antioxidants to inhibit the breakage of molecular chains and extend the performance of the product. The antioxidant is a very important additive in plastics and their products (films, sheets, pipes, etc.). It can effectively protect plastic products from being oxidized and aged by oxygen in the air. There are many varieties of antioxidants, and different antioxidants have greatly different functions and application effects. Including different types of primary and secondary antioxidants, or the same type with different molecular structures. According to the supply of antioxidants: According to molecular structure and mechanism of action, commonly used plastic antioxidants are generally divided into five categories: hindered phenols, phosphites, sulfonates, composites and hindered amines (HALS). . Commonly used antioxidants include antioxidant 1010, antioxidant 168, antioxidant 1076, and compounded ones include B215, B225, etc.
In the plastics industry, appropriate selection and use can effectively inhibit or reduce the thermal oxidation reaction speed of polymer macromolecules, delay the thermal and oxygen degradation process of materials, extend the service life of plastic products, and improve the performance of plastic products. Use value. When selecting antioxidants, it should be comprehensively determined based on factors such as the type and model of plastic materials, processing equipment and process conditions, the types and amounts of other chemical additives, the use environment and life span of the product.
The following points should be considered when selecting antioxidants for plastics industry:
Compatibility:
The compatibility between plastic polymers and antioxidants is often poor. The antioxidants are usually combined with the polymer melt at high temperatures. When the polymer solidifies, the antioxidant molecules are compatible with the polymer. in the middle of the molecule. Within the dosage range of the formula, the antioxidant should melt at the processing temperature. Special attention should be paid to the fact that when designing the formula, the melting point or upper melting range of the solid antioxidant and light stabilizer should not be lower than the processing temperature of the plastic polymer.
Migration:
Plastic products, especially products with a small surface area to volume ratio (or mass ratio), oxidation mainly occurs on the surface of the product. Surface, which requires antioxidants to continuously migrate from the interior of the plastic product to the surface of the product to play its role. However, if the migration speed to the surface of the product is too fast and the amount of migration is too large, the antioxidant will volatilize into the environment on the surface of the product, or be lost in other media where the diffusing agent contacts the surface of the product. This loss is actually irreversible. To avoid, take it into consideration when designing the formula. When there is room for selection of antioxidant varieties, varieties with relatively large molecular weight and appropriately high melting points should be selected, and the dosage of antioxidants should be determined based on the harshest use environment.
Stability:
Antioxidants should remain stable in plastic materials, with little volatilization loss and no discoloration in the use environment and during high-temperature processing. Or it does not develop color, does not decompose (except for antioxidants used for heat stabilization during processing), does not have adverse chemical reactions with other additives, does not corrode mechanical equipment, and is not easily extracted by other substances on the surface of the product.
Processability:
When processing plastic products, adding antioxidants may change the resin viscosity and screw torque. If the melting range of the antioxidant and the resin is greatly different, the antioxidant will flow or the screw will be suppressed. When the melting point of the antioxidant is more than 100°C lower than the processing temperature, the antioxidant should be made into a certain masterbatch first, and then mixed with the resin to process the product to avoid uneven distribution of antioxidants in the product and processing yield due to bias flow. decline.
Environment and hygiene:
Antioxidants should be non-toxic or low-toxic, dust-free or low-dust, and should be used in the processing, manufacturing and use of plastic products It has no harmful effects on the human body, no harm to animals and plants, and no pollution to the air, soil and water systems. For plastic products that come into indirect or direct contact with the human body, such as food packaging boxes, children’s toys, and disposable infusions, antioxidants that have been inspected and approved by the U.S. Food and Drug Administration (FDA) or permitted by EC Commission decrees should not only be used Variety, and the amount added should be strictly controlled within the maximum allowable limit.
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