Antioxidants are a class of chemicals that, when present in only a small amount in a polymer system, can delay or inhibit the oxidation process of the polymer, thus Prevents the aging of polymers and extends their service life, also known as “anti-aging agents”. For engineering plastics processing, antioxidants can prevent thermal oxidation degradation during the processing of certain polymers (such as ABS, etc.), allowing the molding process to proceed smoothly. The amount of antioxidants added is generally only 0.1-0.5 parts.
When selecting antioxidants for plastics, attention should be paid to the following four aspects:
Compatibility:
The compatibility of plastic polymers and antioxidants is often poor. The antioxidants are usually combined with the polymer melt at high temperatures, and the polymer The antioxidant molecules are incorporated into the polymer molecules during curing. 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 upper limit of the melting point and 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 those with a small surface area to volume ratio (or mass ratio), are mainly oxidized Occurs on the surface of the product, which requires antioxidants to continuously migrate from the inside 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 choice among antioxidant products, products with relatively large molecular weights 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 and evaporate in the use environment and during high-temperature processing. Less, no discoloration or color development, no decomposition (except for antioxidants used for heat stabilization during processing), no adverse chemical reactions with other additives, no corrosion of mechanical equipment, and not easily absorbed by other substances on the surface of the product. carry.
Environment and hygiene:
Antioxidants should be non-toxic or low-toxic, dust-free or low-dust, and should be used on plastic products. It has no harmful effects on the human body during processing, manufacturing and use, no harm to animals and plants, and no pollution to air, soil, water systems, etc.
For agricultural film food packaging boxes, children’s toys, disposable infusions and other plastic products that indirectly or directly come into contact with food, medicine, medical equipment and the human body, not only should they use products that have passed the U.S. Food and Drug Administration (FDA) ) inspected and licensed, or in antioxidant products permitted by EC Commission decrees, and the amount added should be strictly controlled within the maximum allowable limit.
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