Brief description of the role of antioxidants in plastics and their selection principles

The addition of suitable antioxidants in plastic processing can stop or delay the ageing process, thus extending the service life of plastic products. The selection of antioxidants should be based on the type of plastic, processing equipment, process conditions, the variety of other additives and the amount added, the environment in which the product is used and the duration of the product. The choice of antioxidants for plastics should basically refer to the following principles.

I. Compatibility. Plastic polymer and antioxidant compatibility is often poor, usually at high temperatures will be antioxidant and polymer melt combined, polymer curing will be compatible with antioxidant molecules in the middle of the polymer molecules. Within the formulation dosage range, the antioxidant is to be melted at the processing temperature. Design formulations, the choice of solid antioxidants, light stabilizers, the melting point or melting range of the upper limit, should not be higher than the processing temperature of plastic polymers.

Second, migration. Plastic products, especially the surface area and volume ratio (or mass ratio) of the smaller value of the product, oxidation mainly occurs on the surface of the product, which requires continuous migration of antioxidants from the plastic products to the surface of the product and play a role. However, if the migration rate to the surface of the product is too fast, the migration amount is too large, the antioxidant should be volatile to the surface of the product in the environment, or diffusion agent and product surface contact with other media and loss, this loss is in fact unavoidable, design formulations to consider. When there is a choice of antioxidant varieties, should choose a relatively large molecular weight, melting point appropriate high species, and to the most severe use of the environment to determine the amount of antioxidant use.

Third, stability. Anti-oxidant in plastic materials should remain stable, in the use of environmental and high-temperature processing volatile loss, no discoloration or colour, not decomposition (in addition to the role of antioxidants for processing heat stabilization), not with other additives adverse chemical reactions, not corrosive machinery and equipment, not easily extracted by other substances on the surface of the product.

Fourth, processability. Plastic products processing, adding antioxidants to the resin viscosity and screw torque may change. Antioxidant and resin melt range if the difference is large, will produce antioxidant bias flow or inhibition of screw phenomenon. The melting point of the antioxidant is lower than the processing temperature of 100 ℃ or more, the antioxidant should first be made into a certain master batch, and then mixed with resin processing products, in order to avoid uneven distribution of antioxidant in the product due to bias flow and processing yield decline.

Fifth, the environment and health. Antioxidant should be non-toxic or low toxicity, no dust or low dust, no harmful effects on human body in the processing and use of plastic products, no harm to animals and plants, no pollution of air, soil and water system.