Reference principle for selection of antioxidant and light s

(1) Compatibility

The polymer of plastic material is generally nonpolar, while the molecules of antioxidant and light stabilizer have different degrees of polarity, and their solubility is poor. Generally, antioxidant and light stabilizer are combined with polymer melt at high temperature, and the molecules of antioxidant and light stabilizer are contained between polymer molecules during polymer curing. In the range of formula dosage, antioxidant and light stabilizer should be melted under the processing temperature. Special attention should be paid to that the melting point or upper limit of melting range of solid antioxidant and light stabilizer should be lower than the processing temperature of plastic material polymer when designing the formula.

Billingham and Calvert have proved that the amorphous phase at the spherulite interface of the polymer crystal area is the most vulnerable part of the polymer matrix to oxidation, and the antioxidant with good solubility is just concentrated in the area where the polymer needs them most.

(2) Mobility

For plastic products, especially opaque products with relatively small surface area volume ratio (or weight ratio), oxidation reaction mainly occurs on the surface of products, which requires antioxidant and light stabilizer to continuously migrate from the inside of plastic products to the surface of products. However, if the migration speed to the product surface is too fast and the migration amount is too large, the antioxidant and light stabilizer will volatilize to the environment on the product surface, or diffuse to other media in contact with the product surface and lose. In fact, this loss is inevitable and should be considered when designing the formula. When the varieties of antioxidant and light stabilizer have choice, the varieties with relatively large molecular weight and appropriate high melting point should be selected, and the addition amount of antioxidant and light stabilizer should be determined on the premise of the most severe processing conditions and use environment.

(3) Stability

Antioxidants and light stabilizers shall be stable in plastic materials, with little volatile loss, no discoloration or color rendering, no decomposition (except for antioxidants used for processing thermal stability), no adverse chemical reaction with other additives, no corrosion to mechanical equipment, and no extraction by other substances on the surface of products. Hindered amine light stabilizers are generally low alkaline chemicals. When hindered amine is selected as light stabilizers in plastic materials, other acidic additives shall not be included in the formula, and corresponding plastic materials and products shall not be used in acid environment.

(4) Processability

During the processing of plastic material products, the addition of antioxidant and light stabilizer may change the melting viscosity and screw torque of resin. If there is a large difference between the melting point of antioxidant and light stabilizer and the melting range of resin, the phenomenon of eccentric flow or screw holding of antioxidant and light stabilizer will occur. When the melting point of antioxidant and light stabilizer is lower than the processing temperature by more than 100 ℃, the antioxidant and light stabilizer shall be made into a certain concentration of masterbatch first, and then mixed with resin to process products, so as to avoid uneven distribution of antioxidant and light stabilizer in products and decrease of processing output due to bias current.

(5) Environment and hygiene

Antioxidants and light stabilizers shall be non-toxic or low toxic, free of dust or low dust, have no harmful effect on human body, no harm to animals and plants, and no pollution to air, soil and water system in the processing, manufacturing and use of plastic materials and products.

For agricultural films, food packaging boxes, children's toys, disposable infusion sets and other plastic products that directly or indirectly contact with food, drugs, medical devices and human body, not only the antioxidant and light stabilizer varieties that have passed the inspection and approval of FDA or the European Commission's decrees should be selected, but also the dosage should be strictly controlled within the maximum allowable Below the allowable limit.

LD50 of UV-326 is more than 5000mg / kg, which is a non-toxic chemical substance. However, the EC Commission decree still stipulates the maximum limit of UV-326 in plastic materials in contact with food, which is 0.5% in PP and PE, 0.3% in PVC and 0.6% in PS.