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Evaluation method for the function of antioxidants and light stabilizers To evaluate the functions and functions of antioxidants and light stabilizers in plastic materials or products, tests are generally carried out according to different formula designs, and the test data are compared and evaluated. The formula design is as follows: blank resin; resin + antioxidant; resin + light stabilizer; resin + antioxidant + light stabilizer.
There are mainly 5 commonly used test methods.
① Oxidation induction period test. For general plastic materials, the Brabender plasticizer is generally used to mix the materials for 10 minutes under nitrogen protection, and then molded into a 001mm film sample, and the oxygen absorption rate is directly measured at 0.1MPa and 150°C.
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② Multiple extrusion tests. The sample is repeatedly extruded in the extruder, and the sample can be tested after continuous extrusion, or the sample can be tested after every other extrusion. Test the melt flow index MFI of the sample, or make the sample into a standard test piece to test the mechanical properties or color difference. This test mainly evaluates the thermo-oxidative stabilization effect of antioxidants on plastic materials during processing.
③ Oven heat aging test. The samples are placed in an oven maintained at a certain temperature with hot air (and sometimes oxygen) circulation. Detect the carbonyl index, mechanical properties or color difference of the sample. This test mainly evaluates the thermo-oxidative stabilization effect of antioxidants and light stabilizers on plastic materials during storage and use.
④ Artificial accelerated aging test. Place the sample in an all-weather aging box or UV aging machine to conduct an aging test that simulates the natural environment or conditions. Detect the carbonyl index mechanical properties or color difference of the sample. This test mainly evaluates the stabilizing effect of antioxidants and light stabilizers on oxygen aging or photoaging of plastic materials during use.
⑤ Natural climate test. The samples were placed in a natural environment with certain conditions, and the light and oxygen aging tests in the natural environment were carried out. The carbonyl index and mechanical properties of the samples were tested. This test evaluates the light and oxygen stabilization effects of antioxidants and light stabilizers on plastic materials during use in natural environment. Only the data and results of the natural climate test can really guide the practical application of plastic products, but the time period of the natural climate test is long, sometimes even two or three years. Therefore, the comprehensive evaluation results of the first four tests can basically determine the light and oxygen stabilization functions and effects of antioxidants and light stabilizers in the processing and application of plastic products.
*Selection principles of antioxidants and light stabilizers
a. Compatibility. The macromolecules of plastic polymers are generally non-polar, while the molecules of antioxidants and light stabilizers have different degrees of polarity, and the compatibility between the two is poor. Usually, antioxidants and light stabilizers are mixed at high temperature. Combined with the polymer melt, the antioxidant and light stabilizer molecules are melted between the polymer molecules when the polymer is cured. Within the dosage range of the formula, the antioxidant and light stabilizer should be melted at the processing temperature. Special attention should be paid to the melting point or melting range upper limit of the solid antioxidant and light stabilizer when designing the formula, which should not be lower than plastic polymerization. the processing temperature of the material.
b. Mobility. Plastic products, especially opaque products with relatively small surface area to volume ratio (or weight ratio), the oxidation reaction mainly occurs on the surface of the product, which requires the continuous migration of antioxidants and light stabilizers from the inside of the plastic product to the plastic product. function on the surface of the product. However, if the migration speed to the surface of the product is too fast and the amount of migration is too large, the antioxidant and light stabilizer will be volatilized into the environment of the surface of the product, or diffused into other media in contact with the surface of the product and lost. It is in fact unavoidable and should be taken into account when designing the formulation. When there is room for selection of antioxidants and light stabilizers, the varieties with relatively large molecular weight and appropriately high melting point should be selected, and the most severe processing conditions and use environment should be used as the premise to determine the antioxidants and light stabilizers. added amount
c. Stability. Antioxidants and light stabilizers should be stable in plastic materials, with less volatilization loss under the use environment and high temperature processing, no discoloration or color development, and no decomposition (except for the antioxidants used for thermal stabilization of 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.
d. Processability. When plastic products are processed, antioxidants and light stabilizers are added to the resin.Both melt viscosity and screw torque may vary. If the melting point of the antioxidant and light stabilizer is quite different from the melting range of the resin, the phenomenon of anti-oxidant and light stabilizer drift or screw locking will occur. When the melting point of the antioxidant and light stabilizer is lower than the processing temperature by more than 100 °C, the antioxidant and light stabilizer should be made into a certain concentration of masterbatch, and then mixed with the resin to process the product to avoid the anti-resistance in the product caused by the bias current. Oxygen, light stabilizer uneven distribution and decreased processing output
e. Environment and hygiene. Antioxidants and light stabilizers should be non-toxic or low-toxic, dust-free 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 products. .
For agricultural films, food packaging boxes, children's toys, disposable infusion sets and other plastic products that have indirect or direct contact with food, medicines, medical devices and the human body, not only should they be tested and approved by the US Food and Drug Administration (FDA), Or the types of antioxidants and light stabilizers allowed by the decree of the European Community Commission, and the added amount should be strictly controlled under the maximum allowable limit.
The acute oral toxicity test value LD50>5000mg/kg of light stabilizer UV-326 is a relatively non-toxic chemical substance. However, the European Community Commission Decree still stipulates the maximum limit of UV-326 in plastic materials in contact with food, in polypropylene PP, polyethylene PE
The maximum limit is 05% in PVC, 03% in polyvinyl chloride (PVC), and 0.6% in polystyrene PS
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