Mechanism of action and practical application of antioxidants

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This post was last edited by eric420 on 2016-11-29 15:13 Antioxidants are a class of chemical substances that, when present in only a small amount in a polymer system, can delay or inhibit the oxidation process of the polymer, thus preventing the aging of the polymer and extending its service life. They are also called "anti-aging agents". For engineering plastic processing, antioxidants can prevent thermal oxidative degradation of certain polymers (such as ABS, etc.) during the processing, so that the molding process can proceed smoothly. The amount of antioxidants added is generally only 0.1-0.5 parts. An ideal antioxidant should have the following conditions: ① It should have high antioxidant capacity: ② It has good compatibility with the resin and does not precipitate; ③ It has good processing performance. It does not evaporate or decompose at the processing temperature of the polymer; ④ It has good extraction resistance and is insoluble in water and oil; ⑤ Its color should be colorless or light-colored so as not to pollute the product; ⑥ It is non-toxic or low-toxic; ⑦ It is cheap. In fact, no antioxidant can fully meet these conditions. Therefore, in actual use, the strengths of various additives are often used according to the type, purpose and processing method of engineering plastics to produce synergistic effects. 1. Mechanism of action 1. The stability of polymers using chain-breaking antioxidants reflects the mechanism of the chain reaction active species intervened by antioxidants, namely segmented chain donor mechanism (CB-D) and segmented chain acceptor mechanism (CB-A). The typical CB-D mechanism is the reaction between peroxidation groups and inhibitors such as phenols, followed by aromatic amines. The only radical generated from the inhibitor AH can destroy a peroxide group PO2 according to the reaction formula (1-43). 2. High polymer stability using pre-antioxidants. Preventive or co-antioxidants can decompose hydroperoxides without forming free radical intermediates. Therefore, they can prevent chain branching caused by the decomposition of hydroperoxides into free radicals. 3. A very famous example of the synergy between antioxidants is the application of dicinnamoyl thiodipropionate (DLTDP) or distearoyl thiodipropionate (DSTDP) and sterically hindered phenols in the thermal stability of certain polymers. Another very important example of synergy is the complex interaction between sterically hindered phenols and phosphites when improving the melt stability of polyolefins. 2. Practical application 1. The research direction of antioxidants has shifted to the development of high-efficiency and multi-functional additive products and reactive antioxidants. There are domestically produced and imported products on the market in mainland China. Domestic products have a stronger smell and are not easy to preserve. Imported origins include the United States, Belgium, Germany, and Spain. Among them, the ones produced in Germany are used by the most people, because the packaging and quality of antioxidants produced in Germany are more suitable for actual production use. Made in Germany, it is generally called antioxidant BHT. Among them, the antioxidant BHT invented by Bayer Company of Germany is widely used in industrial applications. The following is its detailed use. It must be emphasized that oxidation inhibitors are not recommended. Antioxidant BHT can inhibit or delay the oxidative degradation of plastic or rubber and extend its service life. 2. Antioxidant BHT can prevent the acid value or viscosity of lubricating oil and fuel oil from rising. 3. Antioxidant BHT is also a stabilizer for synthetic rubber (styrene-butadiene, nitrile, polyurethane, butadiene, etc.), polyethylene, and polyvinyl chloride. Antioxidant BHT is a commonly used phenolic antioxidant in rubber. Antioxidant B HT has a protective effect on the thermal oxidative aging of natural rubber, cis-butadiene, styrene-butadiene, butyl, isopentyl, nitrile, ethylene-propylene and other synthetic rubber, acrylic and latex products. The antioxidant BHT can inhibit copper damage and resist odor. The combined use of oxygen and wax can prevent damage to vulcanized rubber caused by various weather factors. This product is easily dispersed in rubber. The antioxidant BHT can be directly mixed into rubber or added to latex as a dispersion. It can be used to manufacture the sidewalls of tires, various rubbers and dairy products in white, bright and transparent colors, as well as daily, medical and health, tapes, rubber shoes and edible rubber products. The antioxidant BHT can also be used as a stabilizer for post-processing and storage of synthetic rubber. 4. The solubility of antioxidant BHT is: ethanol 25% (20), soybean oil 30% (25), cottonseed oil 20% (25), lard 40% (40). 5. The antioxidant BHT, as a food additive, can delay the rancidity of food. Antioxidant BHT is used in animal and vegetable fats and foods containing animal and vegetable fats. In addition, antioxidant BHT can also be used in inks, adhesives, leather, casting, printing and dyeing, coatings and electronic industries. 6. The antioxidant BHT is also a stabilizer in cosmetics, medicines, etc. Addition amount of antioxidant BHT: 0.01%-2%. 7. Antioxidant BHT is an excellent antioxidant additive for various petroleum products. When the working temperature of antioxidant BHT is 100 degrees, the antioxidant effect is best. Antioxidant BHT is widely used as antioxidant and anti-adhesive agent in turbine oil, transformer oil, hydraulic oil, thermal oil, brake oil, spindle oil, precision machinery oil and paraffin. The antioxidant BHT can be added to the product directly or as a mother liquor. To improve the antioxidant properties of the product and extend its service life. Antioxidant BHT is used in combination with long-chain alkaline ZDDP and TCP metal deactivation and anti-rust agents to prepare anti-wear hydraulic oil and other products. The dosage is generally 0.1-1%.