News Details
Use of antioxidants
2017-12-31 19:00:08
Use of antioxidants
The use of antioxidants depends on the types of polymers, the system of crosslinking, the efficiency of antioxidants, synergistic effects, and the conditions and costs of the use of the products.
Most of the antioxidants have the most suitable concentration and dosage. The use of antioxidant more than the suitable concentration has adverse effects.
The effects of other processes, such as the volatilization, extraction and oxidation loss of antioxidants, should also be considered. In these cases, the use of antioxidants should be increased to maintain the most suitable concentration. Polymers with large unsaturation also require more antioxidants.
Action mechanism of antioxidant 1, stability of polymer using broken chain antioxidant
Reaction mechanism of reactive species of antioxidants in intervention chain, namely, segment chain donor mechanism (CB-D) and segment chain receptor mechanism (CB-A)
The typical CB-D mechanism is the free radicals of peroxidation and the inhibitors such as phenols, followed by the reaction between aromatic amines. The free radical produced from the inhibitor AH can eliminate a peroxide group PO2 as the reaction type (1-43).
Action mechanism of antioxidant 2, stability of high polymer using pre antioxidant
Preventive or auxiliary antioxidants can decompose hydroperoxide but do not form free radical intermediates. Therefore, they prevent the decomposition of hydrogen peroxide from free radicals to chain branching.
Action mechanism of antioxidant 3 and synergism between antioxidants
A famous example is the application of cinnamoyl thiocarbamate (DLTDP) or double stearyl thiocarbamate (DSTDP) and sterically hindered phenol in some polymers' thermal stability. Another important example of synergy is the synergistic effect of sterically hindered phenol and phosphite on improving the stability of polyolefin melt.
At the same time, we should pay attention to some factors that promote the oxidation of fat, such as light, especially ultraviolet, which is easy to cause the oxidation of fat. We can use light resistant packaging materials, such as aluminum composite plastic bags, to preserve fat foods.
High temperature in processing and storage promotes the oxidation of fat in food. On the other hand, increase the volatilization of antioxidants, such as BHT in soybean oil heated to 170 degrees C, 90 minutes, completely decomposed or volatilized.
The presence of a large amount of oxygen accelerates oxidation, and in fact, the oil will automatically oxidize as long as it is exposed to the air. It is very important to avoid contact with oxygen, especially for powder - like food with a large specific surface. Generally, nitrogen filling or vacuum sealing packaging can be used. Oxygen inhalants or deoxidants can also be used. Otherwise, if food is directly contacted with oxygen, even if a large number of antioxidants are added, it is difficult to achieve the desired effect.
Triphenyl phosphite (antioxidant, stabilizer TPPi) production process
1. Phosphorus oxychloride as the direct method (also called thermal method) phenol with pyridine and anhydrous benzene as solvent, in no more than 10 ℃ temperature, slowly add oxygen phosphorus chloride, then under reflux temperature, the reaction of 3 ~ 4 h. After cooling to room temperature, the reactants are washed by water to recycle pyridine. After centrifugal dehydration, the reagents are dehydrated with dried sodium sulfate, which is filtered to remove sodium sulfate. The first atmospheric distillation recovery of benzene, vacuum distillation, collected 243 ~ 245 ℃ (1.47 kPa) fraction, by cooling, crystallization, crushing is the finished product.
2. After phenol melting, stirring under add phosphorus trichloride under 25 ℃, Triphenyl phosphite is generated; Then heat up to 70 ℃ ventilation with chlorine gas, generated two chlorinated triphenyl phosphate; Again at 50 ℃ water hydrolysis, triphenyl phosphate. The hydrolysate with 5% soda solution for neutralization, water washing, the evaporation and vacuum distillation, collected 243 ~ 245 ℃ (1.47 kPa) fractions, cooling, crystallization, crushing, packaging is the finished product.
Triphenyl phosphite (TPPi antioxidants, stabilizer) is mainly used in PVC, polyethylene, polypropylene, polystyrene, polyester, abs resin, epoxy resin, synthetic rubber antioxidant stabilizer, used in polyvinyl chloride (PVC) products as a chelating agent.
Most industrial organic materials, whether natural or synthetic, are prone to oxidation reactions, such as plastics, fibers, rubber, adhesives, lubricants, food and feedstuffs. After the reaction with oxygen, the substance will lose its original beneficial attribute. The oxidation of fuel oil will precipitate, block the valve or tubing of the machine, and cause the engine to not work properly. The acidic oxidation products will accelerate the corrosion rate of the machine and make the fuel oil advance in advance. The oxidation of the lubricating oil increases the viscosity and produces gels and impurities, as well as accelerating the corrosion and wear of the equipment. Food and feed oxidation will be corrupted and lose its original flavor. The lipoproteins and their associations formed by oxidation in mammals are the culprit of diseases such as arteriosclerosis.
In order to control the phenomenon of inhibition or delay oxidation, an effective and convenient method without changing the existing production technology is put forward, that is, adding antioxidants.
Antioxidants are organic compounds that can inhibit or delay the thermal oxidation of polymers and other organic compounds in the air. In general, it is the material that can prevent the polymer material from deteriorating by oxidation.
Antioxidant is itself a reducing agent. When the material is at the same time, antioxidants are oxidized first and then protect the components which are easy to oxidize, so as to ensure the stability of materials.
In the process of self oxidation, the antioxidant function is to provide electronic or effective hydrogen ions, to supply free radicals to accept, and to break the reaction of the self oxidation chain.
When choosing antioxidants, we should pay attention to the discoloration and pollution of the antioxidant itself. Such as phenolic antioxidants, colorless or light color, is a non polluting antioxidant, can be used in colorless or light colored plastic products.
Aromatic amine antioxidant, with strong color change and pollution, is not suitable for light colored plastic products. As for the products of polyurethane, polycarbonate and polystyrene, the discoloration of matrix is more serious when the color resistant antioxidant is used.
Many types of discoloration can be overcome by adding some kind of phosphite or thioether.
Copyright: Zhang Jia Gang YaRui Chemical co.,Ltd
http://www.yaruichem.com
The use of antioxidants depends on the types of polymers, the system of crosslinking, the efficiency of antioxidants, synergistic effects, and the conditions and costs of the use of the products.
Most of the antioxidants have the most suitable concentration and dosage. The use of antioxidant more than the suitable concentration has adverse effects.
The effects of other processes, such as the volatilization, extraction and oxidation loss of antioxidants, should also be considered. In these cases, the use of antioxidants should be increased to maintain the most suitable concentration. Polymers with large unsaturation also require more antioxidants.
Action mechanism of antioxidant 1, stability of polymer using broken chain antioxidant
Reaction mechanism of reactive species of antioxidants in intervention chain, namely, segment chain donor mechanism (CB-D) and segment chain receptor mechanism (CB-A)
The typical CB-D mechanism is the free radicals of peroxidation and the inhibitors such as phenols, followed by the reaction between aromatic amines. The free radical produced from the inhibitor AH can eliminate a peroxide group PO2 as the reaction type (1-43).
Action mechanism of antioxidant 2, stability of high polymer using pre antioxidant
Preventive or auxiliary antioxidants can decompose hydroperoxide but do not form free radical intermediates. Therefore, they prevent the decomposition of hydrogen peroxide from free radicals to chain branching.
Action mechanism of antioxidant 3 and synergism between antioxidants
A famous example is the application of cinnamoyl thiocarbamate (DLTDP) or double stearyl thiocarbamate (DSTDP) and sterically hindered phenol in some polymers' thermal stability. Another important example of synergy is the synergistic effect of sterically hindered phenol and phosphite on improving the stability of polyolefin melt.
At the same time, we should pay attention to some factors that promote the oxidation of fat, such as light, especially ultraviolet, which is easy to cause the oxidation of fat. We can use light resistant packaging materials, such as aluminum composite plastic bags, to preserve fat foods.
High temperature in processing and storage promotes the oxidation of fat in food. On the other hand, increase the volatilization of antioxidants, such as BHT in soybean oil heated to 170 degrees C, 90 minutes, completely decomposed or volatilized.
The presence of a large amount of oxygen accelerates oxidation, and in fact, the oil will automatically oxidize as long as it is exposed to the air. It is very important to avoid contact with oxygen, especially for powder - like food with a large specific surface. Generally, nitrogen filling or vacuum sealing packaging can be used. Oxygen inhalants or deoxidants can also be used. Otherwise, if food is directly contacted with oxygen, even if a large number of antioxidants are added, it is difficult to achieve the desired effect.
Triphenyl phosphite (antioxidant, stabilizer TPPi) production process
1. Phosphorus oxychloride as the direct method (also called thermal method) phenol with pyridine and anhydrous benzene as solvent, in no more than 10 ℃ temperature, slowly add oxygen phosphorus chloride, then under reflux temperature, the reaction of 3 ~ 4 h. After cooling to room temperature, the reactants are washed by water to recycle pyridine. After centrifugal dehydration, the reagents are dehydrated with dried sodium sulfate, which is filtered to remove sodium sulfate. The first atmospheric distillation recovery of benzene, vacuum distillation, collected 243 ~ 245 ℃ (1.47 kPa) fraction, by cooling, crystallization, crushing is the finished product.
2. After phenol melting, stirring under add phosphorus trichloride under 25 ℃, Triphenyl phosphite is generated; Then heat up to 70 ℃ ventilation with chlorine gas, generated two chlorinated triphenyl phosphate; Again at 50 ℃ water hydrolysis, triphenyl phosphate. The hydrolysate with 5% soda solution for neutralization, water washing, the evaporation and vacuum distillation, collected 243 ~ 245 ℃ (1.47 kPa) fractions, cooling, crystallization, crushing, packaging is the finished product.
Triphenyl phosphite (TPPi antioxidants, stabilizer) is mainly used in PVC, polyethylene, polypropylene, polystyrene, polyester, abs resin, epoxy resin, synthetic rubber antioxidant stabilizer, used in polyvinyl chloride (PVC) products as a chelating agent.
Most industrial organic materials, whether natural or synthetic, are prone to oxidation reactions, such as plastics, fibers, rubber, adhesives, lubricants, food and feedstuffs. After the reaction with oxygen, the substance will lose its original beneficial attribute. The oxidation of fuel oil will precipitate, block the valve or tubing of the machine, and cause the engine to not work properly. The acidic oxidation products will accelerate the corrosion rate of the machine and make the fuel oil advance in advance. The oxidation of the lubricating oil increases the viscosity and produces gels and impurities, as well as accelerating the corrosion and wear of the equipment. Food and feed oxidation will be corrupted and lose its original flavor. The lipoproteins and their associations formed by oxidation in mammals are the culprit of diseases such as arteriosclerosis.
In order to control the phenomenon of inhibition or delay oxidation, an effective and convenient method without changing the existing production technology is put forward, that is, adding antioxidants.
Antioxidants are organic compounds that can inhibit or delay the thermal oxidation of polymers and other organic compounds in the air. In general, it is the material that can prevent the polymer material from deteriorating by oxidation.
Antioxidant is itself a reducing agent. When the material is at the same time, antioxidants are oxidized first and then protect the components which are easy to oxidize, so as to ensure the stability of materials.
In the process of self oxidation, the antioxidant function is to provide electronic or effective hydrogen ions, to supply free radicals to accept, and to break the reaction of the self oxidation chain.
When choosing antioxidants, we should pay attention to the discoloration and pollution of the antioxidant itself. Such as phenolic antioxidants, colorless or light color, is a non polluting antioxidant, can be used in colorless or light colored plastic products.
Aromatic amine antioxidant, with strong color change and pollution, is not suitable for light colored plastic products. As for the products of polyurethane, polycarbonate and polystyrene, the discoloration of matrix is more serious when the color resistant antioxidant is used.
Many types of discoloration can be overcome by adding some kind of phosphite or thioether.
Copyright: Zhang Jia Gang YaRui Chemical co.,Ltd
http://www.yaruichem.com
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