The role of the hottest antioxidant in the high te

2022-08-06
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The role of antioxidants in the high temperature production and use of plastics

during the synthesis and post-treatment of plastic resins and the processing and use of plastic products, plastic polymers will be degraded to varying degrees due to the effects of heat, oxygen and other factors. The degradation will directly have a negative effect on the physical properties, mechanical properties, appearance color, use function and other aspects of the resins and products

the use of antioxidants is one of the effective methods to delay the degradation or thermal oxygen aging of resins and products. The variety and amount of antioxidants used are mainly determined by the molecular structure, polymerization process, processing conditions and product uses of the plastic resin

1. functions and types of plastic antioxidants

plastic resins have different thermal oxidation reaction rates and thermal oxidation resistance due to different molecular structures, or different polymerization processes, different processing processes, different use environments and conditions for the same molecular structure

antioxidant is a plastic additive added to plastic resin to effectively inhibit or reduce the thermal oxidation reaction rate of plastic macromolecules, delay the thermal and oxygen degradation process of plastic resin, significantly improve the heat resistance of plastic resin, prolong the service life of plastic products, and improve the service value of plastic products

antioxidants are the most widely used additives in plastics. One of the most widely used contents refers to the application of antioxidants in different stages of plastic polymerization, granulation, storage, processing, use and recycling. The second most widely used content refers to the variety of plastic materials with different molecular structures that have emerged in the world today, such as polyethylene, polypropylene, styrene polymers, engineering plastics, special plastics and other materials. Among them, the types of plastic materials using antioxidants are the most

according to the molecular structure and action mechanism, the commonly used plastic antioxidants are generally divided into five categories: hindered phenols, phosphites, thios, compounds and hindered amines (HALS)

hindered phenol antioxidant is the main antioxidant of plastic materials. Its main function is to react with R ·, roo · produced by oxidation in plastic materials to interrupt the growth of active chain. Hindered phenol antioxidants can be divided into monophenols, bisphenols, polyphenols, nitrogen heterocyclic polyphenols and other varieties according to their molecular structure

phosphite antioxidant and sulfur-containing antioxidant are both auxiliary antioxidants. The main mechanism of auxiliary antioxidant is to decompose the high active hydroperoxide in plastics into low active molecules. The production and consumption of phosphite antioxidant in China accounts for about 30% of the total production and consumption of antioxidant in China. Domestic sulfur-containing antioxidants can be divided into thioester antioxidants, thiobisphenol antioxidants and thioether phenols according to their molecular structure

different types of main and auxiliary antioxidants, or the same type of antioxidants with different molecular structures, have different functions and application effects, resulting in less waste heat. Each has its own advantages and disadvantages. The composite antioxidant is composed of two or more different types of antioxidants or different varieties of the same type. It can learn from each other in plastic materials, showing a synergistic effect, and achieving the best effect of thermal oxygen aging resistance with the minimum addition and the lowest cost. Synergistic effect means that when two or more additives are used in combination, their application effect is greater than the sum of the effects of each additive used alone, i.e. 1+12

2. stabilizing effect and selection of antioxidant in high-temperature production process

sufficient heat must be provided in the process of polymerization, post-treatment of plastic resin or processing of plastic products. Heat is one of the main reasons for the degradation of resin

the use of antioxidants in the resin polymerization process or post-treatment process has gradually been recognized by the industry

pvc resin degradation is accompanied by the whole process of resin polymerization. Generally, hindered phenolic antioxidants such as 246, 1076 and 245 and phosphite antioxidants such as pky-618 are used to form a stable system with fatty acid zinc, epoxy soybean oil and jc-zh21. Jc-zh21 is a new nitrogen heterocyclic compound with low addition, free radical capture, good stability and high cost performance

calcium zinc heat stabilizer + composite antioxidant (jc-1215) system has good heat stability and color stability in the processing and use of PVC products. The weight ratio of composite antioxidant in calcium zinc heat stabilizer is 5% ~ 10%

abs, SBS, PS, POM and other resins all use antioxidants or combined heat stable systems, such as thioester antioxidant DLTP, DSTP, phosphite antioxidant pky-136, etc

methyl methacrylate PMMA (commonly known as plexiglass) has the characteristics of chemical stability, good processability and excellent optical performance. At the later stage of PMMA synthesis, high temperature treatment is generally required to remove the volatile substances in the resin. When the high temperature treatment temperature reaches above 220 ℃, the end groups of some unsaturated PMMA molecular chains formed by the disproportionation termination of chain free radicals begin to break, the PMMA polymer begins to degrade, the mechanical properties and transparency decline, and the color of the resin becomes worse

adding antioxidants in the post-treatment process of PMMA can effectively improve the thermal oxygen stability of PMMA. The role of antioxidants is to increase the initial decomposition temperature of PMMA and the rate of decomposition due to the existence of rebound stress according to the maximum temperature of fatigue curve when the frequently used non-metallic materials are under pressure. Hindered phenolic antioxidants can simultaneously increase the initial decomposition temperature and the maximum decomposition rate temperature of PMMA. Phosphite antioxidant can only increase the initial decomposition temperature of PMMA, but can not increase the maximum decomposition temperature of PMMA

ultra high molecular weight polyethylene fiber (also known as high-performance polyethylene fiber, UHMWPE) has the characteristics of high strength, high modulus, low specific gravity, strong light resistance and high abrasion resistance. It also has the characteristics of water resistance, moisture resistance, seawater resistance and mold resistance, fatigue resistance and long flexural life. It is the commercial high-performance fiber with the highest specific strength in the world

the maximum production temperature of UHMWPE fiber is about 190 ℃, which is not high temperature. However, due to the high viscosity of the melt, the residence time in the extruder is about 10 minutes, and the heating time is long. When domestic enterprises use the common antioxidant system for production, the thermal degradation of the resin is serious, the molecular weight is reduced from 4million to less than 3million, the strength of the silk is 15% ~ 20% lower than that of the imported silk, and the appearance is yellowing. After using the special antioxidant jc-211b system for production, the molecular weight has not decreased significantly, such as door handle, bumper, rearview mirror shell, etc; The strength reaches the level of imported silk, and the appearance is white and bright

polypropylene processing, especially the manufacturing of polypropylene filament, requires very strict extrusion process, and its processing temperature is higher than 200 ℃. Polypropylene hot loaded cement bags and asphalt bags need to be used at a temperature of about 60 ℃ for a period of time; The surface temperature of plastic woven bags used in the open air in summer can reach 70 ℃ under the sun. For the processing of polypropylene plastic woven bags, when there are requirements for heat resistance, the efficient and special composite antioxidant jc-1225 can provide good processing and use stability. Table 1 shows the change of melt index of polypropylene with different antioxidants. The effect of antioxidant jc-1225 is better than that of general antioxidant 2

adding masterbatch to resin to produce various plastic products, which has been widely used in the plastic processing industry. For the products processed and produced by adding masterbatch, when the carrier resin used in the production of masterbatch is heated again in the production process of plastic products, the carrier resin will undergo thermal degradation and mechanical degradation again, which will lead to and accelerate the thermal, oxygen and light aging of the products in the use process. Therefore, although the carrier resin in the masterbatch accounts for a small proportion in the plastic products, the problem of accelerated aging caused by twice or more heating and its impact on the aging performance of plastic products should be paid attention to by the masterbatch production enterprises and product processing enterprises. In general, for the masterbatch production enterprises and the enterprises that use some secondary materials or recycled materials to produce plastic products, the combined stabilization system of hindered phenols and phosphite antioxidants must be used in the processing process

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