Stabilizing effect of the hottest antioxidant in h

The stabilizing effect of antioxidants in the high-temperature production process of plastics

plastic resins in the synthesis and post-treatment process, plastic products in the processing and use process, due to the role of heat, oxygen and other factors, plastic polymers will be degraded to varying degrees, and 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 methods to effectively delay the degradation or thermal oxygen aging of resins and products. The application variety and addition amount of antioxidant are mainly determined by the molecular structure of plastic resin, polymerization process, processing conditions and product use

1. the function and type of plastic antioxidant

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

antioxidant is a plastic additive added to plastic resin to effectively inhibit or reduce the thermal oxidation reaction speed 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 various stages of plastic polymerization and synthesis, granulation, storage, processing, use, recycling and reuse. The second most widely used content refers to the types of plastic materials with different molecular structures that have appeared in the world today, such as polyethylene, polypropylene, styrene polymers, engineering plastics, special plastics and other materials, among which the types of plastic materials using antioxidants are the most

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

hindered phenol antioxidant is the main antioxidant of plastic materials. Its main function is to generate electricity through oxidation in plastic materials. 3 Loading hydraulic cylinder piston stroke: 1000mm (can be increased) the oxidation free radical R and roo reaction produced by the self-sufficiency of existing energy, interrupting 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 action mechanism of auxiliary antioxidant is to decompose the highly active hydroperoxide in plastics into low active molecules. The domestic production and consumption of phosphite antioxidant accounts for about 30% of the total domestic production and consumption of antioxidant. Sulfur containing antioxidants produced in China 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,

each has its own advantages and disadvantages. The composite antioxidant is composed of two or more different types or the same type of antioxidants, and everyone cuts off the power in time, which is very good for the performance stability of this machine. 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 amount of addition and the lowest cost. Synergistic effect refers to 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, that is, 1 + 12

hindered amine stabilizers (HALS) are a class of organic amine compounds with steric hindrance effect. They have four synergistic stabilizing functions: decomposition of hydroperoxide, quenching of excited oxygen, capture of free radicals, and self recycling. Hindered amines with relative high molecular weight are efficient, long-acting antioxidants and efficient light stabilizers. Most varieties of hindered amines take 2,2,6,6-tetramethyl-4-piperidinyl as the parent, and its representative structural formula is:

hindered amine representative structural formula

2. The stabilizing effect and selection of antioxidants in the high-temperature production process

plastic resin polymerization, post-treatment or plastic product processing must provide sufficient heat. Heat is one of the main causes of resin degradation

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

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

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

the polymerization process of ABS, SBS, PS, POM and other resins uses antioxidants or combined heat stable systems, such as thioester antioxidants 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 properties. In the late stage of PMMA synthesis, high temperature treatment is generally required to remove volatile substances from the resin. When the high temperature treatment temperature reaches above 220 ℃, the end groups of unsaturated PMMA molecular chains formed by the disproportionation termination of chain free radicals begin to break bonds, PMMA polymers begin to degrade, 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 and the maximum decomposition rate temperature of PMMA. 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 not 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 wear resistance. At the same time, it has the characteristics of water resistance, humidity resistance, seawater resistance and mold resistance, fatigue resistance and long flexural life. It is a 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, and 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, the strength of the silk has reached the level of imported silk, and the appearance is white and bright

polypropylene processing, especially the manufacturing of polypropylene filament, requires extremely 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 sunlight. 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 225

Table 1 Effects of different antioxidants on the melt fluidity of polypropylene

adding masterbatch to resin to produce various plastic products has been a common method in the plastic processing industry. For 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 products in the process of use. Therefore, although the carrier resin in the masterbatch accounts for a small proportion in 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 masterbatch production enterprises and 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

3. Stability and selection of antioxidants in the process of use

among the antioxidants for long-term thermal oxygen stability protection of plastic materials, hindered phenolic antioxidants are the most important, and the stability effect is better when used together with hindered amine (HALS) antioxidants, phosphite esters or thioester auxiliary antioxidants

engineering plastic materials, with the advantages of light weight, good mechanical strength and corrosion resistance, are increasingly used to manufacture plastic parts with heat-resistant requirements. For example, the modified polyamide PA pipe fittings of automotive engine fuel system require not only low-temperature toughness and high-temperature rigidity, but also long-term use in the temperature environment around the engine of about 120 ℃. It is necessary to improve the long-term thermal oxygen stability of the modified polyamide PA material whose fiber orientation is 0 °. The data in Table 2 shows that the stable system composed of hindered phenol antioxidant and phosphite antioxidant has good stability effect and cost performance for the use of plastic polyamide products

Table 2 stability of hindered phenol and phosphite antioxidant on PA at 100 ℃

asymmetric hindered phenol antioxidant with 2-methyl-6-tert-butylphenol as the skeleton not only has the characteristics of general hindered phenol antioxidant, but also has the synergistic stability and coloring resistance with auxiliary antioxidant, which is better than the traditional symmetrical hindered phenol, and is suitable for thermal oxidative degradation Polymer materials with high heat resistance and high color stability are required

Table 3 shows the effects of general antioxidant 1010 and asymmetric hindered phenolic antioxidant 1790 on the oxidation induction period of polyethylene LDPE. When the asymmetric antioxidant 1790 is at a high temperature above 210 ℃, it shows better thermal oxygen stabilization effect than antioxidant 1010, and is more suitable for plastic materials with high heat resistance

Table 3 data of oxidation induction period of antioxidant 1010 and antioxidant 1790 in LDPE

bisphenol monoacrylate antioxidants have bifunctional group stability, better thermal oxygen and color stability due to the introduction of unsaturated double bond of acrylate in the molecule. They are suitable for ABS, PS and other materials containing butadiene copolymerization components

the data in Table 4 shows that polymeric hindered amines (HALS) antioxidants have high thermal oxygen stability. Polymeric hindered amine antioxidants have good compatibility with resin, resistance to extraction and long-term stability, and can be used in conjunction with traditional antioxidants

Table 4. Thermal oxidation stability of HALS for 0.1mm thick polyethylene LLDPE film

conclusion

when plastic products have high-temperature processing or use requirements, it is generally difficult to meet high-temperature processing and use requirements by using only general antioxidants; Only using high-grade or high price antioxidants, the cost of additives for products is high. Low cost performance

developing the synthesis process and application technology of functional plastic materials and using special antioxidant with high performance price ratio can not only improve the product technical content and product attachment of resin synthesis enterprises and plastic product processing enterprises