Most industrial organic materials, whether natural or synthetic, are prone to oxidation reactions, such as plastics, fibers, rubber, adhesives, fuel oil, lubricating oil, food and feed, which have the nature of reacting with oxygen. After reacting with oxygen, substances will lose their original beneficial properties. If the polymer material is aged, its surface will become sticky, discolored, brittle and cracked, resulting in the loss of use value of the polymer material. The oxidation of fuel oil will produce sediment, block the valve or oil pipe of the machine, and cause abnormal operation of the engine. Lipoprotein and its associated compounds formed by mammalian oxidation are the culprits of diseases such as atherosclerosis.

In order to try to inhibit and prevent the occurrence of the above oxidation phenomenon, people have found an effective, convenient method without changing the existing production process, that is, adding antioxidants.

1 Main antioxidants and their development trend

1.1 Hindered phenolic antioxidants

The hindered phenolic antioxidant is a kind of compound with substituents on one or both sides of the - OH side of the benzene ring. In the presence of hindered phenolic antioxidants, a peroxide free radical (ROO?) will seize a proton from the polymer (RH?) and interrupt this series of free radical reactions, which is the control step of automatic oxidation. When the hindered phenolic antioxidant is added, it is easier to provide protons than those polymers, that is, it provides a more favorable reaction to form phenolic free radicals, which makes the polymer relatively stable without further oxidation.

Contain adjacency α- Development of phenolic antioxidants with hydrogen protonic substituents. Tert-butyl substituents are generally considered to be excellent ortho-p substituents of phenolic antioxidants. However, each phenolic radical can capture at most 2 peroxyradicals, and the captured free radical number decreases with the increase of the free radical capture rate. Therefore, it is considered impossible to capture more free radicals when the number of phenolic radicals exceeds 2.

Development of o-allylphenol antioxidants. Alkyl and peroxy radicals play an important role in the actual degradation of organic materials. For example, the oxygen concentration of plastic film varies in gradient within its thickness range. The surface oxygen concentration is high, and the peroxide free radicals play a major role in the automatic oxidation process. The internal oxygen concentration is low, and alkyl is mainly involved in the reaction during the degradation process. However, in general, because the reaction of alkyl radical is too fast, it is not easy to capture. When it encounters oxygen, it can continue to trigger an automatic oxidation chain reaction. Yasukazu Ohkatsu studied and found a new method called "ortho substituent effect" to capture alkyl radicals at Kogakuin University in Japan. On this basis, they developed antioxidants with the structure of o-allyl phenol.

1.2 Phosphorus antioxidants

Phosphorus-containing antioxidants are mainly phosphite esters. Phosphite, as a decomposition agent of hydroperoxide and a free radical catcher, plays an anti-oxygen role in plastics, which has been reported in many previous literatures. In recent years, it has been found that the structure of phosphite has a direct impact on some of its properties as an antioxidant.

Improving hydrolysis stability is still a key topic in the development of phosphite antioxidants. While seeking new structures, some companies have begun to focus on the modification of existing products. Ciba-Geigy is actively promoting its newly developed phosphite stabilizer CGA 12. This product introduces the alcohol amine structure into the phosphite molecule, showing a unique stabilization effect. Its goal is to replace Irganos 168 for polyolefins.

At present, the development focus of phosphite antioxidants is:

(1) Improve hydrolysis stability. (2) Polymer quantification. (3) Main and auxiliary complex antioxidants.

At present, the development trend and focus of phosphite antioxidants at home and abroad is to develop varieties that improve hydrolysis stability and high temperature resistance. Some of the developed products have been industrialized and have shown good application performance and market prospects. Its main varieties include Ethanox 398, Phosphite A, XR-633, complex phosphite antioxidant, etc.

Phosphite antioxidants are the main varieties of auxiliary antioxidants for polyolefin processing. They can effectively improve the processing stability and thermal stability of polyolefin resin when used together with hindered phenolic antioxidants. Many advantages make phosphite antioxidant a good multifunctional auxiliary antioxidant for polyolefins:

(1) Composite type of main and auxiliary antioxidants: the combination of phosphite and phenolic antioxidants can give full play to the synergistic effect. At present, the widely used phosphorus-containing composite antioxidant is mainly composed of Irgafos 168 and hindered phenols Irganox 1010, Inganox 1425, etc., which can be used in a variety of polymers. (2) Polymer quantification: Recently, one of the trends in the development of antioxidants is to make the molecules have as many functional structures and polymer quantification as possible. The representative varieties of phosphorus-containing antioxidants include Sandtab P-EPQ, Phosphite A, etc. (3) Pentaerythritol diphosphite: Since the 1980s, pentaerythritol diphosphite has formed a series of products. It has outstanding effects on preventing IF oxidation and improving color, and has high thermal, light stability, weather resistance and hydrolysis resistance. (4) Fluorophosphite: Fluorophosphite is also one of the new varieties of phosphorus antioxidant. Ethanox398 fluorophosphite newly developed by American Ethyl Company is non hygroscopic and has anti hydrolysis effect when used in lotion polymerization or solution polymerization, which can solve many problems in processing and storage. (5) High heat-resistant phosphite antioxidant: phosphite antioxidant has low possibility of forming pre-oxidant at high temperature above 300 ℃, and has been used in general plastics and engineering plastics. In recent years, special engineering plastics have developed rapidly, and higher requirements have been put forward for the heat resistance of antioxidants. If the structure of phosphite can be improved, it will play a greater role in the processing and application of special engineering plastics.

1.3 Phenolic ester low pollution compound antioxidant

The compound antioxidant has high antioxidant activity and low volatility, and is especially suitable for high-temperature processing. It is an excellent plastic antioxidant and hydrolytic stabilizer. In recent years, the development of phenolic ester low pollution composite antioxidants has been very active. The most typical example is the combined use of BHT and DLTP as antioxidants, which not only reduces the cost, but also extends the anti-oxidation life of polymer materials. Cyanox XS4, an antioxidant developed by Cytec, is a composite system containing hindered phenol and phosphite, which can be used in polyolefins to enhance processing stability and long-term stability.

The phenolic ester low-pollution composite antioxidant YHK-1 developed by Bao Jingyan has reached the international advanced level in performance and low cost. Later, she developed a phenolic ester low-pollution composite antioxidant YHK-4 with excellent oxidation resistance, processing stability, weather resistance and hydrolysis resistance, which can completely replace the imported phenolic ester low-pollution composite antioxidant YHK-4 used for ABS production.

According to the type of resin, it is a shortcut for the research and development of antioxidants to study the corresponding phenolic ester low pollution composite antioxidants. In recent years, some new composite antioxidants with market prospects and phosphite as components have been developed at home and abroad, such as:

1.3.1 PL-440

PL-440, a complex of polyalkyl bisphenol A phosphite dimer and trimer, was developed by Beijing Research Institute of Chemical Industry. PL-440 is a phosphite antioxidant with excellent performance. It is widely used in PVC, PET, ABS, polyolefin, nylon, PPO, PBT alloy, PS and other polymers as a co-antioxidant and heat stabilizer of polymers.

1.3.2 Compound "green" antioxidant

In recent years, in order to prevent the toxic effect of 2,6-di-tert-butyl-p-cresol (BHT), some foreign companies, such as Roche, Ciba Refinery, BASF, and other companies, have launched a solid composite "green" antioxidant based on VE and combined with phosphite, glycerin, polyethylene glycol, high porosity resin carrier and other components.

2 Conclusion

With the rapid development of China's plastics industry, China has become the main target market of many large auxiliary companies in the world, which has a great impact on China's antioxidant market. At the same time, the vigorous development of China's plastics industry has brought huge space for the development of the antioxidant industry. Therefore, opportunities and challenges coexist in China's antioxidant industry.