Application of antioxidant in PVC resin

PVC plastic is one of the commonly used plastics, more varieties of products. But some products give the impression of not being durable. PVC raincoats, films, sandals and so on will become brittle or even cracked after three or two years of use. If used outdoors, the life span is even shorter. This has two aspects of the reason: one is in the process of cutting corners, a large number of filler to add plastic performance decline.

Second, the structure of PVC itself has many weaknesses, initiator, the funds belong to impurity, structure of oxygen, allyl chloride, poly and degree, molecular weight distribution and so on, these unstable factors in the external causes (such as light, heat, oxygen, solvents, additives, and other factors, such as HCl) under the action of aging, the degradation or crosslinking, make its physical and mechanical properties worse, losing application value.

PVC resin oxidation resistance requirements are not very high, much smaller than polyolefin. However, in some cases, antioxidants are also needed. Outdoor products, such as agricultural film formulations, can be added in small amounts to slow the degradation of BPA. Since most PVC degradation processes are ionized, main antioxidants should only be used when free radical degradation processes are considered. Because oxygen can aggravate the thermal and photodegradation process of PVC, the oxidation of plasticizer at high temperature is also very fast.

After oxidation of plasticizer stone compatibility will decrease, "volatility" increased. All these damage, so that the performance of PVC products rapidly decline, and there will be smell. Once a double bond is formed during the oxidation of PVC, the subsequent oxidation process is the same as that of other unsaturated polymers. In order to prevent and alleviate PVC aging in the process of processing and use, improve the quality of PVC products, in some formulations should be added a certain amount of antioxidant.

Antioxidants are generally used in combination with main and auxiliary antioxidants. Considering from comprehensive performance, source and cost, the most widely used in PVC is bisphenol A. The combination of bisphenol A and phosphite as antioxidant agent has A significant effect. The antioxidant bisphenol A is an inefficient antioxidant, but it can fully meet the use requirements of PVC, and the dosage is generally 0.3 ~ 0.5%. Antioxidant phosphite (TPP) is widely used as PVC chelating agent, especially when adding metal soap as the main stabilizer, with which the harm of metal chloride can be reduced and the transparency and coloration of products can be protected. The addition amount is generally 0.3 ~ 1%.

In addition, the main antioxidants used in PVC are: antioxidant CA, antioxidant 264, antioxidant 2246, antioxidant 1076 and so on. Its adding amount is generally 0.01~0.5%. Epoxy lipids, such as epoxy soybean oil, inhibit the thermal oxidation of PVC and act synergistically with antioxidants.

Antioxidant in practical application, the basic use of mixed in resin or plasticizer in the method. When producing soft PVC material, antioxidant with the help of plasticizer is better, when producing hard PVC material, antioxidant is added by conventional dry mixing method.

Excerpted from - Shanghai KAIN Chemical Zhihu