Application of zeolite in PVC and CPVC heat stabilizer

Application of zeolite in PVC and CPVC heat stabilizer

Natural zeolite is mined from volcanic tuff deposits. Because the heating of this mineral powder will have crystal water from the internal escape, produce similar bubble boiling phenomenon, hence the name - zeolite. In industry, natural zeolite has been used as ion exchange agent, adsorbent and catalyst, is also used as paper and plastic filler, animal feed additives, soil improvement absorbent, especially in environmental protection (such as water treatment) has a broad application prospect. However, only a few kinds of natural zeolite (such as clinoptilolite, mordenite, zeolite, zeolite, zeolite, zeolite flake, calcium cross zeolite, etc.) have been found in more than 60 kinds of natural zeolite.

Because the quality of natural zeolite can not meet the increasing demand for quality in industry, so in many uses of synthetic zeolite has replaced the natural zeolite. The main elements of zeolite synthesis are silicon, aluminum and sodium, and hydrogen and oxygen exist in the form of crystalline water. According to different needs, metal ions such as zinc, magnesium, calcium, strontium and nickel can be introduced (to replace the position of sodium), as well as anions such as perchlorate, phosphite and other organic acid groups can be introduced to improve the desired performance. The most basic structural unit of the zeolite skeleton is TO4 tetrahedron. The central atom T of tetrahedron is Si and Al most commonly, and it can also be Ga, B, Ti, Fe and other elements.

Because sodium, aluminum, silicon and other elements can be combined in any proportion, there can be an infinite number of varieties of synthetic zeolite, currently the world has been synthesized zeolite varieties of about hundreds (many varieties often called molecular sieves). Zeolite is also divided into many types, as an auxiliary stabilizer for PVC resin mainly A type, X type and Y type. Because their particle surface Lewis alkalinity is very strong, the cage structure gravity is very strong, and has the ability of ion exchange. Zeolite with these properties is an excellent performance of PVC auxiliary heat stabilizer, in the process of PVC can play a good role in thermal stability, and is expected to be used in CPVC processing. Current synthetic technology and specific preparation methods can effectively improve these properties, which can largely meet the processing needs of PVC and CPVC resins.

At present, the production of PVC resin on the market is very large, and the products of CPVC resin are also increasing rapidly. However, they are easy to decompose in the process, especially CPVC. The release of sodium chloride will accelerate the decomposition of resin, so CPVC has higher requirements for stabilizers. So a lot of people are working on heat stabilizers these days. Since the new century, there have been many high efficient stabilizers in China, which can better meet the processing needs of soft and hard PVC resin. At present, PVC and CPVC heat stabilizers are mainly dependent on organic tin and lead salts, but tin and lead are toxic heavy metals, and the price of organic tin is high. Therefore, replacing tin and lead or reducing the proportion of tin and lead in stabilizers will be the development direction of future stabilizers. Under current technology and market conditions, inorganic stabilizers such as hydrotalcite and hydroaluminite will be a good choice, but the price of these raw materials is too high, so zeolite will be the best choice, both have excellent thermal stability, and the price is low.

In recent years, the study of zeolite has been more in-depth, especially in the aspects of molecular sieves and catalysts have been a lot of research results.