Simple PVC resin is extremely sensitive to heat, and slight thermal decomposition occurs when the heating temperature is above 900C; when the temperature reaches 1200C, obvious thermal decomposition reaction occurs, which deepens the color of PVC resin gradually, and the thermal degradation mechanism of PVC is very complex, but the essence of PVC thermal decomposition reaction is a series of reactions caused by deHCl reaction, which finally leads to the fracture of the macromolecular chain.
The same stabilizer can achieve thermal stability according to several different mechanisms. It is proved that adding a heat stabilizer is an effective method to improve the thermal stability of PVC. There are many kinds of PVC heat stabilizers. According to its chemical composition, there are basic lead salts, metal soaps (higher fatty acid barium, lead, separator, calcium, zinc, magnesium, potassium, strontium, etc.), organotin, epoxide, phosphite, rare earth compounds, and mercaptan antimony, etc. In formulation design, several stabilizers of different kinds or the same kind are usually used together to produce synergistic, additive, or complementary effects. Because the single component heat stabilizer is difficult to meet the requirements of thermal stability and comprehensive performance, the development and application of composite heat stabilizer have been developed rapidly. With the strengthening of the national environmental protection system, environmentally friendly and non-toxic calcium-zinc composite stabilizers are being promoted in the market.
Calcium stearate / Zinc composite heat stabilizer Calcium stearate, Zinc non-toxic heat stabilizer, low price, suitable for food packaging PVC products. The results show that Zinc soap stabilizer has high ionization potential energy and reacts with allyl chloride on PVC molecule to stabilize PVC and inhibit initial coloring. However, the ZnCl2 produced by the reaction is a catalyst for deHCl and can promote the degradation of PVC. The Calcium soap not only reacts with HCl but also reacts with ZnCl2 to form CaCl2 and regenerate Zinc soap. CaCl2 has no catalytic effect on the removal of HCl, and the complexation of calcium derivatives with ZnCl2 can reduce the catalytic ability of HCl removal. There is a good synergistic effect between epoxides and Calcium and Zinc soaps. Usually, the non-toxic compound heat stabilizer is composed of Calcium stearate, Zinc stearate, and epoxy soybean oleate. It is worth paying attention to that the combination of new auxiliary heat stabilizers of β-diketones and calcium and zinc soap stabilizers promotes the expansion of the use of non-toxic calcium and zinc composite stabilizers. It is used in some food packaging materials such as PVC bottles and sheets.
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