In the process of PVC processing, the unstable chlorine atoms on the macromolecular chain are easy to remove HCL by heat, forming a polyene structure with conjugated double bonds, resulting in the following changes in the color of PVC: colorless (or white) -- light yellow -- yellow orange -- red orange -- red brown -- brown, so that the physical and chemical properties of PVC become worse. The mechanism of action of calcium and zinc stabilizer is: Zn soap as the main stabilizer, at the same time has the function of replacing active chlorine and absorbing HCL, and then the generated metal chloride is Lewis acid, which can remove HCL reaction.
PVC will occur in a very short period of time malignant degradation, resulting in "zinc burning" phenomenon. Therefore, zinc soaps and co-effect stabilizers mainly include stearic acid soaps. Because of calcium stearate, zinc soap is often combined with calcium stearate. Calcium soap only shows the effect of capturing HCL, can not replace the active chlorine, the generated metal chloride has no catalytic effect on the HCL removal reaction, but can effectively replace the chloride generated by zinc soap to regenerate it.
Generally speaking, the increase of calcium soap content can improve the long-term stability of the product, but inhibit the poor initial coloring performance: on the contrary, the high content of zinc soap, the initial coloring of the product can be changed, because "zinc burning" will lead to a decline in long-term stability. Therefore, a better stabilization effect can be achieved by choosing a reasonable ratio of calcium and zinc soap in calcium and zinc composite stabilizer.