Can PVC calcium zinc stabilizer(PVC aids) replace the lead stabilizer?

Problems that must be solved when PVC calcium-zinc stabilizer replaces lead stabilizer:

 

Liquid calcium and zinc stabilizer is a compound of calcium and zinc organic salt, phosphite, polyol, antioxidant and solvent. Liquid calcium zinc stabilizer has good compatibility with resin and plasticizer, good transparency, not easy to precipitate, less dosage, and convenient use. The main disadvantages are poor lubricity, lower softening point of products, and deterioration in long-term storage.

 

The solid composite powder calcium-zinc  stabilizer is mainly stearic acid soap reaction, followed by lauric acid soap and oleic acid soap. The product is characterized by good lubricity, does not reduce the softening point of PVC hard products, and is suitable for processing hard PVC pipes and profiles.

 

The products processed by microemulsification technology overcome the above shortcomings. People focus on improving from two aspects: in order to improve the initial coloring, a sufficient amount of zinc soap is used, and a chelating agent is used to make zinc chloride harmless. As a high-zinc compound: reduce the compounding amount of zinc soap to suppress zinc burning, and use additives to change the initial coloration. This approach becomes a low-zinc compound. , Not only widely used in soft products, its thermal stability effect and transparency have been recognized, but also successfully applied to the processing of hard products. In order to make the calcium/zinc system maintain a small initial coloring, it can also inhibit zinc burning.

 

Generally, lead salt is only attached to the surface of PVC particles. Its effect is equivalent to hindering the fusion between PVC particles, which will significantly delay plasticization, reduce the friction between PVC particles, reduce the shearing effect in PVC, and the processing equipment bears lower load. The more lead salt is used, the finer the lead salt particles, the more obvious the secondary effect.

 

Traditional environmentally friendly products such as calcium and zinc stabilizers, in the plasticizing process, due to the greater electronegativity, the polar groups have a certain affinity with the acute nodes of the PVC resin, forming a bond with a strong bond energy, thereby weakening or The attraction of the ionic bonds of each layer of PVC is eliminated, and the intertwined segments of PVC are easy to diffuse, and the boundary between molecular groups is easy to be small, which promotes the plasticization of PVC resin. This caused the resin to be partially plasticized in the feeding section, the melt pressure increased rapidly, the melt viscosity decreased, the temperature increased, and the plasticizing temperature decreased. The resin is also over-plasticized.

 

Also, because traditional PVC processing equipment is used for processing using lead salt stabilizers, even if a sufficient amount of lubricant is added, it cannot prevent the resin from further plasticizing in a sufficient time, and it destroys the original lubrication balance. In the later stage of use, the PVC melt consumes a large amount of heat stabilizer in the homogenization section, but cannot reach the ideal viscosity and elasticity to meet the needs of rigid PVC production. This is a problem that calcium and zinc stabilizers must solve in the replacement of lead salts.


Post time: Apr-16-2021