In the process of PVC production and processing, PVC is easy to break chain and cross-linking due to dechlorination, so that the color of the material deepens and the performance deteriorates. Various methods can be used to judge the effect of calcium stearate on the properties of PVC materials. For example, color change was studied by yellowing index and refraction meter, carbonyl formation was studied by Fourier transform infrared analyzer (FTIR), and cross-linking and degradation of materials were studied by relative molecular mass and gel content. It is found that although the temperature has no effect on the dechlorination amount, the dechlorination rate is greatly affected by the temperature.
Calcium stearate can delay the thermal chlorination of PVC and reduce the dechlorination rate, which indicates that the presence of calcium stearate has an inhibitory effect on the dechlorination of PVC. The reason why calcium stearate inhibits PVC dechlorination is that calcium stearate can absorb free radicals formed during pyrolysis and react with HCl produced during dechlorination to reduce dechlorination rate. The stabilization mechanism of the modifier is as follows: in practice, calcium stearate is rarely used as a heat stabilizer alone. Calcium stearate - zinc stearate complex has obvious synergistic effect on PVC stabilization.
The thermal stability of PVC was improved by introducing calcium stearate-zinc stearate complex. Calcium stearate-barium stearate composite system also has good heat stability effect on PVC, and the effect is better when used with organotin. The test results show that the thermal stability, workability and mechanical strength of PVC resin can be obviously changed by using rare earth metal salt of stearate, zinc stearate and calcium stearate as composite stabilizer. The research results show that calcium stearate and barium stearate mainly play a long-term thermal stabilization role on PVC, while zinc stearate mainly plays an initial thermal stabilization role. The stability of zinc stearate-barium stearate composite system is slightly better than that of zinc stearate-calcium stearate composite system.
The experiment also confirmed that although zinc stearate-barium stearate-LDH composite system had synergistic effect, the overall thermal stability was not as good as zinc stearate-calcium stearate-LDH composite system, m(zinc stearate) /m(Barium stearate or calcium stearate) /m(LDH) was 1.1:2.0: The stability effect reaches a good value when 0.8. Calcium stearate is used as a heat stabilizer and lubricant for polyvinyl chloride. Calcium stearate is used as β-crystalline nucleator and halogen absorbent of polypropylene. Calcium stearate is not only a stabilizer and sulfurization speed inhibitor of halogenated butyl rubber products, but also a dispersant and lubricant in the production process of halogenated butyl rubber. Calcium stearate is a metallic soap surfactant. Because the preparation method is simple and cheap, calcium stearate is widely used in paint leveling, paper coating additives, etc. In addition, calcium stearate is also used in pencil lead lubrication and building waterproofing. In the field of polymer material processing, calcium stearate is a common release agent. In fact, in addition to being used as a release agent, calcium stearate has a very wide range of uses in the field of polymer materials because of its environmental protection and weak alkaline properties.
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