| PVC resin's processing temperature is close to its thermal decomposition temperature, which is very easy to cause "zipper dehydrochlorination " during heat melt processing. In order to process successfully, we should add in thermal stabilizer to increase the thermal decomposition temperature of PVC. As a result of the increase in the worldwide environmental awareness and the limits on the use of heavy metals, More and more attention of PVC thermal stabilizer is being paid on nontoxic, environment-friendly, high efficiency and multi-functional.In this paper, we synthesized hydrotalcite by different molar ratios of Mg / Al and mixed it with calcium soap and zinc soap which have a high metal content to prepare LDHs/Ca/Zn composited thermal stabilizer which is high-effective and nontoxic. Mg-Al hydrotalcite is a nontoxic inorganic material with layered structure. Its hydroxy group of the basic layer and CO32- of the inter layer could react with free HCl which was released by heated PVC, thereby the thermal stability of PVC was improved. The thermal stability mechanism of hydrotalcite on PVC and that of LDHs/Ca/Zn composited stabilizer on PVC were rarely reported at home and abroad.The thermal stability mechanism of hydrotalcite on PVC was studied with industrial hydritalcite. The results of FT-IR and XRD analysis showed that the thermal stability of LDHs on PVC roled in two stages: on the first stage, hydroxy group of the basic layer reacted with HCl which was released by heated PVC, and the size of crystal grains decreased gradually; on the second stage, Cl- went into the inter-layer, made ion exchange reaction with CO32-, then generated MgAl-Cl-LDHs until layer anion exchange reached a state of equilibrium.In this paper, hydrotalcite was prepared at a fixed crystallization temperature and crystallization time with different metal molar ratios in different dispersant systems. The results of XRD analysis indicated that when the dosage of dispersant CMC was 0.1% and the metal mole ratio was 2/1, the synthesized hydrotalcite had an excellent accumulation order, a good shape of crystal and a high regularity of inter-layer. The results of its aid thermal stabilization on Ca/Zn stabilizer indicated that the self-made hydrotalcite had a very good crystal structure, which had an excellent aid thermal stabilization on Ca/Zn stabilizer and could improve the long-stabilization obviously.The cross-mixing of zinc stearate and calcium stearate was used to select Ca/Zn soap. The results suggested that the system of Zinc Benzoate/Calcium Isooctoate with high metal content had the most excellent thermal stabilization.The compound of hydrotalcite/Ca/Zn soap was made on the basic formulation. The results of static thermal aging method, dehydrochlorination method and FT-IR analysis showed that the thermal stabilization of single Ca/Zn soap was very poor. And the addition of hydrotalcite improved the long-stabilization of PVC obviously.The thermal stabilization of self-made Ca/Zn stabilizer, imported Ca/Zn composited stabilizer and composited lead stabilizer for rigid PVC was investigated by oven aging method, congo red method and dehydrochlorination method. The results showed that the primary stability of self-made stabilizer was parallel to the imported stabilizer, while, the self-made Ca/Zn stabilizer had a better long-time stability. The degradation activation energy of self-made Ca/Zn stabilizer was between the imported Ca/Zn stabilizer and self-made composited lead stabilizer. The difference of degradation activation energy was about 1-2KJ/mol, which indicated that the thermal stability of self-made stabilizer was closed to that of composited lead stabilizer, so that the needs of rigid PVC processing could be satisfied.
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