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Application of Calcium Acetylacetonate/zinc Composite in Thermal Stability of PVC

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Update time : 2019-10-23 14:41:22

A calcium acetylacetonate/zinc composite was synthesized under alkaline conditions using zinc nitrate hexahydrate, calcium chloride, and acetylacetone as raw materials. It used as an auxiliary heat stabilizer in polyvinyl chloride PVC. The thermal stability of PVC products was investigated by the oven heat aging and Congo red test, and the thermal stability mechanism was explored. The results showed that the synergistic effect was achieved at a calcium/zinc molar ratio of 15:1, the thermal stability time reached 70 min, and the PVC test piece completely blackened to 110 min, which was significantly better than the single component acetyl. Acetone calcium. Also, the addition of a mass fraction of 1.2% calcium acetylacetonate/zinc, thermal stability time of up to 81min, PVC test piece to 190 min wholly blackened and better than the commonly used epoxy soybean oil and dipentaerythritol auxiliary class Heat stabilizers.

 
 

Polyvinyl chloride PVC has excellent performances such as low price, corrosion resistance, high strength, and flame retardancy. It is widely used in building materials, chemicals, packaging, and other fields, and has become one of the world's five general-purpose plastics. However, the thermal stability of PVC is poor. The processing temperature is generally around 180 °C. After the temperature reaches 130 °C, the PVC products begin to degrade, releasing toxic hydrogen chloride gas. The color of PVC products is deepened, and the mechanical and mechanical properties are reduced. Therefore, PVC is. The addition of heat stabilizers to products is an essential measure. The heat stabilizers currently used mainly include lead salts, organotins, metal soaps, and auxiliary heat stabilizers. Heavy metals in lead-based heat stabilizers are highly harmful to humans and the environment, so they are slowly being replaced. The organotins with excellent performance are disadvantageous in that they are expensive, and the metal soap heat stabilizers are inexpensive and non-toxic, but the thermal stability is reduced, and it is necessary to add an auxiliary heat stabilizer.

 

The β-diketone heat stabilizer has low toxicity. It can be widely used as an auxiliary stabilizer for metal soaps to significantly improve the thermal stability and weather resistance of PVC products. At present, β-diketone calcium or β-diketone zinc materials are usually synthesized separately, and their coloration of PVC products is examined independently.
 

 

Based on the synergistic effect of calcium acetylacetonate/zinc composite on the thermal stability of PVC, under the alkaline condition, the PVC auxiliary heat stabilizer acetylacetonate calcium composite was synthesized at room temperature. A series of characterization methods characterized the product. Finally, it was added to PVC with the metal soap heat stabilizer calcium stearate to investigate its effect on the thermal stability of PVC.

 

Calcium acetylacetonate/zinc belongs to the β-diketone salt-assisted heat stabilizer, and its heat stabilizer mechanism is the same as that of β-diketone. First, the PVC product will continuously remove HCl gas during heating, and a large amount of conjugated double bonds will make the color of the PVC product deeper, while the calcium acetylacetonate/zinc mixture can effectively absorb the HCl gas removed by PVC and produce acetylacetone. The simultaneously produced acetylacetone ligand can replace the active allyl chloride atom in the PVC chain under ZnCl2 catalysis, crosslink to the PVC chain to form a stable structure, reduce the active site on the PVC chain, but ZnCl2 also accelerates PVC degradation and The root cause of the phenomenon of zinc burning, and the ZnCl2 produced by the replacement of calcium acetylacetonate/zinc reduces its concentration to an equilibrium, so the molar ratio between calcium acetylacetonate/zinc is essential.
 
 

The oven heat aging and Congo red tests showed that the synergistic effect between the two was the best when the calcium acetylacetonate/zinc molar ratio was 15:1. The heat stability time was better than that of the single component acetylacetonate. Copper calcium or zinc acetylacetonate. And when the sample with a PVC mass fraction of 1.2% calcium acetylacetonate/zinc acetylacetonate has a molar ratio of 15:1, the thermal stability time is as high as 81 min, which is significantly better than the commonly used auxiliary heat stabilizer epoxy soybean oil and double. Pentaerythritol.

 

The calcium acetylacetonate/zinc composite material significantly increases the thermal stability time by absorbing HCl and replaces the active allyl chloride on the PVC chain by acetylacetone ligand, which can effectively inhibit the initial coloration and degradation of PVC samples, and finally, utilize acetyl Acetone calcium absorbs excess ZnCl2 to reduce its concentration to equilibrium.