Synthesis Of Calcium Zincate/Magnesium Zincate/Hydrocalumite And Effects On The Thermal Stability Of PVC

Calcium zincate, magnesium zincate and hydrocalumite are Layered Double Hydroxide compounds (LDHs). As hydrotalcite-like compounds, they are expected to be excellent heat stabilizers to polyvinyl chloride (PVC). With advantages of simple preparation, low cost and environmental friendship, they have the potential to replace traditional heat stabilizers.Calcium zincate, magnesium zincate and hydrocalumite were synthesized by different methods and the relationship between preparation technology and product performance were explored, and then sodium stearate was used to modified calcium zincate and magnesium zincatein order to enhance their compatibility in PVC. The thermal stability of single heat stabilizers, products after modification and composites after blending with synergistic stabilizers were compared by static thermal aging test and Congo red test. Finally, the stabilizing mechanism of thermal stabilizers was also discussed detailedly.The study focused on the following three specific works:(1) Calcium zincate was synthesized by chemical reaction and hydrothermal method. The sample synthesized by chemical reaction was parallelogram-shape, regular and larger particle size crystal, while the sample synthesized by hydrothermal method was irregular crystal with smaller particle size and had less crystal water. The experimental results showed that the modification effect was best when the modified time was120min, the modified temperature was80℃, and the weight of hydrotalcite was6%. The results indicated that the layered structure was not broken which proved that the sodium stearate only modified the surface of hydrotalcite. When used as a single heat stabilizer, the primary stability of calcium zincate was good but "zinc burning" effect came out later. Besides, the thermal stable time was prolonged after modification. The results also showed that the stabilization effect of composite PVC sample was improved greatly when PVC:DOP:CaZn:St:CaSt: β-diketone=100:50:0.3:2:0.5:0.4. (2) The XRD and IR results proved that magnesium zincate were prepared by chemical reaction and hydrothermal method successfully. The experimental results showed that the modification effect was best when the modified time was150min, the modified temperature was60℃, and the weight of hydrotalcite was8%. The thermal stable test results showed that the stabilization effect of composite PVC sample was improved greatly when PVC:DOP:MgZn:St:CaSt:β-diketone=100:50:0.3:2:0.5:0.4.(3) The products prepared by five different system or method contained hydrocalumite crystal while the form, crystal water and the impurity content were different. By comparison, the XRD results showed that sample synthesized with sodium metaaluminate had the weakest impurity peak and was most close to the standard one. When used as a single heat stabilizer, the long term stability was excellent. The results also showed that the stabilization effect of composite PVC sample was improved greatly when PVC:DOP:CaAl:St:CaSt:β-diketone=100:50:4:4:0.5.Finally,the thermal stabilizing mechanism of the composite heat stabilizers was also discussed.