Preparation Of Calcium Lanthanum And Zinc Lanthanum Hydrotalcites And The Effects On The Thermal Stability Of PVC

This thesis firstly studies the synthesis of rare earth hydrotalcites and their effects on thermal stability.Using lanthanum nitrate,calcium nitrate,zinc nitrate,aluminum nitrate,sodium bicarbonate and sodium hydroxide as raw materials,calcium-lanthanum hydrotalcite,zinc-lanthanum hydrotalcite and zinc-aluminum-lanthanum hydrotalcites（rare earth hydrotalcites）were prepared by hydrothermal method.X-ray diffraction,infrared Spectroscopy,thermal analysis and scanning electron microscope were used to characterize the products.The effects of different cation ratios,hydrothermal time and hydrothermal temperatures on the synthesis of rare earth hydrotalcites and their thermal stability were studied.The experimental results show that the best preparation conditions for calcium lanthanum and zinc lanthanum（zinc aluminum lanthanum）hydrotalcites are:n(M²⁺):n(M³⁺)=3:1,hydrothermal temperature of 170℃,hydrothermal time of 8h.Then the effects of calcium lanthanum and zinc lanthanum（zinc aluminum lanthanum）hydrotalcites on the thermal stability and mechanical properties of PVC were studied.The rare earth hydrotalcites were compounded with zinc stearate,calcium stearate,pentaerythritol andβ-diketone in binary,ternary and quaternary compounds,respectively.The static thermal stability properties of rare earth hydrotalcites’single and compound thermal stabilizers were studied through Congo red experiment and high temperature aging experiment.The dynamic thermal stability properties of rare earth hydrotalcites on PVC were studied through conductivity experiment and acid absorption experiment.The degradation activation energy was calculated.The effects of mechanical properties were studied by torque rheological experiments and tensile experiments.In the static thermal stability experiment and electrical conductivity test,the order of single thermal stability is:calcium lanthanum hydrotalcite>zinc lanthanum hydrotalcite>zinc aluminum lanthanum hydrotalcite,and the best single thermal stabilizer is calcium lanthanum hydrotalcite（87min）.The order of preferred compound thermal stability is:zinc-lanthanum compound sample>zinc-aluminum-lanthanum compound sample>calcium-lanthanum compound sample,and the best compound sample is that zinc-lanthanum hydrotalcite:β-diketone:pentaerythritol=2:1:2（102min）.Rare earth hydrotalcite can improve the degradation activation energy of PVC and achieve the effect of improving thermal stability.Among them,calcium lanthanum hydrotalcite can increase the degradation activation energy of PVC to the utmost extent.In the mechanical property test,the balance torque of the zinc lanthanum（zinc aluminum lanthanum）hydrotalcites’sample dropped the balance torque to below 15N·m,which increased the degradation time and thus improved the plasticization performance.Rare earth hydrotalcite improves the tensile strength and elongation at break of PVC sheets.Finally,the thermal stabilization mechanism of rare earth hydrotalcite stabilizers was studied:rare earth hydrotalcite thermal stabilizers hindered the breaking of C-Cl and C-H bonds in PVC,inhibited the formation of HCl and C=C bonds,and reduced further catalysis of PVC degradation by HCl.