Hydrotalcite Synthesis And Modification

Hydroxides (LDHs) is a new type of nano-particles, and the specific composition determines its absorption of hydrogen chloride gas. Generally, LDHs was mixed with other auxiliary heat stabilizers (such as metal soap, etc.) to form a composite heat stabilizer for PVC resin.In this study, MgAl-CO3-LDHs and MgAlCe-CO3-LDHs were prepared by the constant pH coprecipitation method. The synthesized factors (reaction temperature, pH value, the Ce/Al molar ratio of MgAlCe-C03-LDHs, aging time, aging temperature, etc) for the nucleation and growth of hydrotalcite crystal, and the formation of crystalline were discussed. Sodium stearate was used to modified MgAl-CO3-LDHs and MgAlCe-CO3-LDHs in order to enhance its compatibility in PVC. The thermal stability of PVC composites between MgAl-CO3-LDHs and MgAlCe-CO3-LDHs after modification was compared by static thermal aging test and Congo red test. MgAlCe-CO3-LDHs together with metal soaps (both CaSt2 and ZnSt2) were mixed with PVC, and the optimum formula was obtained by the single factor method to get good thermal stability of PVC. Finally, the thermal stabilizing mechanism of thermal stabilizers was also discussed detailedly.The study focused on the following three specific works:1) MgAl-CO3-LDHs and MgAlCe-CO3-LDHs were prepared by the constant pH coprecipitation method, and the various prepared conditions were studied. The prepared MgAlCe-CO3-LDHs and MgAl-CO3-LDHs were characterized by XRD, FT-IR, SEM and TG-DTA. The results showed that MgAl-CO3-LDHs were synthesized when n(Mg2+)/n(Al3+)=2:1, PH≥11, and the solution was stirred for 4 h at 85℃, and then the resulting slurry was aged for 8 h at 110℃. Based on the preparation of MgAl-CO3-LDHs, the MgAlCe-CO3-LDHs were prepared when n(M2+)/n(M3+)= 2:1 and 0.025≤(n(Ce3+)/n(Al3+))≤0.05, which are high crystallization degrees and uniform structures.2) Sodium stearate was used to modify LDHs, and the modified conditions on the modification effect were explored. The experimental results showed that the degree of activation hydrotalcite was the greatest value (or the modification effect was best) when the dosage of modifier was 6% of the weight of hydrotalcite, the modified temperature was 80℃, and the modified time was 120 min. LDHs and LDHs after modification were characterized by XRD and FT-IR. The results indicated that the adsorption between sodium stearate and LDHs can be occurred, but the layered structure of LDHs was not broken and the layered spacing was not changed, which proved that the sodium stearate only modified the surface of hydrotalcite, but not inserted into the LDHs layer.3) The thermal stability of the singe LDHs and the composite LDHs after modification for PVC was compared by static thermal aging test and Congo red test. The Comparison revealed that the thermal stability of the singe MgAlCe-CO3-LDHs was obviously better than the singe MgAl-CO3-LDHs. The thermal stable time was 158 min when the Ce/Al molar ratio was 0.075, the amount of MgAlCe-CO3-LDHs was 3ph. Subsequently, MgAlCe-CO3-LDHs, CaSt2 and ZnSt2 were mixed with PVC. The results showed that the early and late heat stabilization effect of PVC samples have been improved greatly and the thermal stable time was over 190 min when PVC:DOP:CaSt2:ZnSt2:MgAlCe-CO3-LDHs=100:50:0.3: 1.0:3. Finally, the thermal stabilizing mechanism of the composite heat stabilizers was also discussed.