Preparation Of Hydrotalcite-like Compounds, Modified In Pvc Applications

Layered Double Hydroxides (LDHs) or hydrotalcite-like compounds (HTLcs) are a category of anionic layered materials, which contain exchangeable anions in the interlayer. LDHs will replace traditional heat stabilizers to become a new kind of PVC heat stabilizer which have the advantage of non-toxic, inexpensive, efficient due to their special layer structure and chemical composition.In this thesis, on the principle of reducing cost, simplifying preparation process and improving the properties of products, synthetic conditions of MgAl-CO3-LDHs with constant pH method were studied. MgAl-CO3-LDHs were modified by the improved wet surface modification process, related conditions of ZnAlLa-CO3-LDHs with anion-exchange method were also investigated and the composites of MgAl-CO3-LDHs/ZnAlLa-CO3-LDHs were applied in PVC.The thermal stable time for PVC (congo red test) as the main performance index of LDHs, the samples were tested and characterized by XRD, FT-IR, SEM, ICP, TG-DSC and grading analysis. In this thesis, effects of pH values and materials types on the synthesis of MgAl-CO3-LDHs were investigated; surface modification effects of MgAl-CO3-LDHs prepared with routine wet modification process and improved wet modification process were compared when sodium stearate was used as surface modifier; effects of pH values, n(La3+)/n(Al3+) values of initial solution and aging time on the synthesis of precursor ZnAlLa-NO3-LDHs were discussed; influences of anion-exchange time on the preparation of ZnAlLa-CO3-LDHs were also explored. Besides, effects of composite ratios of MgAl-CO3-LDHs and ZnAlLa-CO3-LDHs on PVC thermal stabilities were investigated.The results showed that the optimal pH value was 10.0 when MgAl-CO3-LDHs were prepared with MgCl2 and A12(SO4)3 as the raw materials; the materials types had influences on crystallinity, micro-morphology, infrared feature and thermal stabilities of PVC; the optimum dosage of sodium stearate was 6% of the LDHs weight in routine wet modification process while 7% in improved wet modification process, the later had smaller average diameter, narrower particle distribution and better thermal stabilities of PVC than the former; the optimum reaction conditions of precursor ZnAlLa-NO3-LDHs were:the reaction pH was 8.0, the molar ration of n(La3+)/n(Al3+) was 1/8 in the initial solution, aging time was 24h; the crystallinity and purity of ZnAlLa-CO3-LDHs were higher when anion-exchange time was 1～2h; the heat-stable time for PVC could reach to 49.3min when MgAl-CO3-LDHs and ZnAlLa-CO3-LDHs were composited at mass ratio of 1:0.2, and had better thermal stabilities of PVC than single LDHs, which all suggested there was "synergistic effect" in composite LDHs system.In conclusion, MgAl-CO3-LDHs were synthesized using MgCl2 and A12(SO4)3 as materials, which could reduce costs on the base of guaranteeing the properties of products; the surface modification process of LDHs was simplified and surface modification effects was improved by improved wet modification process. ZnAlLa-CO3-LDHs were synthesized with anion exchange method and thermal stabilities of LDHs for PVC were improved when MgAl-CO3-LDHs and ZnAlLa-CO3-LDHs were composited. This thesis provided important theoretical basis for production and application of LDHs as heat stabilizers.