The Synthesis, Characterization Of Rare Earth Carboxylate Stabilizers And Application In PVC Materials

On the basis of the literature review, the general situation of PVC industry at homeand abroad, the mechanism of thermal degradation of PVC and the function of thermalstabilizers were summarized and analyzed. At the same time a review was madesystematically in the field of thermal stabilizers for PVC. Rare earth carboxylates asmultifunctional stabilizers has a series of virtues such as green, non-toxicity, low price,good thermal stability for PVC and coupling effect on the interfaces between mineralfiller and polymer. Our country is rich in rare earth element resource, so developing rareearth stabilizers has broad prospects in our country. The work in the thesis include:(1) Rare earth stearates synthesis and characterization. Rare earth stearates areknown to be one of commonly used thermal stabilizers. Synthesis of rare earth sterarate isalways using the traditional double decomposition technique with water as solvent, thereare many defects in this technique. To deal with the afore mentioned problems, the methodof synthesis was improved in this paper. We synthesized rare earth sterarate using ethanolabsolute as solvent and the synthesis has high reaction rate and high yield. Then productsstructures were identified by FTIR and XRD.(2) Rare earth sterarate application. Effects of rare earth sterarate available for PVCwere tested by the ways of Congo Red Method, Heating Method and TG. Testing resultsshowed that lanthanum sterarate have better thermal stability for PVC than ceriumsterarate. Using Brabender Plasticorder, effects of rare earth stearate on rheologicalproperties of rigid PVC were discussed and analyzed. The results show that rare earthstearate can improve plasticization of rigid PVC, especially lanthanum sterarate for PVChas better processing properties than cerium sterarate for PVC. From the study, we foundthat lanthanum sterarate for PVC has better thermal stabilityand processing propertiesthan cerium sterarate for PVC,so we choose lanthanum stearate and study effects oflanthanum sterarate on properties of rigid PVC.(a)PVC/CaCO₃ blends.The surface ofCaCO₃ powder was modified with lanthanum stearare, the polarity and surface energy ofmodified CaCO₃ powder were decreased.So this modified CaCO₃ was not easy toaccumulate. The coating material filled with modified CaCO₃ has better properties inhardness, flexibility and processing than that filled with unmodified CaCO₃. The morphology of the fracture surfaces of the blends was observed by SEM. It was foundthat the dispersion and interfacial adhesion of CaCO₃ particles modified by lanthanumstearare were improved in PVC matrix. (b) PVC/CPE/CaCO₃ blends. The effect of CPEon microstructure, heat resistant, mechanical and rheological properties and interfacialadhesion of PVC composites filled with CaCO₃ particles was investigated inPVC/CPE/CaCO₃ blends with lanthanum stearare and PVC/CPE/CaCO₃ blends with leadsalt composite stabilizer.PVC/CPE/CaCO₃ blends with lanthanum stearare has betterproperties in hardness, flexibility and processing than PVC/CPE/CaCO₃ blends with leadsalt composite stabilizer.(3) Rare Earth dicarboxylates synthesis and characterization. Rare Earthdicarboxylates were prepared by adding dicarboxylic acid and liquid sodium hydroxide toliquid rare earth nitrates simultaneously. Then their yields were determined bycomplexometric titration of rare earth ions and their structures were identified by FTIRand XRD.(4) Rare Earth dicarboxylates application. Effects of this new kind of heat stabilizersavailable for PVC were tested by the ways of Congo Red Method, Heating Method andTG, which were compared with other heat stabilizers, such as rare earth stearates,calcium dimeric carboxylates. Testing results showed that those new heat stabilizers forPVC were of the best performance, especially alkali lanthanum dimeric carboxylates (â…¡),which can make PVC thermal stability last for 74 minutes and without color changing in90 minutes at 170℃. The heat stability of PVC with lanthanum salts is better than thatwith cerium salts, and we also found that rare earth dimeric carboxylates have betterthermal stability for PVC than rare earth adipates and alkali dimeric carboxylates havebetter thermal stability for PVC than dimeric carboxylates. PVC/CaCO₃ blends with rareearth dicarboxylates has better properties in flexibility and processing than PVC/CaCO₃blends with lead salt composite stabilizer.