Dispersion And Encapsulation Of Nanometer Calcium Carbonate With Polymer

Nanometer inorganic particles have been widely used in the modification of polymer materials. However, it is difficult to achieve a homogeneous dispersion of nano-particles in the polymer matrix due to the great surface energy and the great polarity difference between the inorganic particles and the polymer. In recent decades, extensive research efforts have been directed towards the encapsulation of nanometer particle with polymer, to improve the dispersion of nano-particles in polymer matrix and the interfacial adhesion between the inorganic particles and polymer. In this thesis, the aggregation of nano-CaCO₃ particles was analyzed using the thermodynamics approach based on the fundamental characterization of the chemical and particle features of nano-CaCO₃, and a model simulating the aggregation process was proposed. The dispersion, disaggregation, surface modification of nano-CaCO₃, the encapsulation of nano-CaCO₃ by poly(methyl methacrylate) (PMMA), and the dispersion of encapsulated nano-CaCO₃ in poly(vinyl chloride) matrix were investigated.Firstly, the characterization on nano-CaCO₃ was carried out. It showed that the primary particles of original nano-CaCO₃ exhibited calcite cube crystal, with average size of about 43nm. Nano-CaCO₃ exhibited many hydroxyl groups, which would favor to further surface modification. Nano-CaCO₃ was easy to aggregate because of the high surface energy, the aggregate of primary particles was in the micron size and many pores existed inside the aggregates. Simulating of nanometer particle aggregation process was proposed, the result shows that the aggregation rate slow down sharply with the increase of the cluster size, and the aggregation and dispersion rate was in balance in the end.Based on the aggregation model of nano-CaCO₃, the dispersion stability and disaggregation of nano-CaCO₃ in aqueous and organic phase were studied. It found that nano-CaCO₃ aggregates could stably existed in water phase to form a colloid dispersion when their size was smaller than 200nm. The dispersion stabilityincreased as the pH value of aqueous phase increased. When nano-CaCO3 was dispersed in the aqueous solution of poly(sodium acid) (PSA), the absorption of PSA on CaCO3 was decreased with the increase of pH, and the dispersion stability was increased. It also found that ultrasonic action had better effect on the disaggregation of nano-CaCC>3 when the pH value was greater. The aggregates of nano-CaCC>3 could be separated into smaller ones in the organic medium which was easier to soak with nano-CaCCb, and the volume ratio of particle in size of 0-1 um was greater.Nano-CaCC>3 particles were surface modified with stearic acid, titanate and y-methacryloxypropyltrimethoxy silane (MPTMS) respectively. PMMA/ nano-CaCO3 composite particles were prepared by soapless emulsion of MMA in the presence of the surface modified nano-CaCC^. The greater grafting degree and grafting efficiency of PMMA were achieved by using of MPTMS modified nano-CaCC>3 due to the introduction of vinyl groups onto nano-CaCCb particles surface. When CaCC>3 was modified with more MPTMS, the molecular weight of PMMA grafted was decreased and the molecular weight distribution became wider. The aggregates of nano-CaCO3 were separated into smaller ones as the polymerization proceeded.Nano-CaCC^ particles chelated with 4,4'-azobis(4-cyanopentanoic acid) (ACPA) were used to initiate the in-situ dispersion polymerization of MMA in ethanol. The kinetics of polymerization and the grafting process of PMMA on nano-CaCO3 were investigated. Differential scanning calorimetry results showed that the decomposition activation energy and half-life of decay of ACPA decreased when ACPA was chelated onto the particles surface. The apparent activation energy for the polymerization initiated by the ACPA chelated on CaCO3 particles was 130kJ/mol. It also showed that the grafting degree pf PMMA increased and the grafting efficiency decreased as the conversion of MMA monomer increased. The diameter of aggregates of nano-CaCO] decreased gradually as the polymerization proceeded.Nano-CaCC>3 was modified with 3-aminopropyltriethoxysilane, followed by the reaction with ACPA. It found that the anchoring efficiency of ACPA was about 50%, and the decomposition activation energy and half-life of decay of ACPA were decreased when ACPA molecules were anchored onto the particles surface. In-situ dispersion polymerization of MMA in ethanol was initiated by the ACPA anchored nano-CaCC>3. The grafting degree of PMMA increased linearly with the increase of the conversion,and the maximum grafting degree of PMMA was about 43%. When the conversion of MMA monomer increased, the molecular weight became great and the molecular weight distribution became wider. The molecular weight of PMMA grafted could be adjusted by adding of dodecyl mercaptane chain transfer agent.The surface properties were investigated by contact angle methods. It found that the particle surface energy, van de waals force and liquid bridge force between particles reduced when PMMA was grafted onto nano-CaCC>3 particles. The dispersion stability of nano-CaCO3 in THF and MMA was improved greatly as PMMA grafted.PMMA encapsulated nano-CaCC<3 composite particles were melt-mixed with PVC resin. It showed that the dispersion of nano-CaCC>3 in PVC matrix was improved greatly after the grafting of PMMA. The adhesion capability between PMMA/nano-CaCO3 composite particles and PVC was also improved. The dispersed size of PMMA/nano-CaCO3 composite particles was the smallest when they were prepared by in-situ emulsion polymerization. The mechanical properties of the composites were raised efficiently than those filled with unmodified nanometer-CaCO3, the impact strength of the composite increased about 100% comparing to the pure PVC.The innovative points of this thesis included: (1) A model was proposed to simulate the aggregation process of nano-particle aggregation process by thermodynamic methods, the relationship between aggregation rate and aggregated particle number was derived.(2) ACPA initiator was chelated directly onto the nan-CaCO3 surface by the action of ACPA with Ca+, or nano-CaCO3 was first modified with 3-aminopropyltriethoxysilane, followed by the reaction with ACPA. (3) The kinetics of in-situ MMA polymerization initiated by chelated or anchored ACPA on nano-CaCO3 and the grafting behavior of PMMA was studied, PMMA/nano-CaCCb composite particles with well encapsulation and the greater grafting degree of PMMA were prepared based on the fundamental research.