Simulation And Synthesis Of Comb Polymer Superplasticizers

Simulation and Synthesis of Comb Polymer SuperplasticizerComb polymer superplasticizer can improve the concrete's workability obviously and reduce the dosage of water, which has the most widely used to concrete admixtures. Now, the naphthalene, amino acid and melamine etc. superplasticizers using widely in domestic have had obviously shortage. Comparing with ordinary water-reducing agent, the comb polymer superplasticizer could improve the dispersion of cement significantly, and which had a high water-reducing rate, low content, high slump loss resistance and a significant enhancement. More and more researchers paid attention to the comb polymer superplasticize, which had became a research focus in the field of concrete admixtures.The interaction mechanism between comb polymer superplasticizer and cement particles obtaining from experimental test was lack of visibility, and brought some trouble in the research of theory. Monte Carlo simulation could provide opportunities of direct observation, and describe the process and reflect the natural evolution of rules and attributes, Therefore, this method had aroused people's concern in recent years. The Monte Carlo simulation method was randomized algorithm and it does not use any approximate treatment. The Monte Carlo simulation method was applied to the study of polymer adsorption theory, which could not only understand the kind of comb polymer adsorption on solid law, but would also provide practical molecular design of its theoretical guidance. This approach was different from the traditional theoretical and experimental research, both as a theoretical guidance for experimental validation experiments can. It had served as a bridge between theory and experiment and became a new means of scientific research today.In the paper, the application of domestic and international progress of superplasticizer was introduced, and comb polymer superplasticizer trends were explored. The adsorption characteristics of comb-type polymer superplasticizer were studied via computer simulation. Comb polymer superplasticizer with a hydroxyl, carboxyl, sulfonate, poly vinyl groups was synthesized through the molecular design.The conformation of PAA/PEO comb polymer adsorbed on the solid-liquid interface was investigated using three-dimensional cubic lattice model of Monte Carlo. The conformation images in the liquid and on the solid surface of various architecture polymer molecules were obtained. The microstructure information of various architecture polymer molecules, including the mean square radius of gyration, the thickness of adsorbed layer and the number of various segments adsorbed on solid surface were collected. The results showed that when polymerization degree Np<6. two strong hydrophilic group (—COO- and—OH) of comb polymer will form bridge structure conformation on solid surface, the bridge structure only play steric repulsive effect; when polymerization degree Np>6, the comb polymer molecular will form reverse saddle-like conformation on solid surface, and the carboxylate radical anion (—COO-) with electric charge placed in the rind of adsorption layer will form a negative electric charge layer. The adsorption conformation of reverse saddle-like have the peculiarity of steric repulsive effect as first and electrostatic repulsive effect as second.The diffusion coefficients in the liquid gradually reduced and the relative viscosity gradually rose with the polymer grafting number (Np) increasing. Whether in the liquid or on the solid surface, the mean square radius of gyration of PAA/PEO comb polymer all will increase with length of PEO side chain Lc or polymerization degree Np increasing. When Np≥6, the most carboxyl anion groups of comb polymer were placed outside of the adsorbed layer and the thickness of adsorbed layer approximated the length of the PEO side chains, the conformation of a comb polymer molecule on solid surface mainly played a steric barrier effect and secondly electrostatic repulsive; Meanwhile the polymer molecule should have suitable density of steric scattering and could keep self balance of adsorbing-desorbing.The density of polymer adsorbed on the solid surface will sharply reduces with Lc increasing. When polymerization degree Np>some specific value, the dosages of superplasticizers will reduce with Lc increasing. For reducing the dosages of superplasticizers, we usually need to keep established polymerization degree Np of comb polymer molecule and increase the length of PEO side chain Lc. But only Lc has an appropriate range, the polymer can take good effect of steric repulsive. when Np>6, the thickness of adsorption layerδmax approximately equals to the length of PEO side chain. The comb polymer has bigger thickness of adsorption layerδmax and better steric repulsive effect fsteric than uncomplicated organic molecule.Comb polymer superplasticizer was synthesized by using macromonomer OXAA, maleic anhydride, acrylic acid and sodium methacrylate as copolymerization monomer. Initiator used in the synthesis of an investment as the mainstay, supplemented by additional means continuing. The reaction temperature was 85℃, reaction time was 7h, the best ratio was nAPEG:nMAH:nAA:nSMAAS=1:2:1.5:1.5. and initiator dosage was 2.5% of total mass of monomers. As dosage of the superplasticizer was 0.2% of ash, ratio of water to ash was 0.29, the cement paste fluidities were tested, it's average fluidity was 281mm.The influences of different monomer dosage and the length of side chain to the paste fluidity were been investigated. With the dosage of SMAS increasing, the fluidity of cement paste had changed due to the electrostatic effect. The superplasticizer having longer side chain had better paste fluidity than the shorter chain. Lower the temperature, the viscosity of superplasticizer increases, is not conducive to molecular diffusion, so the summer fluidity of cement paste is better than winter.This simulation method of superplasticizer would guide theoretical research, the synthesizedf comb polymer superplasticizer had good flow properties and a good pplication prospects.