Effect of a Cationic Polymer on the Rheology of Cement Pastes Containing Na-Bentonite

This paper studies how a cationic polymer affects the rheological properties of cement pastes containing Na-bentonite in the presence of a polycarboxylate superplasticizer (PCE), and the fluidity was also investigated. The Herschel–Bulkley model was applied to fit the rheological data of cement pastes at the beginning and after 1 and 3 h. The results show that the cement pastes exhibit a significant increase in fluidity and turn to be a shear-thickening fluid with the addition of the cationic polymer KN, as indicated by the pseudoplastic index n. The yield stress and plastic viscosity of cement pastes containing Na-bentonite obviously decrease with the addition of KN. Statistical analysis was performed to evaluate the impact of KN and PCE on the rheological properties. PCE exhibits a significant influence on both yield stress and plastic viscosity, while KN also exerts an obvious effect on the yield stress for cement pastes containing minor amounts of PCE. The equations for yield stress and plastic viscosity are obtained, which will allow us to predict the yield stress and plastic viscosity of cement pastes containing various contents of PCE and KN

Study on the Impact of Na/Ca Bentonites on the Dispersion Performance of Conventional and Modified Phosphate Polycarboxylate Superplasticizers in Cement Mortar

Through molecular structure design, modified polycarboxylate superplasticizers (PCEs) were synthesized via copolymerization using isoprenyl oxy poly­(ethylene glycol) ether (TPEG), acrylic acid, and hydroxyethyl methacrylate phosphate. TPEG-PCEs were selected as potential dispersants for Na/Ca-bentonite containing cement mortar. Other two kinds of commercial PCE that were obtained based on methallyl ether (HPEG) and ethylene-glycol monovinyl polyethylene glycol (EPEG) as macromonomers were also applied in the mortar. The effects of the type of bentonite and its dosage, as well as the monomer structure of PCEs and the type of cement, on the dispersion properties of the bentonite-containing mortar were studied. According to the findings, the initial fluidity of the mortar was reduced by about 20 mm when two kinds of bentonite were used. Applying 3% Ca-bentonite resulted in 40% flow loss in the mortar after 1 h. The fluidity of the mortar with Na-bentonite exhibited lower dispersion ability than that with Ca-bentonite when HPEG-PCE and EPEG-PCE were chosen as dispersants. The TPEG-PCE exhibited superior dispersing performance over HPEG-PCE and EPEG-PCE and exerted a retarding effect on cement, being also weakly sensitive to clay content. Thus, TPEG-PCEs with phosphate groups present a viable alternative to conventional PCEs

Effect of comb polymer dispersants with different molecular structures on the performance of LiFePO₄ suspensions

A series of comb polymers poly(2-(dimethylamino)ethyl methacrylate (DMAEMA)-co-methacrylic acid (MAA)-co-methoxy polyethylene glycol methacrylate (MPEGMA)) (poly(DMAEMA-MAA-MPEGMA, DMM) were synthesized and used as N-methyl-2-pyrolidinone (NMP)-based lithium iron phosphate (LFP) suspension dispersants. The effects of the grafting density of the carboxyl group as the anchoring group and the chain length of the side chain of PEG, which plays the role of spatial site resistance, on the rheological properties and suspension stability of the slurry were systematically investigated. By investigating the adsorption amount and thickness of DMM on the LFP surface, combined with calculations based on the scalar law and Flory theory, the molecular structure of the comb polymer dispersant was revealed to influence the adsorption and dispersion performance. The dispersion of LiFePO4 was due to the synergistic effects of adsorption and steric hindrance effect, which resulted that dispersants with medium carboxyl density and PEG side chain length can improve the dispersion performance and stability.</p