Study on properties of PB-g-PS latex-modified cement mortars
The PB-g-PS latex was used to modify cement mortar, and the weight ratios of polybutadiene to styrene ranged from 70/30, 50/50 to 30/70. In the constant water-cement ratio of 0.5, and curing 24h at 20°C, RH90% air followed by 27d at 20°Cwater. This study examines the effects of weight ratios polybutadiene to styrene and the polymer-cement ratios on the flow, compressive and flexural strength and water absorption rate of PB-g-PS latex modified cement mortar. The experimental results show that the flow of modified mortar is increased with increasing polymer-cement ratios and decreasing weight ratios of polybutadiene to styrene, PB-g-PS latex can markedly reduce capillary water absorption rate. The minimum is 1.33Kg/m2. PB-g-PS latex can marked influences much on the mechanical properties of modified mortars. The compressive of the polymer modified mortar decreased, and the flexural strength of polymer modified mortar decreased as well. Overview on, PB-g-PS latex can be incorporated into cement mortars as cement modifier.
Process parameters and their effect on grafting reactions in core/shell latexes
The grafting of methyl methacrylate (MMA) onto polybutadiene (PB) latexes prepared by seeded emulsion polymerization at 50°C was investigated as a function of: (a) initiator concentration used in the secondary polymerization, (b) monomer-to-polymer ratio, (c) the specific surface area of the seed latex, and (d) the degree of conversion. The thin layer chromatography/flame ionization detection (TLC/FID) technique was used to determine the proportion of graft copolymer in the core/shell latex, It was found that grafting PMMA onto PB depended upon the concentration of initiator, decreasing as the concentration was increased. The amount of grafting increased with increasing specific surface area of the seed latex, while the molecular weight of the acetone-soluble graft copolymer decreased. The amount of graft copolymer was found to decrease concurrently with increasing monomer-to-polymer ratio and degree of conversion. These results suggest a hydrogen abstraction mechanism in the formation of graft PB–PMMA through a chain transfer process.
DEVELOPMENT OF STRENGTH AND FRACTURE PROPERTIES OF STYRENE-BUTADIENE COPOLYMER LATEX-MODIFIED CONCRETE
This paper reports latex-modified concrete (LMC) strength and fracture properties at ages ranging from 5 hours to 28 days. The development of strength, deformability, and fracture properties were slightly different from conventional concrete. Test results indicate a significant improvement in reducing and bridging microcracks, especially in the prepeak load region. The load deflection relationship was observed to be highly linear up to 0.93 of peak load. Fracture toughness and deformability increased significantly. Fracture energy varies from 2.3 N/m to 133.1 N/m, depending on age, and to some degree, on notch depth ratio. However, the postpeak behavior was quite similar to conventional concrete. In the range studied, notch depth appears to have less effect, compared with normal concrete. The crack mouth opening displacement control method provided consistent values that may benefit other researchers.