Effects of cyclodextrin-modified polycarboxylate superplasticizers on the dispersion and hydration properties of cement paste

A new series of poly (AA-co-beta-CD-A-co-TPEG) (PACDs) copolymers were prepared by the copolymerization of a novel monovinyl beta-cyclodextrin monomer (beta-CD-A), acrylic acid and isoprenyl oxy polyethylene glycol (TPEG-2400), which could be used as superplasticizers and shown excellent dispersion ability. Therefore, this work mainly investigated the adsorption behavior, dispersing properties as well as hydration behavior of cement pastes. Optical microscopy was employed to describe dispersing performance. X-ray diffraction (XRD) and TGA/DTG were utilized to account for the cement hydration process. We found that the PACDs with beta-CD-A exhibited outstanding dispersion ability. In addition, the performances of the PACDs were monitored by evaluating the setting time and fluidity of the cement paste. The results clearly shown that the setting time was longer and slump loss was smaller than that of PACD(0) that without beta-CD-A. Therefore, PACDs with the proper content of beta-CD pendants had excellent performances due to the steric hindrance of the CD moieties

Reactive block copolymers for the toughening of epoxies: Effect of nanostructured morphology and reactivity

Block copolymers (BCPs) have stimulated widespread research interest due to their applications as facile templates in the fabrication of optimized thermosets with micro- or nanostructured morphologies. In the present work, a novel block copolymer was obtained from a commercial poly(styrene-block-butadiene-block-styrene) (SBS) triblock copolymer precursor by a two-step process including reaction with hydrogen peroxide in a water/dichloroethane biphasic system to achieve an epoxidized derivative with a 46mol% degree of epoxidation (thus denoted as eSBS46), which was then followed by reaction with 1-(2-aminoethyl)piperazine (AEP, thus yielding eSBS46-AEP) as a reactive functional group that was incorporated to prepare nanostructured epoxy thermosetting blends. As a result of the oxirane ring-opening achieved (to a conversion degree of 10mol%) by reaction with AEP, the nanostructured morphology was converted from spherical micelles in the case of eSBS46 to branched wormlike micelles for eSBS46-AEP. At 5wt% loading of this BCP material, the fracture toughness was improved by 51% over the neat epoxy. These findings were compared with data obtained from the same epoxy thermoset formulation containing the eSBS46. Various measurements including transmission electron microscopy (TEM), scanning electron microscopy (SEM), dynamic mechanical analysis (DMA), and measuring stress field factor (K-IC) analysis were employed to investigate the morphology, fracture graph, storage modulus, glass transition temperature (T-g), and fracture toughness of the epoxy thermosets containing these BCPs. The specific side-groups of eSBS46-AEP containing secondary amines and ternary amines increased the reactivity to epoxy matrices. A combination of fracture mechanisms including shear deformation, crack tip blunting, and matrix ductility enhancement contributed toward helped enhance the toughness. These results demonstrate that the role of modulating the reactivity of BCP has a significant effect on the final morphology and properties of the epoxy composites

Investigation of the clay sensitivity and cement hydration process of modified HPEG-type polycarboxylate superplasticizers

In this work, three kinds of HPEG-type polycarboxylate superplasticizers (PCs) were synthesized with three kinds of typical functional monomers: [diallyl dimethyl ammonium chloride (DMDAAC), 2-hydroxyethyl methacrylate (HEMA), and 2-(dimethylamino) ethyl methacrylate (DMAM), respectively. The effects of montmorillonite clay on the fluidity of cement/PC pastes were investigated. It was found that the fluidity was negatively affected by the clays in the order: DMAM-PC<HEMA-PC<conventional PC (CPC)<DMDAAC-PC. The DMAM-PC was found to disperse cement well even in presence of montmorillonite clay. The dispersion performance of DMDAAC-PC was much more effectively affected by clay due to the reaction between ammonium and montmorillonite. More study including mortar fluidity, adsorption behavior and morphology of the cement samples were investigated in details. Thermogravimetric analysis and X-ray diffraction experiments allowed us to observe the influence of PCs on the hydrated products. (c) 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46572

Regulating the arm structure of star-shaped polycarboxylate superplasticizers as a means to enhance cement paste workability

Star-shaped superplasticizers, which incorporated polyol ester with unsaturated bond at their cores and bore comb-type structures as their arms were synthesized via esterification-copolymerization in aqueous phase from pentaerythritol, acrylic acid (AA), and isopentenyl oxy poly(ethylene glycol ether) (TPEG). The monomer ratios of AA and TPEG were varied and comonomer sodium methallyl sulfonate (SMAS) bearing short side chains was added to regulate the arm structure of star-shaped polycarboxylate superplasticizers (SPCEs). The effects of the SPCEs on cement paste were investigated and the cement dispersion as well as early hydration mechanism were explored. As a main result, SPCEs with SMAS and certain molar ratios for anchoring groups and PEO side-chains in their arm structure exhibited good paste dispersion and fluidity retention, which also delayed the early hydration process and prolonged both the initial and the final setting time. (c) 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46312

Synthesis, characterization, and performance of a novel polycarboxylate superplasticizer with a crosslinked topological structure

In this work, a novel crosslinked topological polycarboxylate superplasticizer (TPC) was successfully synthesized. In comparison with conventional comb-shaped superplasticizer (CPC), the TPC performed better dispersion maintaining stronger water reduction capabilities. The TPC provided a large spherical space due to its crosslinked molecular structure, which was the main reason for enhanced dispersion performance. It was evident that the addition of TPC leads to a delayed and lowered heat flow peak during the early stage of the hydration process. Thermogravimetric analysis showed that the hydrated products exhibited a more stable performance in the presence of the TPC. Changing the molecular structure from a comb-shape to a crosslinked topological could effectively improve the comprehensive performances of the PCs. (c) 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46716