Synthesis and characteristics of pectiniform polyurethane‐modified polycarboxylate and its effects on behavior of cement paste

Abstract

In this research, two kinds of polycarboxylate (M-PCE and O-PCE) with the same degree of polymerization in side chains but different main chains were synthesized via a radical polymerization reaction at room temperature. Along with two commercial polycarboxylates (C-PCE-1 and C-PCE-2), their properties on adsorption, hydration, zeta potential, liquid surface tension, and flowability of cement pastes were investigated. The results showed that the adsorption of M-PCE on the surface of cement particles increased 14.1% and the adsorption rate increased 24% compared with C-PCEs. Furthermore, three polycarboxylates (O-PCE, C-PCE-1, and C-PCE-2) exhibited a delayed effect on the hydration of cement due to the shielding effect of their chain alkyl groups, meanwhile the hydration of the cementitious materials by the M-PCE was not delayed but promoted because of its incomplete hydrolysis of the siloxane. As a result of the higher adsorption amount, M-PCE with siloxane groups exhibited favorable effects in terms of zeta potential, liquid surface tension, and flowability of cement pastes.

Influence of a polyurethane‐modified polycarboxylate on properties of cement mortar

“…In the molecular structure of M‐PCE, the organosiloxane groups have big density and the most irregular oriented arrangement. Therefore, M‐PCE had the lowest surface tension in the surface tension experiment, 1 and lower surface tension results in the lowest drying shrinkage value of the cement mortar.…”

“…The dispersion principle was mainly electrostatic repulsion and steric hindrance. In contrast, the dispersibility of M‐PCE was because the strong chemical bonds induced by the siloxane groups in the M‐PCE and silicate phase promote the dispersibility of M‐PCE 1 . In addition, due to its chemical structure, M‐PCE had longer side chains than PCE, which means its better steric hindrance, 11 so M‐PCE had better dispersibility in cement.…”

“…M‐PCE mortar incorporated at high water reduction rate of 44.7% exhibited great fluid state, with bleeding degree increased. On the one hand, the free water in the mortar was easy to evaporate, and on the other hand, the “free water” content in the mortar increased, which slowed down the development of capillary water pressure, so that the time to reach the critical pressure Pc was prolonged, and the autogenous shrinkage was reduced 1 . Moreover, in this extended period of time, the hydration reaction enabled further formation of rigid structure in the mixture, reduced the plastic deformation ability of the Portland cement mortar, and increased the tensile strength of the Portland cement mortar.…”

“…By adhering to the surface of Portland cement hydration products and its particles, these groups could not only form an adsorption layer, but also destroy the flocculation structure between silicate particles. After the incorporation of PCE, its electrostatic repulsion and steric hindrance could greatly change the force between the Portland cement particles as well as the physical and chemical properties of the solid–liquid interface, so that the Portland cement particles were evenly distributed, which in turn affected the flowability and other properties 1 . Nowadays, in PCE's molecular design, a more scientific way was to use the ester group(polyurethane) to protect the COO on the its main chains, which also had important applications of amino‐functional substrates to remove heavy metal in water 2 .…”