Influences of HPMC on adsorption of styrene-acrylic ester latex particles on cement grains

Abstract

In order to understand why polymer-modified mortars (PMMs) with hydroxypropylmethyl cellulose (HPMC) often show better properties than that without HPMC, the influence of HPMC on the adsorption of styrene-acrylic ester (SAE) latex particles on cement grains was studied through the particle size distribution and the zeta potential of latex modified cement paste (LMCP) with and without HPMC keep the latex/cement ratio (L/C) to 10%. The differences between the calculated and measured particle size distribution curves of LMCP indicate strong interactions between latex particles and cement grains in fresh cement pastes. The particle size distribution results show that the adsorbed rate of SAE on cement is 75.24% in LMCP, while the adsorbed rate of SAE latex particles in LMCP with HPMC is 4% lower than that in LMCP without HPMC. The zeta potential results show that the zeta potential of LMCP is negative, the equilibrium zeta potential of LMCP with HPMC is more negative than that of LMCP without HPMC and decreases with the increase of the HPMC to cement ratio (HPMC/C). The microstructures of hardened LMCP with and without HPMC were observed using scanning electronic microscopy (SEM). Without etching of LMCP with or without HPMC, the polymer films are more easily seen in pores while hard to found at the cement matrix. After etching the specimen in diluted hydrochloric acid (HCl), coherent polymer films were observed. The differences of the polymer films in samples prepared with different procedures, that is the specimens stored in absolute alcohol or not, show that they are composite films of SAE latex and HPMC in LMCP with HPMC. Higher the HPMC/C is, bigger the covered area of the polymer films is on the surface of pores, and more rigid the polymer films are, what can be confirmed from the tensile test results of films made from the HPMC and SAE latex mixture that show decreased elongation at break and increased tensile strength with the increase of HPMC to latex ratio (HPMC/L).