(380u) Surface Functionalization of Polymer Latex Particles and Its Effect on in-Situ Deposition of Nano-Sized Calcium Silicate Hydrate

Polymer latexes have been widely used in cementitious materials to improve their workability and mechanical properties. However, the reduced hydration activity is often found after the polymer latexes are added, especially during the first hours and days. Nucleation seeding with synthetic nanoscale calcium silicate hydrate (C-S-H) is a possible method to compensate for the retarded effect, as it has enormous potential to accelerate the cement hydration. But how to play the role of them effectively and conveniently are still the challenges. In this work, the polymer latex particles with hydrophilic carboxylic/sulfonic chains grafted from the surface were first fabricated via soap-free emulsion polymerization. And then, some of them were modified by amino/phosphate groups respectively. The nanoscale C-S-H was anchored on the particle surface by in-situ deposition reaction of Ca(NO₃)₂ and Na₂SiO₃ afterwards. The effects of different functional groups on the deposition process of nanoscale C-S-H were investigated, and its application in cement paste was attempted.

The surface hydrophilic groups content of the latex particles was measured by conductometric titration. The interaction between particles and Ca²⁺ was studied by treatment with Ca(NO₃)₂ individually. The deposition process was analyzed by centrifugal titration and inductively coupled plasma optical emission spectrometry (ICP-OES). The morphologies of the latex particles and composite microspheres were characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Thermos gravimetric analyzer (TGA) and dynamic light scattering (DLS) were employed to characterize the composition and the dispersibility of the composite microspheres, respectively. After adding the composite microspheres into paste, the hydration process of the fresh mixture was monitored by cement hydration heat analyzer. Its workability and mechanical properties were tested via conventional methods. The porosity of the hardened specimens was characterized by mercury injection method.

The results show that the surface hydrophilic groups content of P(St-co-MAA) latex was around 2×10^-4 mol/g. The enrichment of Ca²⁺ on the particle surface can be observed, and that with carboxylic groups has the highest content. The C-S-H gel always exhibits an amorphous phase, and the maximum mass ratio of C-S-H is about 8.0 wt% which also appears in the carboxylated particles. The accelerated hydration can be observed for all types of composite microspheres, in which those with exposed sulfonic chains have the most significant effect. No obvious effects on the paste fluidity and the water absorption of the hardened specimen can be observed. The modified mechanism of the composite microspheres for paste was proposed.