Effect of the particle size distribution on the low shear viscosity of high‐solid‐content latexes

Abstract

The production of high-solid-content, low-viscosity latexes is an active field in both industry and academia. The viscosity of polymer dispersions has a clear dependence on the particle size distribution (PSD). An example is the rule of thumb that a bimodal PSD enables the reduction of the viscosity with respect to monomodal systems. Despite important progress in theoretical work, not much has been done to quantitatively predict the low shear viscosity of aqueous polymer dispersions as a function of the complex PSD. In this work, the capability of a low-shear-viscosity equation to quantitatively account for the influence of both the PSD and the physicochemical characteristics of the dispersions is experimentally assessed. An analysis, consistent with theoretical concepts, of the data with semiempirical correlations is proposed. Next, with values of the parameters of the viscosity equation obtained experimentally, the effect of a latex with a 70% solid content on the low shear viscosity is examined.

Synthesis of High Solid‐Content Latex using Alkali‐Soluble Resin as Sole Surfactant

“…[21] A sample was taken out of the flat-bottom beaker and cooled to room temperature before the viscosity was recorded with an ELV-8 viscosimeter (Viscometer UK) with spindle 2 at 60 rpm. An aliquot of the same sample was used to measure the solids content by gravimetry.…”

“…Among the number of semiempirical and empirical equations available to describe the rheological behavior of latexes in a low-shear regime, [22][23][24] do Amaral et al [21] have assessed the capacity of using the equation proposed by Sudduth [25,26] (Equation (1)) to determine the effect of the particle size distribution on the low-shear viscosity of concentrated latexes based on the experimentally determined values of the equation parameters.…”

“…Such a tendency was not observed in systems stabilized with low-molar-mass surfactants. [21] Compared to the results obtained for systems using conventional low-molecular-weight surfactants, [21] the values for the ASR-stabilized latex (s ¼ 1.0 þ 75.3/D n ) showed some differences. The value of 1.0 for s s was lower than the previously estimated values (1.37 < s s < 1.63).…”

“…The value of 1.0 for s s was lower than the previously estimated values (1.37 < s s < 1.63). [21] The result for the ASR system is probably attributable to the high concentration of ionic species in aqueous media, especially ASR molecules dispersed in the water phase, and not adsorbed onto the particle surface. Ionic species in the aqueous phase favor the repulsion of particles, leading to a decrease in the magnitude of the contribution of s s to the particle interaction coefficient.…”

“…[21] Picturing the polymer particles stabilized by a dense and large hairy layer of ASR molecules, [10] it is reasonable to expect a much higher particle interaction. The result indicated that the molecular weight of the surfactant could influence the value of s pc , i.e., the higher the surfactant molecular weight, the larger the value of s pc .…”