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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.

Summary: A novel polymerization procedure to synthesize latex stabilized by alkali‐soluble resin (ASR) is detailed. According to this process, latexes with a high solid content and low viscosity are obtained using a substantially lower amount of ASR when compared with existing techniques. Similar rewet properties were found for the latexes obtained by a standard process and for the one obtained by the process described in this work.Comparison of the particle size distributions obtained by conventional emulsion polymerization (○) and by miniemulsion polymerization (□).magnified imageComparison of the particle size distributions obtained by conventional emulsion polymerization (○) and by miniemulsion polymerization (□).

Summary: The development of a model‐assisted methodology for the synthesis of high solids‐low viscosity latexes is presented. A simplified polymerization model for systems with a polydisperse particle size distribution, PSD, was developed. The polymerization model was then coupled with an equation for the computation of the viscosity. Their combination resulted in a powerful tool that helped to screen strategies for the synthesis of high solids‐low viscosity latexes. Furthermore, using the model‐assisted methodology it was possible to determine the workable viscosity boundary for a given formulation. The evolution of the viscosity with the volume fraction was calculated for different polymerization strategies.

Summary: In this work hybrid latexes of poly(styrene-co-butyl acrylate)/montmorillonite were synthesized via miniemulsion polymerization using a Brazilian organically modified montmorillonite. The natural clay was previously treated with Cetyltrimethyl ammonium chloride (CTAC) in order to increase the interaction between the clay and the monomer phase. Three different methodologies to modify the clay and their influence on the final properties of the composites obtained were evaluated in this work. The modified clays were characterized by X-ray diffraction (XRD). The films obtained after drying the latexes were characterized by dynamicmechanical thermal analyses (DMTA), small amplitude oscillatory shear (SAOS), transmission electronic microscopy (TEM) and Cobb test. The X-ray diffractograms, showed an increase of basal spacing after organic treatment indicating the introduction of CTA þ within the clay interlamelar space. This interlamelar space was further increased after polymerization for all of the three differently modified clays studied, indicating that in situ polymerization occurred. The introduction of organically modified clays did not influence the kinetics of polymerization. Stable latexes were obtained. The DMTA presented improved mechanical properties for the materials charged with two of the modified clays studied when compared to a conventional composite. SAOS analysis revealed that an exfoliated structure might have been obtained when adding one of the modified clays to the reacting medium. Cobb tests showed that the permeability to water was reduced by the incorporation of clays to the copolymer.

Multiple and diverse applications have been recently found for miniemulsions and miniemulsion polymerization. In this work, miniemulsion polymerization is presented as a suitable technique for the preparation of high‐solid‐content latices with large particle sizes. Monomer miniemulsions were prepared with a high‐pressure homogenizer, and droplet sizes of 200–700 nm were obtained. Latexes with particle sizes larger than the sizes commonly accepted for miniemulsion polymerization were obtained. With fixed operational conditions of the homogenizer, the type of stabilizer was the key parameter determining the droplet size and the droplet size distribution. The particle size of the latices obtained by miniemulsion polymerization indicated that the particles were mainly formed by droplet nucleation. Latexes obtained by this process have multiple applications, including use as seeds in the polymerization of high‐solid‐content latices. This article shows that potential new applications for miniemulsion polymerization are far from being exhausted. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4222–4227, 2004

A rheological model that accounts for the effect of the volume fraction, the particle size distribution (PSD), and the shear rate on the dispersion viscosity was developed. The model contains three parameters (k 1, k 2, and k 3) that accounted for the interaction among particles. The model was validated in experiments in which the surfactant type and concentration, the volume fraction, the PSD, and the shear rate were widely varied. The parameters were observed to be independent of the volume fraction, the PSD, and the shear rate. Parameter k 1 increases with the surfactant content but was independent of the ratio anionic surfactant/nonionic surfactant. On the other hand, under the range of experimental conditions studied, k 2 and k 3 were not affected by the surfactant type and concentration.

ABSTRACT:Multiple strategies for the synthesis of highsolids, low-viscosity latices have been established in modern polymer industry. The basic principle supporting these strategies is the polydispersity of the particle size distribution. However, polymerization procedures are often based on experience, tacit knowledge acquired with time and repetitive trial-and-error procedures. Recently, a novel coupled polymerization-viscosity model has been proposed. The model aids screening of potential polymerization strategies. This work presents use of the model as a powerful tool to design new strategies for obtaining highly concentrated aqueous polymer dispersions. By incorporating some simplifying assumptions into the coupled model, the feasibility for synthesizing high-solids latex with low viscosity using novel polymerization strategies was assessed.