Dispersion latexes

Acrylic polymers are considered to be nontoxic. In fact, the FDA allows certain acrylate polymers to be used in the packaging and handling of food. However, care must be exercised because additives or residual monomers present in various types of polymers can display toxicity. For example, some acryflc latex dispersions can be mild skin or eye irritants. This toxicity is usually ascribed to the surfactants in the latex and not to the polymer itself. 

Polymeric binder can be added to the network either as an aqueous latex dispersion or as a solution that should be dried prior to lamination in this process. In either case, the polymer should form a film and join adjacent fibers together and thus improve the stress transfer characteristics of the fibrous network. Provided that the proper film forming conditions are available, the property profile of the bonded network is determined to a significant degree by the properties of the polymeric binder at the temperature of use [20,22]. For example, if a softer type of product is desired, a binder with a relatively low glass transition temperature Tg) is often chosen. 

Storage stability of latex dispersion at various temperatures... 

The cross-linking efficiency of the more branched polychloroprene latex (mercaptan modified) has been found to be higher than the less branched sulfur-modified one. The latex dispersion is found to display higher rate of cross-linking than the coagulated and subsequently dried mbber films [386] due to higher concentration of radical in the former. 

FIG. 17 Plot of normalized surface coverage C of self-assembled layer of particles Ic vs. dipping time of substrate for different concentrations of the latex dispersion (T = 23.5°C, pH = 5.8). 

FIG. 18 SEM pictures of self-assembled layers of particles Ic prepared from latex dispersions of different pH value (substrate glass support modified with 3-AMDS, dipping time 1 h, latex concentration 3 mg/mL T = 23.5°C). (From Ref. 98, with permission from Elsevier, Amsterdam.)... 

Resin cements or polymer cements have been reviewed by Chandra, Justnes, and Ohama [343]. Polymer cements are materials made by replacing the cement at least partly with polymers. Cements can be modified by latex, dispersions, polymer powders, water-soluble polymers, liquid resins, and monomers. 

The study of materials by the use of any type of microscope. The structure of latex, dispersion of compounding ingredients in elastomers and identification of blooms are typical uses in rubber technology. 

The s.a.n.s. experiments were carried out using the D17 camera at the I.L.L., Grenoble. Data were collected at two wavelengths, 0.8 and 1.4 nm at a sample to detector distance of 1.8 m. The overlapping spectra were combined to give a sufficiently wide Q range to enable the data to be numerically inverted to obtain the density distributions. The latex dispersions were prepared at a solids concentration of 4% and polymer solution concentrations between 200 and 300 ppm. 

The p.c.s. measurements were carried out using a Malvern multibit correlator and spectrometer together with a mode stabilized Coherent Krypton-ion laser. The resulting time correlation functions were analysed using a non-linear least squares procedure on a PDP11 computer. The latex dispersions were first diluted to approximately 0.02% solids after which polymer solution of the required concentration was added. 

Rheological Studies of Aqueous Concentrated Polystyrene Latex Dispersions with Adsorbed Poly(vinyl alcohol) Layers... 

The viscoelastic behavior of concentrated (20% w/w)aqueous polystryene latex dispersions (particle radius 92nm), in the presence of physically adsorbed poly(vinyl alcohol), has been investigated as a function of surface coverage by the polymer using creep measurements. From the creep curves both the instantaneous shear modulus, G0, and residual viscosity, nQ, were calculated. 

Any fundamental study of the rheology of concentrated suspensions necessitates the use of simple systems of well-defined geometry and where the surface characteristics of the particles are well established. For that purpose well-characterized polymer particles of narrow size distribution are used in aqueous or non-aqueous systems. For interpretation of the rheological results, the inter-particle pair-potential must be well-defined and theories must be available for its calculation. The simplest system to consider is that where the pair potential may be represented by a hard sphere model. This, for example, is the case for polystyrene latex dispersions in organic solvents such as benzyl alcohol or cresol, whereby electrostatic interactions are well screened (1). Concentrated dispersions in non-polar media in which the particles are stabilized by a "built-in" stabilizer layer, may also be used, since the pair-potential can be represented by a hard-sphere interaction, where the hard sphere radius is given by the particles radius plus the adsorbed layer thickness. Systems of this type have been recently studied by Croucher and coworkers. (10,11) and Strivens (12). 

In this paper we report some rheological studies of aqueous concentrated polystyrene latex dispersions, in the presence of physically adsorbed poly(vinyl alcohol). This system has been chosen in view of its relevance to many practical systems and since many of the parameters needed for interpretation of the rheological results are available (15-18). The viscoelastic properties of a 20% w/w latex dispersion were investigated as a function of polymer coverage, using creep measurements. 

Figure 6.17 Plot of the pseudo-melting curve calculated from a strain sweep. This data is for a polyvinylidene fluoride latex. Similar curves can be obtained for silica and polystyrene latex dispersions...

In commercial latex dispersions this is often a mixture of acrylic acid and butyl and ethyl acrylates. 

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