Latex characterization

Nick L, Lammel R and Fuhrmann J 1995 Latex characterization by atomic force microscopy Chem. Eng. Technol. 18 310... 

These results on viscosity behavior are in good agreement with the results of the latex characterization by conductometric titration (see Figures 5 6), which showed that the carboxyl groups are uniformly distributed within the particle for the semi-continuous latex, whereas in the batch latex the carboxyl groups are concentrated at the water-particle interface. 

Aramendia et al. [20] have compared the nonreactive sodium lauryl sulfate (SLS) to the polymerizable sodium tetradecyl maleate (M14), synthesized according to the procedure described by Stahler [21] in the seeded polymerization of methyl methacrylate/butyl acry-late/acrylic acid using tert-butyl hydroperoxide and ascorbic acid as initiator. Nonyl phenol 30 EO (NP30) was the nonionic surfactant used in the seed latex. Latex characterization... 

Figure 3. Electron micrograph (4000 X) of typical latex section (top) ana latex dispersity graph (bottom). 5000-A latex characterization (Run A-32).

A considerable amount of work has been published during the past 20 years on a wide variety of emulsion polymerization and latex problems. A list of 11, mostly recent, general reference books is included at the end of this chapter. Areas in which significant advances have been reported include reaction mechanisms and kinetics, latex characterization and analysis, copolymerization and particle morphology control, reactor mathematical modeling, control of adsorbed and bound surface groups, particle size control reactor parameters. Readers who are interested in a more in-depth study of emulsion polymerization will find extensive literature sources. 

Transmission Spectroscopy An Analysis Tool for Emulsion Latex Characterization... 

Using this method of latex characterization, we determined the number of sulfate endgroups on the particle surface and inside the... 

Chloroprene polymerizes thermally to yield a true rubbery solid with a characteristic liquid-like structure. Stretching produces crystallinity and the expected X-ray pattern for an oriented fiber. A detailed mechanistic analysis yielded the multiple structures that appear during the reaction. Another synthetic pathway leads to polychloroprene latex. Characterization of these particles with the ultracentrifuge yielded a highly peaked distribution with a mean radius near 0.06 micron. Because of the very small particle size compared with natural mbber latex, this material can be used for many applications requiring minute particles. The detailed analysis and keen structural insight set a standard that is rarely met, even today. 

El-Aasser, M.S. (1983) Methods of latex cleaning. In G.W. Poehlein, R.H. Ottewill and J.W. Goodwin (eds). Science Technology of Polymer Colloids. Surface Characterization of Latexes. Characterization, Stabilization and Application Properties, Vol. 11, No. 68. Martinus Nijhoff Publishers, The Hauge, p. 422. 

Three generations of latices as characterized by the type of surfactant used in manufacture have been defined (53). The first generation includes latices made with conventional (/) anionic surfactants like fatty acid soaps, alkyl carboxylates, alkyl sulfates, and alkyl sulfonates (54) (2) nonionic surfactants like poly(ethylene oxide) or poly(vinyl alcohol) used to improve freeze—thaw and shear stabiUty and (J) cationic surfactants like amines, nitriles, and other nitrogen bases, rarely used because of incompatibiUty problems. Portiand cement latex modifiers are one example where cationic surfactants are used. Anionic surfactants yield smaller particles than nonionic surfactants (55). Often a combination of anionic surfactants or anionic and nonionic surfactants are used to provide improved stabiUty. The stabilizing abiUty of anionic fatty acid soaps diminishes at lower pH as the soaps revert to their acids. First-generation latices also suffer from the presence of soap on the polymer particles at the end of the polymerization. Steam and vacuum stripping methods are often used to remove the soap and unreacted monomer from the final product (56). 

The Metravib Micromecanalyser is an inverted torsional pendulum, but unlike the torsional pendulums described eadier, it can be operated as a forced-vibration instmment. It is fully computerized and automatically determines G, and tan 5 as a function of temperature at low frequencies (10 1 Hz). Stress relaxation and creep measurements are also possible. The temperature range is —170 to 400°C. The Micromecanalyser probably has been used more for the characterization of glasses and metals than for polymers, but has proved useful for determining glassy-state relaxations and microstmctures of polymer blends (285) and latex films (286). 

The AeroSizer, manufactured by Amherst Process Instmments Inc. (Hadley, Massachusetts), is equipped with a special device called the AeroDisperser for ensuring efficient dispersal of the powders to be inspected. The disperser and the measurement instmment are shown schematically in Figure 13. The aerosol particles to be characterized are sucked into the inspection zone which operates at a partial vacuum. As the air leaves the nozzle at near sonic velocities, the particles in the stream are accelerated across an inspection zone where they cross two laser beams. The time of flight between the two laser beams is used to deduce the size of the particles. The instmment is caUbrated with latex particles of known size. A stream of clean air confines the aerosol stream to the measurement zone. This technique is known as hydrodynamic focusing. A computer correlation estabUshes which peak in the second laser inspection matches the initiation of action from the first laser beam. The equipment can measure particles at a rate of 10,000/s. The output from the AeroSizer can either be displayed as a number count or a volume percentage count. 

The mechanism of B polymerization is summarized in Scheme 4,9. 1,2-, and cis- and trews-1,4-butadiene units may be discriminated by IR, Raman, or H or nC MMR speclroseopy.1 92 94 PB comprises predominantly 1,4-rra//.v-units. A typical composition formed by radical polymerization is 57.3 23.7 19.0 for trans-1,4- c7a -1,4- 1,2-. While the ratio of 1,2- to 1,4-units shows only a small temperature dependence, the effect on the cis-trans ratio appears substantial. Sato et al9J have determined dyad sequences by solution, 3C NMR and found that the distribution of isomeric structures and tacticity is adequately described by Bernoullian statistics. Kawahara et al.94 determined the microslructure (ratio // measurements directly on PB latexes and obtained similar data to that obtained by solution I3C NMR. They94 also characterized crosslinked PB. 

Moller, M., Kayma, M., Vieluf, D., Paschke, A., and Steinhart, H. (1998). Determination and characterization of cross-reacting allergens in latex, avocado, banana, and kiwi fruit. Allergy 53,289-296. 

Polymerization processes are not easy" processes to handle experimentally. There exist a wide variety of operating factors that could cause the production of a latex or polymer with totally different properties than the previous one. Long reaction times and time-consuming analytical techniques to fully characterize a given product make the situation more complicated in that one does not always have the freedom to run a specific experiment or change some conditions in order just to check the process behaviour. In addition, plant personnel are in many cases understandably reluctant to even attempt... 

Then, since in any system accumulation is the net result of both evolution and birth/death processes, and since any latex particle can be characterized by a set of physical quantities which will fully specify a given particle or class of particles, one can obtain the following population balance equation (33) ... 

The parameters K1/ K2/ and K3 are defined by the refractive indices of the crystal and sample and by the incidence angle [32]. If the sample has uniaxial symmetry, only two polarized spectra are necessary to characterize the orientation. If the optical axis is along the plane of the sample, such as for stretched polymer films, only the two s-polarized spectra are needed to determine kz and kx. These are then used to calculate a dichroic ratio or a P2) value with Equation (25) (replacing absorbance with absorption index). In contrast, a uniaxial sample with its optical axis perpendicular to the crystal surface requires the acquisition of spectra with both p- and s-polarizations, but the Z- and X-axes are now equivalent. This approach was used, through dichroic ratio measurements, to monitor the orientation of polymer chains at various depths during the drying of latex [33]. This type of symmetry is often encountered in non-polymeric samples, for instance, in ultrathin films of lipids or self-assembled monolayers. 

Acrylic resins are generally well characterized by Py-GC/MS without the need for any derivatization reaction. However, in waterborne polymer dispersions it is common to have minor amounts of acrylic and/or methacrylic acid monomers added in the copolymerization to help the stability of the final latex. These monomers can also appear in the pyrolysis products, and it has been shown that with on-line derivatization they can be more efficiently revealed [85]. 

The determination of adsorption isotherms at liquid-solid interfaces involves a mass balance on the amount of polymer added to the dispersion, which requires the separation of the liquid phase from the particle phase. Centrifugation is often used for this separation, under the assumption that the adsorption-desorption equilibrium does not change during this process. Serum replacement (6) allows the separation of the liquid phase without assumptions as to the configuration of the adsorbed polymer molecules. This method has been used to determine the adsorption isotherms of anionic and nonionic emulsifiers on various types of latex particles (7,8). This paper describes the adsorption of fully and partially hydrolyzed PVA on different-size PS latex particles. PS latex was chosen over polyvinyl acetate (PVAc) latex because of its well-characterized surface PVAc latexes will be studied later. 

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). 

Ali, S. A. Sengupta, M. J., Preparation and characterization of monodisperse polystyrene latexes of varying particle sizes without the use of surfactants, Polym. Mater. Sci. Eng. 1991, 8, 243 250... 

High Tg monomers, for latex acrylic polymers, 22 41-42 High-throughput characterization, 7 419-120... 

Bonardi, C., Christou, Ph., Llauro-Darricades, M.E., Guillot, J., Guyot, A. and Pichot, C., 1989, Polymer Latex III International Conference, Characterization of Acrylic Latexes Functionalized by N-Methylol Acrylamide, 6/1-6/14, Plastics and Rubber Institute, London. 

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