Concentrated latexes

In latex technology, concentrated latex is first blended with the different additives required. To prevent premature destabilisation the powders are added as dispersions and non-aqueous liquids are generally added as emulsions. Care must be taken to avoid destabilisation, which can be brought about in different ways such as... 

A method of concentrating latex by passing an electric current through the latex contained in a rectangular tank. The rubber particles move toward the anode and also tend to rise because of their lower specific gravity. The separation is facilitated by a large number of semi-permeable membranes fitted between the electrodes. 

Latex of natural rubber which has had a preservative (usually ammonia) added, but which has not been concentrated. See Concentrated Latex. 

Methylinositol, one of the constituents of natural rubber latex. Although it is present at about 1% it does not appear to have any effect on the properties of either field latex or concentrated latex. 

Attached-growth waste stabilization ponds have been used to remove 65-70% TKN (total Kjeldahl nitrogen), and 70-83% NH3-N from concentrated latex and rubber sheet plant wastewaters [8]. A combined algae and water hyacinth system has been used to remove 96.41% COD, 98.93% TKN, 99.28% NH3-N, 100% NO2-N, and 100% NO3-N [9]. 

It was established by Yeliseyeva and Bakaeva (1968) that in the polymerization of polar monomers (MA) the decrease of emulsifier adsorption depends on tbe structure of the latter and for some types of emulsifiers may reach limiting values. This was observed in tbe polymerization ofMA in the presence of a mixed type of emulsifier, partially sulfurated with sulfuric acid oxyethylated alkylphenol (emulsifier C-I0 ). Its adsorption on the particle surface increases with the initial concentration and reaches > 100% filling of the adsorption layer, conditionally corresponding to 0.3S nm per molecule. Stable, concentrated latexes with small particles are formed. Therefore, emulsifier adsorption and the mechanism ctf particle formation associated with it depends not only on monomer polarity but also on the chemical structure of the emulsifier. 

Spiral wound elements have been used by a number of companies in the water purification area since 1968. Osmonics has been unique in that we have used spirals on a very large number of non-water purification applications, including oil concentration, latex concentration and of course, the concentration and fractionation of cheese whey. In fact, our installed capacity on cheese whey is approximately 324,000 sq. ft. (29,160 m2) of membrane or 20 miles (32 km) of membrane as it comes off of our machinery 3 ft. (1 meter) wide. Or, if you prefer the installed capacity is capable of handling 800,000 lbs (360,000 kg) of cheese whey per hour. 

Concentration of latex is necessary because of the preference by the latex products manufacturing industry for latex with high dry rubber content (DRC), and for transport economy and purification of the latex. The processes for concentration include evaporation, electrodecantation, creaming, and centrifuging. Evaporation removes only water and hence the ratio of non-rubber constituents to rubber, and the particle size distribution remain unchanged. However, the other three processes involve the partial removal of non-rubber materials and smaller rubber particles. Centrifuging and creaming are more popularly used for the production of concentrated latex. 

Figure 13.6 Efriect of charges on the particle sur ce. At low ionic strength, the electrical double layers around the latex particles become very large, and contribute significantly to the low shear viscosity in concentrated latexes (0 = 0.26). Open symbols data from a cone-and-plate viscometer. Closed symbols data from a ct rillaiy viscometer. (Rqno-duced by peimissicRi of Acadonic Press from lef. [62].)...

Emulsion polymerization, being one of the methods of polymer synthesis, enables the proeess to proeeed with a high rate to form a polymer with a high molecular weight, high-concentrated latexes with a relatively low viscosity to be obtained, polymeric dispersions to be rrsed at their processing without separation of the polymer from the reaetion mixture, and the fire-resistance of the product to be significantly raised. At the... 

The photon-diffusion approximation has been shown to be effective for the analysis the size and concentration of concentrated latex dispersions. 

In some instances, however, the use of a finer pore-sized membrane provides hi er stable fluxes over longer periods than is found with coarser membranes. This is particularly true when the suspended sohds particle size is close enough to the membrane pore size for internal filter clogging to occur. Figure 10.10 illustrates an experiment conducted with two polymer membranes and a very low concentration latex su ension, with particle size in the range 0,2-2 pm. 

D15. An UF system is being used to concentrate latex particles in an aqueous suspension. The... 

This method allows the sol-gel siliea NR latex eompound to be moulded into the desired shape. TESPT was eo-mixed with TEOS and eoneentrated NR latex. Ammonia which functioned as base catalyst was added into the concentrated NR latex. The silica-TESPT-NR latex compound was then subjected to heat to complete the sol-gel silica conversion process. The dried sol-gel silica-NR mixture was compounded as per normal mixing procedure. A good dispersion of silica particles of the size between 100 and 500 nm was achieved. Using the two-level factorial design, it was concluded that the mechanical properties, i.e. tensile properties and tear strength, were significantly affected by the TEOS loading. It was also found that the amount of ammonia present in the concentrated latex, i.e. 0.7% (w/w) was sufficient to convert TEOS into silica. 

NR is a naturally existing elastomer composed mainly of cis-l, 4-poly-isoprene. It is collected from more than 400 different species of plants but the main source is Hevea brasiliettsis. The collection is in the form of latex, a colloidal solution of NR, which contains about 70% of water and other materials in smaller quantities such as proteins, fatty acids, resins, etc. After removing the excess water by centrifugation two products based on NR can be obtained concentrated latex and dry natural rubber. Concentrated latex has about 60%... 

H. Wiese, D. Horn, Single-mode fibers in fibta -optic quasielastic light scattering a study of the d5mamics of concentrated latex dispersions. J. Chem. Phys. 94(10), 6429-6443 (1991). doi 10. 1063/1.460272... 

NR can also be exported as concentrated latex. Fresh field latex consists of 30-40% dry rubber content (DRC), the other 60-70% being mainly water-containing non-rubber substances. The non-rubber components, e.g. proteins, carbohydrates, lipids and inorganic salts, vary according to clones, season and age of rubber tree. The latex collected from the plantation is preserved with ammonia (NH3) and then undergoes continuous centrifugation to produce the... 

Centrifugation is just one of many techniques used for concentrating latex, to increase the solids content of NR field latex which at about 30% solids is not suitable for many of the industrial applications of latex and is uneconomical in terms of transportation costs. Another advantage of concentrating the field latex is that it offers a more consistent feedstock compared with the dilute field latex. 

Table 4.4 ASTM 1076-10 specifications for Types I, II and III concentrated latex.

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