Centrifuged latex

Figure 9.5.6 Various fractions of centrifuged latex. From Moir. ...

The preservatives may function as bactericides, enzyme inhibitors, sequestering agents or stabilizers. They are often used in combination. A system widely used today is zinc oxide/TMTD 0.025% lauric acid or ammonium laurate 0.05% and ammonia (NH3) 0.2%. This is the low ammonia LA-TZ centrifuged latex corresponding to Type III. 

HA and LA-TZ centrifuged latex concentrates make up the bulk of the commercial supplies of NR latex. They are the general-purpose latex concentrates that meet most of the demands of diverse latex product manufacturers. Some producers also include in their product range a medium level ammonia variation at 0.45-0.50% w/w. The volumes of creamed latex concentrate and the evaporated latex concentrate e.g. Revertex LCS) remain small in comparison, serving the specific requirements of certain manufacturers. In addition, there... 

Most latex concentrate produced today would fall into one of the four types specified by ASTM specification D 1076 (1) centrifuged latex with normal ammonia, centrifuged with low ammonia, creamed latex with normal ammonia, and creamed with low ammonia. The minimum content for latex solids varies from 61.5% to 64.0% and dry rubber content minima from 60.0% to 62.0%. Total alkalinity is calculated as NH3 based on the water phase of the latex and is 1.6% minimum for normal ammonia latex, 1.0% for the minimum ammonia type. Lx)w-ammonia latex (often made with a second stabilizer) has less odor and requires less neutralization in subsequent processing, but other factors hinder its use. A very small amount of latex is vulcanized in the liquid state and sold for special compounding. 

Centrifuged latex is by far the most important type, accounting for about 95% of latex production. A significant proportion of the water soluble non-rubber components is removed by centrifuging or creaming. It is usually safe to assume that natural rubber latex formulations will be based on centrifuged latex unless otherwise specified. 

Double centrifuged latex is made by diluting centrifuged latex and recentrifuging. As a result of this, the non-rubber content (TSC — DRC total solids content minus dry rubber content) is reduced significantly. This is of interest mainly in medical applications. 

Sub-stage centrifuged latex is produced by creaming to about 50% solids content and then centrifuging. This enables a higher solids (67%) to be achieved. 

A number of preservative systems are in use (Table 1). Evaporated latex may be preserved by ammonia or potassium hydroxide. Centrifuged latex is always preserved by ammonia, either on its own as in high ammonia (HA) latex or at a lower level in combination with a secondary preservative as in grades of low ammonia (LA) latex. The LA grades are typified by the type of secondary preservative, of which... 

In this study, the degree of autohesion between two layers deposited on the surface of a glass mold was investigated. The Latex blend consisted of (in weight parts) rubber of natural centrifugated latex - 100 sulphur - 2 zinc dimethyldithiocar-bamate - 1 zinc mercaptobenzothiazole - 1 2,2 -methylenebis (6-tert-butyl-4-methylphenol) - 0.5. 

The ABS polymer is recovered through coagulation of the ABS latex. Coagulation is usually achieved by the addition of an agent to the latex which destabilizes the emulsion. The resulting slurry can then be filtered or centrifuged to recover the ABS resin. The wet resin is dried to a low moisture content. A variety of dryers can be used for ABS, including tray, fluid bed, and rotary kiln type dryers. 

Type of dryer tions, extracts, milk, blood, waste liquors, rubber latex, etc. gents, calcium carbonate, bentonite, clay sbp, lead concentrates, etc. trifuged sobds, starch, etc. dry. Examples centrifuged precipitates, pigments, clay, cement. ores, potato strips, synthetic rubber. objects, rayon skeins, lumber. sheets. her sheets. 

The latex may then either be concentrated to about 60% DRC, usually by centrifuging or evaporation, or alternately coagulated and dried. The two approaches lead to two quite distinct branches of rubber technology, namely latex technology and dry rubber technology. 

NR latex grades are described by the method of concentration used. Evaporation, creaming and centrifuging are the most common methods used in the industry. 

Concrete Styrene-butadiene copolymer latex additions on centrifugally cast concrete [271]... 

R. G. Buchheit, T. E. Hinkebein, R F. Hlava, and D. G. Melton. The effects of latex additions on centrifugally cast concrete for internal pipeline protection. In Proceedings Volume, volume 4, pages 2854-2864.12th SPE/NACE Int Corrosion Congr (Houston, TX, 9/19-9/24), 1993. 

A process for separating particles from a suspension by using centrifugal force. It is the most popular method for concentrating natural rubber latex before shipment from plantation to country of use. 

Natural rubber latex as obtained from the tree contains only about 30% by weight of rubber. Concentration of the latex is done by either centrifuging, creaming, electro-decantation or evaporation. 

Natural latex is concentrated by three main methods centrifuging, evaporation and creaming electrodecantation once showed promise, but the output of latex concentrated by this method is now negligible. 

When natural rubber latex is concentrated by centrifuging there are produced approximately equal volumes of concentrate containing most of the rubber, and skim latex with a low proportion of rubber. The rubber obtained by coagulation of skim latex is termed skim rubber. Due to the high content of non-rubber substances such rubber may give difficulty in processing. 

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. 

The amounts oi adsorption of the polymer on latex and silica particles were measured as follows. Three milliliters of the polymer solution containing a known concentration was introduced into an adsorption tube(lO ml volume) which contained 2 ml of latex (C = l+.O wt %) and silica(C = 2.0 wt %) suspensions. After being rotated(l0 rpm) end-over-end for 1 hr in a water bath at a constant temperature, the colloid particles were separated from the solution by centrifugation(25000 G, 30 min.) under a controlled temperature. The polymer concentration that remained in the supernatant was measured colorimetrically, using sulfuric acid and phenol for the cellulose derivatives(12), and potassium iodide, iodine and boric acid for PVA(13). From these measurements, the number of milligrams of adsorbed polymer per square meter of the adsorbent surface was calculated using a calibration curve. 

It is generally accepted that the time required for desorption of adsorbed polymer is very long, and this process seems to appear to be irreversible(ljO. Accordingly, it is expected that the high adsorption values which appeared near the LCST may be held for a long time under different temperature conditions. In Table 3, experimental results for irreversibility of adsorption in the HPC-latex systems are shown. After the HPC samples and the latex particles were mixed for 2 hrs at 1+8 °C under the same condition as in the case of the adsorption process, one portion of one of the samples was separated immediately by centrifugation at 1+8 °C. The other half portion of the HPC-coated latex suspension was kept at room temperature for 1+8 hrs and then centrifuged at 6 °C. As... 

Enzymatically active, partially purified (washed) rubber particles can be isolated such that, when provided with an appropriate APP primer, magnesium ion cofactor, and IPP monomer, rubber is produced in vitro [253-255]. Fresh latex can be separated by centrifugation into three phases. The bottom fraction (20% of the latex) contains membrane-bound organelles. The middle fraction is called the C-serum. The top fraction phase contains the rubber particles. Biochemical smdies have established that latex in this fractionated form is unstable. These smdies also suggest that the bottom fraction is required for initiation of polymer synthesis. 

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