Centrifuged latex rubber

Materials High ammonia type centrifuged natural rubber latex from Pasir Waringin Rubber Plantation. FTP XI, West Jawa, lndone.sia was used (Table 1). Carbon tetrachloride and normal butil acrylate were used as sensitizer. Nocract 300 was used as antioxidant. All the chemicals were technical grade without further purification. 

Table 1. Properties of centrifuged natural rubber latex for the experiment...

SULPHUR PREVULCANIZATION OF DOUBLE CENTRIFUGED NATURAL RUBBER LATEX... 

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. 

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. 

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. 

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. 

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. 

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. 

Field latex is bulked in large tanks at a factory adjacent to the rubber estate. If a high-solids latex is desired, the field latex is strained, stabilized with ammonia or other chemicals, such as soap and bactericide, and either centrifuged or creamed to 62-68% total solids,... 

Perrin (Ann. Chim. Phys. 1909,18.55,63) measured the distribution in the earth s gravitational fidd of an aqueous emulsion of rubber latex. Partides of uniform size were obtained by fractional centrifuging. Their size was determined by dialdng some emulsion containing a known total mass of latex with sli tly addified water and then putting a drop of known volume on to a microscope slide. The latex partides then adhere to the surface of the glass and can be counted through a microscope. 

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. 

When making a large article such as a mattress, a metal mold may be filled with the foamed latex and heated by steam at atmospheric pressure. After removing the foamed rubber article from the mold, it may be dewatered by compressing it between rolls or by centrifuging and by drying with hot air in a tunnel dryer. In foamed rubber formulation a part of the NR latex can be replaced by a synthetic rubber latex. One such combination is shown in Table 2.3. 

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