DRY RUBBER CONTENT

Abbreviation for dry rubber content, generally of latices and similar dispersions. 

A hydrometer with a special scale, used for the determination of the approximate dry rubber content of latex. 

Figure 11.31 13C-NMR spectra of polybutadiene containing 80% gel (a) Solution measurement (10 w/v% CDC13 solution), (b) latex measurement (10 w/v % dry rubber content), and (c) solid state measurement [133]...

Total solids contents 36% (including dry rubber content... 

NR occurs as particles dispersed in an aqueous serum, i.e., latex, which are contained in bundles of tubular vessels in the trunk of the tree [7]. Latex is harvested from the tree by a process called tapping. The latex of the Hevea braziliensis tree has been described as a cytoplasmic system containing rubber and nonrubber particles dispersed in an aqueous serum phase. Freshly tapped Hevea latex has a pH of 6.5-7 and a density of 0.98 gcm . The total solids of fresh field latex vary typically from 30 to 40%, depending on weather and tapping frequency and other factors. The dry rubber content is approximately 3 wt% less than the total solids [8]. 

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. 

The requirement is for either total solids content or dry rubber content. The difference between the total solids content and dry rubber content. 

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... 

Fresh natural rubber latex contains about 30-40% of rubber hydrocarbon that is normally referred to as dry rubber content (DRC). However, the total solid content (TSC) is higher than the DRC due to the presence of non-rubbers in the latex, at around 5%. The DRC and non-rubber content may change due to many factors such as clone, soil and climate conditions, season, type of fertilizers used, and tapping frequency. Most of these non-rubbers are dissolved or suspended in the aqueous serum or adsorbed on the surface of rubber particles. They become trapped, tenaciously held, or co-precipitated during coagulation of the rubber probably due to their poor solubility in the aqueous medium or strong entanglement with the rubber molecule. The major non-rubbers are lipids, proteins and amino acids, minerals, inositols and carbohydrates, as shown in Table 3.1. 

Dry rubber content by definition and use is the acid coagulable portion of latex, after washing and drying. 

Latex is concentrated to 60% to 68% dry rubber content. This is done by either centrifuging, evaporating, or creaming. By far, the most popular method... 

Creamed latex is made by the use of a creaming agent such as ammonium alginate. The creaming agent helps form a rubber-rich layer at the top of the holding tank. This is a slow process several weeks may be required before the desired concentration is reached in the top layer, which is drawn off for shipment. Creamed latex has a minimum dry rubber content of 62% and is preferred by rubber thread manufacturers because of its good filterability. 

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. 

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. 

As above, let M = 7833 and M = 527, and let the outer radius of the shell Bq = 2Aq. The swollen volume of the core in benzene will be 1.498 times the initial volume, while the shell will swell, in accordance with fig.5, to give a radius b = 3,22 Aq. The total volume of the sphere (core and shell) therefore equals 4.19 X (3,22A(,) 135.59 Aq. The average dry rubber content in... 

On gouging the bark of Hevea brasiliensis, hevea latex is collected, which has close to a 33% dry rubber content. Natural mbber, a long-chain polyisoprene, given by... 

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