Primary Processing

PRIMARY PROCESSING: The main crop from rubber trees consists of field natural latex and coagulum. Field latex is the fluid that you get directly from tapping the trees and coagulum is the latex in solidified form, usually on the bottom of the collecting cups which is called cup lump. Field latex can be processed and marketed in the forms of latex concentrate, ribbed smoked sheet and technically specified rubber, while coagulum is mainly used to produce lower grade of TSR 10 and 20. Whichever processing method, field latex has to be preserved adequately to prevent coagulation in the field and also during various processing operations. Therefore, we shall start to discuss about the preservation of latex first. Without proper preservation, field latex will auto-coagulate due to the bacterial proliferation at the expense of the non-rubber substances, like carbohydrates, proteins and lipids. This bacterial proliferation will form volatile fatty acids (VFA) and when VFA increases, coagulation will take place. There are other theories on latex auto-coagulation but this is the most likely one. Therefore, it is important to find a suitable preservation material which will prevent auto-coagulation. To work as an effective preservative for natural latex, it must have the following basic features: a. as a bactericide b. has alkaline nature c. has some chelating or precipitting effect d. as an enzyme poison to minimize the effect of coagulase e. has substrate-complexing activity to prevent decomposition of carbohydrates To prevent pre-coagulation in the field for a few hours, formalin, sodium sulphate and ammonia are used. Ammonia has been recognized as the most effective preservative for latex but there are certain drawbacks: a. higher dosage is needed to be effective for longer period b. high dosage causes atmospheric pollution Therefore low ammonia system is needed and the first commercially available system contained sodium pentachlorophenate (SPP), boric acid with 0.2% ammonia. But this system has high toxicity, lower mechanical and storage stability. Then in 1975, LA-TZ system was introduced and it is still being used until today. This system contains of tetramethyl thiuram disulphide, zink oxide and ammonia, but the only drawback is the chemicals TMTD and zinc oxide will sediment during long term storage, thus not suitable for natural latex to be processed as block rubber and sheet as it affects plasticity retention index (PRI). Therefore, the search for better preservative or preservation system continues until today and it has become even more urgent to look for ammonia-free preservative system when Shum and Wren discovered ammonia-loving bacteria in 1977.

Primary Processing

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Primary Processing

Primary Processing

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