Fresh Latex collected from rubber plantation contains only 30 to 40 % dry rubber content, balance being mainly water. Fresh latex, because of the high water content and presence of non rubber solids, it is susceptible to bacterial attack and hence a perishable material. It can not be used directly for manufacturing any rubber products. Therefore a proper system for preservation and concentration was developed. Now different technologies are adopted for producing stable latex concentrates with suitable latex preservatives. Different types of latex concentrates with a dry rubber content of up to 60 % are produced either by centrifuging or creaming.
The following are the important types of latex concentrates.
Ammonium alginate or tamarind seed powder solution is added to ammonia preserved field latex. The rubber containing particles form clusters at the top separating the serum fraction below. Creamed concentrates are ideal for thread rubber production, form production etc. It has relatively high viscosity and low ZST. Creamed concentrates are available in HA or LA types.
The process of production of centrifuged latex concentrate involves the separation of preserved latex into two fractions, using a high speed centrifuge, one containing the concentrated latex and the other containing serum. Both HA and LA types are available. Centrifuged latex concentrates accounts for over 90% of world latex concentrates production.
| No | ISI Specifications for Centrifuged Concentrated Latex | Type H A | Type L A |
|---|---|---|---|
| 1 | Dry rubber content, percent by mass, Min | 60.00 | 60.00 |
| 2 | Non-rubber solids, percent by massm Max | 2.00 | 2.00 |
| 3 | Coagulum content, percent by massof latex, Max | 0.05 | 0.05 |
| 4 | Sludge content, percent by mass, Max | 0.10 | 0.10 |
| 5 | Alkalinity as ammonia, percent by mass of latex | 0.6 (Min) | 0.3 (Max) |
| 6 | KOH number, Max | 1.0 | 1.0 |
| 7 | Mechanical stability, s, Min | 475 | 475 |
| 8 | Volatile fatty acid number, Max | 0.15 | 0.15 |
| 9 | Copper content, ppm of total solids, Max | 8 | |
| 10 | Manganese content, ppm of total solids, Max | 8 | 8 |
The serum separated during centrifuging of latex contains 3 to 8 % of dry rubber. This is the skim rubber. It is a low quality product which contains many of the non rubbers.