Abstract
Rubber latex is collected by periodic excision of a thin shaving of the bark of Hevea tree. In addition to the volume, its value is determined by the dry rubber content (DRC) of latex. Dry rubber content of latex varies usually in the range of 20-45% and depends on several factors such as clone, season, climate and weather condition, stimulation program, tapping system, soil condition etc. Hydrometry (using the Metrolac) is the most widely used method in the determination of DRC in the Sri Lankan rubber industry. Metrolac measurements are highly vulnerable to temperature of the latex/water mixture. Existing ready-reckoner for Metrolac readings is valid only at 290C, hence the present study was aimed at developing a Metrolac ready-reckoner chart corrected for temperature variation in latex. Under natural and adjusted conditions, the new ready-reckoner chart showed an accuracy level of 84% on average in the estimation of dry rubber content whilst the average accuracy by the existing chart was below 50%. The Metrolac estimated DRC differed in the range of -12.69% to 9.25% from the actual under existing ready reckoner whilst that was limited to -7.56% to 5.31% with the use of new ready-reckoner chart.
Highlights
Rubber is one of the major agricultural crops in Sri Lanka
Even though there are several accurate methods for determination of dry rubber content (DRC) in rubber latex, Metrolac is widely used in Sri Lanka due to the convenience in field use
Since existing Metrolac ready-reckoner chart had been standardised at 29°C, corresponding dry rubber content given in the Metrolac ready-reckoner chart was taken as the base value for building up the temperature corrected ready-reckoner Metrolac chart
Summary
Rubber is one of the major agricultural crops in Sri Lanka. Even though there are several accurate methods for determination of dry rubber content (DRC) in rubber latex, Metrolac is widely used in Sri Lanka due to the convenience in field use. Methodology Development of the temperature corrected ready-reckoner chart About 400 fresh latex samples were collected and one fold of latex from each sample was mixed with two folds of clean water as per the requirements for Metrolac latex weighing (Sarath Kumara, 2003) Temperature of these latex water mixtures was adjusted using an ice bath or a hot water bath and Metrolac reading was taken at each degree from 15°C to 35°C. Linear relationship of MDRC estimated at 29°C of latex samples were regressed with MDRC estimated at each degree of temperature and equations were built up for the linear relationships between MDRC at 29°C and different temperatures Using these equations the MDRC at each temperature for different Metrolac readings was estimated and developed the ready-reckoner chart for estimation of dry rubber content with temperature correction. Actual dry rubber content of each sample was determined by the standard laboratory method (Anon, 1984)
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