Determination of Dry Rubber Content of Hevea Latex by Microwave Technique

The measurement of the dry rubber content of the fresh hevea latex by microwave technique is described. In this technique the attenuation of microwave by latex is measured at 10.7 GHz and is then calibrated against the standard laboratory method. Compared with the standard method this instrument is able to reduce the measuring time 8 - 16 hours to three minutes. The correlation coefficient between the DRC determined using this instrument and the standard laboratory method is 0.998 and the standard deviation is less than 0.7%. The reproducibility is at a level of 0.8% unit DRC

Microwave aquametry: a growing technology

A rapid growth of microwaves system has taken place after the Second World War in the area of telecommunication and navigation in both civilian and military. However, industrial, scientific, medical and domestic applications have developed at a slower pace. By far, the most popular application of microwave power is in microwave oven for domestic and commercial cooking. On the other hand, a greater variety of industrial applications of high microwave power has been demonstrated including applications in various industries such as rubber, food, textiles, plastics, foundry, building materials, paper, pharmaceuticals, cosmetics, and coal. The main advantage of microwave power in processing of materials are increased rate of production, improved product characteristics, uniform processing and controllability of the process. Low-intensity microwaves have found industrial, scientific and medical application in a non-destructive testing and monitoring of material, objects and people. These include microwave aquametry and mechanical parameters monitoring and the first known patent was granted in Sweden in 1945. Microwave methods have also been used in medical diagnosis such as cancer detection and monitoring of respiratory systems. It was only recently that the measurement of dielectric properties has been applied to microwave aquametry for on-line process control in the manufacturing industries. However, the measurement and use of dielectric properties has been a concern of the physical sciences for almost a decade ago. In past years, two Nobel Prizes have been awarded to scientists Debye (1936) and Onsager (1968) for their work involving dielectric theory and the application of Maxwell's electromagnetic theory. The objective of this paper is to expose the growing technology of microwave aquametry and highlight its most interesting and successful applications. In organising and presenting the material, an attempt was made to meet four goals. First to show the dielectric properties of water and moist substances, second the state of the art of microwave aquametry system, third to show the development of microwave sensors and instrumentation for that could benefit our agriculture and manufacturing industries and fourth the current development of microwave aquametry for various applications. This work highlights the findings of research over the past 23 years especially in the application of microwave aquametry in rubber and oil palm industries

Microwave Drying of Hevea Rubber Latex and Total Solid Content (TSC) Determination

This paper deals with the microwave drying of the hevea rubber latex. It outlines the theoretical and experimental aspects on the effect of sample weight (5 gm to 15 gm), microwave power levels (3W/ cm3 to 10.6W/cm3) and initial TSC (25% to 60%) to the drying rate and final drying time. A series of drying curves (mass versus drying times) was generated and optimum conditions for drying were determined. A close relationship between theory and experiment has been found. The drying rate and final drying time for 5 to 15 gm samples with TSC = 39.2% at 9.3 W/cm 3 is approximately 0.07 gm/sec and 4 minutes respectively. A large amount of sample > 20 gm is avoided to prevent any explosion and sputtering of the sample during drying process. It is suggested that the optimal mass and power level are 10 gm and 9.3 W/cm 3 respectively. The experimental results clearly showed that micro were drying is very efficient for drying of fresh hevea latex as the conventional drying method needs 1 to 2 hours

Simultaneous analysis of conductivity and concentration of saline solutions and sea water at microwave frequencies from dielectric investigation.

Prediction of conductivity and concentration of saline solutions and sea water are calculated from dielectric spectra at microwave frequencies of 2 GHz and 5 GHz respectively. The calculation is based on two different previously published empirical models relating to conductivity and concentration. An empirical relationship is established and is used to find corrected calculated conductivity and concentration. The expected results are verified with standard measurement where correlation coefficient of given is 0.98 and above. The data is useful as tools for quality indication of liquid samples

Microwave dielectric characterization of hevea rubber latex at 2.6, 10 and 18 GHz

Dielectric properties of natural rubber Hevea brasiliensis latex were measured at frequencies 0.2 to 20 GHz, at temperatures of 2, 15, 25, 35, and 50°C and around 30-98% moisture content. Measurements were done using open-ended coaxial line sensor and automated network analyzer. As expected, results showed that dielectric constant increased with increasing moisture. From 0.2 to 2.6 GHz, the losses were governed by conductive losses but for frequencies greater than 2.6 GHz, these were mainly due to dipolar losses. The former is due to conducting phases in hevea latex, while the latter is mainly governed by the orientation of water molecules. The results were analyzed at 2.6, 10, and 18 GHz, respectively. These were then compared with the values predicted by the dielectric mixture equations recommended by Weiner, Bruggeman and Kraszewski. All the measured values were found to be within the Weiner's boundaries and close to the upper limit of Weiner's model. It is also close to the predicted values of Bruggeman's model with a/b = 0.1. All the models including Kraszewski are suitable for predicting the dielectric properties of hevea latex for frequencies 2.6 to 18 GHz, moisture content 30 to 98% and temperatures 2 to 50°C

Monitoring microwave dielectric properties during transesterification reaction for palm biodiesel production

Microwave energy offers a fast method to produce biodiesel with advantages of enhancing the reaction rate and improving the reaction separation. The dielectric properties at frequency range from 0.2 GHz to 20 GHz of a mixture during transesterification reaction which are used for producing palm biodiesel were presented. The monitoring was done by placing a dielectric probe at the upper level and lower level of the mixture to measure the dielectric properties during the formation of biodiesel and glycerin respectively. In the transesterification reaction, the mixture consisting of vegetable oil, methanol and sodium hydroxide was heated at a constant temperature of about 45-50 o C and stirred for homogeneity. Results of the measurement over the frequency range showed drastic changes on the dielectric properties in the first 3 minutes of the reaction and after 3 minutes, the dielectric properties slowly decreased and approached the dielectric properties of biodiesel or glycerin. This study gives valuable information on the optimum mixing time for microwave transesterification reaction. These properties could be used to estimate absorbed power by the mixture for application in microwave transesterification process as dielectric loss of the mixture changed from 20 to about 0.5 as the transesterification reaction was completed

Microwave Drying of Palm Oil Mill Effluent

This paper describes the treatment of palm oil mill effluent (POME) by using microwave drying. The study concentrated on the variation of the drying rate with respect to different initial mass and microwave power and the effect of silicon carbide (SiC) to enhance the drying. The initial mass of sample and energy level ranges from 20. - 50 g and 91 - 504 watt respectively. The experimental results show that under the microwave treatment the drying time required to reduce the amount of sample to 25% of its initial mass at power level of 504 watt was within 3.5 - 6.4 min. While with SiC and at the same power level the drying time was only 1.8 - 3.6 min. This time is almost one-third of the time taken by conventional drying. The experimental results clearly showed that microwave drying can be considered as an alternative technique for the POME treatment since it is efficient, quick and does not pollute the environment

Microwave Dielectric Properties of Hevea Rubber Latex in the Temperature Range of -30°C to 50°C

The dielectric properties of hevea rubber latex were measured at selected microwave frequencies over the temperature range of -30°C to 50°C. The measurements were made on latex concentrate, fresh latex and diluted fresh latex by using an open-ended coaxial-line probe and an automated network analyser. There is a steep increase in the dielectric constant of about one order and dielectric loss factor of about two orders as the phase of latex changes from solid to liquid. The effect of temperature on the ionic conductivity at 0.2 GHz and dipole orientation at 2.6 GHz and above can be clearly seen in these studies. It was found that, the frequency around 10 GHz is a suitable operating frequency for microwave latexometer as dielectric properties are fairly independent of the temperature