Supawan Tirawanichakul, Sutian Sanai, Chayanuch Sangwichien, and Yuthana Tirawanicahkul

pp. 335 - 346

Abstract

The purpose of this research was to study and develop a mathematical model of essential parameters affecting drying process in terms of equilibrium moisture content (EMC), apparent density, percentage of void fraction, specific heat capacity and effective diffusion coefficient (D) for three kinds of natural rubber.
Three raw natural rubber samples in this work used crumb rubber, rubber stick and rubber sheet with an initial moisture content ranging between 30 and 45% wet-basis that were normally used for producing the standardized Thai rubber (STR) block rubber and air dried rubber sheet (ADS). The results show that the
apparent density and specific heat of all natural rubber samples were linearly dependent on the moisture content whilst the percentage of void fraction of natural rubber was inversely related to moisture content. The isotherm EMC equations formulated by the Herderson model for the crumb rubber and rubber stick were the best fitting with the experimental values, and for the rubber sheet. The isotherm EMC equation using the Halsey model was the most appropriable to the experimental results. In addition, the effective diffusion coefficients of all natural rubber materials, which were the function of drying temperature and drying time, were in range of 10^-6-10^-7 m²/hr. However, prediction of the evolution of moisture content of thin-layer drying under the condition of drying temperatures of 40-70°C (rubber stick and rubber sheet) and100-130°C (crumb rubber) could be explained by the empirical model, which was the function of drying temperature and drying time.