Mathematical modeling of drying kinetics and property investigation of natural crepe rubber sheets dried with infrared radiation and hot air

In this research study, infrared radiation was combined with hot-air drying to dry natural crepe rubber sheets (NCRS). The system was built and installed with real-time automatic measurement tools to collect data on drying kinetics. The drying temperature was set at 40, 50, or 60 degrees C. Seven mathematical models were tested for fitting the drying kinetics at each temperature. The two statistical indicators used to select the best fit model were the coefficient of determination (R-2) and the chi-square (chi(2)). The appropriate drying temperature was 50 degrees C because NCRS tends to melt and tear beyond this temperature. The dried NCRS was analyzed for raw rubber properties in terms of Mooney viscosity, initial plasticity (Po), and plasticity retention index (PRI), and the dried NCRS was vulcanized with chemical crosslinking agents. Vulcanized NCRS samples were characterized for mechanical properties (tensile strength and elongation at break) and thermal properties (differential scanning calorimetry and dynamic mechanical analysis). The drying at 50 degrees C gave good rubber properties with high PRI value, good mechanical properties, and thermal properties in the normal range. Especially, the mechanical properties were improved by the use of infrared radiation during drying, which is due to the shift of double and conjugated double bond crosslinks. Finally, the energy consumption was 92 kWh over the typical 6 days of drying.