Drying kinetics of unsmoked rubber sheet by forced and natural convection

The objectives of this research were to investigate model for describing equilibrium moisture content of fresh rubber sheet and drying kinetics of Air Dried Sheet (ADS) rubber using hot air (HA) drying, green house (GH) drying and conventional open-air (OA) drying. The experimental results were mathematical simulated by non-linear regression analysis. Equilibrium moisture content (EMC) of natural rubber (NR) were evaluated using the gravimetric-static method among surrounding temperature of 40-60°C provided to relative humidity surrounding of 10-90%. The results showed that The Modified Halsey model was found to be the most suitable for describing the relationship among equilibrium moisture content, relative humidity and temperature. The appropriate thin-layer drying equation model for predicting the drying kinetic of rubber sheet. The experiments were carried out under the conditions of constant drying temperature 30-55°C, the initial moisture contents of sample rubber were operated in range of 15-40 % dry-basis. The final moisture content for each drying strategies was fixed at 1±0.05 % dry-basis. The effects of drying conditions on evolution of moisture content, drying rate and quality of rubber were determined. The experimental results showed that for both forced and natural convection the drying rate of rubber sheet was relatively related to drying temperature. The fresh rubber sheets were dried by OA drying took longer drying period than those of HA drying. Twelve thin layer drying equation models were used for evaluating experimental data and the results showed that the simulated data using Weibull Distribution model had a good relation to the experimental values of sample drying with HA, experiment results using Modified Henderson and Pabis model was the best fitting model for GH and conventional OA drying. According to the quality and energy analysis, the results showed that quality of the rubber sheet was acceptable in market level for all drying heat sources. However, ADS rubber drying with HA and OA were slightly better than GH drying.