Vulcanization of Natural Rubber

Natural rubber is a typical representative of a cross linking material. The increase of viscosity is measured using a special variant of a viscosimeter. Mostly an isothermal regime is applied. Displayed is the torque moment/dNm over time. The relative increase of torque moment is used as an indicator of degree of reaction.

The energy-plot, based on Friedman analysis, demonstrating that the activation energy in the central part of the reaction is nearly constant, exhibits a value of 155 kJ/mol.

From this picture it is visible that a first order reaction is able to describe the cross-linking reaction of natural rubber with a high fit quality.

The advantage of using Thermokinetics instead of simple routines based on the successive calculation of reaction rate and activation energy is that the error propagation is always included in the result and all measurement points are taken into account. Therefore the estimated standard errors are more confident.

Results of Kinetic Analysis
ParameterValueStandard Dev.
lg A/s^-116.020.05
Activation Energy/(kJ/mol)154.90.41
Correlation Coefficient0.9987

Fig.1. Friedman energy plot for isothermal vulcanization of natural rubber
Fig2. Measured data (symbols) and Kinetic model (solid lines) for vulcanization of natural rubber.