A Comparative Study on the Thermal Behaviour of Natural Rubber Filled with Carbon Black and Plant Residues

Aims: A comparative study on the thermal behavior of natural rubber (NR) filled with different plant wastes and carbon black was carried out with the aim to evaluate green fillers that can replace carbon black filler in natural rubber vulcanisates for thermal applications.

Study Design: The plant wastes used for this study were carbonized and un carbonized cocoa pod husk, corncob and empty palm fruit bunch. Natural rubber vulcanisates filled with 10 phr carbon black (reference) and the various plant waste materials were prepared.

Methodology: The thermal behaviour of the vulcanisates and the fillers was studied by thermogravimetric analysis (TGA). The glass transition temperature (Tg) for the vulcanisates was determined by differential scanning calorimetry (DSC). The shape of the decomposition curve was obtained from the derivative of the TGA curve (DTGA). The amount of residue remaining at various temperatures for the different samples was calculated from the TGA curve. Activation energies of degradation were calculated using Horowitz–Metzger equation.

Results: The carbonised fillers and carbon black were more thermally stable than the un carbonised fillers and raw rubber. The decomposition behavior of vulcanisates followed a similar trend; with a single main decomposition peak at about 380°C. Samples with un carbonised fillers had higher residues than those filled with carbon black and carbonized plant wastes. From the activation energy values, it was found that vulcanisates, filled with carbonized corncob and carbonized cocoa pod husk were very close in thermal stability to those filled with carbon black and they were more stable than those filled with un carbonised plant wastes. DSC studies revealed that the fillers had non-significant effects on the Tg of the vulcanisates. This was evident from the very close nature of the Tg values for the different vulcanisates. Among the plant wastes studied, carbonised cocoa pod husk and corncob presented very close values of Ea and Tg to carbon black as fillers for raw natural rubber.

The vulcanisates with un carbonised fillers were less thermally stable than vulcanisates filled with carbonized fillers and carbon black.