Thermal degradation of rice husk-scrap tyre blends

P.M. STEFANI; D. GARCIA; J. LOPEZ; A. JIMENEZ

Praga- República Checa

Congreso; Degradation, stabilization and recycling of polymers; 2003

The disposal of used automotive tyres has caused many environmental and economical problems to most countries. Particularly Spain makes every year 250.000 tons of tyres, it represents 63,9 percent of rubber products. Most of the scrap tyres are dumped in open or landfill sites. As known, tyre is made of rubbery materials in the form of Cx Hy with some fibrous materials. It has high volatile and fixed carbon contents with heating value greater than that of coal. But some environmental concern has raised during the last years regarding incineration of tyre rubber (1). Therefore, the proposal of recycling of tyres once used must be seriously considered. Some recent studies have proposed the use of recycled tyre rubber to produce thermoplastic elastomers (2). However, despite promising results, this possibility seems difficult for industrial use as the resulting product is still too expensive. The addition of another waste product for reducing costs seems necessary. We propose the use of rice husk as filler for this purpose(3). World rice production in 2002/03 is projected at approximately 582 million tons. As a consequence 145 million tons of  husk residue will be produced. It is important, then, to consider the use of  this residue in polymer formulations with a clear positive effect to the environment. Thermal decomposition of rice husk occurs in various steps in the temperature range between 150 and 550°C. This complex process is the result of the overlapping of thermal decomposition of the three major constituents that are common in all lignocellulosic materials, i.e., hemicellulose, lignin and cellulose. Hemicellulose is degraded at temperatures between 150 and 350°C, cellulose from 275 to 380°C and lignin from 250 to 550°C. The degradation process of major constituents of scrap tyres or their combinations is observed at temperatures between 340 and 550°C. For blends, the addition of rice husk (maximum 25%) produces an increase in the weight loss rate. This effect is higher as the amount of rice husk increases. Apparent kinetic parameters were also studied by several isoconversional methods. We observed that the addition of rice husk produces a decrease in apparent activation energy for low conversions (up to 0.6). For higher conversions this decrease was not so clearly observed.