Effect of carbonization on the processing characteristics of rubber seed shell

1 Introduction

Fillers in rubber compounds play a major role in physico-mechanical properties and exercise control over cost of the products (Bledzki and Gassan, 1999). It is well established that carbon black is one of the most important classical reinforcing fillers, especially for the rubber industry. However, carbon black is expensive and petroleum from which it is derived is non renewable (Mwaikambo and Ansell, 2002). Therefore, considerable research and development efforts are being carried out to investigate the possibility of replacing this filler with renewable raw materials as fillers (Okieimen and Imanah, 2005).

The use of carbon from agricultural by-products (maize cob groundnut husk, cassava peel, cocoa pod husk, plantain peel, rubber seed shell, etc.) for producing vulcanizate materials that are competitive with synthetic composites has been gaining attention in the last decade because of availability of materials, easy processing, low cost, and high volume applications (Okieimen and Imanah, 2005; Okieimen and Imanah, 2003).

Agricultural residues as by-products and co-products of agriculture and processing of agricultural products represent a large feedstock of underutilized resources which can be used directly or converted by fairly simple chemical processes into higher value added materials.

Rubber seed shell is an agricultural by-product of the rubber tree. The economic importance of the rubber tree has largely focused on the rubber latex with little attention paid to the potential usefulness of its by-product. While significant progress has been made in the development and utilization of modified agricultural by-product in water and wastewater treatment, (Toles et al., 1997; Ricordel et al., 2001; Imanah and Okieimen, 2003; Jideonwo and Utuk, 2001) there is little information on the potential for the application of these by-products.

Previous studies (Sun and Jiang, 2010; Ekebafe et al., 2010) revealed that the temperature at which carbonization of agricultural by-products is carried out could affect the characteristics of the carbon obtained and therefore, the physico-mechanical properties of the rubber vulcanizate. The present research work was undertaken, with an objective to explore the influence of carbonization on the processing characteristics of rubber seed shell.

2 Experimental

3 Results and discussion

The weight of the rubber seed shells on carbonization for 3 h at different temperatures shows a progressive decrease as the temperature increases due to the combustion of the residual materials in the shells. The relationship between weight after carbonization and the carbonization temperature is shown in Fig. 3.1. Most fibers are composed of cellulose, hemicellulose, lignin, waxes, and some water-soluble compounds, where cellulose, hemicelluloses, and lignin are the major constituents (Eichhorn et al., 2001). The percentage composition of each of these components varies for different fibers. Generally, the fiber contains 60–80% cellulose, 5–20% lignin and up to 20% moisture. The moisture content of the rubber seed shell is as shown in Table 1.

Close

Figure 3.1

Variation of yield of carbon with carbonization temperature.

Export to PPT

The variation of the pH of the rubber seed shell carbon as a function of the carbonizing temperature and the metal content of the seed shell is shown in Fig. 3.2 and Table 1. The pH varied over a range of 4.79–8.77. The results show a progressive increase in pH with increase in carbonization temperature, the possible reason could be that as the residual material is being lost on combustion, the metal content activity is enhanced in view of the Magnesium, Sodium, Potassium and Calcium oxide contents in the seed shell (Table 1) which increase alkalinity and hence pH. These corroborate the results of Sun and Jiang (2010).

Close

Figure 3.2

Variation of pH of RSSC with carbonization temperature.

Export to PPT

Electrical conductivity is defined as the conducting power of all ions produced by 1 g of electrolyte in solution and it has a reciprocal relationship with resistance (Sharma and Sharma, 2004). The results in Fig. 3.3 show that the electrical conductivity of RSSC increases with the rising of temperature. At 600 °C, the resistance in RSSC becomes very small, meaning good conductivity, while above 600 °C the conductivity descended slightly.

Close

Figure 3.3

Variation of conductivity of RSSC with temperature of carbonization.

Export to PPT

The bulk density is principally influenced by the particle size and structure of the fiber and the lower the particle size the lower the bulk density and therefore better the interaction between the polymer matrix and the reinforcing filler, this would enhance the processing and improve the quality of the end product as the desirable properties for particulate fillers include excellent tensile strength and modulus, high durability, low bulk density, good mouldability and recyclability (Sharma and Sharma, 2004). This further explains the reasons for the results in Ekebafe et al. (2010). Variation in Fig. 3.4, shows that at high heating temperature, the bulk density reduces which may be due to the opening of the interstitial spaces (microspores) in the carbon residue.

Close

Figure 3.4

Variation of bulk density of RSSC with carbonization temperature.

Export to PPT

The iodine adsorption number from Fig. 3.5, reveals that as the filler carbonizing temperature increases the amount of iodine adsorbed per 100 g of the material increases. One important application of iodine adsorption number is that it elicits the surface area of the material. It is a parameter that indicates the macrostructure of fillers and reflects the reaction and adsorption abilities (Moloney, 1995). Like wood fiber, at high temperature, all kinds of porosities will form inside RSSC, which bring RSSC a certain specific surface area, reaction and adsorption capacity. The variation between the iodine adsorption number and the filler temperature is shown in Fig. 3.5.

Close

Figure 3.5

Variation of iodine adsorption of RSSC with carbonization temperature.

Export to PPT

The maximum iodine adsorption number (66.75 mg/100 g) was obtained when the carbonizing temperature reaches 600 °C; eliciting the fact that maximum surface area occurs at this temperature; the surface area value is much smaller when carbonizing under low temperature (200 °C) due to the low porosity resulting from incomplete carbonization. At higher temperature (>600 °C), the porosity reduces too, the reason might be that some cavities have been burned and the corresponding surface area reduced. So when carbonizing temperature reaches 800 °C, the surface area value is small too.

Fig. 3.6 presents the relationship between loss on ignition of RSSC and the filler carbonizing temperature. It can be seen that the loss on ignition percentage increases from 7.1% to 83.2% with increase in the heating temperature, the loss on ignition percentage increased rapidly with the rising of temperature up to 800 °C, this might be caused by the almost completed volatilization of the volatile matter at the temperature above 600 °C.

Close

Figure 3.6

Relationship between loss on ignition and the filler temperature.

Export to PPT

4 Conclusion

The work is an attempt at exploring the effect of carbonization on the processing characteristics of rubber seed shell powder. The result shows that heating temperature affects the properties of the rubber seed shell. These results predict the vulcanization rate and the potential application of the filler.