4. Results and discussion

### 4.1. Char characterization

The char yield, oil yield, and gas yield from the pyrolysis process are 31.6, 16.0 and 52.4%, respectively. The char yield is satisfying and encouraging in terms of the potential commercial opportunity for coconut shell to be used as a feedstock to produce a substitute carbon black. The oil yield and gas yield are both beneficial so that further implications of these two byproducts have great potential.

Table 4 summarizes the transmittance of toluene extract (T%), pH value, BET surface area, Tplot surface area, and acidic groups and basic groups on the surface of both commercial carbon black N772 and the pyrolytic coconut char filler.

Toluene transmittance correlates to the amount of tarry or leachable contents in the carbon black as the leachable and unburned tarry or oil-residues on the surface of carbon black or the char can be dissolved into it. This is very important for potential applications, since the presence of a high leachable (oily) content may cause contamination during processing into rubber or other applications and present problems in the appearance and performance of the final rubber products. According to Table 4, the toluene transmittance of char fill is 99.95; it


Table 4. Characterization of char filler and carbon black N772.

shows that the filler is quite clean and pure with little surface contamination. However, the carbon black N772 only has 65.9% of the T%, which indicates that a significant amount of leachable components exists indicating a limiting effect on the purposes.

It is widely known that pores on the surface of solids are classified into three size ranges: micropores (<2 nm width), mesopores (<2–<50 nm with), and macropores (>50 nm width). Normally, if the pores (micropores and small mesopores) are significantly smaller than the very large rubber polymer chains, then the polymer molecules cannot access to these pores. Therefore, unlike micropores present in activated carbon, meso- and macropores may play the decisive role on the filler surface. From Table 4, the area of all pores on N772 is 28.5 m2 /g and the area of meso- and macropores is 26.6 m2 /g. The results indicate that meso- and macropores occupied most of the surface area of carbon black, which reaffirms previous statements about the importance of these pores in carbon black's application in the rubber industry. The BET surface area of the char filler is 373.31 m2 /g, whereas the t-plot surface area is 315.86 m2 /g, which follows the same trend with N772. Moreover, the surface areas are much greater than N772. These data further support the assertion that char samples can be used as an alternative rubber filler.

The pH value of the char surface has been recognized as a foundation of the reinforcing ability of the fillers. It is reported that basic materials may accelerate vulcanization reactions, while acidic ones may delay the vulcanization time of a rubber compound [17, 48]. According to the above, a solution pH value close to 9 makes N772 suitable filler for a wide range of application with reasonable vulcanization time and ideal amount of free radicals. The pH value of the char sample was close to 9, which also supports the proposition that coconut shell could be a promising feedstock for rubber fillers. The surface chemical groups on the surface of char filler are much more plentiful than the carbon black N772, which makes char surface more active resulting in a better interaction and reinforcement from coconut shell char.

#### 4.2. In-rubber characterization

formulation is shown in Table 3, which was applied in the compounding process to investigate the performance of the char filler in rubber. Compounds were produced using a 60 cc

Ingredient Parts per hundred of rubber

SBR 1502 100 Char filler 60 TDAE oil 10 Zinc oxide 5 Stearic acid 2 6PPD 1.5 TBBS 1.5 Sulfur 1.5

The moving die rheometer (MDR) test was conducted based on ASTM D5289, at 160C for 30 min. The results of the MDR were used to evaluate the cure characteristics of each compound and to allow preparation of cured sheet using a cure time of T90 + 5 min. Shore A hardness was tested according ASTM D2240. Tensile properties were determined following ASTM D412. A scanning electron microscopy (SEM) (Auriga Cross Beam, Zeiss) was applied to analyze the surface morphology of the char filler-filled rubber sample and to understand the

The char yield, oil yield, and gas yield from the pyrolysis process are 31.6, 16.0 and 52.4%, respectively. The char yield is satisfying and encouraging in terms of the potential commercial opportunity for coconut shell to be used as a feedstock to produce a substitute carbon black. The oil yield and gas yield are both beneficial so that further implications of these two by-

Table 4 summarizes the transmittance of toluene extract (T%), pH value, BET surface area, Tplot surface area, and acidic groups and basic groups on the surface of both commercial carbon

Toluene transmittance correlates to the amount of tarry or leachable contents in the carbon black as the leachable and unburned tarry or oil-residues on the surface of carbon black or the char can be dissolved into it. This is very important for potential applications, since the presence of a high leachable (oily) content may cause contamination during processing into rubber or other applications and present problems in the appearance and performance of the final rubber products. According to Table 4, the toluene transmittance of char fill is 99.95; it

Brabender mixer set at 40C and 60 rpm.

Table 3. SBR formulation [9, 11].

96 Advanced Surface Engineering Research

4. Results and discussion

4.1. Char characterization

products have great potential.

mechanism of the char filler with the rubber matrix.

black N772 and the pyrolytic coconut char filler.

The cure and physical properties of the rubber compounds filler with the two fillers assessed by the moving die rheometer (MDR) test are summarized in Table 5. At the beginning, a mixture is heated in the cavity of the rheometer under pressure. Then, the viscosity decreases


Table 5. Rheology and physical data of coconut shell char and N772.

and the torque exerted on the rotor drops. The lowest torque value is called moment lowest (ML), which can be used to study the stiffness of the uncured rubber compound at a given temperature, noted as "Min" in Table 5. After the curing process begins, the torque rises. When the torque increases 2 dNm unit above ML value, the time is recorded as Ts2. It tells about the moment the curing process actually starts. With the curing progressing, the torque

continues increasing. After some time, the torque reaches the maximum value and a plateau appears. The highest torque is regarded as moment highest (MH), also noted as "Max" in Table 5. The time from the beginning of the test to the point where 90% of the MH value attained is called T90. The hardness of the filled rubber compound is tested by the Shore A with degree unit according to the ASTM D2240 standard. The M100 and M300% are the stresses required to produce an elongation of 100 and 300% of the test sample. The maximum tensile stress recorded in extending the test piece to a breaking point is shown as tensile strength; and the elongation at break is the tensile strain in the test length at breaking point

The Potential of Pyrolytic Biomass as a Sustainable Biofiller for Styrene-Butadiene Rubber

http://dx.doi.org/10.5772/intechopen.79994

99

According to Table 5, the time to onset of cure (Ts2) and cure times (T90) of the coconut char filled SBR were comparable but slightly longer than conventional carbon black N772. Different surface chemistry may be the reason, since it may have some interactions with the cure package. The hardness value was slightly high than N772, also indicating that coconut shell has the potential to be used as the parent material of rubber filler. The M100% values are found to be higher than the commercial carbon black. The low tensile strength and high elongation to break values imply that there are low filler-polymer interactions and structure levels, allowing for chain slippage over the filler surface, which can be enhanced through modification of the rubber mix formulation [9]. Based on this data, the sample can be considered as a semi- to lowreinforcing filler with broadly similar cure characteristics to conventional carbon black.

The SEM plots of coconut char compounded rubber sheet and N660 (which behaves better in the rubber matrix than N772) filled rubber sheet at 25 K magnification are shown in Figure 4. According to the images that base layer is the rubber matrix, the small particles on the surface are fillers (char filler and N660). It can be seen from the images, the fillers are unevenly attached to the surface of the rubber, indicating that the mechanism of the interaction between char filler and rubber is similar to conventional carbon black. Particle shapes, sizes, and its distribution are the main differences between coconut char and commercial carbon black. Smaller aggregate size and more uniform size distribution of carbon black plus spheroid particles may be helpful during the vulcanization process leading to good rein-

Coconut shell, as a high-volume problematic waste material, has the potential to be successfully converted into a high-quality carbon black-like char filler, and high heat value, renewable energy materials (mainly oil and some gases) at relatively small scale. Thus, global fossil fuelderived emissions can be reduced by the help of the ability of biochar to sequester the carbon contained in the coconut shell by conversion into a stable and nonavailable form. This type of process has been regarded as popular sector with growth potential in the global carbon market

suitable surface pH (9.70), can be achieved by the coconut shell char filler. The char filler produced

/g), along with high levels of purity (99.95%) and

with a controllable, clean, and simple manufacturing process.

High external surface area values (315.89 m2

[11, 52].

forcement.

5. Conclusion

Figure 4. SEM plots of compounded rubber sheets at 25 K magnification, illustrating rubber-filler bonding system [11]. (a) SEM plot of Run 20 filled rubber sheet. (b) SEM plot of N660 filled rubber sheet.

continues increasing. After some time, the torque reaches the maximum value and a plateau appears. The highest torque is regarded as moment highest (MH), also noted as "Max" in Table 5. The time from the beginning of the test to the point where 90% of the MH value attained is called T90. The hardness of the filled rubber compound is tested by the Shore A with degree unit according to the ASTM D2240 standard. The M100 and M300% are the stresses required to produce an elongation of 100 and 300% of the test sample. The maximum tensile stress recorded in extending the test piece to a breaking point is shown as tensile strength; and the elongation at break is the tensile strain in the test length at breaking point [11, 52].

According to Table 5, the time to onset of cure (Ts2) and cure times (T90) of the coconut char filled SBR were comparable but slightly longer than conventional carbon black N772. Different surface chemistry may be the reason, since it may have some interactions with the cure package. The hardness value was slightly high than N772, also indicating that coconut shell has the potential to be used as the parent material of rubber filler. The M100% values are found to be higher than the commercial carbon black. The low tensile strength and high elongation to break values imply that there are low filler-polymer interactions and structure levels, allowing for chain slippage over the filler surface, which can be enhanced through modification of the rubber mix formulation [9]. Based on this data, the sample can be considered as a semi- to lowreinforcing filler with broadly similar cure characteristics to conventional carbon black.

The SEM plots of coconut char compounded rubber sheet and N660 (which behaves better in the rubber matrix than N772) filled rubber sheet at 25 K magnification are shown in Figure 4. According to the images that base layer is the rubber matrix, the small particles on the surface are fillers (char filler and N660). It can be seen from the images, the fillers are unevenly attached to the surface of the rubber, indicating that the mechanism of the interaction between char filler and rubber is similar to conventional carbon black. Particle shapes, sizes, and its distribution are the main differences between coconut char and commercial carbon black. Smaller aggregate size and more uniform size distribution of carbon black plus spheroid particles may be helpful during the vulcanization process leading to good reinforcement.
