3.4.4. Boehm titration

The oxygen surface groups on char filler were investigated by the Boehm titration [17]. This method is based on the principle that oxygen groups on surfaces have different acidities and can be neutralized by bases of different strengths. Sodium hydroxide (NaOH) is the strongest base generally used, and is assumed to neutralize all Brønsted acids, while sodium carbonate (Na2CO3) neutralizes carboxylic and lactonic groups and sodium bicarbonate (NaHCO3) neutralizes carboxylic acids. The difference between the uptake of the bases can be used to quantify the oxygen surface groups on a char sample [50].

#### 3.4.5. In-rubber testing

Styrene-butadiene rubber (SBR) is widely applied in tire treads. When protected by additives, excellent traction properties, good abrasion resistance, and good aging stability can be achieved [51]. It is reported that the most common use of SBR is in pneumatic tires with around 50% of car tires being made from a range of types of SBR. A widely used generic SBR

#### 96 Advanced Surface Engineering Research


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

Char filler 99.95 9.70 373.3 315.89 0.062 0.316 CB N772 65.9 8.5 28.5 26.6 0 0.079

T-plot surface area (m2 /g)

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

Acidic groups (mmol/g)

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

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

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

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

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

> Shore A ()

Char filler 1.16 14.42 7.04 13.48 59 1.99 2.82 5.68 653 CB N772 1.23 13.66 4.33 9.19 57 1.63 9.3 20.4 586

M100% (Mpa)

M300% (Mpa)

Tensile strength (Mpa)

Elongation at break (%)

/g, whereas the t-plot surface area is 315.86 m2

/g. The results indicate that meso- and macropores occupied

/g and the area of

Basic groups (mmol/g)

97

/g, which follows the

leachable components exists indicating a limiting effect on the purposes.

area (m<sup>2</sup> /g)

T% pH value BET surface

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

on the filler surface. From Table 4, the area of all pores on N772 is 28.5 m2

resulting in a better interaction and reinforcement from coconut shell char.

T90 (mm:ss)

meso- and macropores is 26.6 m2

the char filler is 373.31 m2

4.2. In-rubber characterization

Max (dNm) Ts2 (mm:ss)

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

Min (dNm)

Table 3. SBR formulation [9, 11].

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 Brabender mixer set at 40C and 60 rpm.

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 mechanism of the char filler with the rubber matrix.
