2. Rubber reinforcing filler: carbon black

Over the past century, the importance of rubber to human society has been paid more and more attentions. Several types of particulate fillers have been applied in rubber industry for different purposes, which are based on reinforcement, low material cost, and processing ease. The presence of fillers is key to achieve durable products, increase strength, and prolong life. The modulus of elasticity which is a measure of stiffness of the given materials can also be improved by fillers. Currently, carbon black is the most widely used particulate fillers, which has the ability to bond with the elastomer component enhancing the strength of vulcanized rubbers more than 10-fold as well as imparting durability to the materials [3]. Due to the incomplete combustion of fossil-origin hydrocarbon fuels during the carbon black manufacture, the process has a considerable carbon footprint. About 2.4 tons of CO2 are estimated to be emitted per ton of carbon black, which compares to 0.8 tons of CO2 per ton of cement for cement manufacture [4, 5].

Carbon black is usually present as types of aggregates. According to the TEM graph, its structure can be defined as partly graphitic. More graphitic structure can be observed from the outer layers than from center. Although carbon black particle aggregates are reported to work as a unit in the rubber matrix, its reinforcement ability is not determined by the aggregate units but by each individual particle within the unit. With the particle size decrease, the dispersion ability of carbon black, as well as the interface extension, can be improved, resulting in good reinforcement ability [6, 7].

Particle size, the morphology of aggregates, and the microstructure offered by carbon black can be considered as the key properties contributing to the reinforcement of elastomers. Furthermore, the surface of carbon black and its structural organization, surface area, and its chemical composition are also important. The development of a large polymer-filler interface is highly expected. The upper limit of useful specific surface area for significant reinforcement can reach 300–400 m2 /cm<sup>3</sup> , and is determined by considerations of dispersibility, processability of the unvulcanized mix, and serious loss of rubbery characteristics of the composite [8, 9].

The surface area of carbon black is an important morphological characteristic for reinforcing. It indicates how much available surface can be accessed by rubber molecules for the interaction between the rubber and the filler surface. It is necessary to note that meso- and macropores seem to play the decisive role on the surface unlike micropores for the application of activated carbon. Since the rubber polymer chains are much larger than the micropores, the polymer cannot access these pores.

unsustainable in the long term as a feedstock due to the finite supply and the contribution to

Given the increasing pressure against using nonrenewable resources, it is essential to develop alternative materials to act as novel rubber fillers. Recently, several researches have been conducted focusing "green" fillers, which are based on the waste materials having potential "renewability" [2]. By using bio-based fillers, the dependence on fossil fuel would be improved and a sustainable material basis for rubber filler production could be established. In this chapter, the development of new type of fillers for rubber materials based on char produced

Over the past century, the importance of rubber to human society has been paid more and more attentions. Several types of particulate fillers have been applied in rubber industry for different purposes, which are based on reinforcement, low material cost, and processing ease. The presence of fillers is key to achieve durable products, increase strength, and prolong life. The modulus of elasticity which is a measure of stiffness of the given materials can also be improved by fillers. Currently, carbon black is the most widely used particulate fillers, which has the ability to bond with the elastomer component enhancing the strength of vulcanized rubbers more than 10-fold as well as imparting durability to the materials [3]. Due to the incomplete combustion of fossil-origin hydrocarbon fuels during the carbon black manufacture, the process has a considerable carbon footprint. About 2.4 tons of CO2 are estimated to be emitted per ton of carbon black, which compares to 0.8 tons of CO2 per ton of cement for

Carbon black is usually present as types of aggregates. According to the TEM graph, its structure can be defined as partly graphitic. More graphitic structure can be observed from the outer layers than from center. Although carbon black particle aggregates are reported to work as a unit in the rubber matrix, its reinforcement ability is not determined by the aggregate units but by each individual particle within the unit. With the particle size decrease, the dispersion ability of carbon black, as well as the interface extension, can be improved, resulting

Particle size, the morphology of aggregates, and the microstructure offered by carbon black can be considered as the key properties contributing to the reinforcement of elastomers. Furthermore, the surface of carbon black and its structural organization, surface area, and its chemical composition are also important. The development of a large polymer-filler interface is highly expected. The upper limit of useful specific surface area for significant reinforcement

of the unvulcanized mix, and serious loss of rubbery characteristics of the composite [8, 9].

The surface area of carbon black is an important morphological characteristic for reinforcing. It indicates how much available surface can be accessed by rubber molecules for the interaction

, and is determined by considerations of dispersibility, processability

during pyrolysis of biomass (coconut shell) is illustrated.

2. Rubber reinforcing filler: carbon black

global warming.

90 Advanced Surface Engineering Research

cement manufacture [4, 5].

in good reinforcement ability [6, 7].

/cm<sup>3</sup>

can reach 300–400 m2

The research of the reinforcement mechanism offered by carbon black has been widely undertaken since 1960s [10]. It is widely known that the vulcanization process can only achieve resilient properties with little strength. Then, the strength properties need to be introduced by the addition of "reinforcement" fillers. After carbon blacks are added to the rubber compound, several changes occur: (1) an increase in modulus, or stress at a particular strain, (2) an increase in elongation at break for vulcanizates having a given degree of cross-linking, and (3) consequently, an increase in tensile strength [10, 11]. The improvement of stiffness and the physical properties such as tear resistance, tensile strength, and abrasion resistance are regarded as the crucial contribution of carbon black. The reinforcing ability of a filler can be demonstrated in Figure 1; the only difference between two SBR vulcanizates is the presence or absence of 50phr carbon black N220 in the recipe. With the addition of carbon black N220, the stress-strain curve shows a sharp rise, almost 10-fold compared with the unfilled rubber.

Large amount of literatures report about the reinforcement properties of carbon black for decades. So far, there are more than eight postulations have been wieldy applied to explain the reinforcement mechanisms, which are given in Table 1.

Due to the increasing price of natural rubber and other compounding ingredients, there are several concerns about the ongoing use of nonrenewable resources based carbon black feedstock.

Figure 1. Comparison between filled and unfilled rubber matrix [11, 12]. (Rubber: SBR 1502, 100; zinc oxide, 3; stearic acid, 1.5; Santoflex 13, 0.5; Santoflex 77, 0.5; Sundex 8125, 3; DPG, 0.3; Santousure NS, 1.2; Sulfur, 2. Press cure: 40 min at 153C. Same formulation with addition of 50 phr N220 carbon black).


On one hand, the price of carbon black feedstock witnesses a gradual increase every year. On the other hand, severe environmental problems have been caused by the nondegradability feedstock of carbon black. Consequently, many researches have been conducted in the rubber industry to develop fillers derived from biodegradable waste feedstock, by which transforming its sourcing to a sustainable material basis. Their recyclability and utilization has become a major driving factor in their acceptance and employability, as well as low cost and abundant availability. This new class of carbon black-like feedstock includes natural sources (e.g., natural fibers), industrial by-products (e.g., saw dust, rice husk, coconut shell), and even industrial waste material (e.g., rice husk ash). This field is very attractive from both the ecological and economic point of view, since it could enable rejected material to become valuable material, which could be reused in industry [32, 33]. Some of the popular green feedstocks of novel rubber filler have been summa-

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

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

93

As a single and simple genus species, coconut is grown around the world sharing similar properties. In order to make the experiments standardized, after being crushed into to small pieces (less than 10 mm) by a laboratory-scale hammer miller (Glen Creston, UK), the small pieces of coconut shell were then dried at 105C to constant weight, to reduce the moisture

Carbon black N772 belongs to low to semidispersion, middle-active grades of carbon black, which has the largest particle size and lowest structural and surface area among the whole

rized in Table 2.

3. Process description

3.1.1. Feedstock: coconut shell

Figure 2. Dried coconut shell [11].

content (Figure 2).

3.1. Feedstock and reference material

3.1.2. Reference material: carbon black N772

Table 1. Eight postulations of carbon black reinforcement mechanisms [11].


Table 2. Novel rubber filler from green feedstock [11].

On one hand, the price of carbon black feedstock witnesses a gradual increase every year. On the other hand, severe environmental problems have been caused by the nondegradability feedstock of carbon black. Consequently, many researches have been conducted in the rubber industry to develop fillers derived from biodegradable waste feedstock, by which transforming its sourcing to a sustainable material basis. Their recyclability and utilization has become a major driving factor in their acceptance and employability, as well as low cost and abundant availability. This new class of carbon black-like feedstock includes natural sources (e.g., natural fibers), industrial by-products (e.g., saw dust, rice husk, coconut shell), and even industrial waste material (e.g., rice husk ash). This field is very attractive from both the ecological and economic point of view, since it could enable rejected material to become valuable material, which could be reused in industry [32, 33]. Some of the popular green feedstocks of novel rubber filler have been summarized in Table 2.
