The physical and chemical attributes (particle size, surface area, structure, surface activity) of carbon black can change the characteristics of the elastomer in different ways and to different degrees. The carbon black loading is a critical factor in achieving the desired degree of modification of the elastomer which will impart suitable properties to the rubber compound for a given application.
A rubber compounder must know how to select the correct polymer, carbon black and filler combination, and the proper vulcanization system, to achieve a rubber compound at the lowest possible cost.
Surface Area: The surface area of a carbon black is very important because it defines how much surface area is available to interact with other materials present in a rubber compound. Small particle size blacks generally have a high surface area. The size of the particle exerts a great influence on the chromatic properties. Smaller sized particles have more intense colors and higher viscosity and require more energy for dispersion.
Structure: Primary structure is used to describe the degree to which carbon black particles are bound together in aggregates. The secondary structure is the agglomeration of the aggregates, due to Van der Waals forces and they are formed during the pelletization of the carbon black. Aggregation contributes almost all of the structure-related effects observed in rubber compounds, while agglomeration is easily destroyed during rubber mixing and has less effect on the properties of rubber compounds. Carbon Blacks with a high structure provide higher viscosity and easier dispersion.
Chemical Properties and Surface Activity: The chemical nature of the carbon black surface is variable. There is evidence for the presence on the surface of at least four oxygen-containing groups: Carboxyl, Phenol, Quinone, and Lactone. The surfaces may also differ in adsorptive capacity and in the distribution of high-energy sites. Carbon blacks with chemically modified surfaces have not shown any noticeable improvement in reinforcement in rubber compounds. Chemical surface groups affect the rate of cure with many vulcanizing systems. There is no standard procedure for the quantitative estimation of the chemical surface and surface activity of carbon black. However, a relative measure of surface oxidation can be obtained from pH measurement and weight loss on drying carbon black at 950°C.
Electrical and Thermal Conductivity: Carbon blacks are generally electrically conductive because of the highly conjugated bonding scheme present in the crystalline regions. Increasing the structure and surface area, both contribute to increased electrical conductivity.
In thermal conductivity, the effects of the elastomer overshadow the effects of the carbon black. Specialty blacks for high electrical conductivity are usually high in structure and may be porous. These blacks do not necessarily give the highest thermal conductivity, perhaps due to their porous nature which provides a measure of heat insulation.
Pellet Quality: Pellets are required for economical transportation and for adequate flow in bulk shipping containers and conveying equipment. These pellets must have sufficient strength to resist physical breakdown during transportation and plant handling yet be weak enough to break up and disperse during rubber mixing.
Pellet Hardness requirements depend on the nature of the compound in which the carbon black is to be used. Compounds using low viscosity polymers usually require soft pellets.
The percent Fines and Attrition are considered as indicators of bulk-handling characteristics. High fines may also signal the possibility of mixing difficulties.
Mass Strength: Reflects carbon black flowability in bulk shipments.
Pellet Size Distribution is sometimes important. A high concentration of large pellets is generally believed to be undesirable because of their tendency to fragment rather than to crumble and hence to give poor dispersion.
Purity: The purity of carbon blacks is generally judged from toluene discoloration, ash, grit residue and sulfur content.
Toluene Discoloration gives a rough estimate of the amount of extractable material present.
The Ash arises mostly from salts in quench and pelleting water with some contribution from non-hydrocarbon impurities in the feedstock.
Grit or Sieve Residue is material suffiently large to remain on a U.S. 35 to 325 mesh screen. Primary sources of grit are coke formed in the reactor, pieces of refractory that have eroded from the reactor, and metal scale from the process equipment.
Sulfur in furnace blacks comes from the feedstock and varies with the sulfur content of the feedstock. Most of the sulfur is chemically bound and appears to be distributed throughout the carbon black aggregate. Carbon black with sulfur levels up to 1.5 percent do not appear to influence cure rates.
The Oxygen present is chemically combined on the surface of the black, while hydrogen is distributed throughout the particle.
The Carbon Black is chemically pure carbon.
Is produced in special reactors by the thermal decomposition of an oil used as raw material.
The high temperatures in the reactor cause the rupture of the oil molecules in their two basic components: carbon and hydrogen. At this stage variables air, oil and natural gas, as well as temperature and reaction time are controlled.
The Carbon Black obtained, together with the combustion gases, advances to the filtering step where carbon black is separated from the gases.
Next, the powdered Carbon Black that comes from the filtering phase, goes to the pelletizing phase and then to the drying phase where it acquires the final product conditions.
It is then sent to the storage silos, from where the feed bagging systems and bulk filling. The entire process, from receipt of raw materials to the dispatch of the finished product is controlled under a harsh environment.
The entire process, from receipt of raw materials to the dispatch of the finished product is controlled under a harsh quality environment, in order to guarantee its quality to customers.
Globally, rubber products consume 90% of the Carbon Black produced, where it is used to give it reinforcement characteristics, wear resistance, tear resistance, ease of extrusion, UV protection, among other characteristics, constituting an important percentage in the composition between the materials that make up rubber products.
The remaining 10% of world production of this versatile raw material finds application in inks for paper, inks for printers, inks for pens, paints, carbon paper, plastics, food packaging, eyeliners, as well as many other items for use industrial, domestic and even personal and beauty, for which, in many cases, different special Carbon Black are used to achieve specific characteristics required for each item carefully.