In order to understand what coal tar pitch is, it’s important to understand its origins and refinement methods. Coal tar can be refined from a number of sources including coal, wood,
peat, petroleum, and other organic materials. The tar is removed by burning or heating the base substance and selectively distilling fractions of the burned chemical.
Distillation involves heating the substance to a point where different fractions of the substance become volatile. The fractions are then collected by condensing the fraction at a specific temperature. A base substance can be split into any number of fractions through distillation. A good example of industrial distillation is the oil refining process. Through distillation, crude oil can be separated into fractions that include gasoline, jet fuel, motor oil bases, and other specialty chemicals. Fractionation or distillation is a tried-and-true method for breaking a substance into different parts of its composition. One of the first uses of coal tar was in the maritime industry. Trees stumps were burned and the tar fractions were collected through distillation of the tar. The tar was then used to coat wood boats. Tar was an excellent waterproofing agent and it also helped to protect the wood from insects. The tar used in roofing is a derivative of the fractional distillation of coal gas, which is sometimes referred to as coke. Many other chemicals are produced in this and subsequent fractioning processes, including naptha, creosote, benzene, toluene, and phenol. Coal tar pitch consists of a collection of cyclical hydrocarbons of various molecular weights and configurations. Every coal tar pitch can be refined to a greater or lesser degree; greater refinement yields a stiff, glassy product, while reduced refinement yields a highly viscous fluid.
Coal tar and coal tar derivatives are used in a variety of industrial applications. Tar pitch from wood is used in soap, food, and medical applications, while coal tar derivatives can be found in dyes and cosmetics. One of the predominant uses for coal tar derivatives is construction material.
Coal tar pitch has been used as the base media for coatings and adhesives for many years,including roofing bitumen. Built-up commercial coal tar pitch roofing has historically provided long lasting and sustainable protection for the building envelope. The inherent waterproof nature of coal tar pitch provides a tight waterproof roof construction. The self-healing properties of coal tar pitch tend to bridge small deformities created by debris, stress movement, hail, and other surface punctures.
Further, coal tar pitch is highly chemically resistant, resisting exposure to a large variety of acids,bases, and solvents. These properties have led to some of the most sustainable roof systems available in the market place. It is not unusual to observe coal tar pitch roofs that last up to 40 years. Today, coal tar pitch roofing adhesives can be installed hot or cold, while maintaining the same level of waterproofing protection and chemical resistance as traditional coal tar pitch roof systems. In addition, recent manufacturing advancements take the base technology another step forward. By incorporating a blend of specialized polymers with the coal tar, polymer-modified coal tar achieves low-temperature performance that surpasses that of traditional coal tar products. Tests show that modified coal tar pitch can achieve flexibility numbers as low as 30 degrees Fahrenheit. As an added benefit, the polymer additive greatly improves the elongation of the coal tar pitch base; products are currently available with elongations of greater than 2,000 percent.
Further, these new compounds have dramatically improved impact resistance. In essence, recent technology results in the first truly elastomeric coal tar pitch. Most promising of all, these new compounds improve the environmental nature of the coal tar pitch. Through the polymer blending process and the preconditioning of the coal tar pitch, many of the volatile emissions are reduced or eliminated. Independent testing by the Environmental Protection Agency methods indicates a minimum reduction of 50 percent of the volatile emissions, in comparison with traditional coal tar pitch. Significantly, a good portion of these reductions take place within the most hazardous compounds present in standard coal tar pitch.