Meet Carbon Black: The Ubiquitous Polymer Additive

Chemistry and baking have a lot in common. In both disciplines, the ingredients you add (or leave out), and the quantities and order in which you add them greatly affect the end product. Short your cake batter an egg or two and you’ll end up with a chewy, unappetizing mess. Skimp on — or skip — the carbon black in the tire-manufacturing process and you’ll wind up trying to sell white tires to consumers who’ve come to expect rubber to be black and shiny.

Carbon black is one of the most common additives we test for at Polymer Solutions. It’s the material that makes rubber tires and ink toner black, and it helps tires and polypropylene pipes last longer.

Although in its raw form carbon black’s powdery persona may remind you of soot, it’s much more sophisticated than the residue you get after a wood fire burns out. Carbon black is the product of incomplete combustion of heavy petroleum products. It’s a much finer powder than soot, causing it to react more quickly in chemical processes. It’s chemically different from soot, too; while most types of carbon black contain more than 97 percent elemental carbon, soot is usually less than 60 percent carbon[E1] .

How carbon black functions in products

Adding carbon black to products affects materials in a few ways. When used in tires and other rubber products, it’s primarily a filler, taking the place of more costly binder materials. As a filler in tires, carbon black also helps extend the life of the tire by conducting heat away from the tread and belt area. It also acts as a pigment, making rubber materials black.

Pigmentation is carbon black’s primary function in plastics, paints, ink, laser printer toner and some radar absorbent materials. Its high tinting strength and inherent stability make it an especially good pigment, and it’s also used to color resins and films. When added to polypropylene, carbon black also helps preserve the material from ultraviolet damage since it absorbs UV rays.

Carbon black is also a good electro-conductor, so it’s used in certain electronics applications as well. It may also be used as an antistatic agent for products where it’s important to control static electricity, such as vehicle gas caps and fuel pipes. In Europe, some forms of carbon black that are derived from vegetable products are used as a food coloring, but that’s not a permitted use in the U.S.

Carbon black testing

Working with many polymer, metals and medical device clients, the Polymer Solutions team does a good deal of carbon black testing. Two basic types of testing tell us a lot about carbon black’s presence in a material and the job it will — or won’t — do.

In the polyethylene pipe industry, carbon black is often added to assist with maintaining physical and mechanical properties. Carbon black dispersion testing requires the scientist to cut a sample of a material, press it between two microscope slides and then heat the material to between 150 and 201 degrees Centigrade. We then examine the sample under high magnification to grade the dispersed particles based on their size distribution.

Filler content analysis is also useful in carbon black testing. Since most polymers aren’t 100 percent composed of polymers alone, it’s important to understand the filler content in a material. The type and quantity of filler in a material affects the performance of the polymer.

Through Thermogravimetric Analysis (TGA), we can determine the quantity of filler within a material. We place the material on a balance inside a furnace and heat it to burn away all the organic material. What’s left is just the filler, so we can establish the percentage of the material that remains based on how much material we began the test with.

Carbon black is just one of the many additives we can test for at Polymer Solutions, and it’s a well-established workhorse additive for many industries.