Recently, there has been a shift towards sustainable production, leaving manufacturers searching for new ways to become greener. Virgin carbon black is widely used in rubber, plastics, paints, and coatings for pigmentation and reinforcement.  However, virgin carbon black is produced from oil and natural gas which is unsustainable. Recovered carbon black (rCB) is sourced from end-of-life tires and offers a solution to this problem by using more sustainable feedstock.

What is Virgin Carbon Black?

Virgin carbon black is a fine black powder composed of elemental carbon. It has remarkable properties owing to its small particle size, aggregate structure & surface chemistry. Nowadays, virgin carbon black can be used in a multitude of applications due to its excellent properties. Generally, the particles are spherical and small in size, creating a large surface area, and making virgin carbon black a fantastic pigment in paints, printing inks, and coatings.

What is Virgin Carbon Black Used For?

Plastics like refuse sacks, industrial bags, and household containers all contain carbon black. Conventionally, carbon black is added via masterbatch due to its excellent dispersibility and tinting properties. It also offers UV protection by absorbing UV light and converting it into heat, resulting in the polymer being more resistant to thermal degradation whilst providing color.

High-performance coatings in wood, marine, aerospace, decorative, and industrial applications also implement the use of carbon black for pigmentation & UV-protection. Similarly, it is used in toner for laser printers and screen ink electronics due to its superior efficiency, and fastness against light.

Aside from pigmentation and UV protection, the structure of carbon black makes it a brilliant reinforcing filler. Consequently, many rubber products such as hoses, belts, and gaskets use carbon black.

Environmental Impact of Carbon Black

In April 2022 a Plastic Packaging Tax of £200 per tonne was introduced by the UK government to reduce the amount of plastic waste that ends up in landfill. It applies to producers and importers of plastic packaging with less than 30% v/v of recycled content. Virgin carbon black is widely used in plastics, however, is not produced from recycled feedstock. Instead, it is synthesized during the incomplete combustion of petroleum products such as oil and natural gas. As the demand for carbon black surges, significant environmental and health concerns are associated with its use. Typically, the production of carbon black uses a furnace process at elevated temperatures of 1200-1900°C. This uses a substantial amount of energy and creates sulfur and nitrogen oxide emissions, making the entire process undesirable from a green perspective. Producing 1 tonne of virgin carbon black generates 2.5-3 tonnes of CO₂, this is problematic and raises the question of how we can make virgin carbon black a more sustainable material.

Can the Production of Carbon Black be More Sustainable?

Recovered carbon black (rCB) is a substitute for virgin carbon black, manufactured using sustainable material from end-of-life tyres. End-of-life tires are a plentiful feedstock. Each year, 1.5 billion tires enter the waste stream raising even more waste and environmental concerns. The circular economy approach used with rCB drastically reduces the CO₂ emissions that would otherwise be used in virgin carbon black production, whilst contributing towards the 30% of recycled material needed to avoid the UK plastic tax.

Production of Recovered Carbon Black

Production of rCB involves pyrolysis which uses lower temperatures than the furnace process of virgin carbon black. During pyrolysis, the thermal components of the tyre are broken down, which results in a condensed gas called tyre pyrolysis oil (TPO) being produced. Usually, this oil is sold and can be used for energy production in industrial settings or can be processed further in refineries. At the end of the process, a carbon-containing residue called char remains. Char resembles carbon black but lacks the consistency and quality to be used directly as a carbon black substitute. This is attributable to the metal contaminants present and the variable particle size of char. Therefore, it is essential to refine the char to produce high-quality rCB.

Klean Industries (“Klean”) provides technology to manufacture high-quality. Klean provides the technology and know-how needed to source high-quality tyre char from various pyrolysis plants and how to focus on refinement of the tire char can be done cost-effectively. This includes the key steps post pyrolysis such as devolatisation, milling, and optional pelleting. Tire char quality can vary depending on the type of tyres used and the temperature used in tire pyrolysis. ‘Dirty’ char can be produced if the pyrolyzer is not run at a high enough temperature resulting in a strong odor and weak reinforcement properties. Klean’s process puts the spotlight on refining rather than producing char, this means the char is tested before refinement, to ensure it has exceptional quality and is ‘clean’.

How Does rCB Compare to Virgin Carbon Black?

The carbon content of traditional virgin carbon black is close to 100%, as it’s sourced from heavy petroleum products such as coal. On the other hand, rCB is acquired from end-of-life tyres so contains 80-85% carbon black and 15-20% inert ash, predominantly consisting of silica & zinc.

Jetness & Reinforcing Properties

In the polymer industry, one of the most important properties of virgin carbon black is the deep jet-black color which arises from the large surface area of the small particles. During production, Klean’s technology refines rCB into a small uniform particle size in the milling process, creating a large surface area for good jetness and opacity. This is especially useful for coatings, plastics, and rubber. However, the major difference between using rCB over virgin carbon black is the ash content, which leads to a slight reduction in the overall jetness.

To counter this Klean uses modified feedstock. By sourcing truck and passenger tires as opposed to passenger tyres alone, lower levels of ash content can be attained, resulting in a higher degree of jetness.

In rubber, various grades of virgin carbon black exist. N-550 is a grade of virgin carbon black commonly used in the cord layer of tyres and calendared sheets for the roofing industry due to its reinforcing properties. In addition to providing reinforcement, virgin carbon black can also be used in rubber due to its damping properties. rCB by Klean’s process exhibits similar reinforcement properties to grades N-550 and above which are considered semi-reinforcing grades, whilst improving the damping properties of rubber. So in conclusion, rCB should be considered a sustainable replacement for virgin carbon black for most rubbers containing semi-reinforcing carbon blacks and for pigmenting purposes.

Polycyclic Aromatic Hydrocarbons (PAH) Levels

Polycyclic aromatic hydrocarbons (PAH’s) are found in virgin carbon black, which is renowned for being hazardous to human health and the environment. PAHs have been discovered in many consumer products and have been restricted by the EU and businesses due to health concerns. Therefore, it is more vital than ever to minimize the levels of PAH’s.

Benzo-alpha-pyrene is the common benchmark used to determine the concentration of PAH. During testing, benzo-alpha-pyrene could not be detected in rCB by the Klean process as these are destroyed during the thermal homogenization process. For that reason, KleanCarbon can be considered a safer, more sustainable alternative to virgin carbon black.

Formulating with Carbon Black

Virgin carbon black can be produced in powder and pellet form. Powder form carbon black is semi-free flowing so is usually employed in pigments. However, this can be challenging to handle as it tends to cake, pack, dust, and deposit onto equipment. From a health and safety point of view, this is troubling as carbon black is a potential carcinogen. For this reason, Klean Industries has developed rCB in pelleted form which closely matches the characteristics of pelleted virgin carbon black. Pelletized carbon black is made from larger particles, so the bulk density is higher resulting in easy shipping, storage, handling, and most importantly less dusting.

Summary

rCB produced by Klean’s process is a more sustainable alternative to virgin carbon black. Whilst marginally higher concentrations of rCB may be required to achieve the same level of opacity, this can be offset by the environmental benefit of rCB. rCB plays a critical role in the drive to create a circular economy by using more sustainable materials.

If you would like more information about Recovered Carbon Black or you would like to discuss how it could work in your applications, please contact us » GO.