Without good quality reliable ingredients, even the very best chefs’ struggle. The same is true in the production of Recovered Carbon Black (rCB). Only good quality tyre char from a consistent pyrolysis process, coupled with a shrewd processor, can produce an rCB that is an excellent sustainable alternative to virgin carbon black. Unfortunately, regional variations in tyres, which provide the feedstock for tyre pyrolysis and the resulting char, have a significant impact on the subsequent quality of rCB.
With the right quality and consistency, rCB can be used in a wide range of applications across the plastics, rubber, and coatings industries, helping industry take a huge stride towards global sustainability goals. Unfortunately, poorly produced rCB created from char with high levels of volatiles, variation, or high concentration of ash content lacks the dependability required by these sectors and cannot be considered as a reliable alternative to virgin carbon black. Even geography can impact, as tyre composition varies depending on what region they are destined for use. Regional variations in the quantity of ash and composition of the tyre greatly impacts the quality of the sustainable material that can be produced.
Regional tyre composition
European passenger tyres tend to have high quantities of additives, such as silica and zinc. These additives are turned into ash during the pyrolysis process and sit with the carbon black in the pyrolysed char. The ash is inert, and unfortunately offers no reinforcing or pigmentation properties. As such, the greater the ash content in the char, the less carbon black present, and the weaker the reinforcing properties. It follows logically therefore that the lower the ash, the more superior the rCB.
European passenger tyres contain larger quantities of silica and zinc as they are highly engineered and carefully designed to meet the demands of the wet and icy roads common in northern Europe. These are great for driving conditions, not so great to recycle into rCB. This is in contrast to tyres from warmer climates which contain less additives and are a better raw material for rCB, as the carbon black content is greater.
As the table below from carbon black market expert Martin Van Wolfersdorff shows, tyres from the Middle East, India, Africa, and even America all have less amounts of silica than European tyres.
The average ash content in tyre char produced from European passenger tyres is 24%, compared to 12-18% from elsewhere. Given that ash content has a major influence on reinforcing properties, European passenger tyres are not necessarily the best feedstock to use.
However, with the right production methodology, rCB from European tyres has its own unique characteristics which can work well in the right applications. This is where the science plays a considerable role in ensuring that the grade of rCB produced meets the characteristics required.
Quality, consistent rCB
Testing that we have carried out on African tyre chars show ash content ranging from 14% to 19%, depending on whether they are from passenger or truck tyres. Thus far, a sample from a US truck tyre derived char with an ash content of 13% has the highest proportion of carbon black content that we have evaluated.
Ash content is a significant factor and, along with surface volatiles and underlying carbon black grades, plays a key role in determining the ultimate reinforcing, mechanical properties and performance of the rCB. Therefore, careful tyre feedstock selection, optimised pyrolysis process of the tyres (to ensure volatiles are removed and to minimise variation), and small particle milling to aid dispersibility, all contribute to overall reinforcing and pigmentation properties.
Succeed with these processes and there is a whole realm of recovered carbon black grades accessible to all and waiting to be exploited. Waverly Carbon has invested in state-of-the-art laboratory and processing facilities. We carefully analyse all potential feedstock for consistency and volatiles to apply the correct processing. This ensures that we create rCB grades that are consistently of the highest quality and fit for purpose for the rubber, plastics, and coatings sectors.
You can download the full report for more insight or get in touch.