Sustainability and heavy manufacturing have long had a strained relationship, shaped by scale, cost pressures and the technical demands of industrial production. While scientists and engineers work to decarbonize complex processes, greenwashing has seeped into industry rhetoric, undermining trust in legitimate sustainable alternatives. However, in tire manufacturing, recovered carbon black (rCB) sits apart from this rhetoric.
“rCB is not carbon black; it is a new type of material,” stated Prof. Jorge Lacayo-Pineda, head expert in materials evaluation at Continental Tires, during his presentation at the Tire Technology Expo Conference today.
In ‘Identification of rCB in cured rubber compounds,’ Prof. Lacayo-Pineda examined the morphological and structural differences between rCB and virgin carbon black, proposing Raman spectroscopy as a practical method for distinguishing between the two.
Pyrolysis process
Recovered carbon black (rCB) is produced from end-of-life tires, which are first processed to separate their three primary components: textile fibers, steel and rubber granulate. The rubber granulate then undergoes pyrolysis – a thermochemical decomposition process in which organic material is heated to high temperatures in the absence of oxygen, preventing combustion. This process yields gas, pyrolysis oil and rCB. The recovered carbon black can then be used in tire manufacturing, partially replacing virgin carbon black in new compounds.
Morphology and carbonaceous residues
Material morphology plays a critical role in tire manufacturing. Because tire performance depends on tightly controlled properties such as temperature resistance, hardness, rolling resistance and traction, even minor variations in compound structure can significantly affect overall performance.
Prof. Lacayo-Pineda noted a growing consensus within the rCB and tire sectors that rCB is not carbon black, but a new, sustainable type of filler. He pointed to key differences between the two, including rCB’s heterogeneous composition, residual carbonaceous materials and altered thermal history.
Referring to transmission electron microscopy (TEM) images, he demonstrated that the residual carbonaceous materials in rCB are clearly distinguishable from the morphology of virgin carbon black.
Raman spectroscopy
Prof. Lacayo-Pineda explained that Raman spectroscopy is a specific type of molecular spectroscopy used to identify the structure of carbon black within a rubber compound. It looks for the different vibrational modes to identify the turbostratic structure of carbon black within the compound.
The turbostratic structure of carbon black is the specific, disordered arrangement of graphene layers that form the primary particles. These layers are randomly rotated and relatively displaced from each other. This disorder increases surface area and chemical reactivity, which is beneficial for the polymer-filler interaction and, therefore, for rubber reinforcement.
In a turbostratic structure, Raman spectroscopy typically exhibits a strong D-band (disorder) and a broadened G-band (graphitic), reflecting the structural imperfections. The ratio of D and G bands intensities can be used to interpret the influence of thermal process on carbon materials – in this case, the pyrolysis of carbon black. The values of the G band indicate the extent of graphitization during pyrolysis, highlighting the presence of rCB.
The Tire Technology Expo Conference continues on March 4 and 5. Click here to see the program, and here to purchase your delegate pass
