April 28, 2026

Introduction

Rubber Compounds

    Rubber compounds are made up of raw elastomeric materials, additives, reinforcements, curing agents, and stabilizers. These elements define the final rubber product's flexibility, hardness, durability, and performance. This is achieved by selecting a base polymer, curing system, fillers, and stabilizers to meet requirements.
The base polymer – natural or synthetic rubber – provides the primary elasticity, flexibility, and mechanical strength. Common synthetic rubbers include Styrene-Butadiene rubber (SBR), Nitrile rubber (NBR), and Ethylene Propylene Diene Monomer (EPDM) (Patel, 2025). For this project, however, natural rubber was selected. Derived from Hevea Brasiliens trees, these compounds are known for their exceptional elasticity, tensile strength, and abrasion resistance.
After selecting the polymer, fillers are added to adjust the hardness, flexibility, and performance of the rubber compound. Reinforcing agents like carbon black and silica improve tensile strength and durability, while other fillers, such as clay and calcium carbonate, act as plasticizers and softeners, improving processability (Patel, 2025).

    To further enhance long-term performance, chemical additives such as antioxidants and antiozonants protect rubber compounds from degradation caused by oxygen, ozone, heat, and UV exposure. These agents prevent cracking, brittleness, and loss of elasticity over time (Patel, 2025).
In addition to polymer, filler, and additive selection, vulcanization is another essential factor for the characteristics of rubber compounds. This chemical process cross-links polymer chains, improving rubber strength, elasticity, and resistance to wear. Accelerators are typically used to ensure an even, consistent cure of the rubber, ensure structural stability, and reduce cure time (Patel, 2025). Because rubber components in automotive applications encounter harsh environments, resistance to heat, chemicals, weather, and mechanical stress is imperative (Patel, 2025).

Literature Review

    Vibracoustic is a leading global noise, vibration, and harshness expert. The company aims to ensure a smooth, safe, and quiet ride by reducing noise and vibrations originating from the engine, motor, drive train, and road surfaces, and transmitted into the chassis (Vibracoustic, 2024). To reduce NVH, it is important to use a cushion, typically rubber in automotive applications.
Historically, Vibracoustic only used natural rubber (NR) combined with carbon black, standard oils, and fillers. However, because sustainability has become a growing concern worldwide, reliance on conventional compounds has raised environmental and ethical issues. These challenges drove the company to reevaluate its material choices and explore more sustainable options.

    In response to these concerns, the Material Technologies team launched the Green Rubber Project in 2016 at Vibracoustic's lab in Weinheim, Germany. The team focused on identifying sustainable raw materials, reducing environmental impact, and improving recyclability. To address these, the team shifted from synthetic rubber derived from fossil fuels to natural rubber (NR). This approach was considered more sustainable if deforestation and intense working conditions are avoided (Maust, 2026). In addition to the polymer selection, the oil used in the rubber was replaced with a more sustainable bio-oil derived from end-of-life tire pyrolysis. The oil has a renewable carbon content of 30%, shows improvements in tensile strength, curing time, and elongation at low temperatures, and complies with PAH regulations. At the same time, carbon black was partially replaced with recycled carbon black (rCB), an alternative that reduces emissions and improves recyclability (Plaettner, 2023).

    Pyrolysis, by definition, is the thermal decomposition of organic substances under inert conditions (absence of oxygen) at high temperatures between 400-800˚C. The process starts with pretreating the tires to remove impurities, then they are fed into a shredder and into a pyrolysis reactor, where they are heated. The oil and gas mixture generated enters a separator, where it is separated based on temperature and pressure differences. The oil is cooled in a condenser and collected as liquid in a storage tank. The gas enters a processing system for purification, recovery, or utilization, and the carbon black is collected from the bottom of the furnace where the tires are heated (GEP ECOTECH, 2025). Overall, the pyrolysis process increases the recycled content in the product, reduces the carbon footprint, and helps address waste tire pollution. Unlike incineration, this process yields higher material recovery and lower emissions of airborne particles and contaminants (Costa, 2022).

    Using these more sustainable rubber components, the Material Technologies Team developed two sets of recipes to test against a control group in the first phase of the project. The first set of recipes had one modification, which changed either the rCB material or the oil. The second set of recipes applied both changes: rCB and oil. Both sets were tested against the control group, NR-C010A-560, with standard carbon black and oil. The tests performed were tensile strength, elongation, compression, TeCo, and durability. Tension-compression (TeCo) testing provides the static and dynamic stiffnesses of a rubber sample. These showed promising results with an increase in sustainable content to about 60%, and 5-15% recycled or renewable content. The compounds also showed strong durability and tensile strength and were considered an option when quoting new customer parts (Maust, 2026).

    For this phase of the project, the goal was to increase the sustainability content in the rubber using three new carbon blacks and a new bio-oil provided by Dr. Stephanie Deike and Dr. Stephania Schamber. The plan focused on refining the carbon black-to-recovered carbon black ratio to decrease the amount of carbon black and increase the recovered carbon black in the recipe. This allows for more rubber solutions for customers in the future, helps lower the company's carbon footprint, and increases recyclability. The limitations of this project included timing, location, and workload. The time available to collect data for this project was six weeks, and the research was conducted at the Vibracoustic Material Technologies lab in South Haven. The team that originally began work on the Green Rubber Project worked out of Weinheim, Germany, so communication while in different time zones proved difficult. Time was split between working on this project and supporting the application team, which proved slightly challenging, as there were many critical tasks to complete on other teams.

    The control group used in this phase consisted of a rubber compound containing carbon black, standard oil, fillers, raw rubber, and plasticizers. The experimental recipes included three new carbon black compounds: Bolder Black, Greenblack 7200, and Continua 8000SCM. Bolder Black and Continua 8000SCM are both produced from end-of-life (EOL) tires and rubber scrap. Bolder Black requires 90% less water than other processes and produces 90% fewer greenhouse gases (Bolder Industries). Continua 8000SCM also provides significant environmental benefits, with a net-negative carbon footprint, as it recovers steel and produces renewable fuels. 1 ton of Continua 8000SCM reduces CO₂ emissions by 0.73 tons. In contrast, Greenblack 7200 is not produced from EOL tire pyrolysis but instead by a plasma process using raw materials. Although it is not a recovered carbon black, the process to create Greenblack 7200 is still more environmentally friendly than traditional manufacturing processes (Monolith Materials).

    These compounds were combined with a newer, more sustainable oil, natural rubber, and standard fillers and plasticizers. The difference in this phase of testing in South Haven is that the compounds were created as a single set, with both recipe changes. TeCo or durability testing were also not completed due to time constraints and machine availability. Through the development of these new recipes, it was expected that the new compounds would exhibit greater correlation to the original carbon black compound while increasing the sustainable content.