By Sunish Vadakkeveetil, Mehran Shams Kondori, and Saied Taheri

Center for Tire Research (CenTiRe), Virginia Tech

 

 

 

 

 

 

 

 

Rubber, mainly because of its viscous nature, is a widely used material for most contact applications such as, seals, tyres, footwear, wiper blades, bushings etc. The material possesses the property of both a liquid (viscous) and a solid (elastic). Hence, rubber frictional losses at the contact interface is classified into three mechanisms as shown in Figure 1. Hysteresis  (μ_hys ) – Energy dissipated due to internal damping of rubber caused by undulation in the surface. Adhesion (μ_adh ) – Due to intermolecular or Vander Waals attraction at the contact interface. It vanishes in the presence of contaminants or lubricants on the surface. Viscous (μ_visc ) – Due to hydrodynamic resistance caused by the fluid in the contact interface. It mainly occurs under the presence of lubricant or fluid in between the contact interface.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Friction as a concept has evolved, as shown in Figure 2 from a simple empirical relation, developed by Amonton’s (1699) and Columb (1785) to more complex representations by considering these different mechanisms of friction. Initial experimental observations by Bowden and Tabor [1] observed the microscopic behaviour of the contact and obtained that the real area of contact is only a part of the nominal contact area. Grosch & Schallamach [2] performed experimental observation to determine the influential factors and obtain a relation between temperature and velocity-dependent friction to frequency-dependent viscoelastic behaviour. Savkoor[3] considers the frictional losses due to adhesive mechanism at the contact interface using a rudimentary theory where the interaction is considered as a series of processes from the growth of contact area in the initial stage to initiation and propagation of crack in the final stage.

Heinrich [4] developed an analytical representation to estimate the hysteretic component of friction by considering the energy losses at the contact interface to the internal damping of rubber from the undulations of the surface. The energy loss thus obtained is related to the frictional shear stress by the energy relation given by Eq. (2).

            ΔE=∫d^3 x dt u ̇ . σ (1)

           σ_f=ΔE/(A_0 v t)     (2)

Persson and Klüppel [5] extended the theory to consider the effect of the surface roughness by assuming the surface to behave as a fractal nature and obtaining the total energy loss being the sum over the different length scales. Klüppel considers the GW theory to consider the contact mechanics where Persson developed a stochastic based contact mechanics theory assuming the rubber deformations to follow the surface asperities, the results are as shown in Figure 3. To consider the actual deformation profile of rubber, an affine transformation approach [6] is considered to obtain the actual deformation of rubber contact. The results are as shown in Figure 4.

 

 

 

 

 

 

 

In addition to analytical methods, computational approaches are also considered to estimate deformation behaviour of a rubber block on a rough substrate (Figure 5). The numerical model [7] is validated using indentation experiment and compared against a single asperity model as shown in Figure 6. This is later being extended to obtain friction and wear characteristics of rubber at the contact interface by considering the deformations at the contact interface and obtaining the frictional force [5], [8].

 

 

 

 

 

 

 

 

 

 

Figure 6: FE Model Of Single Asperity Model & Comparison Of Results With Experimental & Analytical Approach

Wear is mainly due to the frictional shear stress generated at the contact interface leads to energy dissipation at the rubber – substrate contact interface that is either transformed into heat or responsible for crack initiation and propagation eventually leading to material removal. The major contribution of the wear occurs either due to the interaction of smooth asperity and rubber surface (adhesive wear), Figure 7 (a) instantaneous tearing of rubber by sharp asperities (abrasive wear), Figure 7 (b) or due to repeated cyclic contact stress (fatigue wear, Figure 7 (c)).

Due to the importance and complexity of the wear problem, it has been a vital topic of interest studied by many researchers [2]. Numerical techniques and empirical approaches have seen their light in the midst of the expensive and cumbersome experimental observations [9], [10]. Archard’s law states that “the volume rate of wear (W) is proportional to the work done by the frictional forces” as given by Eq. (3), where τ_f is the frictional shear stress and v is sliding velocity.

            W∝τ_f  v       (3)

 

 

 

 

 

 

 

 

 

 

 

In the case of road surfaces, the removal of rubber particles can be considered as a process of nucleation and propagation of crack like defects until it is detached to form a wear particle, as shown in Figure 8. Based on this mechanism of crack propagation, a physics-based theory assuming the crack propagates (Figure 9 & Figure 10) from already present defects or voids on the rubber surface was considered and then later compared with experimental methods performed using Dynamic Friction Tester (Figure 11) [6], [11], [12]. Future studies are being performed using analytical and computational approached to estimate the wear characteristics of a rubber material considering damage mechanics [8] and crack propagation theory considering the effect of surface roughness. An experimental technique is also being developed based on the Leonardo Da Vinci concept to experimental test the friction and wear characteristics of a rubber block under pure sliding.

 

References:

[1]       D. Bowden, F. P., & Tabor, The friction and lubrication of solids. Oxford university press., 2001.

[2]       A. Gent and J. Walter, The Pneumatic Tire, no. February. 2006.

[3]       A. R. Savkoor, “Dry adhesive friction of elastomers: a study of the fundamental mechanical aspects,” 1987.

[4]       H. Gert, “Hysteresis friction of sliding rubber on rough and fractal surfaces,” Pochvozn. i Agrokhimiya, vol. 25, no. 5, pp. 62–68, 1990.

[5]       S. Vadakkeveetil, “Analytical Modeling for Sliding Friction of Rubber-Road Contact,” Virginia Tech, 2017.

[6]       A. Emami and S. Taheri, “Investigation on Physics-based Multi-scale Modeling of Contact, Friction, and Wear in Viscoelastic Materials with Application in Rubber Compounds,” Virginia Tech, 2018.

[7]       S. Vadakkeveetil, A. Nouri, and S. Taheri, “Comparison of Analytical Model for Contact Mechanics Parameters with Numerical Analysis and Experimental Results,” Tire Sci. Technol., p. tire.19.180198, May 2019.

[8]       S. Vadakkeveetil and S. Taheri, “MULTI – LENGTH SCALE MODELING OF RUBBER TRIBOLOGY FOR TIRE APPLICATIONS,” Virginia Tech, 2019.

[9]       K. R. Smith, R. H. Kennedy, and S. B. Knisley, “Prediction of Tire Profile Wear by Steady-state FEM,” Tire Sci. Technol., vol. 36, no. 4, pp. 290–303, 2008.

[10]    B. W. and R. N. D. Stalnaker, J. Turner, D.Parekh, “Indoor Simulation of Tire Wear: Some Case Studies,” Tire Sci. Technol., vol. 24, no. 2, pp. 94–118, 1996.

[11]    A. Emami, S. Khaleghian, C. Su, and S. Taheri, “Comparison of multiscale analytical model of friction and wear of viscoelastic materials with experiments,” in ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE), 2017, vol. 9.

[12]    M. Motamedi, C. Su, M. Craft, S. Taheri, and C. Sandu, “Development of a Laboratory Based Dynamic Friction Tester,” in ISTVS 7th Americas Regional Conference, 2013.

 

Zeon Corporation has announced the development of Nipol BR1300, a novel hydrophilic styrene butadiene rubber (SBR) for winter tyres. Synthesised with a polybutadiene rubber base, the material delivers unprecedented hydrophilicity for tyre applications. Commercial production began in May 2025 at Zeon’s Tokuyama plant in Yamaguchi Prefecture.

As part of its strategic portfolio optimization, Zeon plans to phase out low-profitability products like ESBR-1 and NBR latex by 2026. However, it will continue manufacturing high-margin products, including ESBR-2, nitrile butadiene rubber and solution SBR. This shift underscores Zeon’s focus on advanced, value-driven rubber solutions.

Covestro India has entered into a strategic collaboration with CSIR-National Chemical Laboratory (NCL) through an innovative CSR initiative focused on developing sustainable upcycling technologies for polyurethane waste. This partnership aims to overcome existing recycling limitations by transforming discarded polyurethane materials into valuable chemical feedstocks, potentially revolutionising the material's circular economy.

This collaboration underscores both organisations' commitment to environmental innovation, leveraging NCL's advanced research infrastructure and Covestro's market leadership to address critical gaps in plastic circularity. Current polyurethane recycling methods, predominantly mechanical with some emerging chemical processes, face substantial challenges including material degradation, high energy consumption and hazardous byproduct generation. The project seeks to develop commercially viable chemical recycling solutions that maintain material integrity while minimising environmental impact.

Polyurethanes, widely used in furniture, automotive parts and insulation, present unique recycling difficulties due to their complex molecular structure. Most end up in landfills after use, creating significant sustainability challenges. By combining Covestro's industrial expertise with NCL's seven decades of chemical research excellence, the partnership aims to create breakthrough upcycling technologies.

Avinash Bagdi, Director & Head of Sales & MD Solutions India & Projects – Tailored Urethanes, said, "This partnership strengthens our commitment to finding innovative solutions for polyurethane waste and directly supports Covestro's vision of becoming fully circular. By developing effective methods to upcycle polyurethanes, we're taking concrete steps towards creating a more sustainable future in line with our corporate vision of driving the transition to a circular economy."

Dr Ashish Lele, Director of NCL, said, "CSIR-National Chemical Laboratory is excited to partner with Covestro (India) in this groundbreaking initiative to develop novel chemical upcycling methods for polyurethane waste. The conventional and electrochemical strategies we're developing address the critical limitations of current recycling technologies and align perfectly with our shared vision of a circular economy. This collaboration represents a significant step towards sustainable plastic management in India and globally, with potential to transform polyurethane waste into valuable chemical resources."

Zeon Corporation has begun building a pilot facility at its Tokuyama Plant in Shunan City, Yamaguchi Prefecture, to test a new method for efficiently producing butadiene from plant-derived ethanol. The demonstration plant, expected to start operations in 2026, will supply butadiene for manufacturing trial batches of polybutadiene rubber, bringing the company closer to commercialising this sustainable production process.

This project is a key part of a joint initiative between Zeon and The Yokohama Rubber Co., Ltd. to develop eco-friendly methods for producing butadiene and isoprene from renewable sources, with full-scale adoption targeted for the 2030s. Under the collaboration, Zeon will produce butadiene rubber at the new facility, while Yokohama Rubber will use the material to create experimental tyres and conduct performance testing. The data collected will help refine the technology ahead of larger-scale trials. The companies aim to finalise the production process by 2030 using an expanded pilot plant, with plans for industrial-scale commercialisation by 2034.

A ceremonial groundbreaking event took place on 10 July 2025, with 33 attendees, including local government officials from Yamaguchi Prefecture and Shunan City, construction partners and Zeon executives such as Chairman Kimiaki Tanaka and Tokuyama Plant Manager Akira Honma. The gathering included traditional safety prayers for the construction phase, marking the official start of this sustainability-focused industrial project.

Continental is increasing its use of renewable and recycled materials in tyre production, aiming to exceed 40 percent by 2030 while maintaining high safety and performance standards. In 2024, these materials accounted for 26 percent of tyre composition, with a projected 2-3 percent increase in 2025. Key to this shift are carbon black and silica – essential fillers that enhance durability, grip and braking performance.

Silica, a critical component for optimising grip and minimising rolling resistance, is traditionally derived from quartz sand. However, Continental now obtains silica from rice husks, an agricultural by-product of risotto rice production. This innovative approach not only repurposes waste but also requires less energy than conventional methods. Partnering with manufacturers like Solvay in Italy, Continental integrates rice husk-derived silica across its entire tyre portfolio. Silica has been a game-changer in tyre technology for decades, significantly improving safety and energy efficiency. Its use in tread compounds has contributed to a nearly 50 percent reduction in braking distances while also lowering rolling resistance, thereby reducing fuel consumption and CO₂ emissions.

Carbon black, another vital material making up to 20 percent of a passenger car tyre's weight, is being sourced through sustainable alternatives. Continental employs three innovative methods: bio-based carbon black from tall oil (a paper industry by-product), recycled carbon black from pyrolysis oil derived from end-of-life tyres and a direct recovery process that extracts carbon black from used tyres via pyrolysis. The company collaborates with suppliers like Orion Engineered Carbons and Tokai Carbon, utilising different carbon black variants tailored to specific tyre components, such as sidewalls and treads. Through the mass balance approach, Continental substitutes fossil-based raw materials with bio-based or recycled alternatives without altering existing production processes.

Additionally, Continental has partnered with Pyrum Innovations to advance tyre recycling through pyrolysis, a process that recovers carbon black from end-of-life tyres for reuse. While currently applied in forklift tyres, efforts are underway to adapt this recycled carbon black for broader tyre applications, ensuring compliance with performance and safety standards. These initiatives underscore Continental’s dedication to sustainable innovation, demonstrating how eco-friendly materials can enhance both tyre performance and environmental responsibility across the value chain.

Jorge Almeida, head of Sustainability at Continental Tire, said, “Innovation and sustainability go hand in hand at Continental. Using silica from the ashes of rice husks in our tyres shows that we are breaking completely new ground – without compromising on safety, quality or performance.”