Sinopec’s Nd40 Rubber Boosts EV Tire Performance
The rapid rise of electric vehicles (EVs) across China and the globe has placed unprecedented demands on automotive components, particularly tires. With heavier vehicle weights, instant torque delivery, and a strong industry focus on energy efficiency and safety, tire manufacturers are under increasing pressure to develop advanced rubber compounds that can meet these evolving requirements. Among the latest breakthroughs in high-performance tire materials, a new study highlights the significant advantages of Sinopec Yanshan Petrochemical’s rare earth cis-1,4-polybutadiene rubber, specifically the Nd40 grade, in enhancing the performance of EV tires.
Published in the July 2024 issue of Petrochemical Technology, the research conducted by Rong Gang, a senior economist at Sinopec Chemical Commercial Holding Co., Ltd., North China Branch, provides comprehensive evidence that Nd40 not only outperforms domestic nickel-based alternatives but also surpasses leading imported rare earth rubber in key performance metrics. This development marks a pivotal moment for China’s rubber and tire industries, signaling a shift toward domestically developed, high-tech materials capable of competing with global benchmarks.
As governments worldwide push for carbon neutrality and sustainable transportation, EVs have emerged as a central pillar of future mobility. In China, strategic policy support and aggressive investment in EV infrastructure have accelerated adoption rates, making the country the world’s largest EV market. However, this growth brings new engineering challenges. Unlike internal combustion engine vehicles, EVs place unique stress on tires due to their increased curb weight—often 10% to 30% heavier than comparable gasoline models—and higher torque output, which can lead to accelerated tread wear, reduced braking efficiency, and greater rolling resistance. These factors directly impact range, safety, and overall driving experience.
To address these challenges, tire engineers are increasingly focused on optimizing rubber formulations. The choice of base polymer in tire compounds—especially in the tread and sidewall—plays a critical role in determining rolling resistance, wet grip, durability, and heat generation. Traditional nickel-catalyzed cis-1,4-polybutadiene rubber (BR), such as the widely used BR9000, has long been a staple in tire manufacturing. However, its relatively broad molecular weight distribution and lower cis-1,4 content result in higher hysteresis losses, increased heat buildup, and suboptimal rolling resistance—drawbacks that are magnified in EV applications.
Enter rare earth-catalyzed polybutadiene rubber, also known as neodymium-based (Nd) rubber. This advanced material is synthesized using rare earth catalysts that enable a higher degree of cis-1,4 structural regularity—often exceeding 97%—compared to nickel-based systems, which typically achieve around 96%. This higher stereoregularity leads to improved molecular chain alignment, reduced internal friction, and enhanced mechanical properties. The result is a rubber compound with lower rolling resistance, better wear resistance, and superior dynamic performance—qualities that align perfectly with the needs of modern EV tires.
Sinopec Yanshan Petrochemical, a key player in China’s synthetic rubber sector, has been at the forefront of developing and commercializing rare earth polybutadiene rubber. Its Nd40 and Nd60 grades represent a significant advancement in domestic polymer technology. Rong Gang’s study systematically evaluates the performance of Nd40 in both tread and sidewall compounds, comparing it directly with imported rare earth rubber (A1 from Germany’s LANXESS) and domestic nickel-based BR9000.
In the tread compound formulation, Nd40 demonstrated superior physical and mechanical properties. When blended with solution-polymerized styrene-butadiene rubber (SSBR), silica, and carbon black, the Nd40-based compound exhibited a tensile strength of 23.4 MPa—35.3% higher than the BR9000-based compound and notably higher than both Nd60 and the imported A1. Elongation at break reached 526%, significantly outperforming the other materials. These improvements are attributed to the high cis-1,4 content (98.09%) and favorable molecular weight distribution (PDI of 2.48) of Nd40, which promote strain-induced crystallization and enhance overall toughness.
Equally important is the compound’s dynamic mechanical behavior. In tire performance evaluation, the loss factor (tanδ) at 0°C is a key indicator of wet grip, while tanδ at 60°C correlates with rolling resistance. A high tanδ at 0°C ensures better traction on wet surfaces, critical for safety, while a low tanδ at 60°C indicates reduced energy loss and improved fuel (or energy) efficiency. The study found that the Nd40-based tread compound achieved the lowest tanδ at 60°C among all tested materials, translating to a 14.7% reduction in rolling resistance compared to BR9000. At 0°C, its tanδ was slightly lower than that of A1 but still within a range that ensures strong wet grip performance. This balance between low rolling resistance and adequate wet traction makes Nd40 particularly well-suited for EV tires, where energy conservation and safety must be optimized simultaneously.
Wear resistance, another critical factor for EV tires due to increased vehicle weight and torque, was also evaluated through Akron abrasion testing. The Nd40 compound showed excellent abrasion resistance, with a wear loss of 0.129 cm³—better than BR9000 (0.135 cm³) and competitive with A1 (0.104 cm³). While A1 exhibited the best abrasion performance, the overall durability of Nd40 remains highly favorable, especially when considering its superior tensile strength and lower rolling resistance.
Moving to the sidewall application, the performance advantages of Nd40 become even more pronounced. The sidewall is subjected to continuous flexing and must resist heat buildup, cracking, and fatigue over the tire’s lifespan. In the study, sidewall compounds were formulated with a 50/50 blend of natural rubber (SMR20) and various polybutadiene rubbers. Nd40-based compounds demonstrated higher hardness, tensile strength (19.8 MPa), and tear strength (81 kN/m) compared to BR9000. More importantly, they exhibited significantly lower heat buildup during compression testing—48.1°C for Nd40 versus 56.5°C for BR9000, representing a 14.9% reduction in heat generation.
Low heat buildup is crucial for EV tires, as excessive heat can accelerate aging, reduce structural integrity, and increase the risk of failure. The improved thermal performance of Nd40 is linked to its high molecular regularity and chain flexibility, which reduce internal friction and hysteresis during dynamic deformation. Additionally, the compound showed excellent flex-cracking resistance, with all test samples enduring 510,000 cycles without crack formation—a testament to its durability under repeated stress.
Dynamic mechanical analysis of the sidewall compounds further confirmed the superiority of Nd40. At 60°C, the tanδ value for Nd40 was the lowest among all tested materials, indicating the lowest rolling resistance contribution from the sidewall. This is a significant advantage, as sidewall flexing accounts for a substantial portion of total tire energy loss. Compared to BR9000, the Nd40 compound reduced rolling resistance by 15.5%, while Nd60 achieved an even greater reduction of 21.3%. These findings suggest that rare earth polybutadiene not only improves tread performance but also enhances the efficiency of the entire tire structure.
One of the most compelling aspects of the study is the successful application of Nd40 in actual EV tire prototypes. Two passenger car tire models—205/55R16 91V and 235/45ZR18 98W—were manufactured using Nd40 in both tread and sidewall compounds. These tires underwent rigorous testing in accordance with national standards, including dimensional accuracy, high-speed performance, strength, rolling resistance, and wet grip.
The 205/55R16 91V tire demonstrated exceptional performance. Its outer dimensions closely matched the nominal values, confirming manufacturing consistency. In high-speed testing, it exceeded the national standard by sustaining speeds up to 260 km/h—well above the 240 km/h requirement. The tire’s strength was measured at 472 J, significantly surpassing the minimum requirement of 295 J. Most notably, its rolling resistance coefficient was measured at less than 6.5 kg/t, earning it an “A” grade under the EU tire labeling system. This top-tier rating reflects exceptional energy efficiency, directly contributing to extended EV range. Noise levels were recorded at 71 dB, meeting standard requirements.
The 235/45ZR18 98W tire, designed for higher-performance EVs, also performed strongly. Independent testing by TÜV Rheinland Group in Europe confirmed a wet grip rating of 1.415, classified as “B” level—indicating very good traction on wet surfaces. Its rolling resistance coefficient was 8.147 kg/t, placing it in the “C” category. While not as efficient as the smaller tire, this performance still meets the expectations of domestic EV manufacturers and provides a balanced compromise between grip and energy consumption. Noise levels were slightly higher at 72 dB, which is typical for wider, performance-oriented tires.
These real-world results validate the laboratory findings and demonstrate that Nd40 is not just a theoretical improvement but a commercially viable solution for next-generation EV tires. The material enables tire makers to produce products that meet or exceed international performance benchmarks while relying on a domestically produced, high-quality raw material.
From a broader industry perspective, the success of Nd40 represents a significant milestone in China’s efforts to achieve self-reliance in advanced materials. Historically, high-performance synthetic rubbers have been dominated by Western and Japanese manufacturers. The development of competitive rare earth polybutadiene rubber by Sinopec reduces dependence on imports and strengthens the domestic supply chain for the automotive sector.
Moreover, the environmental implications are noteworthy. Lower rolling resistance directly translates to reduced energy consumption, which for EVs means longer driving range on a single charge and lower overall carbon emissions over the vehicle’s lifecycle. This aligns with global sustainability goals and supports the broader mission of electrified transportation.
Rong Gang’s research also highlights the importance of collaboration between material suppliers, tire manufacturers, and automakers. As EV platforms continue to evolve, with increasing demands for silent operation, extended range, and enhanced safety, the role of advanced rubber compounds will only grow. Materials like Nd40 provide a foundation for innovation, enabling tire engineers to push the boundaries of performance without compromising durability or efficiency.
Looking ahead, further optimization of rare earth rubber formulations—such as fine-tuning molecular weight distribution, incorporating functionalized polymers, or blending with other sustainable materials—could unlock even greater performance gains. Additionally, expanding the application of Nd40 beyond passenger car tires to commercial vehicles, off-road EVs, or specialty applications could broaden its impact.
In conclusion, the study published in Petrochemical Technology offers compelling evidence that Sinopec’s Nd40 rare earth polybutadiene rubber is a game-changer for the EV tire industry. Its superior mechanical properties, low rolling resistance, excellent wet grip, and outstanding durability make it an ideal choice for modern electric vehicles. As the automotive world transitions to electrification, materials innovation will be just as critical as battery or motor technology. With Nd40, China has demonstrated its capability to lead in this vital area of advanced materials development.
Rong Gang, Sinopec Chemical Commercial Holding Co., Ltd., North China Branch, Petrochemical Technology, DOI: 10.3969/j.issn.1000-8144.2024.07.013