Tire compound design has long wrestled with a triangular contradiction: conductivity, dynamic performance, and reinforcement effects — three objectives that are exceptionally difficult to achieve within a single filler system.
Passenger car tire treads must dissipate electrostatic charge. The conventional approach is to add conductive carbon black. However, the high specific surface area and high structure of conductive carbon black, while establishing a conductive network, also bring a cascade of penalties — increased heat buildup, elevated hysteresis loss, and rising Mooney viscosity. Formulation engineers are forced into a trade-off between conductivity and dynamic performance — a tension that grows sharper with tightening EU tire label regulations and the reduced electrostatic tolerance of new energy vehicles. Sourcing the right multi walled carbon nanotube for rubber applications has become a strategic priority for forward-looking compounders.
This article examines an alternative approach based on multi-walled carbon nanotubes (MWCNTs). At exceptionally low loading levels, it simultaneously delivers conductivity, reinforcement, and thermal conductivity — without significantly compromising dynamic performance. For those evaluating options, selecting a qualified carbon nanotube for tire compound applications is the critical first step. Many leading carbon nanotube factory China operations now specialize in grades tailored to the rubber industry, and partnering with an experienced conductive carbon nanotube manufacturer ensures access to consistent quality and technical support.
1. The Conductive Carbon Black Dilemma: Easy to Meet the Spec, Hard to Achieve Synergy
Let’s first clarify a technical premise: for passenger car tires, a tread surface resistivity below 10⁶ Ω satisfies the antistatic requirement. Simply adding more conductive carbon black will eventually get you there.
The problem is what happens after “meeting the spec.”
The conductive mechanism of conductive carbon black relies on inter-particle physical contact to form a percolation network. Achieving the percolation threshold requires high filler loading — typically 10–20 phr. Once these high-structure carbon black particles are densely packed within the rubber matrix, several negative effects follow:
- Increased dynamic hysteresis loss: The continuous breakdown and reformation of the filler-filler network consumes additional energy. Tan δ at 60°C increases, and rolling resistance deteriorates.
- Degraded processability: Mooney viscosity climbs with filler loading. Mixing energy consumption rises. The extrusion processing window narrows.
- Conductivity degradation under fatigue: Under flexural deformation, inter-particle contacts are disrupted. The conductive pathway gradually deteriorates. A new tire may pass the resistivity specification, but that same tire may not remain within the safe range after 30,000 kilometers.
Solving the conductivity problem with conductive carbon black comes at the expense of dynamic performance. In the same compound formulation, these two properties exhibit a negative correlation. This trade-off is precisely what drives the need to understand carbon nanotube vs conductive carbon black in rubber properties.
For new energy vehicle tires, the cost of this contradiction is even higher. The electric drive system is more sensitive to accumulated electrostatic charge, while low rolling resistance is a non-negotiable requirement for achieving rated driving range. In this context, conductive carbon black plays the awkward role of “robbing Peter to pay Paul.” This is the fundamental challenge behind the question of how to replace conductive carbon black in tire формул.
2. The Mechanism of Carbon Nanotubes: From Particle Percolation to Fibrous Networks
Multi-walled carbon nanotubes offer a conductive mechanism fundamentally different from that of conductive carbon black. They also serve as a highly effective rubber conductive filler additive capable of transforming compound performance across multiple dimensions.
Structural level: Carbon nanotubes are one-dimensional nanofibers with diameters of 1–100 nm and lengths reaching micrometers to millimeters, yielding aspect ratios exceeding 1000:1. They do not conduct via inter-particle physical contact. Instead, they form a continuous fibrous network within the rubber matrix, providing electron transport pathways. A properly selected electrically conductive nanofiller for antistatic tire application can establish percolation at loadings far below those required by conventional conductive blacks.
Percolation threshold level: The high-efficiency conductive capability of the fibrous network allows percolation to occur at exceptionally low loading levels — 1–2 phr is sufficient to meet antistatic requirements. This stands in sharp contrast to the 10–20 phr required by conductive carbon black.
Mechanical performance level: Carbon nanotubes possess a tensile strength approximately 100 times that of steel, while their density is only one-sixth that of steel. Dispersed in nanofiber form within the rubber, they effectively bear and transfer stress, providing a pronounced reinforcing effect. This dual capability defines the value of multi walled carbon nanotube as rubber reinforcing filler.
| Comparative Dimension | Conductive Carbon Black Approach | Carbon Nanotube Approach |
| Conductive mechanism | Spherical particle percolation forming chain-like pathways | One-dimensional nanofiber constructing a continuous network |
| Typical loading to achieve antistatic properties | 10–20 phr | 1–2 phr |
| Effect on Mooney viscosity | Significant thickening at high loading | Low loading; manageable impact |
| Effect on tan δ @ 60°C | Particle network breakdown and reformation significantly increases hysteresis | Minimal hysteresis effect at low loading |
| Reinforcement contribution | Particulate reinforcement; modulus increase | Nanofiber reinforcement; simultaneous improvement in tensile strength and tear strength |
| Thermal conductivity improvement | Ограниченный | Measured thermal conductivity increase exceeding 10% |
| Conductive stability under flexural deformation | Inter-particle contacts easily disrupted; conductivity degrades | Fibrous network deforms flexibly; conductive pathway is more durable |
Thermal conductivity level: Carbon nanotubes exhibit excellent thermal conductivity. When introduced into the compound, they can construct thermal conduction pathways within the matrix, enhancing overall thermal diffusivity and improving heat dissipation during sustained high-speed driving. This answers the practical question of how to increase rubber thermal conductivity with CNT.
The table below compares the functional differences between the two conductive approaches:
The inherent weakness of the conductive carbon black approach is this: tens of parts of filler become a burden that drags down dynamic performance. The logic of carbon nanotubes is fundamentally different — use an extremely small quantity of nanofibers to form a more stable conductive pathway while simultaneously delivering reinforcement and thermal management. For formulators working with natural rubber, polybutadiene rubber, and styrene-butadiene rubber blends, a well-designed CNT reinforced NR BR SBR tire under tread formulation can unlock all three benefits without the traditional trade-offs. The ultimate goal is to improve tire conductivity without sacrificing rolling resistance.
3. Experimental Validation in Tire Under-Tread Formulations
The following data are drawn from laboratory-scale experiments on under-tread formulations [ref. test methods ISO 1853 / ASTM D991]. Four compound variants were prepared: S1 serves as the all-carbon black reference formulation. S2 and S3 respectively use 2 phr and 3 phr of carbon nanotubes to replace, on an equivalent basis, 3 phr of N660 and 3 phr of N326 each. S4 adds 4 phr of carbon nanotubes directly on top of the reference formulation without removing carbon black. This systematic design allows the formulator to directly assess CNT to reduce electrical resistivity of rubber compound at varying dose levels.
| формулы | Resistance / kΩ | Объемное сопротивление / (Ω·см) |
| S1 (all carbon black) | 5400 | 1.18 × 10⁵ |
| S2 (+2 phr CNT, –6 phr CB) | 1200 | 2.61 × 10⁴ |
| S3 (+3 phr CNT, –6 phr CB) | 410 | 1.01 × 10⁴ |
| S4 (+4 phr CNT, no CB reduction) | 48 | 1.18 × 10³ |
3.1 Electrical Conductivity
With only 2 phr of carbon nanotubes — even while simultaneously removing 6 phr of carbon black — the volume resistivity decreased by nearly one order of magnitude. At 4 phr loading, the volume resistivity dropped to 10³ Ω·cm, a reduction of two orders of magnitude. The conductivity efficiency advantage is clearly established at very low addition levels. These results confirm the value of using carbon nanotube for tire tread compound conductivity as a replacement strategy.
3.2 Physical and Mechanical Properties
| формулы | Modulus @ 300% / MPa | Прочность на растяжение / МПа | Удлинение при разрыве / % | Tear Strength / (kN/m) | DIN Abrasion / mm³ |
| S1 | 11.9 | 17.4 | 434 | 53 | 131 |
| S2 | 11.6 | 18.7 | 469 | 51 | 129 |
| S3 | 11.5 | 18.3 | 473 | 63 | 115 |
| S4 | 14.2 | 19.5 | 425 | 59 | 104 |
In S2 and S3, replacing 6 phr of carbon black with carbon nanotubes resulted in tensile strength and elongation at break both exceeding those of the all-carbon black reference. This demonstrates that the nanofiber reinforcement efficiency of carbon nanotubes far surpasses that of conventional particulate reinforcement. In S4, the DIN abrasion value dropped to 104, indicating a substantial improvement in wear resistance.
3.3 Dynamic Mechanical Properties
| формулы | tan δ @ 0℃ | tan δ @ 60℃ | Tg / ℃ |
| S1 | 0.224 | 0.163 | –44.4 |
| S2 | 0.213 | 0.179 | –46.0 |
| S3 | 0.218 | 0.192 | –46.5 |
| S4 | 0.223 | 0.198 | –46.3 |
It must be candidly noted that the incorporation of carbon nanotubes does produce a measurable increase in tan δ at 60℃. This is an additional hysteresis effect associated with the nanofiber network. However, at reasonable loading levels (≤3 phr) and with proper dispersion process optimization, the magnitude of this increase is controllable. In formulation S4, tan δ at 0℃ remained essentially consistent with the reference, indicating that wet grip performance was not compromised.
4. Dispersion Quality Determines Actual Performance
Carbon nanotube application involves an inescapable processing imperative: dispersion.
The strong van der Waals forces between individual nanotubes cause them to entangle and form agglomerates. If nano-scale dispersion cannot be achieved during the mixing process, these agglomerates do not function as reinforcing elements — they become micron-scale stress concentration defects, precisely the initiation sites for fatigue cracks. Effective carbon nanotube dispersion in rubber mixing process protocols are therefore essential to realizing the material’s full potential.
The formulation defines the theoretical upper bound of what carbon nanotubes can contribute. Mixing dispersion uniformity defines the actual lower bound of what you will get.
Key process points:
- Carbon nanotubes should be added during the masterbatch mixing stage together with the raw rubber and carbon black, using high shear forces to deagglomerate and disperse the nanotubes.
- Strictly monitor the filler dispersion rating of the mixed compound. Do not rely solely on cured physical property data as an indirect indicator.
- Vertically aligned multi-walled carbon nanotubes possess an inherent advantage in dispersibility over randomly entangled carbon nanotube forms — the ordered bundle alignment facilitates disentanglement and dispersion under high-shear mixing conditions.
5. Total Lifecycle Cost and Technical Positioning
It is a fact that the unit price of carbon nanotubes is higher than that of carbon black. But cost assessment should not stop at the per-kilogram compound cost.
Reinforcement efficiency differential: The reinforcement contribution of 2 phr carbon nanotubes exceeds that of 6 phr carbon black — meaning that the total filler loading in the formulation can be reduced, opening up space for lightweighting initiatives.
Conductivity efficiency differential: 2 phr of carbon nanotubes reduces volume resistivity by nearly an order of magnitude. The formulation space this releases can be redeployed to optimize other performance attributes.
Abrasion performance improvement: DIN abrasion decreasing from 131 to 104 translates directly to extended tire service life.
Thermal conductivity improvement exceeding 10%: Enhanced heat dissipation capability delivers performance stability and extended service life during sustained high-speed driving. For high-performance tires and new energy vehicle tires, the value of this attribute is particularly pronounced.
In the application context of new energy vehicles and high-end passenger car tires, electrostatic dissipation, low rolling resistance, and high abrasion mileage are rigid requirements of equal importance. The carbon nanotube approach provides a technical pathway that simultaneously satisfies all three constraints.
FAQ: Three Core Questions from Compound Engineers
Q: How significantly do carbon nanotubes affect Mooney viscosity and processability?
Short answer: Mooney viscosity rises with increasing addition level. At ≤3 phr it remains within an acceptable processing window. Above 4 phr, significant thickening occurs.
In detail: In the S4 formulation, 4 phr of carbon nanotubes caused Mooney viscosity to rise from 63 to 88 — a substantial increase. However, at 2–3 phr loading levels in S2/S3, Mooney viscosity increased from 63 only to 69–71, which remains within the processable window. It is recommended to begin at low addition levels and determine the optimal dosage in conjunction with mixing process optimization.
Q: Is there any interference with the cure system?
Short answer: Carbon nanotubes do not participate in the vulcanization reaction. Their effect on cure rate and crosslink density is limited.
In detail: At 2–3 phr addition levels, the changes in ML, MH, and t90 measured on the cure rheometer are modest. The existing cure system can be used without modification. Above 4 phr, MH does show some increase, which may be related to the physical constraint of nanofibers on polymer chain mobility, but this does not alter the essential chemistry of crosslinking. [ref. ISO 3417]
Q: Are carbon nanotubes applicable in silica-containing formulations?
Short answer: Applicable, but the CNT dosage needs to be appropriately adjusted to compensate for the dilution of the conductive network by the insulating silica.
In detail: Silica is an electrical insulator, and its incorporation dilutes the conductive network. Silica-containing formulations generally require a moderately higher carbon nanotube loading to achieve the same conductivity level as an all-carbon black formulation. It is recommended to start from 2 phr and adjust in gradient increments based on measured resistivity values.
For customized carbon nanotube dosage validation, mixing process optimization, or conductivity performance solutions tailored to your specific compound, contact the SaneZen Group technical team at: yorichen@sanezen.com, or visit www.sanezenrubber.com for the complete application report.
Russian 
English 
Spanish