Positioning and Constraints of rCB

rCB is a carbon material derived from waste tires, and in terms of carbon source transition, it already has rationality. It is inevitably connected within the context of CO₂ emissions, raw material risk diversification, and material traceability.

On the other hand, its constraints as a material are clearly present.

・Carbon surface, ash, and oxygen functional groups coexist
・Reinforcement performance is unstable (converging around N660–N550 range)
・Large Payne effect (strong aggregation)
・Practical loading level plateaus around 20–30 phr

The phenomenon occurring here is not a “filler design problem,” but can be regarded as a structural issue arising from an undefined interface. Simple dispersing aids cannot eliminate the root of aggregation.

Concept of CS₂-Derived Interface Control

The proposed structure is three-layered.

・Aromatic moiety
→ π–π interaction with rCB carbon surface

・CS₂-derived sulfur functional groups
→ interaction with ash and polar sites
→ partial fixation during vulcanization

・Hydrophobic chain
→ dissolution into rubber phase

This design differs from conventional silane systems, which assume a single interface (SiO₂), in that it assumes simultaneous interaction with a composite surface (carbon + inorganic + polar).

The expected changes are as follows.

・Reduction of Payne effect (15–25%)
・Stabilization in high loading region (30 → 50 phr)
・Suppression of excessive Mooney viscosity increase

The key point is not “increasing reinforcement,” but “eliminating instability factors.” Reinforcement follows afterward.

Conditions for Viability and Risk Structure

The key conditions converge on three points.

Persistence of Adsorption

π–π interactions are reversible and may detach under shear during mixing. If this collapses, the overall design does not hold.

Interference with Vulcanization System

Sulfur functional groups are both an advantage and a risk. They inherently carry the possibility of changes in crosslink density, scorch behavior, and network heterogeneity.

Cost Threshold

Positioned between dispersing aids (300–800 JPY/kg) and silanes (500–1200 JPY/kg). Beyond this, it cannot be absorbed on the compounding side.

Positioning of the Technology (Simplified)

The structure compared to existing approaches is as follows.

・Dispersing aids
→ only initial viscosity reduction, no interface fixation

・rCB modification
→ lot-dependent, limited surface control

・Silane
→ effective for inorganic side but not on carbon surface

・CS₂ interface control
→ simultaneous design of carbon surface + ash + vulcanization

Only here does a framework emerge to treat rCB as a composite filler.

Industrial Implication

The value of this concept lies not in material performance, but in expanding formulation freedom.

・Increasing the upper limit of rCB usage
・Absorbing lot-to-lot variation
・Stably increasing recycled material ratio

As material traceability systems in Europe progress, formulation ratios themselves become a competitive axis. In this context, technologies that increase the “usable amount of rCB” directly translate into product design flexibility.

From the perspective of the annual carbon black market size, even a few percent substitution corresponds to a large absolute volume. The additive market scales accordingly.

Summary

The issue with rCB is not lack of performance, but “undefined interfaces.”
The CS₂ concept directly addresses this point.

If it succeeds, not the material but the “conditions” change.
If it fails, it returns to the conventional trajectory.

It is less about technology, and more about where the control point is defined.