r PAN

R-PAN is an organic reinforcement fiber based on polyacrylonitrile (PAN). Its primary function in a friction material is twofold:

• Structural Reinforcement: It provides mechanical integrity and cohesion to the phenolic resin matrix, improving the brake pad's resistance to fracture and cracking.
• Char Formation: At high temperatures (>300°C), the PAN fiber carbonizes, forming a carbonaceous "char" on the pad's surface. This layer acts as a thermal barrier and a high-temperature lubricant, helping to stabilize the coefficient of friction and prevent fading.

"Non-fibrillated" means that R-PAN consists of individual, smooth fibers, without the small branches or "fibrils" that characterize other organic fibers. This has direct implications:

• Lower Specific Surface Area: Lacking fibrils, its surface area is smaller. This reduces the resin demand for wetting the fiber, which can improve processability and lower costs.
• Different Anchoring Mechanism: The anchoring to the matrix is primarily chemical (adhesion to the resin) rather than mechanical (interlocking of fibrils). This makes it ideal for certain matrices but may not be a direct 1-to-1 substitute in formulations optimized for fibrillated fibers.
• Homogeneous Dispersion: Individual fibers tend to disperse very homogeneously in the mix, preventing the formation of clumps.

R-PAN is positioned as an economical and functional alternative to aramid fibers, especially for partial replacements.

• Economic Advantage: It is a significantly more cost-effective option than aramid, allowing for a reduction in formulation costs.
• Performance: Although aramid has superior mechanical and thermal resistance, R-PAN offers excellent reinforcement and a very effective char-forming capability. In many applications, especially in the aftermarket and in mid-performance formulations, a partial or total replacement of aramid with R-PAN can achieve a very favorable cost-performance balance without sacrificing the material's integrity.

Given its non-fibrillated nature and its cost-performance profile, R-PAN is particularly effective in:

• NAO (Non-Asbestos Organic) Formulations: As a primary or secondary reinforcement, where it contributes to structural integrity and high-temperature friction stability.
• Cost-Optimized Applications: In brake pads for the aftermarket, where reliable performance at a competitive cost is sought.
• Low-Steel Formulations: To complement the reinforcement of steel fibers and improve NVH (Noise, Vibration, and Harshness) characteristics and the formation of a stable tribofilm.

• Typical Dosages: Dosages typically range from 2% to 8% by weight, depending on the required level of reinforcement and the presence of other fibers in the formulation.
• Fiber Length: The availability of different fiber lengths allows for reinforcement optimization. Longer fibers (e.g., > 4mm) offer greater macroscopic reinforcement, while shorter fibers (e.g., < 2mm) are easier to disperse and are suitable for complex molding processes. The choice should be based on the balance between processability and the desired mechanical properties for the final pad.