Brake Pads Acrylic Wool(PAN)
Acrylic wool, derived from polyacrylonitrile (PAN) fibers, has emerged as a versatile organic reinforcement in non-asbestos organic (NAO) brake pad formulations, balancing structural integrity, friction stability, and cost-effectiveness for mainstream automotive braking applications.
Material Characteristics and Processing of PAN Acrylic Wool for Brake Pads
PAN-based acrylic wool used in brake pads consists of crimped, short-cut fibers with lengths ranging from 1 to 5 mm and diameters of 15–40 μm, a dimensional profile optimized for uniform dispersion in friction matrices. Its core properties include moderate tensile strength (250–400 MPa), good elasticity, and inherent resistance to chemical degradation—attributes that support long-term pad performance. Unlike inorganic fibers, acrylic wool exhibits excellent compatibility with phenolic resins, the primary binder in NAO formulations, due to its polar molecular structure that facilitates strong interfacial adhesion. Processing typically involves thermal stabilization (at 200–300°C) to enhance thermal resistance, as unmodified PAN fibers decompose at lower temperatures; optional surface sizing with resin-compatible agents further improves fiber-matrix bonding. The cost-effectiveness and consistent quality of PAN acrylic wool make it a staple in mid-range brake pad formulations, with manufacturers like Annat Brake Pads Friction Material prioritizing low-impurity grades to ensure friction uniformity.
Functional Mechanisms in Braking Performance
The primary function of acrylic wool in brake pads is structural reinforcement: the crimped fiber structure forms an interlocking network within the friction matrix, resisting cracking, chunking, and deformation under cyclic braking loads—critical for maintaining pad dimensional stability during everyday driving. During braking, PAN acrylic wool undergoes controlled thermal decomposition at temperatures above 300°C, an endothermic process that absorbs heat and helps moderate the friction interface temperature, mitigating thermal fade in mild to moderate braking scenarios. The carbonaceous residues from decomposition integrate into the third-body transfer film on the rotor surface, enhancing film lubricity and stability while reducing abrasive wear. Additionally, the fibrous network regulates pad porosity, facilitating the escape of wear debris and preventing glazing—a common issue that impairs friction consistency—though excessive porosity, if unmanaged, can compromise pad strength, a balance carefully tuned by formulation engineers.
Formulation Design and Application-Specific Considerations
The dosage of PAN acrylic wool in brake pads typically ranges from 7% to 18% by weight, with variations based on application: standard passenger car disc brakes, which prioritize smooth braking and low noise, often use 10%–15% acrylic wool, while light commercial vehicle pads may employ 12%–18% to enhance structural integrity. Formulation engineers must address thermal stability limitations—blending acrylic wool with inorganic fibers (e.g., rock wool or ceramic fibers) compensates for its reduced performance at temperatures above 600°C, expanding its applicability. Compatibility with other additives is key: combining acrylic wool with graphite improves lubrication and reduces brake noise, while adding alumina particles optimizes friction coefficient stability (target range: 0.33–0.43). Strict control of fiber length and crimp density is essential; overly long fibers can cause agglomeration, leading to uneven wear, while insufficient crimp reduces reinforcement efficiency. Compliance with international standards such as SAE J2522 and ECE R90 requires rigorous testing to ensure consistent performance across temperature and humidity fluctuations.
Advantages and Limitations in NAO Formulations
PAN acrylic wool offers distinct advantages in NAO brake pads: its crimped structure provides superior reinforcement compared to straight organic fibers, enhancing pad durability without excessive rotor wear. Its cost-effectiveness makes it an economical alternative to high-performance synthetic fibers like aramid, suitable for mainstream automotive applications. In everyday driving conditions, acrylic wool-reinforced pads exhibit excellent noise, vibration, and harshness (NVH) performance, outperforming many metallic fiber formulations. Annat Brake Pads Friction Material’s mid-range passenger car formulations, which incorporate optimized acrylic wool ratios, have demonstrated reliable wear rates and low noise levels in urban and highway driving tests. However, limitations exist: poor high-temperature stability restricts its use in high-performance or heavy-duty braking scenarios, where temperatures exceed 700°C. Additionally, moisture absorption can temporarily affect fiber dispersion during processing, though this is mitigated by controlled drying. A minor production consideration is the potential for fiber dust during mixing, which requires basic ventilation to ensure worker comfort, a issue that does not impact end-user safety.
PAN acrylic wool remains a key component in mainstream NAO brake pad formulations, offering an optimal balance of cost, reinforcement, and NVH performance for everyday automotive braking needs.