Friction Materials

Material selection for friction materials

Brake pads, brake linings and clutch facings are composites of fibres, fillers, abrasives, lubricants and a binder, usually a phenolic resin. Cashew nut shell liquid (CNSL) and its derivatives play two roles. CNSL-modified phenolic resins make the binder more flexible and improve noise, vibration and harshness behaviour compared with straight phenolics. Friction dust, made by polymerising CNSL and grinding the cured polymer, acts as an organic friction modifier that helps stabilise the friction coefficient, reduce noise and control wear.

What the process needs. Friction dust producers need a CNSL that polymerises predictably, because curing time, temperature and catalyst demand drive batch throughput and the properties of the dust. Resin producers need a consistent phenolic composition so that the modified resin reaches the same viscosity, flow and cure speed from batch to batch. In both cases, variation in the liquid shows up later as variation in friction performance, which is expensive to trace once pads are in service.

Key specification parameters. For CNSL and decarboxylated CNSL, typical parameters are cardanol and cardol content, polymerised material, viscosity at a stated temperature, specific gravity, moisture, ash, matter insoluble in toluene, iodine value and polymerisation time. Technical CNSL, extracted by heat, is largely decarboxylated, while solvent-extracted CNSL is rich in anacardic acid and releases carbon dioxide when heated, so confirm which type is offered. For distilled cardanol, colour and purity matter most. For friction dust made from these liquids, formulators typically check acetone extract, ash, moisture, particle size and heat loss.

Recommended product types. Technical cashew nut shell liquid for friction dust and resin modification. Decarboxylated CNSL where a lower acid content and more consistent reactivity are required. Cardanol for resin modification and specialty curing agents.

Documentation. Ask for a representative analysis and a certificate of analysis for each lot, together with the safety data sheet. For EU and UK imports, confirm the REACH registration status of the substance and tonnage band. Ask for the certificate scope with your quotation where origin or sustainability evidence is required by your customers.

Handling and shipping. CNSL is a dark brown, viscous liquid that thickens in cold weather and can polymerise slowly on prolonged heating or storage. It is a skin irritant and can cause sensitisation, so use gloves and eye protection and follow the safety data sheet. It is usually shipped in steel drums, IBCs, ISO tanks or flexitanks. Store it closed, away from heat and oxidising agents, and use older stock first.

Qualifying a new source. A raw material that meets its specification can still change friction behaviour. Evaluate new CNSL sources in your full formulation, including dynamometer testing where your customers require it, and keep retained samples of the lots used in approved production.