Cardanol: An Eco-friendly Isocyanate Blocking Agent
Cardanol, a well-known non-edible natural oil, is a USDA certified bio-based (>98% bio-content) alkenyl-phenolic product.
Cashew Nut Shell Liquid (CNSL), largely available in the entire sub-tropical areas (Brazil, India, Vietnam, Ivory Coast, etc.), is a non-food-chain industrial oil found in the honeycomb structure of the cashew nutshell (Anacardium Occidentale) and is typically considered a by-product of the cashew nut industry. The main product isolated by vacuum distillation of CNSL under proper conditions is cardanol.
Given cardanol’s peculiar chemical structure, several chemical routes to cardanol-based derivatives have been reported in the literature, including epoxies, amine curing agents, surfactants, friction particles, and phenolic resins. Once used at very high purity grade in PU prepolymers, this substance has demonstrated various benefits including favorable deblocking conditions, lower viscosity, and excellent storage stability compared to commonly used phenolic compounds. Cardanol has been described as a useful building block for polyols and derivatives suitable for 2K PU applications, aiming, for example, to improve PU adhesives and coatings durability by imparting hydrophobicity and chemical resistance.
By properly selecting suitable conditions (use of catalysts, chain extenders or their combinations) and tuning deblocking temperatures, cardanol is offering formulators a valid and versatile chemical tool.