Cashew nut shell liquid is a co-product of the cashew nut industry and is sourced primarily from South America and Asia. The nut has a shell of about 1/8 inch thickness inside which is a soft honey comb structure containing a dark reddish brown viscous liquid. It is called CASHEW NUT SHELL LIQUID or CNSL. It is a dark liquid comprised of different unsaturated alkenyl substituted phenols Which is the pericap fluid of the Cashew Nut. It is often considered as the better and cheaper material for unsaturated phenols. This is purely a natural product and no chemical is added.
The CNSL process sequence in basic steps :
- Wetting of the cashew nuts by dipping in a hot water vat at 20-25°C to strike a moisture balance between the shell and kernel of the cashew nut and removal of superficial moisture from the nuts and then steaming of the nuts to open up the pores of the shells,
- Subjecting the conditioned nuts dipping in a vat containing cashew nut shell oil where temperature is kept at 170°C to 185°C or preferably at 180°C, for a predetermined period when most of the oil issues out of the shells,
- Vibrating the nuts discharged from the oil bath and subsequent centrifugation in order to remove the adhered oil,
- Incision of the shell walls of the nuts and centrifugation of the seed against a breaking wall,
- Separation of the kernel from the cracked cashew shells and peeling of the skin by heating with hot air and mechanical rubbing of the kernel and effecting the removal of the peel under the action of an air stream; and Classifying the peeled nuts and subsequent packing under inert gas in tightly closed containers.
Industrial Significance of CNSL :
- Low Cost Phenol
- Versatility in Polymerization and Chemical Modification
- Possibilities for Development of High Performance Polymers Property advantage over phenolic in certain applications such as impact resistance; flexibility, faster heat dissipation etc.
- Reactivity CNSL undergoes all the conventional reactions of phenols.
Applications of CARDANOL :
- Oil Soluble Resins
The Meta substitution and the long hydrocarbon chain in its molecule makes the resins prepared with Cardinol, highly soluble in oils and imparts superior properties such as high electric insulation and resistance against chemicals to its films. It is to manufacture both solid and semi solid resol or novolac type of resins depending upon the nature of catalyst and the aldehyde compound. Cardanol resin varnishes have good electrical insulating properties and resistance against water and chemicals. They give superior quality Stamping Varnishes. Because of their high insulation and dielectric losses, these varnishes are preferred to compositions based on usual Phenol such as Cresol or Substituted phenols.
- Surface Coatings and Paints
Cardanol resin Varnishs in addition to water and Chemical resistance have good air drying and baking properties. These compositions are suitable for wood finishes, food can lacquers textile bobins and high quality paints. Stoving paints can be prepared which could be baked at 60°C. The Cardanol based resins have good compatibility with other synthetic resins such as alkydes, epoxies chlorinated rubber, Phenolic etc., and can serve as raw material for variety of paints.
- Lamination Industry
By partly replacing the Phenol or Cresol in alcohol soluble resins used for Lamination one could prepare resins which imparts greater flexibility resistance to Chemical and water, and superior electrical insulation to the lamination sheets.
- Surface Active Agent
Sulphonated ether of Cardanol has been found to be wetting agent and finds use in Textile Industry, ethoxylated TetrahydroCardanol Sulphonate performs better at high temperature than the detergents based on Dodoeyl benzene.
Chlorinated Cardanol is reported to have good insecticidal, pesticidal and germicidal properties. Cardanol Formaldehyde resin is also used as a solvent for well-known pesticides such as Pyrethrin and Rotanes. Paranitro Tetrahydro Cardanol finds use as a coupling compound in sprayable pesticides such as Parathion.
- Rubber Compounding
Oil soluble Cardanol resins are used in Rubber Compounding. They impart high tear strenght and resistance against Petroleum based solvents. Pure Cardanol acts as a Deoxident and Plasticizer when incorporated in rubber. Its ethers are also used as plasticizers for synthetic rubbe to reduce the shore hardness and improve the ageing properties.