The cashew nutshell liquid (CNSL) or cashew shell oil is a natural resin found in the honeycomb structure of the cashew nutshell. It consists of about 90% anacardic acids and 10% cardol. Both substances are dermatogenic, like the oils of the poison ivy, and present danger during manual cashew processing.[1]
It is a raw material of multiple uses in developing drugs, antioxidants, fungicides, etc. It is used in tropical folk medicine and for anti-termite treatment of timber.[1]
The anacardic acids have been used effectively in vivo against tooth abscesses due to their lethality to gram-positive bacteria. They are also active against a wide range of other gram-positive bacteria. Many parts of the plant are used by the Patamona of Guyana medicinally. The bark is scraped and soaked overnight or boiled as an antidiarrheal. Seeds are ground up into powders used for antivenom for snake bites. The nut oil is used topically as an antifungal and for healing cracked heels.[2]
Anacardic acid is also used in the chemical industry for the production of cardanol, the recovery process of cardanol from CNSL can be obtained from thin film distillation. This process also reduces the degree of thermal polymerization of the un-saturated alkyl-phenols present in cashew shell nut liquid. This natural oil phenol has been found to have interesting chemical structural features which enable a range of chemical modifications to create a wide spectrum of bio-based monomers capitalising on the chemically versatile construct it containing three different functional groups, the aromatic ring, the hydroxyl group and the double bonds in the flanking alkyl chain. These can be split into key groups, there use as Polyols. Which have recently seen a dramatic increase in demand for their bio-based origin and key chemical attributes such as high reactivity, range of functionalities, reduction in blowing agents and naturally occurring fire retardant properties in the field of ridged polyurethanes aided by their inherent phenolic structure and larger number of reactive units per unit mass. CNSL based Novolac are another versatile industrial monomer deriving from cardanol typically used as reticulating agents for epoxy matrices in composite applications providing good thermal and mechanical properties to the final composite material. Further examples of applications which are Cashew shell nut liquid derived materials are being evaluated are in the fields of chemical intermediates, additives, stabilizers, lubricants, diesel engine fuel alternatives, poor point dispersants, anti-oxidants, anticorrosive paints. Abrasives and friction dusts have also been developed from Residol, the residue byproduct of this synthesis process.[3]
During World War II it was used as a sabotage device by SOE (Special Operations Executive) for destroying the engines of German vehicles when poured into the crankcase of engines.