Cardanol, also known as cashew phenol, is a monohydroxyl phenol with a long carbon chain in the metaposition. It is derived from natural occurring phenol viz. cashew nut shell liquid (CNSL) which contains anacardic acid. It has great potential to substitute phenol in resin phenolic-based chemical compounds. Different components of cardanol differs in degree of saturation of side chain where around 41% is tri-unsaturated, 31% is monounsaturated, 22% is bi-unsaturated and 2% is saturated.
Cardanol mainly contains cardanol, cardol and some other polymeric materials. Its chemical structure contributes to its chemical resistance, flexibility and increase the hydrocarbon toleration in the resins prepared from it and its unique molecular structure, unsaturation of long Hydrocarbon side chain, makes the cross linking easy on polymerization and these side chains also impact on the hydrophobic nature of polymer.
From the processing of cashew nuts, cashew nut shell liquid (CNSL) is obtained. Cardanol extraction from Natural CNSL comprises of the conversion of natural CNSL into CNSL in which anacardic acid is decarboxylated into cardanol under vacuum and heated to 170 to 180 ℃. Technical CNSL is obtained, consisting of mainly 60-65% cardanol, 15-20% cardol and 10% polymeric material and traces of methyl cardol. Cardanol is sent to distillation for further purification.
Cardanol based resins are highly soluble in oil and alcohol because of their long chain hydrocarbon and meta-substitution. Cardanol resins varnishes have good electrical insulation property and high resistance to water and chemicals property so they are used to manufacture good quality insulating varnishes. Cardanol is also used to prepare novolac type of resins which is capable to form thermo set polymers when blended to epoxy or isocyanate monomers. Cardanol resins also show outstanding resistance to mineral oils and they have antimicrobial and insect resistance properties. They are also used in automotive brake lining applications as binders and friction dust.
Painting and Coating Industry
Unsaturation in the side chain of the Cardanol molecules makes cross linking easy and hence cardanol resins have good drying and baking properties. They have excellent flexibility, good mechanical strength, corrosion inhibiting properties which make them suitable for preparing wood finishes and high quality paint. They also have good compatibility with other synthetic resins and hence they can also serve as raw materials for variety of paints.
Cardanol formaldehyde resins solutions in alcohol are used as adhesives for laminate and for metal bonding. This resin imparts greater flexibility, resistance to Chemical and water, and superior electrical insulation to the lamination sheets. They are also used to save cost as they are inexpensive and are readily available.
Chlorinated cardanol have good pesticidal, insecticidal and germicidal properties. Ethoxylated cardanol are used as oil in water emulsifier in pesticides .The cardinal paranitro tetrahydro is used as coupling compound in spray able pesticides.
Oil soluble Cardanol resins bestow high tear strength and resistance against solvent which are petroleum based so they are used in the compounding of rubber. The pure cardanol behaves as plasticizer and deoxidant when they are incorporated in rubber.
Sulfonated ethers of cardanol and Ethoxylated cardanol are used as wetting agent in textile industries .These cardanol performs much better at high temperature, so they are used as wetting agents instead of dodecyl benzene based detergent as detergents have low efficiency at high temperature.