Cashew Nut Shell Liquid is a natural resin that could be found in the honeycomb structure of the cashew nut shell. Cashew Nut Shell Liquid, a byproduct of processing cashew nuts, is used as a raw material in drugs, antioxidants, fungicides production process and many others. Cashew Nut Shell Liquid contains 90% anacardic acid and 10% cardanol. Cashew Nut Shell Liquid (CNSL) is a reddish brown viscous liquid, having the honeycomb structure of the shell of cashew nut obtained from cashew tree. CNSL can be extracted by the expelled method, but the oil has to be heated after extraction to convert anacardic acid to cardanol. The expelled and heated CNSL will have less amount of polymerized CNSL. However, if there is a requirement for pure monomers, the best source will be solvents extracted CNSL. Each component again is a mixture of four structurally related monomers, the difference being only in the degree of unsaturation. Thus, cardanol is a mixture of four components: saturated (~5%), monoene (~49%), diene (16.8%) and triene (29.3%) (which makes the chemistry of addition polymerization essentially complex).
Cashew processing methods have improved considerably over the years. Difficulties in shelling cashew nuts are due to the irregular shape of the nut, the tough, leathery outer shell, and the CNSL within the shell that must not be allowed to contaminate the kernel during its removal from the shell. An early method used to remove the CNSL in cashew producing countries was to burn the raw nuts for a short period in order to burn the shells and the CNSL without affecting the taste or appearance of the kernel.
The main objective of processing is to remove the valuable cashew kernel from the shell with as little damage as possible. The whole kernels command a higher price than does is broken pieces. Pale, ivory colored or white kernels are preferable to colored or burnt ones. The CNSL must be removed during the process, without either contaminating the cashew kernels or burning the hand of the processor. The processor must therefore, finely tune the process in order to achieve the best quality kernels.
Extraction of the kernel from the shell of the cashew nut has traditionally been a manual operation. Roasting causes brittleness of the shell and loosening of the kernel from within the shell. Soaking, increases the moisture content of the kernel, thereby reducing the risk of it being scorched during roasting and increasing its flexibility so as to make it less likely to crack. The CNSL is released when the nuts are roasted. Collection of this material in sufficient quantities can be economically advantageous. CSNL is unlikely to be collected by very small-scale processors, due to the high cost of the specialized roasting equipment required for its collection.
After the kernels are taken out of the shells, the testa (the thin skin covering the kernel) must be removed, following which the kernels are graded and packaged. The process consists of five main steps:
•Shelling - removal of the outer shell and CNSL
•Peeling - removal of the testa
•Grading - into different sizes and colors in accordance with standard grading
•Drying or humidifying - to a final moisture content of 5 percent
•Packing - into airtight bags or cans, depending upon the scale of operation
Each of these five steps involves a number of operations. The various processing steps differ in accordance with the scale of operation. In some cases, all steps of the process are manually carried out by small-scale processors, while various pieces of equipment are used in commercial scale processing.
CNSL has innumerable applications in polymer based industries such as friction linings, paints and varnishes, laminating resins, rubber compounding, resins, cashew cements, polyurethane based polymers, surfactants, epoxy resins, foundry chemicals and intermediates for the chemical industry. It offers much scope and varied opportunities for the development of other tailor - made polymers.
CNSL products are used as antioxidants, stabilizers and demulsifies for petroleum products. Soluble metal derivatives of CNSL are used to improve the resistance to oxidation and sludge formation of lubricating oils. Oxidized CNSL and its derivatives are also used as demulsifying agents for water in oil type petroleum emulsions.