CASHEW NUTSHELL LIQUID

This is used in manufacture of brake linings and is a polymer based on cashew nutshell liquid admixed with formaldehyde or furfuraldehyde and other ingredients. The polymerised resin mixture is cast into 8 cm thick slabs and then ground finely to produce the friction dust. Several fires have been experienced during bulk storage of the dust, attributed to autoxidation of the still partially unsaturated resin compound. Previously, linseed oil was used in place of the nutshell liquid, but fires were then more frequent. 

Property Modifiers. Property modifiers can, in general, be divided into two classes nonabrasive and abrasive, and the nonabrasive modifiers can be further classified as high friction or low friction. The most frequently used nonabrasive modifier is a cured resinous friction dust derived from cashew nutshell liquid (see Nuts). Ground rubber is used in particle sizes similar to or slightly coarser than those of the cashew friction dusts for noise, wear, and abrasion control. Carbon black (qv), petroleum coke flour, natural and synthetic graphite, or other carbonaceous materials (see Carbon) are used to control the friction and improve wear, when abrasives are used, or to reduce noise. The above mentioned modifiers are primarily used in oiganic and semimetallic materials, except for graphite which is used in all friction materials. 

Historically the main interest in cardanol, in the form of the semisynthetic, technical cashew nutshell liquid, obtained by thermal decarboxylation of natural cashew nutshell liquid, has been in a wide range of technological applications such as in friction dusts and in polymer chemistry many of which have been described in a number of reviews [1,2,11]. Remarkably, very new biological applications have been found for this versatile raw material. 

Constituents of natural cashew nutshell liquid (Anacardium occidentale) are active inhibitors of a-glucosidase, invertase and aldose reductase. The saturated, monoene, diene and triene anacardic acid constituents were the most potent inhibitors compared with commercially structurally-related compounds which showed a negligible activity [283]. 

Anacardic acid n. C22H32O3. Ortho pentade-cadienylsalicylic acid. Principal constituent of cashew nutshell liquid. 

Cardol n. One of the original constituents of cashew nutshell liquid, occurring to the extent of about 10%. It is a dihydroxy phenol, containing a side chain with two double bonds. 

The resins can be a novolak-hexa or a resole-novolak blend. In some applications liquid resoles are used. Addition of alkylated phenol, oil, or cashew nutshell liquid (CNSL) reduces hardness and increases abrasion resistance. Modification by rubber improves the coefficient of friction and reduces brake fading. 

The reaction of formaldehyde with unsubstituted phenols leads to either soluble or cross-linked resins since condensation occurs at either ortho or para positions. Monosubstituted [35] (ortho or para) phenols give cross-linking with difficulty but phenols doubly substituted in ortho or para positions yield only low molecular weight products. If only one ortho or para position is available on the phenol then the phenol cannot produce resins and reacts with difficulty with aldehydes [33]. Sometimes cresols and phenol are blended together to obtain fully cured resins. In addition to phenol, the other important phenols that are used to give phenolic resins are o-cresol, mixed cresols, / -/e/ r-butylphenol (from isobutylene and phenol), p-phenylphenol (by-product from phenol manufacture), resorcinol, and cardanol (from cashew nutshell liquid). 

Toxic 5-alkatrienyl, 5-alkadienyl, 5-alkenyl and 5-alkyl resorcinols, collectively known as cardol, occur in the cashew nutshell liquid (CNSL), also known as cashew shell oil, a natural resin found in the honeycomb structure of the cashew nutshell. It is a byproduct of cashew nuts processing (see Section 8.2.6.1.6). A typical solvent-extracted CNSL contains 15-20% of cardol. The main components are (8Z,llZ)-pentadeca-8,ll,14-trien-l-yl (10-1), (8Z,llZ)-pentadeca-8,ll-dien-l-yl, (8Z)-pentadeca-8-en-1-yl and pentadecyl derivatives. 

Another compound which has been found to somewhat imitate the active site of peroxidases is the commercially available Fe(II)-salen catalyst. This catalyst was used successfully to produce phenol polymers, which could be of interest for industrial production [153,154]. For example, cardanol can be polymerized by the Fe(II)-salen catalyst [155]. Due to the unsaturated bonds in the side chain of the cardanol components, the resulting polymers could be thermally cured, or cured by use of cobalt naphthenate to give brilliant films with a high-gloss surface. This reaction proves that reactive prepolymers can be synthesized from renewable resources (cardanol is the main component obtained by thermal treatment of cashew nutshell liquid). This process could be a true alternative to conventional phenol-formaldehyde resins (Scheme 25) [ 155]. Other non-heme iron complexes have been foimd to... 

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