Cardanol-based epoxy resins

A paint based on an epoxy-cardanol resin has been produced and then characterized in order to compare its performance (i.e. physico-mechanical properties, chemical resistance and corrosion protection efficiency) with that of paints made with unmodified epoxy resin (Aggarwal et al., 2007). It was found that the new bio-based paints show better anticorrosive properties than the unmodified paints and thus the cardanol-based epoxy resin represents an optimal binder medium for the formulation of paints. 

Campaner P, D Amico D, Longo L, Stifani C and Tarzia A (2009), Cardanol-based novolac resins as curing agents of epoxy resins , J Appl Polym Sci, 114, 3585-3591. doi 10.1002/app.30979. 

Most of the BPA-based epoxy resins are quite rigid and are based on petrochemicals. A quite different type of flexible epoxy resin is based on cardanol, derived from cashew nut shell liquid. Mono-, di- and multifunctional derivatives are possible. Mono- and difunctional low viscosity derivatives are used as modifiers and diluents, while complex di- and multifunctional epoxies are used in two-component ambient cure epoxy systems. They give the cross-linked matrix excellent flexibility, toughness and impact resistance. They possess very good water, chemical and corrosion resistance. 

Epoxy resin-based epichlorohydrin,bisphenol-A and cardanol was evaluated as a paint binder and found to show increased tensile strength, elongation, adhesive strength with steel and low water vapour transmission when compared to epoxy resin without cardanol. ... 

An epoxy resin-based on epichlorohydrin, bisphenol-A and cardanol was evaluated as a binder for a paint system and was found to offer better properties in terms of increase in tensile strength, elongation, bonding with steel and lowering of water vapour transmission than epoxy resin. In addition, iron oxide-based paints in epoxy-cardanol resin showed better performance than zinc phosphate-based paints." " ... 

Cardanol is a main component of thermally treated cashew nut shell liquid (CNSL), and is a phenolic compound with a long unsaturated hydrocarbon chain substituted in the meta position (Figure 2.17a). Urushiol, which is obtained from lacquer tree, poison ivy, poison oak, and poison sumac (Toxicodendron), and used for a raw material of a lacquer (urushi) in East Asia, is also a phenolic compound of catechol with a long unsaturated or saturated hydrocarbon chain (Figure 2.17b). Cardanol-based polymers have been reported very often, while there are a few research reports on urushiol-based polymers. Research on polymers synthesized from cardanol or CNSL are reviewed elsewhere.In the late 1980s, cardanol or CNSL-based polymers began to be reported as novel phenol-formaldehyde type resins and novel epoxy resins.Thereafter, Pillai and his co-workers have vigorously studied synthesis of various type of cardanol-based polymers polymers obtained... 

Synthetic resins, such as phenoHc and cresyUc resins (see Phenolic resins), are the most commonly used friction material binders, and are usually modified with drying oils, elastomer, cardanol [37330-39-5] an epoxy, phosphoms- or boron-based compounds, or even combinations of two. They ate prepared by the addition of the appropriate phenol and formaldehyde [50-00-0] in the presence of an acidic or basic catalyst. Polymerization takes place at elevated temperatures. Other resin systems are based on elastomers (see Elastomers, synthetic), drying oils, or combinations of the above or other polymers. 

L. K. Aggarwal, P. C. Thapliyal and S. R. Karade, Anticorrosive properties of the epoxy-cardanol resin based paints . Prog Org Coat, 2007,59,76-80. 

For instance cardanol, a phenol-based by-product of the cashew nut industry, is one of the common precursors used to obtain different types of epoxy bio-based resins. Cardanol is an industrial grade yellow oil obtained by vacuum distillation of cashew nut shell liquid (CNSL), the international name for the alkyl phenolic oil contained in the spongy mesocarp of the cashew nut shell from the cashew tree Anacardium occidentale L. CNSL derived from the most diffused roasted mechanical processes of the cashew industry represents nearly 25% of the total nut weight, and its production worldwide (Africa, Asia and South America being the main producer areas) is estimated to be about 300,000 tons per year (Calo et al., 2007). 

A thermosetting resin containing approximately 40% of cardanol by weight has been synthesized by adding an epoxy monomer and an acid-based catalyst to a resole compound (Maffezzoli et al., 2004). This last was manufactured through a polycondensation reaction between cardanol and formaldehyde in the presence of a basic catalyst. The formulation characterized by adequate properties and curing temperatures was reinforced with natural fibers (i.e. short ramie, flax, hemp fibers and a jute fabric) to obtain samples which were then tested both in tensile and in flexural configurations. 

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