Synthesis and Characterization of Cardanol-Based Epoxy Systems

Abstract

The use of cardanol, a renewable natural resource, in place of a phenol or diphenol, in the synthesis of two different epoxy systems has been studied in this work. Cardanol, prepared by the distillation of cashew nut shell liquid (CNSL), was epoxidised using epichlorohydrin in presence of caustic soda catalyst at different reaction intervals and the products were characterized by spectroscopy, gel-permeation chromatography and by determining the epoxide equivalent. The epoxide equivalent increased sharply with time of epoxidation and reached almost a limiting value around 9 h. Cardanol, being less reactive, undergoes epoxidation to a smaller extent than phenol or bisphenol. Although these epoxy compounds do not form cross-linked networks due to being mono-functional, they are found to be effective in producing relatively flexible systems when reactive blended with commercial DGEBA. Co-epoxides containing bisphenol A and cardanol in varying molar compositions were also synthesised and characterised. Introduction of 20 mol% cardanol into bisphenol A resulted in a resin having reduced tensile, impact and compressive strengths upon curing by a polyamine hardener. However, the resin showed considerable improvement in elongation-at-break without much decrease in energy absorption.

Bio-based epoxy resin toughening with cashew nut shell liquid-derived resin

“…12,13 Epoxy resins derived from cardanol, a by-product of the cashew nut industry, have also received attention from both academic and industrial research groups. [14][15][16][17][18] Relative to DGEBA, cured cardanol-based epoxy resins possess a low modulus and glass transition temperature. 16 However, cross-linked materials from cardanol epoxy resins retain good flexibility.…”

“…Previous work demonstrated that combining DGEBA with the glycidyl ether of cardanol increased cured thermoset flexibility but had little to no effect in changing the material's impact strength. 17 The Cardolite Corporation sells a commercial flexible epoxy resin under the trade name Cardolite NC-514 (NC-514). Its thermomechanical and chemical properties are published.…”

Investigation on mechanical, thermal, and flame retardant properties of particulate SiO2 reinforced cardanol based composites

“…Epoxidation of cardanol was performed based on the previously reported literature. [19,20,26] Equimolar amount of cardanol and epichlorohydrin were introduced in to a three necked round bottom flask equipped with a reflux condenser, mechanical stirrer, thermometer and dropping funnel. The mixture was heated slowly over an oil bath until the content in flask starts refluxing.…”

“…Sharp intense peak of methylene C─H stretching vibration was noticed at 2932, 2853 cm −1. [6,[19][20][21] Peaks at 1585 and 1445 cm −1 recommends to the C═C stretching vibration of benzene ring [30] and the explicit existence of small peaks near 904, 953, and 997 cm −1 showed the presence of adjacent hydrogen atom and substitution in benzene ring. [23] 1267 and 1145 cm −1 peaks correspond to asymmetric C─O stretching vibration of C─O─C linkage and to the C─OH vibration.…”

“…[30] Broad phenolic OH peak appears in the range 3200 to 3500 cm −1. [19][20][21][22][23]30] Apart from spectral data of CD, band intensity of ─OH peak in the range 3200 cm −1 was noticed to be deceased in EPC indicating incomplete epoxidation and the observed oxirane peak at 915 and 875 cm −1 confirmed partial epoxidation. Unsaturated aliphatic carbon chain peak at 2930 cm −1 indicated that epoxidation proceeded via phenolic ─OH group.…”