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An aromatic epoxy monomer, formed by glycidylation of gallic acid, was crosslinked by adopting different curing agents to obtain bio-based, crosslinked resins with suitable engineering properties. Specifically, tri- and tetra-glycidyl ether of gallic acid (GEGA) were obtained using a two-step synthesis. These bio-based monomers were cured in the following three epoxy formulations: a stiff cycloaliphatic primary amine, isophorone diamine, and a flexible polypropylene oxide amine (Jeffamine D-230). Next, the homopolymerization of GEGA was studied using an ionic initiator, N,N-dimethylbenzylamine, and a complex curing mechanism highlighted by calorimetric and mass spectra analysis. Calorimetric and rheological measurements were used to compare the curing behavior of the studied GEGA-based formulations. Mechanical properties of the gallic acid-based epoxy resins were comparable with those of standard epoxy resin formulations, based on di-glycidyl ether of bisphenol A. Thermogravimetric analysis of cured samples showed a relevant char content at high temperatures.

Two different novolac resins, named Nov-I and Nov-II, containing an amount of unreacted cardanol of 35 wt % and 20 wt %, respectively, were synthesized by the condensation reaction of cardanol and paraformaldehyde using oxalic acid as catalyst. Cardanol is the main constituent of cashew nut shell liquid, a renewable natural resource. The cardanol-based novolacs were tested as curing agents of the diglycidyl ether of bisphenol A epoxy resin employing 2-ethyl-4-methyl-imidazole as catalyst and differential scanning calorimeter and thermogravimetric studies were performed to identify the final thermal properties of the cured resins. In addition, tensile tests were carried out to evaluate the mechanical properties of the epoxy resin cured with the novolacs, which showed to deserve consideration as effective epoxy curing agents. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

In this work, the synthesis, formulation and characterization of a thermosetting resin based on cardanol, suitable as composite matrix, is presented. The polycondensation reaction between cardanol, a phenolic based by-product of the cashew nut industry, and formaldehyde in presence of a basic catalyst, in different molar ratios, has been applied to the synthesis of a resole type pre-polymer. A thermosetting resin, containing approximately 40% of cardanol by weight, has been obtained adding an epoxy monomer and an acid based catalyst to the resole compound. The reactivity of different functional groups of the mixture has been studied by FTIR (Fourier Transformed Infrared spectroscopy) while the calorimetric analysis has been applied to the definition of the curing cycle, also taking into account the mechanical performances of the matrix. The glass transition temperature ( T g ) of the resin, in the range 42–56 °C for different curing cycles and formulations, has been determined by dynamic-mechanical analysis. Finally, the formulation characterized by adequate properties and curing temperatures has been reinforced with short ramie, flax, hemp fibres, and with a juta fabric. For comparison purposes a standard polyester resin has been also used as matrix for the same juta fabric. In this last case, two different surface treatments of the fibre surface have been also attempted in order to improve the adhesion characteristics. Coupling natural fibres with a natural based matrix has led to an amount of natural components in the composite that can reach 73% by weight. Starting from the new cardanol based matrix and the above mentioned fibres, flat plane samples have been prepared and tested in tension and bending.

The aim of this work is the development of composite pipes using renewable resources. The pipes, manufactured by filament winding technology, were obtained using an epoxy resin crosslinked with a cardanol based novolac as matrix and jute fibres as reinforcement. Cardanol is a natural oil extracted from the shell of the cashew (Anacardium occidentale L.) nut. An amount of natural materials higher than 50% by weight was achieved in the final composites. Tensile and parallel plate compression tests were carried out on the composite pipes.

The aim of this work is the development of composite materials obtained using as matrix a resin derived from renewable resources. New pre-polymers derived from cardanol, a natural phenol extracted from the shell of the cashew nut, were synthesised. In particular cardanol based novolac-type phenolic resins, capable to form thermoset polymers when blended to commercial epoxy or isocyanate monomers, were successfully developed. Composite laminates obtained using a jute fabric were fabricated and characterised. Jute fabrics were used with and without a surface treatment with NaOH and silane coupling agents. An amount larger than 50% of natural originating materials is present in the laminates.