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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.

The dispersion process of a micro-encapsulated phase change material (n-tetradecane) into a polyurethane foam was studied in order to develop a micro-composite insulating material with both low thermal conductivity and latent heat storage properties. The maximum weight content of micro-capsules added to the cellular matrix was 13.5%. Dynamic thermal properties of hybrid foams were investigated by means of a thermographic analysis. This was found to be a very effective diagnostic technique in detecting the change in heat transfer rate across the micro-composite foam in an indirect way, i.e. by measuring how the surface temperature changes over time under heat irradiation. Such a material would be of interest in the field of transport of perishable goods, particularly those requiring a controlled regime of carriage/storage 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.

An analysis of the crystallization behaviour of a new poly(aryl-ether-ether-ketone-ketone), PK99, by differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) is presented. Isothermal crystallization TG were obtained in the whole range between the glass transition temperature (Tg) and the melting temperature (Tm) as a consequence of the slow crystallization kinetics stemming from the closeness of these transitions. The calorimetric results, compared with WAXD data, were applied to determine the theoretical melting temperature and crystallization enthalpy. The DSC and WAXD data were combined in order to calculate the total amount of the crystallizable fraction of the polymer, and a model was proposed to explain the difference between the fractions of crystallinity observed with these techniques. The thermal and X-ray data were also correlated with different lamellar morphologies arising from the crystallization conditions. Finally, DSC experiments on the crystallized sample were used to detect the presence of a rigid amorphous phase which does not relax at Tg.

Publisher Summary Benzoxazine chemistry is well known and offers many advantages. Only recently polybenzoxazines with enhanced structural properties are successfully synthesized, alone or formulated with suitable additives. Benzoxazines offer many advantages compared with epoxies and other chemical structures, as they are halogen-free, exhibit better flame-resistance and electrical properties than epoxies, and are characterized by an excellent high temperature resistance and low water absorption values. With this combination of properties, benzoxazines hold great promise for performing in applications such as composites, coatings, adhesives, encapsulants, and others. It focuses on the synthesis of new low viscosity cardanol-based benzoxazines, as possible alternatives to the standard petroleum-based ones. This chapter describes that Cardanol is an industrial oily alkyl-phenolic product obtained by the vacuum distillation of “cashew nut shell liquid” (CNSL), a renewable natural resource obtained from the cashew nut as a byproduct during the process of removing the cashew kernel from the nut. A monofunctional liquid cardanol-based benzoxazine is prepared and used as a reactive diluent and toughening agent for a bisphenol A-based benzoxazine. The thermal, viscoelastic, and mechanical properties of benzoxazine resins obtained from the mixture of a low viscosity CA-a and the BA-a are studied in this chapter. Three different mixtures of BA-a and CA-a, containing 10%, 20%, and 30% by weight of CA-a, are prepared and studied to illustrate how different amounts of the cardanol derivative affect the properties of the final benzoxazine resins. The results obtained from the nonisothermal DSC analysis suggested a copolymerization reaction between the two benzoxazines BA-a and CA-a, occurring in a temperature range similar to that shown by the BA-a resin.

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.

A custom-made, air-coupled ultrasonic device was applied to cure monitoring of thick samples (7-10 mm) of unsaturated polyester resin at room temperature. A key point was the optimization of the experimental setup in order to propagate compression waves during the overall curing reaction by suitable placement of the noncontact transducers, placed on the same side of the test material, in the so-called pitch-catch configuration. The progress of polymerization was monitored through the variation of the time of flight of the propagating longitudinal waves. The exothermic character of the polymerization was taken into account by correcting the measured value of time of flight with that one in air, obtained by sampling the air velocity during the experiment. The air-coupled ultrasonic results were compared with those obtained from conventional contact ultrasonic measurements. The good agreement between the air-coupled ultrasonic results and those obtained by the rheological analysis demonstrated the reliability of air-coupled ultrasound in monitoring the changes of viscoelastic properties at gelation and vitrification. The position of the transducers on the same side of the sample makes this technique suitable for on-line cure monitoring during several composite manufacturing technologies.

Air-coupled ultrasound in one-side transmission mode has been applied to monitor the curing process of an unsaturated polyester resin, commonly used as a matrix in glass reinforced composites. The evolution of the resin mechanical properties during cure has been measured from the variation of longitudinal velocity. The technique has demonstrated to be a very powerful tool for detecting the structural changes occurring at gelation and vitrification. The no-contact ultrasonic results have been compared with those obtained using conventional contact ultrasonic measurements, characterized by direct coupling between the transducer and the resin, and with the rheological measurements. The good agreement among the results of the different techniques demonstrates the reliability of air-coupled ultrasound in monitoring the changes of viscoelastic properties occurring during the cure of thermosetting polymers. A further advantage of the proposed one-side ultrasonic technique is the absence of physical contact between the transducers and the sample, which is relevant during composite manufacturing, where probe contact could adversely affect the part quality or access from both sides is not practicable. No-contact ultrasonic cure monitoring is suitable for both stationary and moving liquid or solid samples in several process conditions such as moulding, filament winding, etc., opening the way to new applications of ultrasound in the composite industry.

A complex mechanism characterizes the water uptake kinetics in hydrogels, as a consequence of the strong structural changes occurring in the material during the sorption process. Water acts as a plasticizer, reducing the glass transition temperature of the polymer below the sorption temperature and determining a glass transition in the polymer. In this study the changes in the ultrasonic attenuation and velocity in semicrystalline Poly-vinyl-alcohol (PVA) hydrogel films during water sorption are measured by a pulse-echo system. The ultrasonic wave propagation is applied to monitor the position of the swollen/unswollen fronts and to the measurement of velocity and attenuation. The structural changes in PVA hydrogels, monitored by Wide Angle X-ray Diffractometry (WAXD), performed during the sorption process, are correlated with the ultrasonic data.

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.

A novel pre-polymer deriving from cardanol—a well known renewable organic resource and harmful by-product of the cashew industry—in combination with cellulose based materials (i.e. jute fibres) has been used to produce bio-composites having a high percentage of renewable materials. Cardanol and its derivatives are considered nowadays very attractive precursors to developing new materials from renewable bio-sources to use in eco-friendly processes. This paper deals with the synthesis and characterization of a novel cardanol based benzoxazine monomer used for the preparation of new bio-composites. The new cardanol-based benzoxazine was characterised by 1H and 13C NMR, FT-IR spectroscopies and LC mass spectrometry analysis, while a differential scanning calorimeter was used to study and monitor the polymerization process. Different bio-composites have been obtained by thermal cure of jute fibres impregnated with a cardanol based benzoxazine resin.