Bio-derived epoxy resins

Over the last decade, the synthesis of polymers starting from renewable resources has been the object of significant research efforts. This is mainly 

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. 

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. 

obtained by heating the liquid resin produced by pines and 

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Abstract This chapter discusses the epoxy resins which, thanks to their good and versatile properties, can be considered nowadays the most important class of thermosetting polymers. In particular the chapter first reviews both the epoxy resins commonly available on the market, including a new class of bio-derived epoxy resins, and the most-used curing agents. 

As discussed in Section 5.5, the formulation and use of bio-derived epoxy resins will represent one of the most important challenges both for the academic world and for industry in the next few years. In particular, all industrial fields where composite materials find application will aim to increase the use of epoxy matrices to reduce the environmental impact and CO2 emissions. A further future development of epoxy resins is related to their use as matrices in composites for dental applications, substituting for methacrylate ones, thanks to their lower shrinkage. 

Finally, the formulation and use of bio-derived epoxy resins will represent one of the most important challenges both for the academic world and for industry in the next few years, in order to reduce the environmental impact and CO2 emissions. 

In another study, three types of composite materials were obtained from (i) blends of soybean oil-based epoxy with commercial petroleum-based epoxy resin and E-glass fibre, (ii) blends of epoxidised methyl ester derived from canola oil with petroleum-based epoxy resin and E-glass fibre, and (iii) 100% petroleum-based epoxy resin and E-glass fibre. Panels made as in (i) exhibited comparable dynamic stiffness, flexural modulus and flexural stiffness properties to those derived from composite system (iii) However, bio-based samples from process (ii) were less promising. 

Few examples of nanocomposites in which the cellulosic nanostructure is used in biobased thermosets can be also foimd. Due to the fact that these environment friendly composites suffer from several limitations, such as low mechanical properties due to low strength in reinforcement plus inadequate interfacial strength, and that cellulose nanostructures have been shown to have significant potential as a reinforcement, the possibility of using cellulose nanofibers as reinforcements in a bio-derived resin was revised. In Masoodi et al. [200], cellulose nanofibers were used as reinforcements in the forms of layered films, while in Lee et al. [201] the stability of the gas-soybean oil foam templates and the mechanical properties of the polymer nanocomposite foams are enhanced upon the addition of bacterial cellulose nanofibrils. Other examples of biobased thermosets containing cellulosic nanoreinforcements are the work of Shibata [202] in which the use of a biobased epoxy was revised, and systems in which cellulose nanocrystals are incorporated in biobased polyurethanes [203,204], Few examples exist also in the literature on the polymerization of furfuryl alcohol in presence of CNR [205,206] in these papers, the authors established the feasibility of producing furfuryl... 

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