Elsevier

Progress in Organic Coatings

Volume 91, February 2016, Pages 9-16
Progress in Organic Coatings

Improved cardanol derived epoxy coatings

https://doi.org/10.1016/j.porgcoat.2015.11.012Get rights and content

Highlights

  • Formulation of different epoxy-amine blends based on epoxidized cardanol.

  • Use of different epoxy with different structures.

  • Cure of the different epoxy-amine blends at room temperature.

  • Thermal, mechanical and chemical resistance were studied.

  • Different formulations could replace the use of BADGE.

Abstract

Commercial epoxidized cardanol, from cashew nutshell liquid (CNSL), is a biobased reactant with interesting aromatic structure. Cured with two different diamines, isophorone diamine and Jeffamine T403, the synthesized materials exhibit good properties but they do not meet properties of bisphenol A diglycidyl ether (BADGE) epoxy resins. Therefore epoxidized cardanol cannot replace directly BADGE for the synthesis of epoxy resins. Three epoxy reactants, resorcinol, hBADGE and TMP, were used as reactive additives to enhance the properties of the cardanol derived materials. These epoxy networks with different ratios were characterized by thermogravimetric analysis, differential scanning calorimetry. Their hardness and gloss were measured as well as their resistance to chemical solvents.

Introduction

Epoxy networks are an important class of thermoset polymers used as coatings. Bisphenol A (BPA), a reactant that was initially synthesized as a chemical estrogen [1], is nowadays the most used monomer for the annually production of 2Mt of epoxy polymers. The aromatic ring of BPA is particularly interesting since it confers good thermal resistance to epoxy resins. But this endocrine disruptor can mimic the body's own hormones and may lead to several negative health effects [2], [3], [4], [5]. Thus, a recent review of studies [6] of low-dose effects of BPA, found that 94 of the 115 publications reviewed reported significant effects. Effects include alterations in brain chemistry and structure, behavior, the immune system, enzyme activity, the male reproductive system, and the female reproductive system in a variety of animals, including snails, fish, frogs and mammals [6]. The negative impact of BPA on human health and environment necessarily implies the elimination of BPA. Indeed, some countries, such as Canada or France, have recently banned the use of BPA in food contact materials. Thus, there is an increasing interest of chemical industry for non-harmful reactants allowing the synthesis of epoxy resins without BPA. Moreover, thermoset polymers cannot be easily recovered by mechanical recycling due to their crosslinked networks and consequently they need to be biobased to ensure to reduce environmental impacts. Therefore, non-toxic biobased epoxy reactants are highly needed and studied [7]. Few commercial biobased epoxy reactants are available, except epoxidized vegetable oils which are the most used as biobased monomers [8]. Despite their crosslinked networks, epoxidized vegetable oil based resins exhibit low Tg due to the long aliphatic chain (Tg = −38 °C with epoxidized-linseed oil cured with amine-functionalized grapeseed oil [9]) and low reaction enthalpy. However, epoxy formulations are generally used to confer needed properties, such as high mechanical and chemical resistance, to coatings. These properties are generally brought by aromatic rings, highly stable groups, cycloaliphatic compounds or a highly crosslinked network. Indeed, biobased aromatic epoxy reactants would confer high properties to coatings as the BPA based resins. Even if literature reports some very interesting works based on natural flavonoids [10] or lignin, these resources exhibit strong drawbacks. Indeed, low purity and high molar masses of these resources limit their development in chemistry. Depolymerization of lignin [11], [12] would be an alluring route to give access to biobased aromatics needed by chemical industry. However, this route remains deceptive since despite extensive research, there are very few reports of efficient ways of recovering such aromatic products. Vanillin [13] is a very interesting building block which is industrially produced from lignin, but its availability is not sufficient for coating industry. Cardanol [14], extracted from cashew nut shell liquid (CNSL), a non-edible by product of CNSL industry, is really a promising aromatic renewable source available in large quantity and would be suitable for food contact [15]. Cardanol is a yellow pale liquid composed of four meta-alkyl phenols differing by the unsaturation degree of aliphatic chain: saturated chains (SC) 8.4%, monoolefinic (MO) 48.5%, diolefinic (DO) 16.8% and triolefinic (TO) 29.3% chains [16], [17]. Cardanol was already extensively studied for material synthesis, through direct polymerization [18], as a polyol in new polyurethanes [19], in polyester compositions [20], with partial or total substitution of phenol in thermoset networks such as Novolac [21], [22], [23], vinyl esters [24], [25] and also in epoxy polymers modification [26], [27].

Our team previously worked on epoxy cardanol [28] provided by Cardolite. Even if we cured epoxy formulations at 120 °C at least, the glass transition temperatures, Tg, of polyepoxide cardanol networks were too low and in order to increase them, blends with other epoxy monomers are needed. We used also two kinds of sucrose epoxy derivatives, sorbitol and isosorbide, in addition to epoxided cardanol, to enhance the properties of the epoxy cardanol-derived materials with interesting results [32].

The objective of this work is to use academic products such as hydrogenated BADGE (hBADGE), tris-epoxidized trimethylol propane or tannin derived resorcinol as epoxy additives to epoxidized cardanol to obtain blends of epoxy polymers with good thermal, chemical and mechanical properties in order to meet required properties for coating applications. In literature, few works to the best of our knowledge studied blends of biobased epoxided monomers whereas this is not only the real life of formulation in industry, but it is also crucial since it will be hard to substitute Bisphenol A Diglycidyl Ether (BADGE) by an unique molecule. These polymers were formulated, cured at room temperature and characterized to measure their resistance as coatings in contact with acid or basic solvents. This publication is the first one to compare these epoxidized reactants with epoxidized cardanol in coating application.

Section snippets

Materials

Trifunctional polyetheramine Jeffamine T403 (Amine Hydrogen Equivalent Weight (AHEW) = 81 g/eq), isophorone diamine Aradur 42BD (AHEW = 42,5 g/eq) and triglycidyl ether of trimethylolpropane Aradilte DY-T/CH (Epoxy Equivalent Weight (EEW) = 125 g/eq) were purchased from Huntsman (Switzerland). Diglycidyl ether of cardanol NC-514 (EEW= 400 g/eq) was obtained from Cardolite (Belgium). Diglycidyl ether of resorcinol Denacol EX201 (EEW = 116 g/eq), and hydrogenated Bisphenol A diglycidyl ether Denacol EX252 (EEW

Raw materials

We performed the synthesis of different epoxy-amine polymers at room temperature in order to replace the Bisphenol A DiGlycidyl Ether (BADGE). Firstly, two common amines were used as hardeners: isophorone diamine (IPDA) and a polyetheramine, Jeffamine T403.

Isophorone diamine is a classic cycloaliphatic diamine, often used as hardener for epoxy networks. Jeffamine T403 is a classic polyetheramine, and its use is approved by Huntsman as a non-toxic reactant and suitable for food contact (Fig. 1).

Conclusion

Even if diepoxidized cardanol cannot replace BADGE in epoxy networks, the blends of epoxy cardanol with other epoxy reactants could improve the properties of these networks. Indeed, the addition of either diglycidyl ether of resorcinol or hBADGE allows to increase Tg and hardness of polyepoxide networks, whereas the addition of triglycidyl ether of TMP leads to higher thermal stability of polypeoxide networks. Therefore, owing to the needed properties or the application, some additives should

Acknowledgements

The authors are grateful to Sogatra Nouvelle for their collaboration. Cardolite, Nagase, Huntsman are thanked for the samples.

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