Contents lists available at ScienceDirect Reactive and Functional Polymers journal homepage: www.elsevier.com/locate/react Anticorrosive and insulating properties of cardanol based anhydride curing agent for epoxy coatings Kunal Wazarkar, Mukesh Kathalewar, Anagha Sabnis ⁎ Dept. of Polymer and Surface Engineering, Institute of Chemical Technology, Matunga, Mumbai 400019, India ARTICLE INFO Keywords: CNSL Anhydride Epoxy Anticorrosive Insulation Sustainable ABSTRACT Present research reveals the synthesis of anhydride curing agent for preparation of anticorrosive epoxy coatings. A novel dianhydride compound was synthesized from cardanol and used as a curing agent for commercial epoxy resin. The structure of the curing agent was confirmed by chemical and spectroscopic analysis. Coatings were formulated with varying ratio of epoxy resin to anhydride on equivalent basis such as 1:0.6, 1:0.8, 1:1. The effect of varying concentration of curing agent on mechanical, chemical, optical, thermal, electrical and anticorrosive properties of coatings was investigated and compared to coatings cured with commercial methyltetrahy- drophthalic anhydride (MTHPA). It was observed that, curing agent based on cardanol performed extra- ordinarily in all aspects as compared to the commercial curing agent. 1. Introduction Epoxy resins are versatile class of polymers and one of the most commercially used thermosetting materials. They possess excellent adhesion to the substrate, superior chemical resistance, good mechan- ical properties, excellent anticorrosive and thermal stability [1–3] which make them good candidates for a variety of applications in- cluding adhesives, coatings, moulding compounds, composites, con- struction materials, electronic insulation components etc. [4–7]. The epoxy resins are often mixed with other component to improve the properties of resin further. These are called curing agents or hardener, depending on application variety of curing agents are available for epoxies. Most commonly used hardeners include amines, polyamides, anhydride, carboxyl, phenolic compounds etc. Amongst these, amine curing agents are the most popular as they provide room temperature curing with good performance properties. However, they possess cer- tain disadvantages such as the formation of polar groups which increase water absorption thereby reducing mechanical and electrical properties of the system. This formation of polar groups does not occur when carboxyl or anhydride curing agents are used. Consequently, after amines anhydrides constitute the next most important class of curing agents. The less exothermic reaction of epoxies with anhydride results in low shrinkage, low internal stresses, reduced water absorption, high glass transition temperature and excellent electrical insulation [8,9]. However, most anhydride-epoxy systems are less reactive and require high temperature (> 120 °C) to initiate and propagate curing reaction [10–14]. To increase the rate of curing reaction and lower the curing temperature sometimes accelerators are added to the formulation [14]. These accelerators are mainly lewis bases such as tertiary amines [15,16], imidazoles or quaternary ammonium salts etc. [17,18] These curing agents are generally derived from petroleum based resources and require complicated chemical processes in end product syntheses. Rapid depletion of petroleum resources and their rising cost has forced researchers to develop materials that are sustainable and economical. For this reason, various biobased materials have been ex- plored in the past, including vegetable oils, lignin and its derivatives, sugar derivatives, amino acids, vanillin, eugenol, citric, tartaric and itaconic acid, cashew nut shell liquid (CNSL) and its derivatives etc. Recently, CNSL and its derivatives have received much attention of the scientists as they are easily and abundantly available throughout the world. CNSL mainly contains four components; cardol, 2-methyl cardol, cardanol and anacardic acid. Amongst all these cardanol is mostly preferred as it contains one phenolic ring and C15 unsaturated aliphatic chain which give the perfect balance of hardness and flexibility [19]. In recent years, lots of chemical modifications of cardanol are have been studied to make it suitable for a wide variety of applications in polymer and coatings such as plasticizers, UV diluents, isocyanate free poly- urethanes, epoxies etc. [20–24] Here we have made an attempt to synthesize novel silicon con- taining anhydride curing agent for epoxies. The structure of the curing agent was confirmed by FTIR spectroscopy, 1 H NMR spectroscopy, acid value and iodine value. The curing agent was further used for curing commercial epoxy resin in varying ratio 1:0.6, 1:0.8 and 1:1 on an equivalent basis. Further, the effect of concentration of curing agent on https://doi.org/10.1016/j.reactfunctpolym.2017.11.015 Received 18 January 2017; Received in revised form 7 September 2017; Accepted 28 November 2017 ⁎ Corresponding author. E-mail address: as.sabnis@ictmumbai.edu.in (A. Sabnis). Reactive and Functional Polymers 122 (2018) 148–157 Available online 29 November 2017 1381-5148/ © 2017 Elsevier B.V. All rights reserved. T