Self‐curable epoxide resins based on cardanol for use in surface coatings

Abstract

Purpose -The purpose of this paper is to develop eco-friendly coatings based on low-cost epoxide resins prepared by using a natural phenolic material such as cardanol (non-toxic), in place of ordinary phenol (toxic), which can be self-curable at an optimum temperature. Design/methodology/approach -Cardanol-formaldehyde novolac resins (CNs) were prepared by reacting cardanol with formaldehyde in different molar ratios varying from 1:0.6 to 1:0.9. Prepared CNs were epoxidised by reacting with epichlorohydrin to produce epoxide resins, which would be called as epoxidised CNs (ECNs). Further, ECNs were modified by reacting with diethanolamine (DEtOA), a secondary amine to introduce tertiary amino group(s) into the molecules, required for self-curability of ECNs. These modified ECNs are referred to as MECNs. The molar ratio of ECNs to DEtOA was taken in accordance with epoxy functionality of epoxide resins (ECNs) which ranged from 0.5 to 2.9. Nine numbers of MECNs (MECN 1 to MECN 9 ) were prepared by using four epoxide resins. These resins viz. CNs, ECNs and MECNs were characterized by 1 H NMR and FTIR spectroscopic methods for their structure elucidatation, and by gel permeation chromatography for determining their molecular weights. Findings -The most suitable molar ratio of ECN:DEtOA for the preparation of MECNs was found to be 1:1. The CN prepared by using cardanol and formaldehyde in the molar ratio of 1:0.7 was used for the preparation of ECN 2 and MECN 2 . Applied films of epoxide resins, designated as MECN 2 , had reasonably good physical and chemical resistance properties. With a wide cure window, the films of MECN 2 were found to be self-curable at an optimum cure schedule of 1608C/30 min. Owing to self-curability of the developed epoxide resins, the coatings based on them did not require any additional/external crosslinker to be incorporated in the coating composition.Research limitations/implications -The prepared epoxide resins (MECNs) had good physical and chemical resistance properties, but demonstrated low stability and low resistance to xylene, in particular. Originality/value -The paper shows how the epoxide resins were prepared by using a low-cost phenolic material (cardanol) which is obtained from natural renewable resources, instead of petroleum, and is non-toxic. These developed coatings can be applied as primer coat and top coat on metallic substrates. True self-curability of the coating films has been achieved via anionic polymerization.

Multifunctionality in Epoxy Resins

“…17,18 Epoxidized phenol novolac resins (EPN) came from the reaction product of epichlorohydrin and phenol/cresol-formaldehyde condensates while glycidylamine resins are from aliphatic/aromatic primary or secondary amines precursors that underwent glycidylation reactions. [19][20][21] Glycidylamines are reportedly stable products, especially if the substituent amine is aromatic or when highly substituted alkyl groups are used as precursors. Also, in existence are a class of non-glycidyl ether epoxides such as epoxidized diene polymers, epoxidized oils and polyglycol diepoxides; collectively termed as acyclic aliphatic non-glycidyl ether epoxides.…”

Functionalization of cardanol: towards biobased polymers and additives

“…Various polyamines synthesized from CNSL or cardanol have also been reported to be very effective curing agents for epoxy resins. 14 Shukla et al 246 developed selfcurable epoxide resins based on cardanol for use in surface coatings. Owing to self-curability of the developed epoxide resins, the coatings based on them did not require any additional/external cross-linker to be incorporated in the coating composition.…”

Synthesis and Characterization of Cardanol-Based Non-Isocyanate Polyurethane

“…In Figure 2 b, the peak value of δ 6.66–7.14 ppm in the cardanol formaldehyde oligomer (CFO) spectrum is due to the aromatic matrix of benzene nucleus, and the peak position is virtually unchanged from that of raw cardanol. Notably, new peaks near δ 3.61–3.93 ppm indicate methylene protons (Ar-CH 2 -Ar) at the bridge between the benzene rings [ 34 , 35 ].…”