Tara tannins as phenolic precursors of thermosetting epoxy resins

• Natural phenolic compounds were used in the synthesis of epoxy resins.
• The natural phenolic source was tara powder.
• Tara tannins were functionalised with epichlorohydrin to give bio-based prepolymer.
• Cured epoxidised tannins were compared to DGEBA network.
• Epoxy network from tara tannins showed good thermal and mechanical properties.

Tara pods powder was used as a phenolic source in the synthesis of thermosetting epoxy polymer. The tannase-assisted hydrolysis of galloylquinic acids contained in tara powder allowed the determination of the tannins hydroxyl value (13.7 mmol/g powder). Then, galloylquinic acids were reacted with epichlorohydrin and an aqueous solution of sodium hydroxide in the presence of benzyltriethylammonium chloride as phase transfer catalyst (PTC). The 1D and 2D NMR analyses of glycidylated products revealed the galloylquinic esters hydrolysis and the dimerisation of the glycidylated gallic moities. The glycidylated derivatives of tara tannins (GETT) were cured in epoxy polymer with isophorone diamine (IPD). The glass transition temperature (Tg = 129 °C) and the thermal resistance (Td30 = 294 °C) of the resulting network were determined. Preliminary results showed that this new epoxy polymer based on GETT displayed interesting properties which are close to those of the epoxy polymer formulated with commercial diglycidyl ether of bisphenol A (DGEBA).

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