Tannic acid: A sustainable crosslinking agent for high glass transition epoxy materials

Abstract

Epoxy thermosets have revolutionized the coating, adhesive, and composite industries but the chemicals from which they are synthesized have significant effects on the environment and human health not only precure but also after crosslinking has occurred. In this study, we propose tannic acid (TA) as an alternative epoxy hardening agent for commercially available epoxy resin, the diglycidyl ether of bisphenol A (DGEBA). The resulting thermosets were characterized by Fourier transform infrared spectroscopy, optical microscopy, dynamic mechanical analysis, differential scanning calorimetry, compression testing, and thermogravimetric analysis. The results from this study showed that at temperatures above 100 °C, the compatibility of TA in DGEBA was significantly increased for loading levels up to 37% weight of TA in DGEBA, something that has not been seen before in literature. It was also discovered that at high loading levels, the resulting materials had glass transition temperatures at and above 200 °C. The resulting material was proposed as a more sustainable alternative to amine or acid hardened epoxy thermosets and was particularly useful in high‐temperature applications. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 1468–1480

Tannic acid: a crosslinker leading to versatile functional polymeric networks: a review

“…TA, a low-cost compound, possesses multiple chemical binding sites as well as multiple aromatic rings, ensuring a high T g green epoxy resin. 98–100…”

“…TA, a low-cost compound, possesses multiple chemical binding sites as well as multiple aromatic rings, ensuring a high T g green epoxy resin. [98][99][100] Previous studies have proved that under certain heating conditions, the pyrogallol groups on TA are capable of triggering ring-opening of oxirane rings, making TA a chemical hardener for epoxy material. 101,102 Recently, Feng et al proposed a facile method to prepare a TA-hardened epoxy resin, in which TA was applied as a multifunctional crosslinking agent for diglycidyl ether of bisphenol A (DGEBA) (Fig.…”

Tannic acid based bio‐based epoxy thermosets: Evaluation of thermal, mechanical, and biodegradable behaviors

“…Hence, TA is supposed to act as the branch-generating unit, hydroxyl groups of which could open the epoxy rings of DGEBA additional to end group modification. 25 However, with an increasing percentage of TA, surface epoxidation became more prominent. The gradual replacement of BPA with TA could be understood from the proton NMR peaks (Figure 2c), with decreasing intensity of the aromatic hydrogen peaks near δ values 6.64-7.10 ppm corresponding to BPA aromatic protons and increasing intensity of peaks near δ = 7.19-7.29 ppm due to TA aromatic protons.…”

“…24 However, the process required high amount of solvents, THF for dissolving ECH and toluene for extraction, which was inconsistent with solvent free concept currently emerging in the field of synthetic polymers. As per the current scenario, application of TA is ubiquitous as a cross-linker, 25 toughener or as a curing agent 26 for epoxy resins. In a study by Baruah et al 27 a hyperbranched epoxy was synthesized incorporating diethanolamide of gallic acid into DGEBA.…”

Exploring the optical and dielectric properties of bifunctional and trifunctional epoxy polymers

“…A judicious choice of an epoxy monomer and the further curing agent permits thus to obtain highly crosslinked epoxy thermosets with outstanding physico-chemical properties [8][9][10][11]. Other parameters like the preparation conditions, the duration and the temperature of curing are of prime importance in the network structure of a given epoxy based polymer [12][13][14][15]. Several studies were devoted to the comparison of optical, thermic, and mechanical properties of epoxy polymers.…”