Curing and thermal properties of tannin-based epoxy and its blends with commercial epoxy resin

Abstract

In order to find partial substitution for bisphenol A-based commercial epoxy resin (CE), a bio-based epoxy resin was prepared from eucalyptus tannins through a typical glycidylation reaction with epichlorohydrin. The structure of tannin-based epoxy resin (TE) was confirmed by Fourier transform infrared spectroscopy (FTIR) analysis. Herein, mixtures of TE and CE (TE-CE) were prepared using varying loading amounts (20, 40 and 60) wt/wt%of TE. Tannins used here are produced by solid-liquid extraction from the outer bark of eucalyptus tree, mainly consisting of condensed tannins. Through the use of differential scanning calorimetry (DSC) and FTIR techniques, the reactivity of tannin epoxy with and without commercial epoxy resin to form cross-linking network was investigated. TE was successfully cured with aminebased curing agent. Furthermore, compared to commercial epoxy resin (CE), TE exhibited broad low exothermic peak, insignificant cross-linking properties and low curing enthalpy at different levels of curing agent. Moreover, to study the influence of TE substitution on the curing properties of CE, curing behavior of TE-CE mixtures was investigated by DSC. It was found that TE at high loading levels such as 40 and 60 wt/wt% increases slightly the reactivity of CE by decreasing curing characteristics temperatures such as the initial of curing, peak exotherm and completion of curing temperatures. TE can serve as curing accelerator and has a non-desirable impact on the curing performance of CE resin such as curing enthalpy. And up to 20 wt/wt% of CE could be replaced by TE without any significant reduction in the curing behavior of CE.

Tannin as a renewable raw material for adhesive applications: a review

“…162,163 Among different bio-resources, polyphenolic natured tannins, which are derived from woods, ought to be a multifunctional epoxy hardener. 149,164 Condensed tannins include recurring flavonoid units; on the other hand, hydrolyzable tannins are saccharides partially or wholly replaced by ellagic or gallic acid. The presence of hydroxyl groups as well as aromatic rings in its structure enables covalent and noncovalent interactions at the cost of the mechanical properties of the epoxy resin.…”

“…Tannin also acts as a precursor for bio-derived epoxy resin and possesses the role of a curing accelerator for epoxy resin. 164 The subunits of tannin, namely, catechin, epicatechin, and 2 flavon-3-ol epimers are widely spread across the plant kingdom. In catechin, the molecular structure has two phenolic rings which differ by the hydroxylation pattern: the hydroxyl groups (two OH groups) of the I-ring are in the meta position, whereas in the II-ring they are in the ortho position, as shown in Fig.…”

Curing Kinetics of Bioderived Furan-Based Epoxy Resins: Study on the Effect of the Epoxy Monomer/Hardener Ratio

“…In the case of the Flynn-Wall-Ozawa model, the Arrhenius rate law was integrated and then the Doyle approximation [33,34] was applied to obtain Equation (13). According to ASTM E698, [35] also in this case, the analysis was performed on several heating rates, with T p being independent of the heating rate:…”

“…FTIR instead, despite the easiness of use, is a less accurate technique due to the possible overlapping of the characteristic peaks associated with the reacting groups [ 12 ]. In fact, Shnawa [ 13 ] investigated the structure of a tannin-based epoxy resin (TER) by means of FTIR. Although this equipment provided some insights about the chemical architecture of this compound, it was possible to investigate the formation of the crosslinked network by DSC only.…”

Self-healing Ability of Epoxy Vitrimer Nanocomposites Containing Bio-Based Curing Agents and Carbon Nanotubes for Corrosion Protection

“…The epoxy containing 0.3 wt% HNT-C showed a good self-healing behavior with an approximately 56% increase in tensile strength compared to neat epoxy. Bio-based curing agents for epoxy have become a topic of interest because of their biocompatibility and eco-friendliness (12,13). Cashew nut shell liquid (CNSL) is an inexpensive bio-based curing agent for epoxy that is obtained as the by-product of cashew nut production (14)(15)(16)(17).…”