Efficient Toughening of Epoxy–Anhydride Thermosets with a Biobased Tannic Acid Derivative

Abstract

Research into toughening an epoxy resin using biobased modifiers without trade-offs in its modulus, mechanical strength, and other properties still remains a challenge. In this article, an approach to toughen epoxy resin with tannic acid, a common polyphenolic compound extracted from plants and microorganisms, is presented. First, dodecane functionalized tannic acid (TA-DD) is prepared and subsequently incorporated into epoxy/anhydride curing system. Owing to the modification of long aliphatic chain, TA-DD can induce epoxy matrix yielding phase separation, forming microscaled separated phases. In the meantime, the terminal hydroxyl groups of TA-DD can participate in the curing process, which offers a good interfacial interaction between TA-DD and epoxy matrix. With such a mechanism, the results show that TA-DD can significantly toughen the epoxy resin without trade-offs in its strength, modulus, and T g . The thermoset with only 0.5 wt % TA-DD reaches highest impact strength, which is 196% increase of that of neat epoxy. This article opens up the possibility of utilizing the renewable tannic acid as an effective modifier for epoxy resin with good mechanical and thermal properties.

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

“…Previous researchers have pursued TA as a toughening agent for the diglycidylether of bisphenol A (DGEBA) (Fig. ) in anhydride‐hardened epoxies, but explored loading levels between 0.5% and 2% weight TA in epoxy and did not achieve glass transition temperatures above 151 °C . Other researchers have used pyridine‐catalyzed esterification as a chemical modification to increase compatibility of TA in epoxy and used an anhydride hardening agent as well, but compatibility limitations again prevented loading levels above 2% weight and resulting T g values at all loading levels were lower than 145 °C .…”

Synthesis and Characterization of Nanoclay‐Reinforced Trifunctional “Bioresin‐Modified” Epoxy Blends Enhanced with Mechanical and Thermal Properties

“…But the showing insufficient toughness, poor crack resistance due to the highly cross‐linked structure and brittleness nature confines their application in certain areas . In the current research certain amount of the flexible bio‐polymer such as plant oils, lignin,, and tannic acid, based bioresin used as a successful toughening agent owing to the lower viscosity and renewability has been reported. However, the toughening of the epoxy resin increased without decline of the mechanical and thermal properties.…”

An effective surface modification of UHMWPE fiber for improving the interfacial adhesion of epoxy resin composites

“…TA has the chemical formula C 76 H 52 O 46 and has many phenolic hydroxyl groups in its structure. This naturally extracts compound not only sequesters metal ions, but also forms polyphenol coatings on almost all natural and synthetic substrates . Polyphenols have high surface affinity due to the catechol structure on the surface .…”

“…This naturally extracts compound not only sequesters metal ions, but also forms polyphenol coatings on almost all natural and synthetic substrates. [23] Polyphenols have high surface affinity due to the catechol structure on the surface. [24] In the TA-Na + metal-organic complex, the pyrogallol (1,2,3-trihydroxybenzene) moiety in the TA acts as a ligand for the metal ion and then forms a metalorganic complex.…”