Fully Bio‐Based Epoxy Thermoset Based on Epoxidized Linseed Oil and Tannic Acid

Abstract

Increasing demand for bio-based epoxy thermoset alternatives has risen in the last few years. Epoxidized vegetable oils (EVO) have attracted significant attention due to their bio-based, unharmful nature and high availability. This study proposes a fully bio-based epoxy thermoset based on epoxidized linseed oil (ELO) and tannic acid (TA). TA allows, with its high degree of functionality and aromatic structure as a curing agent for ELO, to create a fully bio-based polymer network with a high glass transition temperature (T g ), high stiffness, and high strength. A maximum T g of 146 °C, a flexural modulus of 2986 MPa, and flexural strength of 72 MPa are obtained. The strong material properties of the TA/ELO thermoset expose its potential as a bio-based substitute for petrochemical-based epoxy resins for high-performance applications. IntroductionEpoxy thermosets (EP) are well established in a large variety of applications, including electronic encapsulation, paints, coatings, adhesives, sealants, and composite materials. EPs represent a prominent place in the thermosetting market. Its market is expected to witness further growth in the forecast period of 2021-2026, growing at a Compound Annual Growth rate (CAGR) of 5%, and is projected to reach ≈4.3 million metric tons by 2026. [1] About 90% of the epoxy thermoset is derived from diglycidyl ether of bisphenol A (DGEBA). The raw materials for DGEBA, bisphenol A (BPA), and epichlorohydrin (ECH) are petroleum-based and cause adverse effects on living organisms and ecosystems. Glycerol, a byproduct from the biodiesel industry, can be used to produce ECH. However, considerable

Effects of Lysine on the Interfacial Bonding of Epoxy Resin Cross-Linked Soy-Based Wood Adhesive

“…Petroleum-based polyamines are commonly used as curing agents, such as dimethylenetriamine and 4,4-diaminodiphenylmethane (DDM) [ 23 ]. However, most polyamines are toxic before curing and toxicity cannot be wholly prevented, as curing agents are generally not entirely consumed and residues can be hazardous [ 24 ]. Amino acids are biobased polyamine curing agents with amino and carboxyl groups and good epoxy curing agents [ 25 ].…”

Contribution of the Surface Treatment of Nanofibrillated Cellulose on the Properties of Bio-Based Epoxy Nanocomposites Intended for Flexible Electronics

“…In addition to their non-renewable origin and toxicological issues, a main drawback of the DGEBA epoxies is their brittleness after curing [ 10 , 11 ]. In the last two decades, a myriad of compounds that originate from renewable resources, including vanillin, eugenol, cardanol, resveratrol, guaiacol, tannic acid, gallic acid, and vegetable oils, have been studied as precursors for obtaining bio-based epoxies [ 2 , 12 , 13 , 14 , 15 , 16 ]. From these, vegetable oils received increased attention due to their easy availability, low price, biodegradability, non-toxicity, [ 13 ], and easy conversion to their epoxidized derivatives thanks to the reactive C=C double bonds from their structure [ 2 ].…”

“…However, common crosslinking agents for epoxy resins are aliphatic and aromatic amines or anhydrides, which are toxic and environmentally unfriendly [ 7 , 18 ]. Several alternatives to standard crosslinking agents have been proposed to date [ 16 , 19 , 20 ]. Citric acid (CA), a naturally occurring compound, holds in its structure three carboxyl groups capable of participating in esterification reactions with the hydroxyl groups of the polymers [ 21 ].…”

“…Reinhardt et al obtained a fully bio-based epoxy by milling TA into a fine powder and incorporating the powder in ELO, without the need for a solvent, followed by curing. The obtained epoxy material was characterized by good mechanical and thermal properties, similar to that of high-performance petrochemical-based epoxy resins [ 16 ]. However, the high flexural strength and modulus were achieved at the expense of flexibility.…”

“…From all epoxidized vegetable oils, epoxidized linseed oil (ELO) is particularly attractive as a precursor for producing bio-based epoxy with increased flexibility and toughness due to its superior reactivity and higher number of epoxy groups in its structure [ 16 ] as compared to other epoxidized vegetable oils, such as the epoxidized soybean oil (ESO) and cottonseed oil. Di Mauro et al synthesized bio-based epoxy resins starting from ESO and ELO, using itaconic acid as crosslinking agents in the absence of any initiator [ 20 ].…”