Vanillin-Based Epoxy Vitrimers: Looking at the Cystamine Hardener from a Different Perspective

Abstract

Epoxy vitrimers encompass many advantages compared to traditional epoxy materials such as recyclability, repairability, and reprocessability. These properties are induced by the incorporation of dynamic reversible covalent bonds. Recently, the incorporation of aromatic disulfide bridges that are dynamic has expanded the development of new eco-friendly epoxy materials. Herein, we studied a bio-based aliphatic disulfide based on cystamine as a hardener with a vanillin-derived biosourced epoxy to prepare fully bio-based epoxy vitrimers. This article provides a comparative study between cystamine and an aromatic disulfide benchmark hardener issued from petrol resources. This work demonstrated that the presence of this aliphatic hardener has a significant influence not only on the reactivity, but most importantly on the resulting dynamic properties. An interesting yet counterintuitive accelerating effect of the dynamic exchanges was clearly demonstrated with only 2 to 20% of molar fraction of cystamine added to the aromatic disulfide formulation. A similar glass transition was obtained compared to the purely aromatic analogue, but relaxation times were decreased by an order of magnitude.

Exploring the Limits of High-Tg Epoxy Vitrimers Produced through Resin-Transfer Molding

“…Hence, 4-aminophenyl disulfide (4-AFD) was selected as a dynamic hardener and its reactivity with RTM6 epoxy resin was deeply investigated and strictly compared to the permanent hardener reference (RTM6-2 part B), Figure . The dynamic properties are introduced through the disulfide linkage embedded within the dynamic hardener, which undergoes both associative and dissociative mechanisms at a high temperature through a radical-mediated mechanism. , The general synthetic routes to obtain both types of networks are described in Figure . Because the difference of structure may lead to non-negligible differences in reactivity and change in viscosity, this aspect is deeply investigated in the following subsection.…”

High-Performance Recyclable and Malleable Epoxy Resin with Vanillin-Based Hyperbranched Epoxy Resin Containing Dual Dynamic Bonds

“…4,5 It is of great importance to develop technologies for recycling epoxy resins at the end of use. 6−8 Many researchers have incorporated covalent adaptable networks (CANs) in synthesizing recyclable epoxy resins, 9−12 including imine exchange, 13,14 transesterification, 15−17 disulfide exchange, 18−20 boronic ester exchange, 21,22 siloxane exchange, 23 and DA/retro-DA reaction. 24 However, due to the introduction of CANs, the dynamic networks were susceptible to creep when used in engineering and structural fields, 25 and creeping of these materials usually occurred around the topology freezing temperature (T v ), which was usually much lower than the T g .…”

“…Many researchers have incorporated covalent adaptable networks (CANs) in synthesizing recyclable epoxy resins, − including imine exchange, , transesterification, − disulfide exchange, − boronic ester exchange, , siloxane exchange, and DA/retro-DA reaction . However, due to the introduction of CANs, the dynamic networks were susceptible to creep when used in engineering and structural fields, and creeping of these materials usually occurred around the topology freezing temperature ( T v ), which was usually much lower than the T g . − Many efforts have been made to improve the creep resistance, such as through controlling the availability of cross-linking or incorporation of permanent cross-linking. − For example, Xu et al prepared a type of dihydrazone-based dynamic covalent epoxy network containing dihydrazone with an initial creep temperature of about 105 °C .…”

On a Biobased Epoxy Vitrimer from a Cardanol Derivative Prepared by a Simple Thiol–Epoxy “Click” Reaction

“…Conversely, in the cases where particularly slow bond-exchange reactions occur, a relaxation phenomenon of the “chemically limited” type occurs, i.e., where the relaxation process is precisely limited by the kinetics of exchange between the reactive groups. In particular, epoxy-based vitrimers, classified according to the exchangeable bonds and reactions in their cross-linked networks, are generally based on disulfide bonds , and the corresponding disulfide-exchange reaction, imine bonds and the corresponding transamination and imine metathesis, siloxane equilibration, , and on ester bonds and the corresponding transesterification, ,− with the latter approach being the most commonly used. Indeed, in order to accelerate the exchange reaction in epoxy/acid and epoxy/anhydride systems, zinc acetate, , zinc acetylacetonate, triazabicyclodecene, , and other transesterification catalysts were used, which, although added in limited amounts, can introduce a potential toxicity risk and reduce the thermomechanical stability of the material.…”