Thermally activated multiple self‐healing diels‐alder epoxy system

Abstract

The introduction of thermo-reversible covalent bonds in the molecular network is a recent approach to prepare self-healing polymers upon a suitable thermal trigger. Among reversible reactions, Diels–Alder (D-A) cycloaddition is an ideal candidate for the synthesis of mendable polymers, such as epoxy resins, with improved operative life. The D-A adduct, referred to as 2Ph2Epo, was synthetized and crosslinked with a mixture of aliphatic and aromatic amines. The resin formulation aimed at reaching a compromise between the mending capability of cured material and its dimensional stability at high temperatures, required during healing cycles. The latter result was achieved by mixing the adduct with commercial DGEBA monomer. The ability of the adduct to give direct D-A and reverse D-A (r D-A) has been verified by FT-IR and rheological analysis on 2Ph2Epo. Mechanical tests were performed for assessing the self-healing efficiency of the crosslinked 2Ph2Epo/DGEBA system. The multiple healing feature of the system was proved. The hybrid epoxy resin is able to recover damages, still exhibiting the pristine stiffness, while the strength of the system decreases after progressing healing cycles

Effect of the conversion degree and multiple healing on the healing efficiency of a thermally reversible self‐healing polymer

“…In the multiple healing processes, it was observed that the failure occurred in the same region that the previous failure happened in the specimen, and only the shape of the failure area experienced change. This observation was because of micro‐defects that were not healed completely after the thermal treatment and acting as crack initiators in the subsequent bending tests . The microscopic images of two multiple healed specimens are shown in Figure .…”

Diels-Alder Chemistry to Develop Self-Healing Epoxy Resins and Composites Thereof

“…The coexistence of a stable and a thermo-reversible polymeric network, required for the development of robust self-healing ability [8,25], is depicted in Figure 2. The hybrid polymer architecture is guaranteed by irreversible cross-links of conventional epoxy (green oval) with tetrafunctional amines (green rectangle) and reversible covalent bonds between The left-hand side of Figure 2 is representative of the cross-linked structure which prevents viscous flows.…”

“…A thermal process is convenient and effective for treatment of polymers with a wide range of sample sizes and treatment durations. As a result, temperature-dependent reversible covalent crosslinking of polymers or block copolymers, such as DA-based materials, represents an effective method for the implementation of intrinsic self-healing into functional materials [5][6][7][8].…”

“…Following, techniques to assess the healing capability of a polymeric material are described. Finally, the effort to fabricate composite structural material made by Diels-Alder (DA) thermoset will be discussed [8][9][10].…”

Synthesis and self‐healing behavior of thermoreversible epoxy resins modified with nitrile butadiene rubber

“…In recent years, the self‐healing polymer composite has attracted increasing attention, as it is able to solve the aforesaid problem . There are basically two types of self‐healing polymers, i.e., extrinsic and intrinsic materials .…”