Ionic Liquid-Cured Epoxy/PCL Blends with Improved Toughness and Adhesive Properties

In this work, ionic liquid (IL)-cured epoxy resins were modified by adding poly(ε-caprolactone) (PCL). Three different ILs were used in order to study how (a) the chemical structure of the ILs and (b) the PCL content affect the phase behaviour, microstructure, mechanical and adhesive properties. Regardless of the IL used or the PCL content, the obtained materials showed a single phase. The addition of PCL to the epoxy resin resulted in plasticizing of the network blends, lower glass transition temperatures (Tg), and crosslinking densities (νe). Low PCL contents did not have a significant impact on the mechanical properties. However, the adhesive properties improved significantly at low PCL contents. Higher PCL contents led to a significant increase in toughness, especially in the case of the imidazolium-based IL. The balance achieved between the mechanical and adhesive properties of these IL-cured epoxy/PCL blends constitutes an important step towards sustainability. This is because a biodegradable polymer (PCL) was used to substitute part of the epoxy resin, and the ILs-which are non-volatile and cure effectively at much lower contents-were used instead of conventional curing agents. Given the wide use of this kind of materials in the adhesive industry, the practical significance of these results must be emphasised.

Reprogrammable Permanent Shape Memory Materials Based on Reversibly Crosslinked Epoxy/PCL Blends

Epoxy/Polycaprolactone (PCL) blends cured with a conventional diamine (4,4′-diaminodiphenylmethane, DDM) and with different amounts of a disulfide containing diamine (4, 4´-dithioaniline, DSS) were prepared through melting. The curing process was studied by FTIR and differential scanning calorimetry (DSC) and the mechanical behavior of the networks was studied by DMA. The shape memory properties and the recyclability of the materials were also analyzed. All blends showed a very high curing degree and temperature activated shape memory effect, related to the glass transition of the epoxy resin. The PCL plasticized the mixture, allowing tailoring of the epoxy glass transition. In addition, in the blends cured with DSS, as a consequence of the disulfide exchange reaction, the permanent shape could be erased and a new shape could be reprogrammed. Using this strategy, reprogrammable permanent shape memory materials were obtained.