New understanding of the shape-memory response in thiol-epoxy click systems: towards controlling the recovery process

Abstract

Our research group has recently found excellent shape-memory response in “thiol-epoxy” thermosets obtained with click-chemistry. In this study, we use their well-designed, homogeneous and tailorable network structures to investigate parameters for better control of the shape-recovery process. We present a new methodology to analyse the shape-recovery process, enabling easy and efficient comparison of shape-memory experiments on the programming conditions. Shape-memory experiments at different programming conditions have been carried out to that end. Additionally, the programming process has been extensively analysed in uniaxial tensile experiments at different shape-memory testing temperatures. The results showed that the shape-memory response for a specific operational design can be optimized by choosing the correct programming conditions and accurately designing the network structure. When programming at a high temperature (T » Tg), under high network mobility conditions, high shape-recovery ratios and homogeneous shape-recovery processes are obtained for the network structure and the programmed strain level (eD). However, considerably lower stress and strain levels can be achieved. Meanwhile, when programming at temperatures lower than Tg, considerably higher stress and strain levels are attained but under low network mobility conditions. The shape-recovery process heavily depends on both the network structure and eD. Network relaxation occurs during the loading stage, resulting in a noticeable decrease in the shape-recovery rate as eD increases. Moreover, at a certain level of strain, permanent and non-recoverable deformations may occur, impeding the completion and modifying the whole path of the shape-recovery process.Postprint (author's final draft

Epoxy-Based Shape-Memory Actuators Obtained via Dual-Curing of Off-Stoichiometric “Thiol–Epoxy” Mixtures

“…As explained above, formulations containing SU8 show higher ∆ T peak due to the broader relaxation process as deduced from the FWHM values in Table 2 . These results point out the close relation between network relaxation and shape-recovery in glassy materials, as previously observed [ 22 ].…”

“…Moreover, these materials are potential candidates for shape-memory applications. On the one hand, it has been shown that the “thiol–epoxy” network leads to SMPs with enhanced response: high performance fixing and recovering the original shape, rapid recovery-process, high strength and extended deformation limits [ 21 , 22 , 23 ]. On the other hand, thanks to the possibility of forming complex-shaped designs, the final material is an interesting candidate for many of the mentioned applications.…”

Actuator Behaviour of Tailored Poly(thiourethane) Shape Memory Thermosets

“…The value of R r slightly decreases as the IPDI content increases, obtaining the lowest R r with the material completely based on IPDI. This is probably due to a stress hardening process taking place during the loading process that generates permanent deformation in the network structure after programming the temporary shape [ 15 ].…”

“…Among SMPs, thermoset-based SMPs are increasingly studied for their easy processing, durability, and superior thermal and mechanical performance in comparison to common shape-memory elastomers or thermoplastic-based SMPs [ 14 , 15 ]. In particular, high-performance shape memory thermosets (HPSMTs) are particularly interesting for industrial applications, since they can perform mechanical work against external loads [ 16 , 17 ].…”

An editable shape-memory transparent wood for smart building materials

“…2b, the characteristic monomer peak, epoxy peak (910 cm -1 ) in E51, and thiol peak (2566 cm -1 ) in Tetra-SH disappeared in the spectra of the vitrimers, while the hydroxyl peak (3200-3600 cm -1 ) appeared. 40,41 The FT-IR spectra of the vitrimers and ESMTW samples exhibited high similarity, indicating that a high content of vitrimers filled the porous structures of the DW scaffold. The density of the ESMTW was approximately 1.232 g cm -3 .…”