Influences of Crystallinity and Crosslinking Density on the Shape Recovery Force in Poly(ε-Caprolactone)-Based Shape-Memory Polymer Blends

Abstract

Shape-memory polymers (SMPs) show great potential in various emerging applications, such as artificial muscles, soft actuators, and biomedical devices, owing to their unique shape recovery-induced contraction force. However, the factors influencing this force remain unclear. Herein, we designed a simple polymer blending system using a series of tetra-branched poly(ε-caprolactone)-based SMPs with long and short branch-chain lengths that demonstrate decreased crystallinity and increased crosslinking density gradients. The resultant polymer blends possessed mechanical properties manipulable across a wide range in accordance with the crystallinity gradient, such as stretchability (50.5–1419.5%) and toughness (0.62–130.4 MJ m−3), while maintaining excellent shape-memory properties. The experimental results show that crosslinking density affected the shape recovery force, which correlates to the SMPs’ energy storage capacity. Such a polymer blending system could provide new insights on how crystallinity and crosslinking density affect macroscopic thermal and mechanical properties as well as the shape recovery force of SMP networks, improving design capability for future applications.

Digital Light Processing 3D Printing of Soft Semicrystalline Acrylates with Localized Shape Memory and Stiffness Control

“…The stress peaked around the peak melting temperature, providing a maximum recovery stress (σ r,max ) value of 190 ± 37 kPa. From this value, W was calculated to be 94 ± 19 kJ/m 3 using the following equation that assumes a linear relationship between the constrained and unconstrained recovery, as described previously in the literature. , A W of ∼100 kJ/m 3 is within the same order of magnitude as compared to previously reported low modulus (≤50 MPa) shape-memory materials. − Additionally, the stress remaining in the sample once melted (∼30 kPa) is comparable to that observed for a sample deformed to 100% strain starting at 65 °C (Figure S19), again demonstrating excellent recovery behavior while displaying supersoft (<100 kPa) mechanical properties.…”

Elastocaloric effect of shape memory polymers in elastic response regime

“…All samples were first equilibrated at 353 K and then cooled to 253 K, followed by performing the measurements during the heating process to 353 K at a rate of 5 K min −1 under nitrogen atmosphere. The value of X c was calculated from the enthalpy change quantified by DSC thermograms and the melting enthalpy of 100% crystalline PCL and that of T m was defined as the temperature at the peak top of DSC thermograms [35,36]. To check the reproducibility and estimate the magnitude of errors, the DSC measurements were conducted three times for each sample.…”

Multiphase PCL semi-interpenetrating networks exhibiting the triple- and stress-free two-way shape memory effect

“…We have reported that the thermal properties, including T m , can be precisely controlled by blended crosslinking of PCLs with controlled branching structures and chain lengths. [30][31][32][33]35 In particular, crosslinked 4b10PCL/2b20PCL blends obtained using thermal polymerisation with BPO by blending equal amounts of 4b10PCL and 2b20PCL macromonomers exhibited relatively sharp endothermic peaks associated with melting and exothermic peaks associated with crystallisation, with T m and T c values of 33.6 and 0.6 °C, respectively (Fig. 1b).…”

“…Generally, when two PCL macromonomers with different T m are blended to produce a crosslinked material (e.g., 4b10PCL/ 4b100PCL blends), the respective polymer chains in the blend are incorporated into a ratio-averaged network structure, such that the T m of each chain can be fused, resulting in a monophasic crosslinked network that exhibits a single T m and T c . 35 Therefore, we hypothesised that by designing PCLs using a semi-IPN structure blended with linear PCLs that are not involved in the crosslinking reaction, it would be possible to fabricate a multiphase network with two distinct peaks (T m and T c ) derived from the crosslinked PCL network and linear PCLs. Fig.…”

“…Furthermore, blended crosslinking results in a monophasic polymer network incorporating each polymer despite the macromonomers having different T m 's. 35 Mather et al fabricated PCL semi-IPNs with linear PCL penetrating the PCL network and showed that T m , T c , and their enthalpy changes in phase transitions increase with increasing molecular weight ( M w = ∼65 000) and content of linear PCL. 36 Furthermore, PCL semi-IPNs exhibited self-healing properties owing to the presence of linear PCLs and demonstrated shape memory assisted self-healing (SMASH) wherein the shape memory of the PCL network can close wounds and cracks.…”