Linear/Network Poly(ε-caprolactone) Blends Exhibiting Shape Memory Assisted Self-Healing (SMASH)

Abstract

Self-healing (SH) polymers are responsive polymeric materials that can repair mechanical damage such as cracks in an autonomous fashion. In most SH polymers studies reported to date, crack closure was either unaddressed or achieved by manual intervention. Here, we report a new strategy that utilizes shape memory (SM) to prepare novel SH polymers that are capable of simultaneously closing and rebonding cracks with a simple thermal trigger. This strategy, termed "shape memory assisted self-healing (SMASH)", is demonstrated in a blend system consisting of cross-linked poly(ε-caprolactone) network (n-PCL) with linear poly(ε-caprolactone) (l-PCL) interpenetrating the network, and exhibits a combination of SM response from the network component and SH capacity from the linear component. Thermomechanical analysis revealed that the thermoset, n-PCL, demonstrates reversible plasticity -a form of shape memory where large plastic deformation at room temperature is fully recoverable upon heating. This SM action assists to close any cracks formed during deformation and/or damage while l-PCL chains tackify the crack surfaces by diffusion to the free surface and ultimately across the area of damage during the same heating step as used for SM. In our study, we investigated the controlled damage and SMASH healing of blends with varying composition using tensile testing of essential work of fracture film specimens. The healing component, l-PCL used had a high M(w) (M(w) ∼65k g/mol) to enable re-entanglement after diffusion across the interface while the shape memory component, n-PCL was prepared from PCL telechelic diacrylates and a tetrathiol cross-linker, yielding excellent shape memory. We found excellent self-healing of films by the SMASH mechanism, with near complete healing for l-PCL contents exceeding 25 wt %. Applications are envisioned in the area of self-healing bladders, inflated structure membranes, and architectural building envelopes.

Biodegradable polyester-based shape memory polymers: Concepts of (supra)molecular architecturing

“…Semi IPNs may not only have SM, but also self healing properties. Though the term 'shape memory assisted self healing' was coined by the Rodriguez et al [61], the concept should be credited to Karger-Kocsis as quoted by Yuan et al [62]. [65] not only confirmed this concept on the same material combination but compared the SM behavior with that of a 'real' semi IPN structured EP/PCL at the same composition (cf.…”

Segmented linear shape memory polyurethanes with thermoreversible Diels-Alder coupling: Effects of polycaprolactone molecular weight and diisocyanate type

“…temperature and strain values. It is noteworthy that due to rubber-like behavior and the thermoreversible feature of the DA coupling, these PUs may show shape memory assisted self healing [36,37] that will be checked next.…”

Self-Healing and Damage Resilience for Soft Robotics: A Review

“…Xiao et al (2010) presented a self-healing SMP which could heal its surface after being scratched, which has initiated research into self-healing coatings (Luo and Mather, 2013;Dalmoro et al, 2016;Lutz et al, 2016). SMPs have also been used in two-step self-healing processes where the SMP can close whole cracks using the shape memory effect then self-heal the cracks through internal chemistry Li, 2010, 2012;Rodriguez et al, 2011). Such hybrid systems that allow both crack closure and crack healing show much promise, though the biggest challenge will be demonstrating this capacity while simultaneously controlling the soft robot using these same materials.…”