Structural relaxation behavior of strain hardened shape memory polymer fibers for self‐healing applications

Abstract

In this study, shape-memory polyurethane (SMPU) fibers were strain hardened by cold-drawing programming (CDP) process. The programmed fibers are experimentally studied on the physical and thermomechanical properties. Structural relaxation, which determines shape memory capability of the SMP fibers, is quantified by conformational entropy change. Based on the entanglement tube theory and reptation theory, the entropic force is derived as a "bridge" to link the stress relaxation and structural relaxation, and thus structural relaxation can be evaluated by stress relaxation. It was found that the CDP SMPU fibers would still have good crackclosing capability after 13 years of hibernation in polymer matrix composite. V C 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 966-977

Healing-on-demand composites based on polymer artificial muscle

“…While healing of cracks in shape memory polymer (SMP) matrix has been successful, the challenge is how to heal cracks in conventional thermosetting polymers which do not have sufficient shape memory capability or do not have any shape memory capability. One way is to add shape memory fibers to the matrix, similar to embedded sutures when doctor stitches wound in human skin [36][37][38][39][40]. However, one challenge is the low recovery force of SMP fibers, which limits the ability to heal wider cracks, particularly when the structural components are constrained in the boundary (free shape recovery is not allowed).…”

Shape memory polymer-based self-healing composites

“…Therefore, we must test the specimens by mimicking the real-world stress condition and boundary condition in order for the lab test to represent scaled-down practical structures. The degradation of shape memory capability of SMPs under long-term service and cyclic loading conditions needs to be taken into consideration when designing this type of self-healing structures [187,188]. ); it also depends on some other parameters such as miscibility between the healing agent and the SMP matrix, crack volume, roughness of the fracture surface, and pressure applied by the constrained shape recovery of the SMP matrix.…”

Overview of crack self-healing

“…The embedded thermoplastic healing agent can then heal the closed crack (healing). The reason is that SMP fibers, unlike SMA wires, are generally very ductile, such as polyurethane fiber [61,62,[83][84][85][86]. Once the temperature is above the transition temperature of the embedded SMP fibers, we will use the autonomous shrinking of prestretched SMP fibers for suturing/closing macroscopic cracks and molten thermoplastic particles for healing molecularly.…”