Recovery stress and work output in hyperbranched poly(ethyleneimine)‐modified shape‐memory epoxy polymers

Abstract

In this study a series of hyperbranched modified shape-memory polymers were subjected to constrained shape recoveries in order to determine their potential use as thermomechanical actuators. Materials were synthesized from a diglycidyl ether of bisphenol A as base epoxy and a polyetheramine and a commercial hyperbranched poly(ethyleneimine) as crosslinker agents. Hyperbranched polymers within the structure of the shape-memory epoxy polymers led to a more heterogeneous network that can substantially modify mechanical properties. Thermomechanical and mechanical properties were analyzed and discussed in terms of the content of hyperbranched polymer. Shape-memory effect was analyzed under fully and partially constrained conditions. When shape recovery was carried out with fixed strain a recovery stress was obtained whereas when it was carried out with a constraining stress the material performs mechanical work. Tensile tests atshowed excellent values of stress and strain at break (up to 15 MPa and almost 60%, respectively). Constrained recovery performances revealed rapid recovery stress generation and unusually high recovery stresses (up to 7 MPa) and extremely high work densities (up to 750 kJ/m 3 ). The network structure of shape-memory polymers was found to be a key factor for actuator-like applications. Results confirm that hyperbranched modified-epoxy shape memory polymers are good candidates for actuator-like shape-memory applications.

Phenomenological characterization of sequential dual-curing of off-stoichiometric “thiol-epoxy” systems: Towards applicability

“…Therefore, complex shapes were successfully achieved, and no cracking was appreciated over the surface due to shrinkage and internal stresses generated during the epoxy homopolymerization process [30]. Taking advantage of this process, it is possible to obtain well-defined circular-shapes for structural applications such as opening and closing mechanisms (shape-memory actuators [31]), or otherwise forming complex shape designs (i.e. a plaited-shape or bent-shape) for more demanding applications.…”

Review of Progress in Shape Memory Epoxies and Their Composites

“…In their presence a co-network, eventually accompanied with strong phase segregation, is formed that markedly enhance the ductility of the parent EP. EPs modified with hyperbranched polyethyleneimine (multifunctional amine-type crosslinking agent) showed excellent shape fixity and shape recovery of 98% along with a fast shape recovery rate [ 64 , 65 ]. Alternatively, EP can be used as minor component to modify hyperbranched polymers, such as polyurethane [ 66 ].…”

Thermally-triggered free-standing shape-memory actuators

“…These temporary shapes are stabilized by the formation of strong interactions within the network that impede the recovery of the original shape until an external stimulus, such as heat, is applied [4,5]. During this process, the material stores an amount of energy that is then released in form of shape-transformation or force [6][7][8][9][10]. This makes this class of materials attractive in many fields of applications, such as industrial applications (i.e.…”