SIM-AM 2023

Tailoring and one-dimensional modelling the stress-free two-way shape-memory effect in photo-crosslinked poly(caprolactone)-based systems

  • Pandini, Stefano (University of Brescia)
  • Scalet, Giulia (University of Pavia)
  • Inverardi, Nicoletta (University of Brescia)
  • Pasini, Chiara (University of Brescia)
  • Toselli, Maurizio (University of Bologna)
  • Messori, Massimo (Politecnico of Torino)
  • Auricchio, Ferdinando (University of Pavia)

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Shape memory effect in polymers is most often known for “one-way” actuation, typically caused by hindering/activating macromolecular chains motions on the basis of the viscoelastic behaviour. Possible strategies to obtain fully reversible shape memory effect (i.e. the ability to change between two configurations upon on-off stimuli) relies on a proper combination of specific polymers and thermo-mechanical histories. This effect is displayed only by some polymer families (semicrystalline co-polymers and semicrystalline networks are the most investigated), under the application of heating-cooling cycles in presence of a stress, either external (“stress-driven”) or internal stress (“stress-free” or “reversible” two-way effect). In this work, with the aim to potentially employ optimised compositions with 3D-printing facilities, photo-crosslinking of methacrylated macro-monomers was chosen as strategy to obtain the network structure. Different semicrystalline networks were investigated, based on poly(caprolactone), poly(ethylene glycole) and their copolymers. They all revealed to be capable of reversible elongation-contraction cycles upon thermo-mechanical cooling-heating histories, either in presence of an external applied load or under “stress-free” conditions [1]. The results were studied at the light of parameters regarding the material macromolecular architecture, the preceding (“training”) history and the applied thermo-mechanical cycle. A phenomenological physically-grounded constitutive model was developed starting from [2] to describe the stress-free conditions in semi-crystalline crosslinked polymers. The original model [2] was verified for the one-way effect and for the two-way response under external stress, showing the advantages of being simple, easy to implement and based on easily measured parameters with physical meaning. The proposed model is based on a phase transition approach, allowing to reproduce macroscopic material behavior under various thermo-mechanical histories. The polymer microstructure is described by phase parameters, considering the material as a fully amorphous networks or as a mixture of amorphous and crystalline phases, depending on temperature. The evolution laws and constitutive equations are based on physical evidences and on thermodynamic principles. REFERENCES [1] N. Inverardi et al., Macromolecules (2022), 55(19), 8533–8547. [2] G. Scalet et al., Polymer (2018) 158: 130-148.