Anti-freezing, highly stretchable, and recyclable composite organohydrogels from bio-macromolecules crosslinked by multi-strength H bonds and chain entanglements

Gels formed by bio-macromolecules, free of any initiators, crosslinkers, and other chemical additive agents, are prospective environmentally friendly materials. In this work, organohydrogels prepared from chitosan and polyvinyl alcohol (PVA) without any chemical additive agents are fabricated based on physical crosslink approach and are endowed with anti-freezing and highly stretchable properties. The mechanical properties and phase transition behaviors are investigated. These highly-stretchable organohydrogels display obvious strain and strain rate-dependent tensile properties, where the rupture strain can reach as large as 17. The samples show reversible elasticity at small strains and irreversible plasticity at large strains, accompanied with first a strain softening and then a strain hardening during the stretching process. The cyclic tensile tests present that the samples exhibit residual strain and hysteresis at step loadings, and the rupture behaviors strongly depend on the strain, strain rate, and waiting time. The differential scanning calorimetry (DSC) tests demonstrate that the organohydrogels present only one endothermic melting peak around 60 & DEG;C without obvious glass transitions at - 60-60 & DEG;C, indicating the stability of the anti-freezing organohydrogels at ultralow temperatures.