Structural relaxation and glass transition in high-solid gelatin systems crosslinked with genipin

Structural relaxation and glass transition were examined in the swelling behaviour of a high-solid biopolymer matrix; genipin-crosslinked gelatin. Degree of swelling was quantified by the Flory-Rehner theory that furnishes estimates of average molecular weight between crosslinks and network mesh size. Fourier transform infrared spectroscopy and wide angle X-ray diffraction described intermolecular interactions and the extent of amorphicity in the crosslinked matrix. Micro differential scanning calorimetry provided evidence of the changing thermodynamic characteristics of the gelatin network in the presence of the crosslinker. Modulated differential scanning calorimetry and small deformation oscillatory rheology unveiled the vitrification properties of the system. Experimental measurements were treated with the time-temperature superposition principle to unveil an extensive master curve through the rubbery, glass transition and glassy states. Viscoelastic behaviour was modelled with the combined predictions of the modified Arrhenius and William-Landel-Ferry theories to pinpoint the mechanical glass transition temperature that was compared with predictions from calorimetry. Comprehensive understanding of polymeric behaviour during swelling affords greater control in the design of targeted delivery matrices for drugs and other bioactive compounds.