Preparation and characterization of plasticized gelatin films cross-linked with low concentrations of Glutaraldehyde

Thermal and mechanical properties as well as moisture resistance and water vapor barrier properties of films from bovine gelatin added with d-sorbitol (30 wt%) as plasticizer and cross-linked with low amounts of glutaraldehyde (GTA, from 0 to 2 wt%) were investigated to determine their suitability as barrier layers for flexible packaging materials. Results revealed that free amino side chain groups of gelatin decreased with GTA, confirming the occurrence of cross-linking between GTA and gelatin. The extent of cross-linking reaction in the presence of d-sorbitol was lower compared with the unplasticized counterpart suggesting that plasticizer hampers GTA to react. The glass transition temperature (T _g) as measured from differential scanning calorimetry (DSC) increased with GTA concentration owing to the formation of more reticulated materials while the incorporation of d-sorbitol led to a small reduction in this parameter due to plasticization. Increasing GTA concentration from 0 to 1 wt% provoked the enhancement of elastic modulus from 3.7 ± 0.2 to 4.9 ± 0.2 GPa. These values reduced significantly by the addition of d-sorbitol, whereas elongation at break improved in about 150%. The optimum formulation for the intended purpose was that containing 1 wt% GTA and 30 wt% d-sorbitol since it exhibited the best set of properties: total soluble mater reduced from 100 to 16%, moisture absorption decreased from 1854.1 ± 85 to 210.4 ± 8%, water vapor permeability at 65% relative humidity improved from 2.42 ± 0.27 to 0.94 ± 0.06 × 10⁻¹⁴ kg m Pa⁻¹ s⁻¹ m⁻², with minor reduction in opacity and with the additional benefit of releasing only 5% of the initial GTA content.