Mechanical and fracture behavior of gelatin gels

Abstract

Hydrogels were prepared from bovine and porcine gelatin powders of different Bloom values. Gelatin concentration and pH were selected to obtain self-supporting gels with stiffness in the range of those employed in structural applications in foodstuff, ballistic and pharmacy. Glycerol and sorbitol were also added in gel formulations. Deformation and fracture behaviors were assessed by means of gel strength measurements, uniaxial compression tests and wire cutting experiments. All gels showed non-linear elastic deformation with strain hardening and brittle fracture. Large deformation was described with a first order Ogden constitutive model. Strain hardening was attributed to protein chains renaturation capability under stress. It was found that neat porcine gelatin gels displayed higher gel strength, shear modulus, failure strain and stress, fracture toughness and water retention than bovine gelatin gels. The addition of sorbitol and glycerol caused an increase in water retention capability and a marked enhancement in gels´ fracture toughness. The major content of hydrophilic amino acids in the gelatin, the stronger the effect of glycerol and sorbitol on gelatin network morphology. The correlation between large deformation and fracture toughness parameters with the technological gel strength values was also investigated.