Abstract
ABSTRACT Influence of dextran and glycerol on fracture properties of 10% polyacrylamide (PAAm) gels was studied as a representative model system for food gels. No direct relationship was found between the fracture properties and gel liquid‐phase viscosity. In general, addition of dextran and glycerol did not affect gel network crosslink density and chain length. With minimal dextran addition, fracture stress and strain experienced large increases. Increase of the fracture stress and strain was attributed to fracture mode transition from elastic to elasto‐plastic fracture, resulting from dextran addition. Plastic deformation at the crack tips, acting as fracture‐initiating points, prior to fracture propagation lowered stress concentration effect. Sensitivity of 10% PAAm gels, with/without dextran, to induced imperfections showed the fracture stress to be higher than expected based on Griffith's energy balance criteria, manifesting in a delayed fracture process. The plastic deformation was ascribed to the delayed crack nucleation resulting from dextran addition. The fracture stress and strain of 10% PAAm gels increased with glycerol addition. The increase in fracture properties was attributed to plastic deformation, caused by a delayed crack nucleation prior to fracture propagation. The mechanism of delayed crack nucleation remains unclear, but the results obtained from this investigation can be used to understand reasons for the change in fracture property of food gels created by additives.
Published Version
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