Question

The following materials exhbit flow properties that can be describes by models that include a yield stress (e.g, Bingham plastic): (a) catsup; (b) toothpaste; (c) paint; (d) coal slurries; (e) printing ink. In terms of typical applications of these materials, describe how the yield stress is beneficial to their behavior, in constrast to how they would behave if they were Newtonian.

Answer 1

Tooth paste is bingham plastic. It behaves as solid upto some stress and further behaves as newtonian fluid.

Toothpaste should remain inside the tube until some force is applied over the tube. After the force is applied it should easily flow out of the tube. If it behaved like newtonian from the begining then we wont be able to contain it inside the tube. Thus bingham plastic nature helps in handling of these materials.

Paint is pseudoplastic fluid. As we stir paint its viscosity decreases. Stirring increases deformation inside the paint which results in decreasing of viscosity. Thinnning of paint is helpful for its application over any surface.

Printing ink is thixotropic fluid. When it is kept idle for long period of time, its viscosity is decreased. Decreased viscosity hinders the printing process as its flow is improper and it spreads over paper.

Coal slurries are Dilatant fluid. Their viscosity increases on deformation. Viscous slurries are easy to handle.