Effect of fibres on wet foams

Wet foam is an excellent carrier phase to produce particle or fibre structures. Thus, it is important to know how particles or fibres affect foam properties. We have studied these effects for foams generated by axially agitated mixing with 60-80% air content. Onset of a flow macro-instability is observed at high rotation speeds both with and without cellulose fibres. The air content of the foam is strongly affected by this instability. By describing the effect of the air content on the stability of bubble interfaces, we explain the bubble size for broad ranges of rotation speed and surface tension. Added fibres usually reduce the bubble size for a fixed rotation speed. After the flow macro-instability, not only the air content but also the bubble size increases with reduced surface tension. Beyond the instability, the effect of fibres on foam properties becomes minor.