Experimental investigation on the effect of fibre consistency on rheology of aqueous foams in pipe flow

Due to recent development of foam forming for making fibrous structures (instead of traditional water forming), understanding on the rheology of aqueous fiber foam has become a necessity. However, this topic has been almost completely neglected in the existing academic literature, and most basic questions remain unanswered. In this paper we present results on the effect of fiber consistency on the rheology of aqueous fiber foams. Hardwood (birch) fibers were used at mass consistencies of 2, 3, 4 and 5%. Air content was 70% and SDS was used as the surfactant. The measurements were performed with a pipe rheometer, as normal rheometer geometries are unsuitable for these materials. In addition to shear rheology, slip flow at the pipe walls was also studied. The viscosity behaviour of the foams followed accurately a power law with all consistencies. Flow index was n ~ 0.4 and it decreased slightly with increasing consistency. The consistency index K was linearly dependent on consistency. The interaction between the fibers is thus clearly weaker in foam than in pure water. The slip behavior was similar for all consistencies.