Viscoelastic properties and flow instabilities of aqueous suspensions of cellulosic fibers.

Processing of concentrated lignocellulosic biomass suspensions typically involves the conversion of the cellulose into sugars and sugars into ethanol. Biomass is usually pre-processed (i.e. via comminution, steam explosion, etc.) to form fine cellulosic fibers to be dispersed into an aqueous phase for further treatment. The resulting cellulose suspensions need to be pressurized and pumped into and out of various processing vessels without allowing the development of flow instabilities that are typically associated with the demixing, i.e., the segregation of the cellulosic biomass from the aqueous phase. Here, it is demonstrated that the use of a gelation agent, hydroxypropyl guar gum (HPG) at the relatively low concentration of 0.5 wt% significantly affects the development of viscoelastic material functions of cellulosic suspensions, and improves the dispersive mixing of the cellulose fibers within the aqueous phase. This results in the reduction of the flow instabilities and associated demixing effects that are ubiquitously observed during the pressurization of cellulosic suspensions in Poiseuille and compressive squeeze flows.