Structure of Filter Cakes during the Electroassisted Filtration of Microfibrillated Cellulose

Abstract

Microfibrillated cellulose (MFC) is a biobased material with unique properties that can be used in a multitude of applications. Water removal from the dilute product streams is, however, challenging and hinders its commercial attractiveness. One possible method of improving dewatering is the use of electroassisted filtration, in which an electric field is applied across part of the filter chamber. In this work, a bench-scale dead-end filter press, modified to allow for electroassisted filtration, was used to dewater a suspension of MFC produced via 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO)-mediated oxidation. A filter cake was produced with a channeled structure related to the design of the anode mesh, indicating that the cellulose microfibrils were aligned in the direction of the electric field. This was investigated, qualitatively and quantitively, using scanning electron microscopy and wide-angle X-ray scattering, which showed a preferred orientation on a microscopic level but only a partial orientation on a molecular level (fc between 0.49 and 0.57). The influence of the density of the anode mesh, in terms of the structure/permeability of the filter cake and dewatering rate, was also evaluated using two different anode mesh densities (5 × 5 and 10 × 10 mm). It was not, however, found to have any major impact on the dewatering rate.