Modifying the flocculation of microfibrillated cellulose suspensions by soluble polysaccharides under conditions unfavorable to adsorption

• CMC and xanthan gum dispersed microfibrillated cellulose (MFC) flocs successfully.
• MFC/polymer suspensions had lower gel strength compared to MFC as such.
• Lower gel strength was related to better dispersed structure under shear.
• Optical coherence tomography (OCT) combined with a rheometer was used for the first time for MFC/polymer suspension.

Carboxymethylcellulose (CMC) and xanthan gum were studied as dispersants for microfibrillated cellulose (MFC) suspension using a rotational rheometer and imaging methods. The imaging was a combination of photography and optical coherence tomography (OCT). Both polymers dispersed MFC fibers, although CMC was more effective than xanthan gum. The negatively charged polymer chains increased the viscosity of the suspending medium and acted as buffers in between the negatively charged fibers. This behavior decreased the number and strength of contacts between the fibers and subsequently dispersed the flocs. The stronger separation of the fibers was reflected in the frequency sweep where the MFC/polymer suspensions had lower gel strength than pure MFC suspension. Dispersing effect was also observed in the flow measurements, where the floc size was more uniform with polymers in the decelerating flow and after long, slow constant shear, which normally induces a heterogeneous structure with large flocs into the MFC suspension.