Tuning the rheological properties of kaolin suspensions using biopolymers

Kaolin based suspensions have wide range of applications such as slurry wall, drilling fluids, adhesives, cosmetics, refractories and pharmaceuticals, due to their abundance in nature, low cost and non-swelling nature. On the other hand, the unique properties (i.e., biodegradability) of biopolymers make them suitable candidate for variety of applications including modification of clay suspensions. In this study, the rheological properties of kaolin suspensions modified with different biopolymers (xanthan gum (XG), sodium carboxymethyl cellulose (CMC), potato starch (PS), chitosan (Ch) and apple fibre (AF)) have been investigated by varying the biopolymer type, content and clay content. The main objective of the present study is to propose a substitute for the natural mud sample. Frequency sweep tests, stress ramp-up tests and time-dependent tests were performed by using the Couette geometry (coaxial cylinders) for the prepared suspensions. The rheological results showed that both viscosity and moduli were significantly influenced by adding different biopolymers into the kaolin suspensions. For instance, an increase in viscosity of modified suspensions was observed: 3 – 4 orders of magnitude by adding xanthan gum (1 wt%) or sodium carboxymethyl cellulose (5 wt%) and 6 orders of magnitude by adding apple fibre (5 wt%). Likewise, the incorporation of different biopolymers significantly affected the complex modulus of modified clay suspensions. For example, similar or higher values of complex modulus than the pure kaolin suspension were observed at low xanthan gum or sodium carboxymethyl cellulose content (0.1 wt%). In case of chitosan, the complex modulus of the modified suspensions was higher than the complex modulus of pure kaolin suspension, even at very low polymer content (1 wt%). In the case of potato starch, a decrease in complex modulus by increasing polymer content till 10 wt% was observed followed by an increase in complex modulus with polymer content. The shear rate ramp-up and ramp-down experiments showed that the time-dependent behaviour of kaolin suspensions was not strongly influenced by adding different biopolymers. This knowledge will provide a base to choose a suitable substitute for the natural mud sample.