Dear Amitabh Roy, the following documents deals with the origins and theories of shear thickening. My Regards

https://doi.org/10.1016/0009-2614(84)85540-2

https://doi.org/10.1016/0377-0257(76)80014-6

https://link.springer.com/article/10.1007/BF01358165

https://doi.org/10.1016/0032-3861(88)90058-4

https://link.springer.com/article/10.1007/s10853-010-4817-5

https://doi.org/10.1122/1.4897267

https://doi.org/10.1122/1.550884

https://doi.org/10.1021/ma100093b

Amitabh Roy

Your paste refers to dilatant systems, as Abdelkader BOUAZIZ . correctly directed you. When moving solid particles, there is not enough water, which plays the role of a lubricant. As a result of this, as the shear stress of the planes increases, the viscosity of the system increases.

The shear thickening behavior is manifested because the conditions have been made favorable for agglomeration by addition of a coagulant. With application of shear stress, agglomerating suspensions have a natural tendency to increase the size of existing agglomerates resulting in higher viscosity which is unsuitable for extrusion. You are essentially dealing with a two-phase system in which there is a dispersed phase that lives inside a suspending medium which acts as a continuous phase. Spatial arrangement and distribution, agglomeration and de-agglomeration during shear are responsible for shear-thickening and shear-thinning behavior. The basic knowledge on such type of systems can be got from the book Aroon V. Shenoy, Rheology of Filled Polymer Systems, Kluwer Academic Publishers, Netherlands (1999).

There is a chapter on constitutive theories and equations of suspensions where the effects of shape, concentration, dimensions, and size distributions of the particles have been discussed. When it comes to controlling the rheology of two-phase systems, mixing plays a critical role in getting the system to the desired level of viscosity and non-Newtonian flow behavior. The entire Chapter 5 in the book is dedicated to the Preparation of filled polymer systems.

In section 5.4, there is a detailed discussion on the compounding /mixing variables that affect the quality of the mix. Variables affecting compounding operations could be machine variables (mixer type, rotor geometry) or operating variables (mixing time, rotor speed, ram pressure, chamber loading, mixing temperature, order of ingredient addition). Some variables are more sensitive to changes than others. It is important to study and identify these variables and understand their sensitivity so that the compounding /mixing can be carried out under optimum conditions. The effect of each of these variables for the specific alumina filler – matrix combination needs to be understood to find the optimum conditions to achieve the proper level of dispersion and distribution of alumina in the polymer solution. The necessary hints on how to go about this can be got by reading Chapter 5 of the book.

The best way to prevent agglomeration of filler particles is by surface-modification of the filler particles. In the Table 1.12 of the book Aroon V. Shenoy, Rheology of Filled Polymer Systems, Kluwer Academic Publishers, Netherlands (1999), there are several suggested surface modifiers that could work. These would be from the categories of silanes, and titanates and their full forms are given in Table 1.8. Which one would be most effective for Al2O3 can only be worked out by some mixing experiments, which are discussed in the book. Particularly for Alumina, one could think of the zircoaluminate (CAVCO MOD APG) surface modifier as it might turn out to be very effective.

Since the interest is specifically for Extrusion, the following book may help: A. V. Shenoy and D. R. Saini, Thermoplastic Melt Rheology and Processing, Marcel Dekker Inc., New York (1996). The other papers that would be relevant to this study would be