It is well known that flexible fibers tend to aggregate, or "flocculate".  The aggregates, termed "flocs" are undesirable in fiber processing as they lead to problems in resulting products (e.g., paper, reinforced composites).  We have found that the addition of a small amount of water-soluble polymer can disperse the fibers, as illustrated in Figure 1 below (left: flocculated suspension; Right: dispersed suspension containing water-soluble polymer).

Dispersing the fibers also results in a dramatic reduction in the apparent viscosity of the fiber suspension, which allows the suspension to flow up to very high fiber concentrations.  We have exploited this feature in the development of an extrusion process, whereby concentrated fiber suspensions can be extruded and formed into solid bodies.  The advantage of this process is that relatively low value solids can be combined with the fiber suspension to produce value-added products.

Designing a process requires selecting the appropriate water-soluble polymers.  A study was conducted to determine the extrudability of concentrated fiber suspensions containing different water-soluble polymers.  The technique chosen was to place the suspension in a torque rheometer (Figure 2), and measure the torque drop that results from the addition of the water-soluble polymer.  Polymers that provide larger torque drops prove to exhibit better extrudability.

An example of an experiment is illustrated in Figure 3 below, where the torque required to rotate the torque rheometer at a specified speed is plotted as a function of time.

When the polymer is added, the torque drops significantly.  THe torque drop is defined to be the difference in torque between the samples with and without polymer at 150 s (30 s after the polymer is added.

The torque drop is plotted as a function of polymer type in Figure 4 below.  This plot shows that carboxymethylcellulose (Aqualon 7H4-F) the performs the best. 

This study spawned several other studies focused on understanding why water soluble polymers alter the structure and rheology of fiber suspensions.