M. Ayora et al., EVALUATION BY TORQUE-RHEOMETER OF SUSPENSIONS OF SEMIRIGID AND FLEXIBLE NATURAL FIBERS IN A MATRIX OF POLY(VINYL CHLORIDE), Polymer composites, 18(4), 1997, pp. 549-560
The flow properties of three different PVC-natural fiber suspensions w
ere evaluated using a torque-rheometer. The fibers used were extracted
from henequen leaves, coconut husk, and bovine leather. They have dis
tinct mechanical properties that produce suspensions with different fl
ow behaviors. Nevertheless, the experimental results show that, at the
rates employed, the behavior of the suspensions can be described by a
power-law (sigma = m gamma(.n)). The flow (n) and consistency (m) ind
exes of each suspension were evaluated using an approximate technique
previously developed. The evolution of these indexes as a function of
the volume fraction of fibers (Phi) are studied and discussed. It was
found that, at diluted concentrations, the value of the flow index une
xpectedly increases with the concentration of fibers, especially in th
ose suspensions containing the more flexible fibers. However, at eleva
ted concentrations it substantially diminishes. To model this behavior
an empirical function for n(Phi) is proposed. The index of consistenc
y (m) presents a continuous increment with the concentration of fibers
. To model the evolution of this parameter with the content of fibers,
we have defined a relative consistency index m(r)(m(r) = m(s)/m(o), w
here m(s) and m(o) are the suspension and matrix indexes) in a similar
form to that established for the relative Newtonian viscosity. The fu
nction m(r)(Phi) is modeled using several equations used to describe t
he behavior of this last viscosity (Maron and Pierce, Mooney, Thomas,
Sudduth and Polynomial models). Among them, the Sudduth and Polynomial
equations were those that better fit the behavior of these type of su
spensions. Finally, to test the previous methodology, the theoretical
torque values obtained were compared with experimental data for each s
uspension. Excellent agreement among them was found.