Study of the flow behavior of polymer-natural fiber suspensions in the power law validity range

The melt flow properties of WC suspensions with henequen, coconut and bovin e leather, in their raw condition, and after extraction of all their low mo lecular weight substances were studied. The experimental results show that, at the strain rates employed, the behavior of the suspensions is described by a power law (eta = m(gamma) over dot(n-1)). It is important to mention that in the present work we do not restrict our analysis to the evolution o f the suspension Newtonian viscosity with the fiber concentration (as commo nly is reported in the literature), but a more complete analysis is perform ed by describing the evolution of the consistency (m) and the power law (n) indices with the fiber concentration. Both indices were evaluated using a technique previously developed. The flow index (n) presents an anomalous be havior, it increases when the fibers are incorporated into the melted matri x at low fiber concentrations. This unexpected behavior is very different f rom that commonly reported in the literature and is apparently due to the f lexibility of fibers. Moreover, the influence of the fiber extractable mate rials on the behavior of these suspensions was also evaluated. It was found that these latter materials apparently influence the value of the consiste ncy index (m) of suspensions, at fiber concentrations above the critical pi gment volume fraction; however, they do not have a significant effect on th e power law index (n). Concerning the mechanical behavior of composites mol ded from the previous suspensions, it was found that when the fiber content augments, their elastic modulus increases, but their tensile strength fall s. This behavior, however, could be improved by increasing the adhesion bet ween the fibers and matrix.