Shear viscosity increased with increasing CNF content. This behavior was attributed to the hindering of the movement of the macromolecular chains of the matrix by the CNF. The importance of the pseudo-plastic behavior is larger as the CNF content in the composite increases. Thus, the higher the amount of CNF, the poorer dispersion of the minor phase in the melt and the higher is the viscosity of the filled polymer. The increase in viscosities attributed to the formation of a stronger cellulosic network, the restriction of molecular mobility and the reduction in free volume induced by the interaction and dispersion of cellulose in the polymer matrices . Shear thinning behavior was also observed for all cases with a Newtonian fluid plateau at low shear rates in Fig. 6. The shear viscosities at shear rate 0.01 (0.01) for PLA + 10 wt.% CNF was 32% higher than that of the PLA matrix. The 0.01 of PLA + 5 wt.% CNF with carrier system was similar to neat PLA. The melt viscosity behavior of composites in this research is in good agreement with the behavior reported
by other authors