The complex viscosity (*) for PLA, PLA + PHB, and CNF composites as a function of frequency (ω) are presented in Fig. 3. The complex viscosities decreased with an increase of ω, indicating shear thinning behavior and pseudoplastic characteristics of PLA, PLA + PHB, and CNF composites. The complex viscosity of the PLA + PHB composite was lower than that of PLA because of the fact that PLA with a 10% PHB content has a higher mobility when subjected to shear deformation. However, with the incorporation of CNF into PLA, the morphology changed, and the chain mobility
decreased, thus preventing complete relaxation. A similar phenomenon was observed for other reinforcement melts. In comparison with PLA, the composites have a higher melt viscosity where contribution of the cellulosic phase becomes apparent. As an example, the zero shear
viscosities ∗ 0, taken as the value at the lowest ω, for PLA + 10 wt.%CNF was 53% higher than that of the neat PLA. This viscosity increase is normal for filled polymer systems. The ∗ 0 of PLA + 5 wt.% CNF with the carrier system was similar to neat PLA.