Rheological properties of starch-based materials and starch/poly(lactic acid) blends

The rheological properties of pure starch and blends of gelatinized starch/ poly(lactic acid) (PLA) were studied using a rheometer incorporating a twin-roll mixer and a single-screw extruder. The mixer provides a useful and convenient tool to study the rheological properties and gelatinization processes of starch. The single-screw extruder with a slit capillary die was used to measure shear stress and viscosity under different shear rates at different temperatures. Starch was shown to increase the shear viscosity of PLA. Methylenediphenyl diisocyanate (MDI) was used as a compatibilizer, and was distributed in different phases through controlled processing. The addition of MDI showed a stronger effect on rheological properties when it was distributed in the PLA phase prior to blending. Both the pure starch and blends showed a power law dependence of viscosity on shear rate.