Rheological properties of amorphous and semicrystalline polylactic acid polymers
1999
Fang, Q. | Hanna, M.A.
Corn starch fermentation provides an abundant supply of lactic acid. Polymerization of lactic acid into polylactic acid (PLA) produces a biodegradable thermoplastic polyester with excellent functional properties comparable to many petroleum-based plastics. PLA polymers are made into useful items using thermal processes, such as injection molding and extrusion. Therefore, its rheological properties, especially the shear viscosity, have important effects on the thermal processes, such as film blowing, paper coating, injection molding, sheet forming and fiber spinning. In this study, viscosities of two types of PLA resins (amorphous and semicrystalline) at 150 and 170 degrees C and at various shear rates (30, 50, 70, 90, 110, 130, and 150 rpm screw speeds) were measured with a tube rheometer on an extruder. The viscosity data was calculated from the pressure profiles and the volume flow rate. Statistical analyses were performed using SAS. The effects of resin type, temperature and shear rate on melt viscosity were determined. Under the same processing conditions, semicrystalline PLA had a higher shear viscosity than amorphous PLA. As the temperature increased, the shear viscosity decreased for both types of PLA. The PLA melt was characterized as a pseudoplastic, non-Newtonian fluid. Power law equations adequately described the behavior of the PLA melts (r(2) > 0.99).
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