First Normal Stress Difference in Capillary Extrusion Flow of Nanometer Calcium Carbonate-Filled PLLA Biocomposites

摘要

The nanometer calcium carbonate (nano-CaCO3)-filled poly-L-lactide (PLLA) biocomposites were prepared using a twin-screw extruder. The first normal stress difference of the composites were measured by means of a capillary rheometer under experimental conditions with temperatures ranging from 170 to 200 C and shear rates varying from 50 to 10~3 s~(-1). The first normal stress difference (AT,) increased roughly linearly with increasing shear stress (τ_w). The sensitivity of the N1, to τ_w increased with an increase of the die length—diameter ratio, and the N1, value varied slightly with the filler weight fraction (Φ_f) as test temperature was constant. When the shear stress was fixed, the N1 reached a minimum value for Φ_f = 1 %. The values of the N1 of the composite melts decreased roughly linearly with a rise of temperature when the shear rate was constant.