Enhancing Compatibilizer Function by Controlled Distribution in Hydrophobic Polylactic Acid/Hydrophilic Starch Blends

Various polylactic acid (PLA)/cornstarch blends, with and without the compatibilizer methylenediphenyl diisocyanate (MDI), were prepared by melt processing using a twin-screw extruder. In the blends where it was included, MDI was distributed in either the PLA or starch phase through controlling processes conditions. The effects of MDI inclusion and its distribution on the resultant microstructures, mechanical properties, and thermal and rheological behaviors of the blends were studied via scanning electron microscopy, differential scanning calorimetry, thermogravimetric analysis, mechanical testing, and Haake rheometer. The results showed that when the MDI was distributed in the starch phase before blending with PLA, the highly reactive isocyanate groups in the MDI were most probably consumed by water, resulting in an overall weakening of its compatibilizing effect. However, when the MDI was distributed in the PLA phase before blending with starch, modulus, yield strength, and impact strength were all increased. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 119:2189-2195, 2011