Multifunctional Epoxy-based copolymers can be used as chain-extender (CE) to increase the molecular weight and create branching in polylactides (PLA). In this study, the effect of a multifunctional epoxy-acrylic-styrene copolymer on the properties of PLA/Thermoplastic Starch (PLA/TPS) blends was investigated. The PLA/TPS blends were prepared by twin-screw extrusion. The dry-starch and plasticizers were mixed together in the first half of the extruder to complete starch gelatinization. Water was removed by devolatilization at midex-truder and the PLA matrix was mixed with the water-free TPS in the latter portion of the compounding process. The standard blends comprised 27% TPS in the PLA matrix. The TPS phase itself comprised 36% plasticizer in the form of glycerol or sorbitol. A maleic anhydride grafted PLA (PLAg) was also used in selected blends to examine the effect of interfacial modification on the morphology of chain-extended blends. The blends were injection molded into standard test bars and their tensile properties were measured. Differential scanning calorimetry was carried out to examine the effect of chain extension on PLA's ability to crystallize. Oscillatory-shear rheology was used to monitor changes in blend viscosity. Finally, scanning electron microscopy on microtomed and acid-etched samples was carried out to assess the blend morphology. It was found that the combination of interfacial modification and chain-extension strategies led to greatly improved ductility. The viscosity of the PLA/TPS blends was also dramatically increased by adding a small amount of epoxy-based chain extender. This is of great interest for polymer processing techniques (such as foaming or film blowing) that require high melt strength. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 134-141, 2011