This research focuses on brittleness improvement of biodegradable poly(lactic acid) (PLA) by reactive melt blending with poly(trimethylene terephthalate) (PTT). First, PLA is simultaneously blended with PTT and a reactive compatibilizer, poly(ethylene‐co‐glycidyl methacrylate) (PEGMA), (one‐step blending procedure). In the PLA/PTT/PEGMA blend, PEGMA mainly disperses in the PLA matrix phase, and the blend shows unimproved tensile properties. To increase the reaction between PTT and PEGMA, PEGMA is sequentially blended with PTT then PLA (two‐step blending procedure). This procedure is effective in drastically enhancing elongation at break of the blend. The strain at break of the blend formed by two‐step blending is significantly improved because the blending procedure affects the blend morphology. PLA‐g‐PEGMA‐g‐PTT graft copolymer is formed at the interface between PLA and PTT during reactive melt blending with PEGMA when the two‐step blending procedure is employed as a blending method which is confirmed by Fourier transform infrared spectroscopy and viscosity measurement. Such features bring about craze formation during tensile test and this is the reason why the toughening is achieved by the two‐step blending procedure.

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Interfacial localization of conductive fillers in a cocontinuous immiscible polymer blend is an efficient way of improving the electrical and thermal conductivities of the composite. Conductive path formation at the interface of a cocontinuous structure is expected to provide high conductivity by a smaller amount of the filler, which can be used for applications as conductive materials. In this study, biobased poly­(lactic acid) (PLA) was blended with poly­(trimethylene terephthalate) (PTT) to make the cocontinuous immiscible polymer blend. Poly­(glycidyl methacrylate) (PGMA) was grafted on reduced graphene oxide (rGO) to make a PGMA-grafted rGO (rGO-PGMA). The epoxy group of GMA on rGO-PGMA reacted with the end groups of both PLA and PTT and localized at the interface between PLA and PTT by a two-step blending procedure to form the conductive path between PLA and PTT. From transmission electron microscopy observation, it was found that rGO-PGMA localized between the interface of PLA and PTT. Both electrical and thermal conductivities of the composite were improved, which was confirmed by the electrical volume resistivity and thermal diffusivity measurements, compared with neat polymers and other blends.