The “EcoBlend” project aims at exploring a new method for the compatibilization of petroleum-based polymer such as acrylonitrile butadiene styrene (ABS) with biobased polymers, namely Poly(lactic acid) (PLA), in order to reduce the final material carbon footprint, while keeping the outstanding thermo-mechanical properties of the final blend.New approach of polymer reactive compatibilization of PLA and ABS will be investigated using an emerging new type of nanofillers: microfibrillated cellulose (MFC) and cellulose nanocrystals (CNC) for tuning the microstructure of immiscible PLA/ABS blends and their related properties. The biobased fillers (MFC and CNC) will be used as an alternative to organo-compatibilizers, classically used in immiscible polymer blend compatibilization. Blending ABS with PLA represents a nice alternative to enhance the biocontent of ABS-based materials as well as to respond to the environmental issues due to the petroleum origin of ABS and the intrinsic brittleness that restricts PLA applications. The cellulosic nanofillers have been selected based on the following criteria: (i) fully bio-based, offering the considerable benefit of further minimizing the fossil fuel dependence for composite manufacturing and helping to the reduction of greenhouse gas emissions, (ii) available in very large content and cost-effective, (iii) easy to modify chemically and to process. The role of the chosen filler will therefore be twofold: (1) act as interfacial compatibilizer between the two polymeric matrices and (2) compensate for the loss in thermo-mechanical properties due to the partial replacement of ABS by PLA.It is expected that the (reactive) compatibilization of PLA and ABS with those two kinds of nanofillers (MFC and CNC) will considerably improve their dispersion and their affinity for both polymers to capitalize the benefits of their large surface area, leading to a significant improvement of the targeted properties (mostly thermal and mechanical), compared to physical blends where the fillers are used as additives only. Special attention will be drawn on the conditions used for i) the production of the cellulose nanofillers by mechanical (MFC) and chemical (CNC) treatments, ii) the surface chemical modification of MFC and CNC, iii) the dispersion of the nanofillers into the PLA/ABS melt blends, incl. (reactive) extrusion conditions, iv) the effect of the nature, amount and chemical surface treatment of the nanofillers on their compatibilizing ability in PLA/ABS blends. Interestingly enough, the crystallinity of the PLA matrix will be the object of intensive study. In this regard, two different kinds of PLA will be studied, namely, PLLA (semi-crystalline) and PLLA/PDLA stereocomplexes as they exhibit very different mechanical and thermal properties. Indeed it has been largely demonstrated that stereocomplexation of PLA chains enhances the mechanical properties, the thermal-resistance, and the hydrolysis-resistance of the related PLA-based materials. Clearly this project will allow for producing a novel family of bio-based thermoplastic materials (likely with 2 to 3 stars within the “OK biobased” international certification by Vinçotte) with tunable properties through a comprehensive and innovative research approach which will also bring more basic concepts in the field of interfacial compatibilization via biosourced crystalline cellulose nanofillers.