In the last decade, tremendous efforts in the scientific community have been made to modify bio-based and/or bio-degradable polymers to achieve the properties of the market needs and to provide sustainable alternatives to the currently used petrochemical based polymers. The bio-based polymer cellulose diacetate (CDA) exhibits outstanding properties, which are comparable with those of polystyrene (PS) or acrylonitrile butadiene styrene (ABS), except its toughness. In this study, we examined the effects of the type of plasticizer and its concentration on the toughness of cellulose acetate. Two different plasticizers are used in the cellulose diacetate blends in concentrations between 15 and 40 wt.-%. Additionally, cellulose diacetates with varying molar masses are investigated. To validate the mechanical properties and especially the toughness of the blends, tensile and instrumented charpy impact tests are applied. The young�`s modulus and tensile strength of the blends decrease with increasing content of plasticizer, corresponding to the rule of mixture. The elongation at break, however, did not follow this rule but increases exponentially. Depending on the plasticizer efficiency, derived from the decrease of the glass transition temperature, the toughness of the plasticized cellulose diacetate can be adjusted [1,2]. With increasing plasticizer content, the impact strength of the notched and unnotched cellulose diacetate is improved. By increasing the temperature of the impact test from -60 °C to 120 �°C, cellulose diacetate shows apparently two kinds of brittle to ductile transitions. This was also recently published [3]. These two transitions refer to the alpha and beta transitions of CDA, which was confirmed by DMTA measurements. REFERENCES 1. V. P. Ghiya, V. Dave, R. A. Gross and S. P. Mc Carthy, Journal of Macromolecular Science, Part A, 33:5, 627-638 (1996). 2. H.-M. Park, M. Misra, L. T. Drzal and A. K. Mohanty, Biomacromolecules, 5, 2281-2288 (2004). 3. A. Charvet, C. Vergelati and D. R. Long, Carbohydrate Polymers, 204, 182-189 (2019).