**5. Conclusions**

In order to extend the biobased polymers application and at the same time to reduce the final costs of the material, the design of suitable biocomposites containing natural fibers coming from industrial and/or agricultural waste is a feasible solution. In this work the addition of wheat bran fibers (from 10 to 30 wt.%) was investigated. In order to limit the excessive embrittlement caused by the bran addition a plasticized ductile matrix was chosen (PLA/PBSA matrix containing 60 wt.% of PLA and 40 wt.% plasticized with Triacetin). The evaluation of the interfacial adhesion (interfacial shear stress, *IFSS*) between the fiber and the matrix was carried out adopting analytical models based on static and dynamic tests. For the first time the essential work of fracture (EWF) approach was adopted on this type of biocomposites. The bran addition caused a decrement of the mechanical

properties in parallel with the EWF reduction. In particular, the essential work of fracture is highly influenced by the presence and content of bran and this is ascribable to the high irregularity of filler geometry and presence of agglomerates especially where the content of filler is high. The combination of reduced adhesion between matrix- filler and increased intensification of stresses is responsible of the observed mechanical behavior as a function of the bran content.

**Author Contributions:** Conceptualization, L.A. and M.-B.C.; methodology, L.A. and A.L.; validation, L.A. and A.V.; formal analysis, L.A. and A.V.; investigation, L.A. and A.V.; resources, M.-B.C. and A.L.; writing—original draft preparation, L.A. and A.V.; writing—review and editing, M.-B.C. and P.C.; supervision, M.-B.C., P.C. and A.L.; funding acquisition, M.-B.C. and P.C. All authors have read and agreed to the published version of the manuscript.

**Funding:** This project has received funding from the Bio-based Industries Joint Undertaking (JU) under the European Union's Horizon 2020 research and innovation programme under grant agreement No 837761 (BIONTOP project, Novel packaging films and textiles with tailored end of life and performance based on bio-based copolymers and coatings). The JU receives support from the European Union's Horizon 2020 research and innovation programme and the Bio-based Industries Consortium.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The data presented in this study are available upon request from the corresponding author.

**Acknowledgments:** Centre for Instrumentation Sharing–University of Pisa (CISUP) is thanked for its support in the use of FEI Quanta 450 FEG scanning electron microscope.

**Conflicts of Interest:** The authors declare no conflict of interest.
