*2.2.3. Preparation of the composites*

Composites were produced in a two-stage process. In the first stage, bio-fillers and polyolefine were compounded with and without compatibilizer using the twin-screw extruder Rheomex CEW100 QC, Haake, Germany. The mixing zone temperature of the extruder was 160°C for PE and 190°C for PP matrix composites. The rotation speed of the screws was 50 rpm. In the second stage, the extrudate in the form of strands was cooled to room temperature and then granulated.

The compound granules were dried at 80°C for 24 h before injection molding. The specimens were prepared using the injection molding machine MiniJet II, Haake, Germany, at cylinder temperatures of 180°C for PE and 190°C for PP matrix composites under an injection pressure of 800 bar.

#### *2.2.4. Mechanical testing*

Tensile and bending tests were conducted with the Universal Testing Machine AG-X plus, Shimadzu, Japan, according to ISO 527-3 and ISO 178, respectively. Notched Izod impact tests were conducted with HIT 50P, Zwick/Roell, Germany, according to ISO 180 at room temperature. Each value obtained represents the average of at least five samples.

#### *2.2.5. Hardness tests*

The hardness determination of the composites was carried out according to ISO 2039-1 on specimens of 80 mm × 10 mm × 4 mm. The specimens were loaded using the force of 132.39 N for a duration of 30 s. Each value obtained represents the average of 10 positions of measurement.

#### *2.2.6. SEM analysis*

Studies on the morphology of fillers and the tensile fracture surfaces of the composites were carried out using a FE-SEM (Ultra 55, Carl Zeiss SMT AG, Germany).
