## 2 Experimental
### Methods  
Extrusion of the pristine PCL and granulated PCL composites was performed at the following temperatures of particular cylinder zones of the co-rotating twin screw extruder:  
Figure 1: SEM image of hemp fibers (HF) structure. 140 \({}^{\circ}\)C, 150 \({}^{\circ}\)C, 160 \({}^{\circ}\)C and 165 \({}^{\circ}\)C. The temperature of the extrusion die head was 160 \({}^{\circ}\)C and the screw rotational speed was constant at 250 min\({}^{-1}\). The screws were in a specific configuration that facilitated adequate dispersion and distribution of HF in the PCL matrix. Moreover, the screws consisted of elements providing intensive HF grinding to obtain fine fractions. Prior to extrusion, HF was dried at 110 \({}^{\circ}\)C for 24 h. PCL was not subjected to drying. Free degassing of any possible released residual moisture was applied at the screws with lengths of L/D = 22 and L/D = 32, respectively. PCL and HF were introduced into the extruder from volume feeders in such proportions that PCL composites with HF contents equal to 2.5, 5, 10 and 20 wt% were obtained. The percentages of fibers added were chosen based on our previous studies [52; 53]. The extrudate was cooled in a water bath at 15 \({}^{\circ}\)C and then dried on a conveyor belt in a stream of dry air and finally granulated. The obtained composites in the form of cylindrical granules (height 5 mm and base diameter 3 mm) were dried at 50 \({}^{\circ}\)C for 24 h to eliminate residual moisture. The prepared samples of the granulated composites were denoted as CF2.5, CF5, CF10 and CF20, where C denotes poly(\(\varepsilon\)-caprolactone), F denotes natural hemp fibers and the numbers represent the fibers percentage content. A reference sample, made of the pristine PCL, was also prepared and denoted as C. During extrusion, basic parameters that include the following were recorded: (i) extruder motor torque (M), (ii) energy consumption (E) by the extruder drive system, (iii) temperature (T) of the material being processed that is measured in the extruder die-head and (iv) pressure (P) of the material being processed that is measured in the extruder die-head. The dumbbell-shaped and bar-shaped specimens were prepared according to a relevant standard (PN-EN ISO 527-2:2012) using a screw injection molding machine (Battenfeld Plus 35/75). The temperatures of the plasticising zones I and II of the barrel were 130 \({}^{\circ}\)C and 140 \({}^{\circ}\)C, respectively, and the temperature of the injection molding die head was 140 \({}^{\circ}\)C. The temperature of the injection mold was 23 \({}^{\circ}\)C and the injection pressure was 157-163 MPa dependent on the kind of composite. The screw rotational speed was constant at 150 min\({}^{-1}\). Sample irradiation was carried out with a linear accelerator type Elektronika 10/10 producing scanned beam of electrons with energy of 10 MeV and of 10 kW power with the possibility of changing the dose rate by controlling the speed of the conveyer. The accelerator is located at the Institute of Nuclear Chemistry and Technology in Warsaw, Poland. The samples (granulated samples and injection-moulded pieces) were irradiated with doses of 10, 20, 40, 60 or 90 kGy. Maximum single doses were 20 kGy. This limitation was caused by an increase in temperature of the irradiated material that was equal to ca. 4-7 \({}^{\circ}\)C for single doses of 10 kGy. Large single doses cause intensive heating of the material, therefore some additional structural changes may occur. Thus, samples were irradiated with lower doses multiple times. During the irradiation procedure, all the granulated samples and moulded pieces were placed in aluminium containers in single layers of the thickness of up to 2 cm. The containers were put on the conveyor belt moving at the speed of 0.3-1.2 m/min under the accelerator scanner. The actual speed was related to the radiation dose absorbed by the polymer material being modified.