## 3 Results and Discussion
### Mechanical Properties  
The mechanical properties test results of non-modified PCL and PCL/HF composites, as well as irradiated PCL and irradiated PCL/HF composites are illustrated in 3D three-dimensional graphs (Figures 4-7) and summarized in Table 2. The three-dimensional graphs (3D) were made using STATISTICA version 10.0 software (StatSoft). Figure 4: Tensile strength results. Figure 5: Elongation at break results. Figure 6: Flexural modulus results. The data from Figure 4 indicates that the tensile strength (\(\sigma_{\rm M}\)) for PCL significantly decreases when the dose of electron radiation is 60 or 90 kGy. The decrease is 3% and 13%, respectively. Smaller doses of irradiation do not affect the \(\sigma_{\rm M}\) of that polymer. Other dependencies can be observed in the case of non-irradiated composites containing HF. In their case, the \(\sigma_{\rm M}\) initially decreases with the rising HF content and then increases. In Figure 4 there is a clear extreme of strength, the lowest value of which can be observed in the 10% HF content composite. When compared to pristine PCL, filling composites with 10% HF causes a decrease in \(\sigma_{\rm M}\) by 27%. Larger amounts of HF do not cause a further decrease in \(\sigma_{\rm M}\), but they are the reason for its increase of 20%, compared to the CF10 sample. However, the \(\sigma_{\rm M}\) value of the non-irradiated CF20 composite is not larger than the \(\sigma_{\rm M}\) value of any PCL sample irradiated with doses ranging from 10 to 90 kGy and it is at most equal to the strength of the PCL irradiated with the dose of 90 kGy. Similar observations are seen in the case of irradiated PCL/HF composites, i.e., for a given dose, as the content of HF in polymer matrix increases, the \(\sigma_{\rm M}\) initially decreases and then increases. However, in this case, the minimum \(\sigma_{\rm M}\) value of irradiated composites depends on the irradiation dose. For doses of 10, 20 and 40 kGy, the minimum occurs in composites with 10% HF filling. In the case of doses of 60 and 90 kGy, the minimum occurs in composites containing 5% HF. Moreover, in composites containing 10 or 20% HF, an increase in \(\sigma_{\rm M}\) with an increasing dose is observed, which is not observed in composites with smaller fiber content. Elongation at break (\(\epsilon_{\rm B}\)) results for the same samples analysed in \(\sigma_{\rm M}\) tests are presented in Figure 5.  
Figure 5 shows that both types of modification applied (irradiation and/or addition of HF) significantly reduces the \(\epsilon_{\rm B}\) value. Elongation decreases both as the electron radiation dose increases and when HF content increases and especially when both of these factors occur simultaneously. Elongation is least influenced by electron radiation, which reduces its value by a maximum of 17% for samples irradiated with 90 kGy. The decrease in elongation at break following electron radiation may result from elongation of the macromolecules due to mutual linking at chain ends or the formation of branched structures in notable amounts [50]. HF induces a significantly higher effect on the \(\epsilon_{\rm B}\) value, where a maximum decrease of 95% is noted. The highest influence on the \(\epsilon_{\rm B}\) value of the studied polymer is the combined action of electron radiation and HF, which reduces \(\epsilon_{\rm B}\) by as much as 99%. There is, at least, a 100 times decrease in the \(\epsilon_{\rm B}\) value in comparison to non-modified PCL and this occurs in composites with 20% HF content and that were irradiated with doses of 40, 60 or 90 kGy. The data in Figure 6 indicates that electron radiation in a dose of 90 kGy causes a growth in PCL's flexural modulus (M\({}_{\rm f}\)) value by up to 13%. Smaller doses cause similar increases where the growth is ca. 11-12%. The flexural modulus of PCL/HF composites increases as the HF content increases. This rate of growth can be considered an exponential function, i.e., at low HF concentration (2.5 or 5%) the modulus increases slightly.