## 3 Results and Discussion  
X-ray diffraction experiments were performed to reveal structural changes that occur under different processing conditions of the FEP polymer. Figure 1 shows the raw diffraction patterns of virgin (FEP-1), heat-treated (FEP-2), UV-treated (FEP-3), and heat-UV-treated (FEP-4) samples, as well as deconvoluted amorphous and crystalline components for each diffraction pattern, respectively. The reflection of the crystalline component remained at \(\sim\)17.69\({}^{\circ}\) in 2\(\theta\) after different FEP treatment procedures. The size of the crystallite was estimated from the reflex of the main crystalline component at 2\(\theta\) -17.69\({}^{\circ}\) according to the Sherrer equation [25]. Crystallite size values were found to be 235.5 A, 232.8 A, 233.1 A, and 234.9 A for FEP-1, FEP-2, FEP-3, and FEP-4, respectively. The crystalline fraction for FEP-1, FEP-2, FEP-3, and FEP-4 was determined to be 43.7%, 45.0%, 44.0%, and 44.1%, respectively. Unfortunately, the obtained results are not sufficient to reveal the full image of structural changes present in FEP after different treatments and may lead to speculative conclusions about the polymer stability and degradation processes. To reveal the polymer chain reorganization in the FEP structure, the macromolecular orientation texture analysis was performed employing XRD via the pole figure measurements. The intensity of 2\(\theta\) maxima of the crystalline component was measured by moving the sample through \(\psi\) (tilt) azimuth angle and \(\varphi\) (spindle) polar rotations and plotting the measured intensities in the hemisphere-like distribution of scattered intensity via orthographic projection on a pole figure. Figure 2 shows the calculated pole figures for the reflexes of the crystalline components of FEP-1, FEP-2, FEP-3, and FEP-4. It can be clearly seen that the FEP treatment processes significantly affected the structural properties of the polymer, producing different crystalline morphologies. Through the intensity distribution analysis based on k-means clustering, the values of the crystalline fraction (denoted as \(C_{f}\)) were refined and displayed with each pole figure, respectively. To quantitatively estimate the degree of anisotropy from the calculated pole figures, the power spectrum method was employed for the determination of the fractal dimension (\(D_{\rm f}\)). This method is based on the power spectrum dependence of the fractional Brownian motion. Every line intensity profile that forms the pole figure underwent Fourier transform analysis, and the power spectrum was evaluated and averaged. The fractal dimension was calculated from the slope \(\beta\) of a least-square regression line fit to the data points in the log-log plot of the power spectrum as \(D_{\rm f}\) = 7/2 \(-\)\(\beta\)/2. In general, \(D_{\rm f}\) directly correlates with the degree of anisotropy: the lower the \(D_{\rm f}\), the higher the anisotropy. Figure 3 shows the power spectra for the pole figures \(\psi=0^{\circ}\) of FEP-1, FEP-2, FEP-3 and FEP-4, respectively. Based on the analysis of power spectra, the heat treatment of FEP at 200 \({}^{\circ}\)C (FEP-2) affected its structural properties by rearranging crystallites and resulting in the highest degree of anisotropy with a \(D_{\rm f}\) value of 2.64. By contrast, the UV treatment of FEP (FEP-3) resulted in a polymer structure with the lowest degree of anisotropy (\(D_{\rm f}=2.71\)). For virgin FEP-1, \(D_{\rm f}\) was determined to be 2.69, while after heat treatment and UV exposure (FEP-4), it was reduced to 2.67, resulting in a higher anisotropy. The increased anisotropy upon heating can be attributed to the rearrangement and alignment of crystallites facilitated by thermal energy.