# Exploring the Cutting Process of Coaxial Phase Change Fibers under Optical Characterization Tests
## 3 Results
### Chemical Test  
The ATR-FTIR test was used to investigate the characteristic absorption bands of PCFs composed of a CA protective sheath and a PEG 2000 core (Figure 12). The chemical characterization of PCFs has received attention in the literature, as it can present functional groups related to molecular interactions within these PCFs [12]. The peak at 2885 cm\({}^{-1}\) is associated with the C-H stretching vibrations of the methyl (-CH3) and methylene (-CH2-) groups [25]. The peak of 1745 cm\({}^{-1}\) indicates the incorporation of the acetate structure, represented by the C=O stretching vibration of the acetate groups [26]. The 1657 cm\({}^{-1}\) peak corresponds to the C=O stretching vibrations originating from the residual DMF in the PCFs. Meanwhile, the 1465, 1376 and 1368 cm\({}^{-1}\) peaks are linked to the vibrations of the PEG 2000 and acetate groups, representing a deformation of the C-H bonds of the methylene group (-CH2-) [27]. However, peaks 1278, 1238 and 1105 cm\({}^{-1}\) stretch C-O and C-O-C, i.e., ester bonds in cellulose acetate and ether bonds of PEG 2000 [28]. In addition, the peaks at 1047 cm\({}^{-1}\) are related to the stretching of the ether bond (C-O-C), while 939 and 901 cm\({}^{-1}\) represent the polysaccharide nature of PCFs, with the 901 cm\({}^{-1}\) peak attributed to the out-of-plane deformation of the C-O group of esters or other oxygenated groups, indicating the out-of-plane vibration of the glycosidic ring of cellulose structures [28]. Finally, the peak at 835 cm\({}^{-1}\) is attributed to C-O-C stretching vibrations in the ether bonds of the PEG 2000 molecule [25]. After carrying out the spectra of the four PCFs, they were subjected to hot cutting, sealing, controlled washing and drying. After this, the sections were subjected to the ATR-FTIR test to calculate the areas of the respective components [29], where optical absorption can be detected and used to identify different functional groups, and thus, it was expected to check possible PEG leaks. Figure 12: ATR\(-\)FTIR spectra of PCFs. To carry out the next step, the aliphatic functional groups (C-H) (1465 cm\({}^{-1}\) and 1368 cm\({}^{-1}\)), characteristic of PEG 2000, the carbonyl groups (C=O) (1745 cm\({}^{-1}\) and 1657 cm\({}^{-1}\)) and characteristic of CA and DMF, respectively, were represented in boxes in Figure 12. From these representations, calculations of the area index of these functional groups were carried out and presented in Figure 13.  
The bar graphs represent the control group (CG) first, showing the PCF index before the controlled cutting and washing process. Next, the PCFs cut at three different temperatures are presented. The objective of studying the functional group indices was to investigate the possibility of leakage of the PEG incorporated into the PCF core after cutting and controlled washing. When calculating the areas of the respective indices, three key points were observed and discussed. Firstly, the carbonyl group of CA presented a higher index compared to the others due to the abundant presence of CA in the protective sheath of PCFs. Secondly, there was a significant reduction in the presence of DMF, due to the decrease in carbonyl, a positive observation, due to its toxic properties affecting the mechanical properties of PCFs and causing undesirable environmental impacts [12]. Finally, interestingly, the areas of PEG aliphatic groups increased smoothly after the cutting and controlled washing process. This observation can be justified in two ways: firstly, by the formation of stable complexes between PEG and CA [30], resulting in a homogeneous distribution of PEG throughout the CA matrix and avoiding leaks; secondly, the increase can be attributed to the fact that residual DMF can mask the representative PEG bands, and its removal during controlled washing allows for better appearance and enhancement of these bands.