# Exploring the Cutting Process of Coaxial Phase Change Fibers under Optical Characterization Tests
## 4 Conclusions  
In this study, an innovative approach was used to test the cutting and sealing of the ends of PCFs produced by the wet-spinning technique. These fibers were composed of cellulose acetate (CA, Mn 50,000) in the sheath, while the core was composed of PEG 2000; only the PEG ejection velocities varied. The main objective of the research was to evaluate the possible leakage of PEG from the PCF core using three different cutting and sealing temperatures. Optical and chemical tests were performed to investigate the presence and leakage of PEG 2000. Initial results obtained by brightfield microscopy confirmed the presence of a well-formed nucleus in PCFs. Among the cutting temperatures tested, 50 \({}^{\circ}\)C showed the smallest chips and sealed ends, according to the literature. To highlight PEG leaks, the calculation of the FTIR indices of the respective functional groups of the materials was analyzed. The PEG interacts molecularly with the CA and forms groups that are retained in the protective sheath of the PCFs, the DMF is also removed, which makes the PEG areas more evident. UV-VIS spectroscopy analyses showed that, although the absorbances are quite similar for the three types of cuts, the cut at 50 \({}^{\circ}\)C presented the lowest presence of materials in the baths, evidenced by the lowest absorbance value among the three. However, due to the overlap of the absorbance curves of DMF and PEG in the same UV domain, it is not possible to confirm with certainty that the leakage exclusively involves PEG. Knowing that the objective of this work was to evaluate the cutting and sealing of PCFs to prevent PEG leakage for applications in civil engineering materials, it is planned to encapsulate the PEG to improve the thermal properties without compromising the mechanical characteristics of the composite materials. In other words, the PCFs must undergo a more automated cutting process to obtain a large volume of material for an application in a real context. For example, the fibers could already be manufactured and simply applied to building materials, as is the case with various additives that are widely used. In relation to better visualization of the cuts and seals, the SEM test may be carried out. Furthermore, the presence of residual DMF complicates the analysis. In future work, a thermal test below the phase change temperature of PEG 2000 could be performed to evaporate the residual DMF and extend the pre-drying time. Another future analysis will be to test PEG 2000 combined with a fluorimeter to measure fluorescence or use PEG linked to modified chemical agents as a detection probe, potentially shifting the absorbance peak to wavelengths different from those coinciding with other components. Finally, it will be possible to study the degradation of PCFs to verify whether, over time, the CA will degrade to the point of contributing to PEG leakage. Therefore, studies using ultraviolet light, solutions with a more acidic pH and weathering can be carried out. Conceptualisation, N.H.; methodology, I.R.S. and H.P.F. ; software, N.H., J.M. and C.P. ; validation, J.C.; formal analysis, N.H., I.R.S. and H.P.F. ; research, N.H., I.R.S. and J.C.; resources, H.P.F., M.F.M.C. and J.C.; data curation, N.H., C.P. and M.F.M.C. ; preparation of the original draft, N.H.; revision and editing of the writing, J.M., C.P., I.R.S., H.P.F., G.M.B.S., M.F.M.C. and J.C.; visualisation, I.R.S. and H.P.F. ; supervision, I.R.S., M.F.M.C. and J.C.; project administration, M.F.M.C. and J.C.; acquisition of funding, M.F.M.C. and J.C. All authors have read and agreed to the published version of the manuscript.