# Coaxial Fibres Incorporated with Phase Change Materials for Thermoregulation Applications
## 4 Conclusions  
In this study, an innovative approach was used to produce coaxial fibres using the wet spinning technique. These fibres were composed of cellulose acetate (CA) in the sheath, with different molecular weights and concentrations, while the core was made up of polyethylene glycol 2000 (PEG2000) with different concentrations and ejection speeds. The research aimed to improve the thermal properties of these fibres for potential applications in civil engineering. Chemical, thermal and mechanical tests were conducted to investigate the presence and impact of PEG2000 on the fibres. The results confirmed the successful production of coaxial fibres (PCFs) and the synthesis of recycled cellulose acetate (CAt). Microscopic analyses, including bright-field microscopy and scanning electron microscopy (SEM), differentiated between the core and the sheath, confirming the existence of coaxial fibres. Despite the challenges in confirming the presence of PEG2000 by SEM due to its liquid state, ATR-FTIR analyses showed representative peaks for CA, CAt and PEG2000 in all PCFs. Thermal tests (TGA and DSC) confirmed the presence of PEG2000, with the CA sheath influencing the displacement of the phase change peak and the decrease in PEG2000 enthalpy. The mechanical tests revealed varied performance between the fibres, with PCF_30_30 exhibiting superior tensile properties. The presence of PEG2000 was shown to improve the fibres' performance in terms of tension. As a next step, we suggest optimising wet spinning production systems to produce a more uniform fibre morphology and structure, exploring alternative solvents, using coagulation baths, and addressing drying processes to avoid mass loss at high temperatures. These improvements aim to enhance fibre consistency, which is fundamental for civil engineering applications that require a phase change between 50 and 60 \({}^{\circ}\)C.  
The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app14062473/s1](https://www.mdpi.com/article/10.3390/app14062473/s1)]([https://www.mdpi.com/article/10.3390/app14062473/s1](https://www.mdpi.com/article/10.3390/app14062473/s1)), Table S1: Qualitative analysis of the production of the fibres. Conceptualisation, N.H. and N.C.H. ; methodology, I.R.S. and N.C.H. ; software, N.H., C.P. and M.M.S. ; validation, J.A.O.C. ; formal analysis, N.H., I.R.S., N.C.H. and H.P.F. ; research, N.H., I.R.S. and J.A.O.C. ; resources, H.P.F., M.F.M.C. and J.A.O.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, C.P., I.R.S., N.C.H., M.M.S., H.P.F., G.M.B.S., E.F., M.F.M.C. and J.A.O.C. ; visualisation, I.R.S. and N.C.H. ; supervision, I.R.S., M.F.M.C. and J.A.O.C. ; project administration, M.F.M.C. and J.A.O.C. ; acquisition of funding, M.F.M.C. and J.A.O.C. All authors have read and agreed to the published version of the manuscript. This research was funded by the Portuguese Foundation for Science and Technology (FCT) under the projects MicroCoolPav EXPL/EQUEQUEQU/1110/2021 and NanoAir PTDC/FISMAC/6606/2020 ([[https://doi.org/10.54499/PTDC/FIS-MAC/6606/2020](https://doi.org/10.54499/PTDC/FIS-MAC/6606/2020)]([https://doi.org/10.54499/PTDC/FIS-MAC/6606/2020](https://doi.org/10.54499/PTDC/FIS-MAC/6606/2020))) and within the framework of Strategic Funding UIDB/04650/2020, UIDB/04029/2020 ([[https://doi.org/10.54499/UIDB/04029/2020](https://doi.org/10.54499/UIDB/04029/2020)]([https://doi.org/10.54499/UIDB/04029/2020](https://doi.org/10.54499/UIDB/04029/2020))) and UID/QUI/0686/2020. I.R.S. and H.P.F.