# Coaxial Fibres Incorporated with Phase Change Materials for Thermoregulation Applications
## 2 Materials and Methods  
### Materials  
The materials used in this work were (i) commercial cellulose acetate (CA, Sigma-Aldrich, St. Louis, MO, USA) powder, with an acetyl content of 39.8 wt. %, average Mn = 30,000 and an acetyl content of 39.8 wt. % by weight, average Mn = 50,000; (ii) N,N-Dimethylformamide (DMF, 99%, Sigma-Aldrich, St. Louis, MO, USA); (iii) N-Methyl-2-pyrrolidone (NMP, 99%, Sigma-Aldrich, St. Louis, MO, USA), (iv) Polyethylene glycol 2,000 H(OCH\({}_{2}\)CH\({}_{2}\))\({}_{\text{n}}\)OH (PEG2000, Thermo Fisher Scientific, Waltham, MA, USA), MP = 53-55 \({}^{\circ}\)C; and (v) dH\({}_{2}\)O. DMF and dH\({}_{2}\)O were used as solvents for the CA and PEG solutions, respectively.  
CA, which is an ester of cellulose acetate and the most common derivative of cellulose, was selected to be the polymeric material of the protective sheath due to its natural and non-toxic characteristics, being a polymer used to produce PCFs that result in good thermal and mechanical properties [24; 35].  
Among the different PCMs available on the market and in the literature, polyethene glycol (PEG), was selected for the core of PCFs as it presents interesting properties such as chemical stability, high storage capacity, a wide temperature range, low overcooling behaviour, and negligible volume change during its phase change [36].  
Regarding the thermal proprieties of the CA and the PEG, Figures 1 and 2 show the TGA and the DSC characterization of the virgin materials under study, respectively. Regarding TGA, studies were carried out on the loss of mass of the virgin materials in relation to the increase in temperature, where the main mass loss phase for PEG2000 starts at \(\approx\)350 \({}^{\circ}\)C and ends at \(\approx\)430 \({}^{\circ}\)C. For commercial CA and CAt, the main mass loss phase starts at \(\approx\)315 \({}^{\circ}\)C and ends at \(\approx\)350 \({}^{\circ}\)C.  
Figure 1: TGA of virgin materials obtained from 25 to 500 \({}^{\circ}\)C under a nitrogen atmosphere, flow rate of 200 mL/min, and temperature rise of 10 \({}^{\circ}\)C/min.  
Figure 2: DSC of virgin materials: (**a**) CA (Mn 30,000); (**b**) CA (Mn 50,000); (**c**) recycled CAtz (**d**) PEG2000.  
In DSC measurements, multiple peaks are observed, a phenomenon not evident in TGA analysis results. The initial two endothermic peaks correspond to melting, as these events do not involve any mass loss. Consequently, these events are not visible in the TGA. In DSC curves, the third thermal effect (above 300 \({}^{\circ}\)C), characterized by irregular peaks and where the baseline is no longer maintained, corresponds to and corroborates degradation, as observed in the TGA results. The fact that the temperatures are not exactly the same is due to the experimental conditions. While the DSC measurements are performed in hermetically closed pans, the TGA analysis is carried out in an open crucible. Consequently, they reveal that the degradation event can start at lower or higher temperatures, as the samples may adsorb any water, for example.  
For the DSC, the peaks, phase change temperatures, and comparison of the PCFs with the H were analysed. In this test, the virgin materials produced results that were expected and in accordance with the literature.  
For the synthesis of the Cat, 100% cotton fabric (from Nostrobiz, Guimaraes, Portugal), glacial acetic acid (CH3 COOH, 100%, Pronolab, Lisbon, Portugal), sulphuric acid (H2 SO4, 95-98%, Sigma-Aldrich) and acetic anhydride ((CH3 CO)2O, 98%, [PERSON], Emmendingen, Germany) were used. Sodium hydroxide (NaOH, JMGJS, Odivelas, Portugal), ethanol absolute (CH3 CH2 OH, 99.5%, Merck, Rahway, NJ, USA), hydrochloric acid (HCl, 37%, Fisher Scientific), sodium hydroxide solution (NaOH, 0.25 mol/L, JMGS), hydrochloric acid solution (HCl, 0.25 mol/L, Fisher Scientific), and phenolphthalein (C20H14O4, [PERSON]) were used to determine the degree of substitution of CAt.