# Exploring the Cutting Process of Coaxial Phase Change Fibers under Optical Characterization Tests
## 1 Introduction  
The need for infrastructures that are resilient to climate change has become a growing challenge for improving the quality of urban life [1]. Due to global warming, the demand for innovative thermal regulation strategies is increasing, as urban heat islands (UHI) [2] and the lack of thermal comfort represent significant challenges as urban cities expand [3]. The heating of asphalt pavements contributes to the formation of UHI, resulting in substantial adverse impacts on the quality of health and life of citizens, thus requiring effective approaches to mitigate temperature extremes [4]. It is, therefore, necessary for the scientific and academic community to aim to develop sustainable and innovative solutions (Figure 1). Amongst the different promising solutions, latent heat thermal energy storage materials (LHTS) [5], commonly called phase change materials (PCMs), stand out among researchers since PCMs take advantage of their latent heat capacity to regulate the temperatures of civil engineering materials [6]. PCM can absorb heat during the hottest hours and release it at night, thus contributing to the thermal regulation of urban environments and improving thermal comfort [7,8]. [PERSON] et al. highlighted that this technology is especially relevant for applications in asphalt pavements, for example, to mitigate the phenomenon of UHI [9]. In contrast, [PERSON] et al. discussed a crucial issue regarding the incorporation of PCMs into civil engineering materials that using traditional methods without any encapsulation method can face negative aspects such as leakage and instability [10]. In response to the various challenges faced by traditional methods with the direct incorporation of PCM [11], the production of co-axial polymeric phase change fibers (PCFs) [12] using the wet-spinning technique [13,14] emerges as an innovative solution to prevent leakage (Figure 2). [PERSON] et al. [15] studied the production of these co-axial fibers, also known as thermoregulatory fibers or PCF, where they have a well-formed sheath-core structure designed to effectively encapsulate PCM in building materials, storing thermal energy during the phase change process and consequently controlling the temperature. A crucial step after producing PCFs is how to cut and seal these fibers so that the PCMs, which are incorporated into the core, do not suffer from leakage and loss of PCF thermal properties. This issue is scarce in the literature and requires attention from researchers, as it is a process that depends on the appropriate cutting procedure and materials to guarantee good protection and performance of PCFs applied in engineering. Cutting Techniques using laser [16], knife [17] and hot cutting [18] are covered in the literature. However, the researchers do not detail the processes nor present leakage results. [PERSON] et al. [18] studied the latter process, called hot cutting, which makes it possible to obtain a higher-performance bond, where the cut is more precise without compromising the integrity of  
Figure 1: Urban heat islands (UHI). (**a**) Thermal effect in urban society. (**b**) The effects of UHI on urban cities. the fiber. In addition, this process incorporates innovative mechanisms that save material and reduce costs. However, it should be noted that the literature does little to address the main limitations and complexities associated with cutting and sealing PCFs. These include concerns about structural integrity, the possible leakage of material from the core with risks of evaporation, material compatibility and impacts on mechanical properties [12]. A major challenge is to check for possible leakage of PCMs from inside PCFs [19]. Laboratory tests such as Fourier transform infrared spectroscopy (FTIR) by calculating the area index of the functional groups, UV-visible spectroscopy and scanning electron microscopy (SEM) are highlighted in the literature to assess PCM leakage.