Photoluminescent PLLA/PET Electrospun Nanofiber Yarns with Sheath/Core Architecture: A Strategy to Preserve Tensile Properties

Photoluminescent PLLA/PET Electrospun Nanofiber Yarns with Sheath/Core Architecture: A Strategy to Preserve Tensile Properties | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Photoluminescent PLLA/PET Electrospun Nanofiber Yarns with Sheath/Core Architecture: A Strategy to Preserve Tensile Properties Rouhollah Semnani Rahbar, Homa Maleki This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7447165/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 10 You are reading this latest preprint version Abstract A sheath/core electrospinning system was employed to fabricate luminescent poly(L-lactic acid) (PLLA) electrospun nanofiber yarns as the sheath, with microfilament poly(ethylene terephthalate) (PET) yarns serving as the core. To achieve this, varying amounts of strontium aluminate (SrAl 2 O 4 : Eu²⁺, Dy³⁺) phosphorescent particles (SAOED) were incorporated into the PLLA matrix. Additionally, (PLLA–SAOED)/PET electrospun nanofiber yarns with different twist levels were also produced. The morphology, crystalline structure, thermal behavior, tensile properties, and luminescent characteristics of the resulting yarns were systematically investigated. SEM images showed that average nanofiber diameter decreased from (661.26±96.10) nm for pure PLLA electrospun nanofiber yarns to (419.18±65.39) nm for PLLA containing 5% SAOED. Correspondingly, the overall yarn diameter also decreased as the SAOED concentration increased, showing a maximum 37% reduction. Thermal analysis revealed that increasing the SAOED content had negligible effects on the thermal properties of the fibers. Tensile tests demonstrated that the incorporation of SAOED particles did not significantly compromise the tensile properties of the (PLLA–SAOED)/PET yarns, with values comparable to those of the non-loaded samples. Moreover, Upon UV light exposure, all luminescent yarn samples emitted a strong green phosphorescent band. The afterglow intensity of the yarns was significantly influenced by both SAOED content and twist level, with higher luminescence observed at increased SAOED loading and lower twist levels. These results suggest that luminescent PLLA nanofiber yarns can be successfully fabricated via sheath/core electrospinning strategy without sacrificing mechanical integrity, highlighting their potential for applications in biomedical engineering, smart textiles, and other advanced functional materials. Sheath/core electrospinning system Luminescent characteristics Tensile properties Poly(L-lactic acid) Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 1. Introduction Luminous nanofibers have attracted increasing interest in recent years due to their potential applications in a wide range of fields, including lighting, nerve regeneration, tissue engineering, anti-counterfeiting technologies, optoelectronics, catalysis, and wearable electronics [ 1 – 5 ]. These nanofibers can be fabricated using various techniques such as electrospinning, centrifugal spinning, and sol-gel modification [ 1 , 6 , 7 ]. Polylactic acid (PLA) is a widely used biodegradable polymer that has been extensively investigated for biomedical applications due to its biocompatibility, renewability, and processability [ 8 – 10 ]. PLA nanofibers, particularly those produced via electrospinning, have garnered attention because of their high surface area, porosity, and potential for functionalization [ 11 – 13 ]. A promising strategy to enhance the functionality of PLA nanofibers is the incorporation of luminescent additives. Photoluminescent materials such as carbon quantum dots [ 14 ], CdTe quantum dots [ 15 ], and alkaline-earth metal aluminates [ 16 ] have been incorporated into PLA matrices to create photoluminescent nanofibers with potential applications in lighting, bioimaging, biosensing, drug delivery, and tracking [ 17 ]. Recent studies have investigated various luminescent materials-including perovskite quantum dots, lanthanide-based compounds, and organic-inorganic hybrids-for the fabrication of luminous nanofibers [ 6 , 7 , 18 ]. Among them, strontium aluminate doped with europium and dysprosium (SrAl 2 O 4 : Eu²⁺, Dy³⁺, abbreviated as SAOED) has received considerable attention due to its high luminous efficiency, color tunability, long afterglow, stability, and environmental safety [ 19 ]. SAOED can be excited by visible or ultraviolet light and continues to emit light in the dark for an extended period after excitation. These particles have been incorporated into various polymer matrices to develop luminescent fibers, fabrics, and composites [ 20 – 24 ]. Ye et al. [ 16 , 25 ] fabricated long-persistent luminescent PLA nanofibers via electrospinning using Sr 2 MgSi 2 O 7 : Eu², Dy³⁺ and Ca 2 MgSi 2 O 7 : Eu²⁺, Dy³⁺, reporting uniform dispersion of the luminescent particles in the PLA matrix. Although the luminescent fibers exhibited similar decay behavior to that of the pure luminescent powders, the emission intensity was somewhat reduced. However, these studies did not evaluate the impact of luminescent particle incorporation on the mechanical properties of the PLA fibers. In another study, composite fibers containing europium complexes were fabricated via electrospinning, and the europium complexes were found to be distributed as irregular crystalline domains (150–300 nm), resulting in bright red fluorescence under UV illumination [ 26 ]. Ni et al. [ 27 ] prepared PLA/SAOED composites using a solvent casting method. To improve interfacial compatibility, a silane coupling agent was used. While composites containing 15 wt.% SAOED exhibited optimal luminescent performance, mechanical properties deteriorated with increasing SAOED content. The most favorable balance of mechanical and optical properties was achieved at 5 wt.% SAOED. Similar surface modification strategies have been employed with other luminescent fillers, such as MgAl₂O₄: Eu, to enhance mechanical performance in PLA-based systems [ 28 ]. To the best of our knowledge, no prior studies have reported the fabrication of PLLA/SAOED electrospun yarns. The present work aims to fill this gap by developing and characterizing luminescent PLLA/SAOED electrospun nanofiber yarns. One of the key challenges in incorporating inorganic fillers into PLLA nanofibers is the associated decline in mechanical performance. To address this, we employed a sheath/core electrospinning configuration, in which the PLLA/SAOED nanofibers serve as the sheath (the luminescent component), while a microfilament poly(ethylene terephthalate) (PET) yarn functions as the core to maintain the mechanical integrity of the composite yarn. 2. Materials and Methods 2.1. Materials Phosphor strontium aluminate (SrAl 2 O 4 : Eu²⁺, Dy³⁺) particles (SAOED) were purchased from Sigma-Aldrich Ltd. (product code: 756539). Poly(l-lactide) (intrinsic viscosity of 2.51 dL/g) was supplied from Purac Biomaterials, Netherlands. 2,2,2-Trifluoroethanol (TFE) (Merck, Germany) was selected as a solvent and used without subsequent purification. PET microfilament yarn (100 den/144 filaments) was kindly provided by Behkoosh Co., Iran. 2.2. Preparation of Polymer Solutions and Electrospinning Process The detailed procedures for the preparation of polymer solutions and the electrospinning process parameters have been previously reported in our earlier publication [ 29 ]. In this study, electrospun PLLA/SAOED nanofibers were fabricated with varying SAOED concentrations of 2 wt.%, 3.5 wt.%, and 5 wt.%. For all these samples, the twist level was constant at 4000 turns per meter (TPM). Additionally, to investigate the effect of twist on photoluminescence properties of yarns, (PLLA–SAOED)/PET electrospun nanofiber yarns containing 5 wt.% SAOED were also produced with two other twist levels: 2000 TPM and 7000 TPM. A schematic of the production of luminous fiber and fabric is shown in Fig. 1 . 2.3. Characterization The morphology and chemical compositions of nanofibers and electrospun nanofiber yarn surfaces were studied using a scanning electron microscope with an energy-dispersive X-ray spectroscopy (EDX) (SEM; TESCAN VEGA, TESCAN Ltd., Czech Republic). The samples were coated with a thin layer of gold under vacuum before SEM observation at an acceleration voltage of 30 kV. From at least 5 SEM images of each sample, nanofiber and yarn diameters were determined using Digimizer 4.1.1.0 software. Confocal Laser Scanning Microscopy (CLSM) was performed by Leica, TCS SPE (Leica Microsystems Inc.) equipped with LAS X Software program. The samples were excited by solid state laser and high-resolution images were obtained. Fluorescent optical microscopy images were taken using a BK-FL4 microscope (Drawell, China). The irradiation source was a UV fluorescence illuminator. Thermal characteristics of electrospun nanofiber yarns were analyzed by differential scanning calorimetry (DSC; DSC 2010 machine, TA Instruments, New Castle, DE). The heating and cooling rates were 10 °C/min under nitrogen atmosphere. The crystallinity of samples (Xc) was calculated using the following equation: Where ∆H f is the heat of fusion of the analyzed sample (J/g), ΔHcc is the cold crystallization enthalpy induced during DSC test, and ∆H f 0 is the heat of fusion for a 100% crystalline PLLA polymer, it was taken as 93.7 J/g [ 30 ]. The wide angle X-ray diffraction (WAXD) patterns of the fibers were collected at a voltage of 40 kV and current of 30 mA using EQUINOX 3000 X-ray diffractometer (Inel, France, Cu Kα λ = 0.1540 nm). The scattering intensities were recorded every 0.04 ◦ in the 2θ of 5-110 ◦ . Tensile properties of electrospun yarns were examined using a universal testing machine (Gotech Co.). From stress-strain curves, tenacity and breaking elongation were evaluated. The cross-head speed of 50 mm/min and initial length of 50 mm were fixed for all samples. At least 10 specimens from each sample were tested, and the values were averaged. Fourier Transform Infrared (FTIR) analysis of electrospun nanofiber yarns was carried out using VERTEX 70 (Bruker, Germany) in the wavenumber range of 4000 − 400 cm − 1 . An average of 40 scans was recorded in the transmission mode. Photoluminescence spectroscopy (PL) was conducted to investigate the luminescence properties of luminous electrospun nanofiber yarns using a Perkin Elmer fluorescence spectrophotometer (model LS55). The samples were excited under ultraviolet light (UV) at 380 nm, and emission spectra representing the amount of reflection were plotted in the range of 400–700 nm. 3. Results and discussion 3.1. Surface morphology The surface morphology of photoluminescent nanofiber yarns-comprising a conventional PET core enveloped by electrospun (PLLA-SAOED) nanofibers with varying SAOED concentrations was examined using scanning electron microscopy (SEM). Representative SEM micrographs of both individual nanofibers and twisted yarn configurations are presented in Fig. 2 . Across all samples, regardless of SAOED content, the nanofibers exhibited continuous, bead-free, and uniform structures, indicating that the electrospinning parameters were effectively optimized. Pure PLLA nanofibers (0% SAOED) displayed a smooth, cylindrical morphology (Fig. 2 a). As the SAOED concentration increased, crystalline SAOED particles became progressively more evident on or near the fiber surfaces, as observed in the SEM images. Importantly, no fiber breakage, discontinuities, or substantial particle agglomeration were detected, suggesting effective dispersion of the SAOED particles and favorable compatibility within the PLLA matrix (Figs. 2 b– 2 d). Additionally, the absence of defects such as fiber fusion or localized thickening further supports the conclusion that particle distribution remained uniform and stable throughout the electrospinning process. The twisted yarn configurations exhibited coherent and uniform structures, characterized by consistent fiber alignment and evenly distributed twists across all SAOED concentrations. SEM analysis revealed that the majority of nanofibers were oriented at an angle relative to the yarn axis, reflecting the directional alignment induced by the applied twist during yarn formation (Fig. 2 c). This organized fiber orientation contributes to both the structural integrity and the uniform visual appearance of the electrospun yarns. Quantitative analysis of the fiber diameters indicated a statistically significant decrease with increasing SAOED concentration (p < 0.05). The average fiber diameter decreased from (661.26 ± 96.10) nm for pure PLLA to (419.18 ± 65.39) nm for PLLA containing 5 wt.% SAOED. Intermediate values were recorded for PLLA with 2 wt.% SAOED (521.75 ± 78.82 nm) and 3.5 wt.% SAOED (505.16 ± 69.47 nm). Correspondingly, the overall yarn diameter also decreased as the SAOED concentration increased. Specifically, the average yarn diameter reduced from (1447.91 ± 25.94) µm at 0 wt.% SAOED to (906.01 ± 10.22) µm at 5 wt.% SAOED, representing an approximate 37% reduction. This significant decrease in bulk yarn size is attributed to the combined effects of reduced fiber diameters and enhanced fiber compaction, promoted by the twisting mechanism during the electrospinning of sheath/core yarns. The twisting process likely contributes to this trend by applying axial tension, thereby increasing fiber packing density. Further SEM analysis of the fractured ends of the electrospun sheath/core yarns distinctly revealed the coexistence of PET microfilaments and PLLA nanofibers within the same structure (Fig. 3 ). The preserved integrity of both individual fibers and twisted yarns across all SAOED concentrations is particularly advantageous for applications requiring both photoluminescence and mechanical durability. The consistent sheath/core configuration ensures that the PET microfilament provides mechanical reinforcement, while the outer (PLLA-SAOED) layer imparts photoluminescent functionality. This robust interface between the core and sheath components is critical for maintaining the overall yarn strength while enabling multifunctional performance. The elemental composition of SAOED in the luminous (PLLA–SAOED)/PET electrospun yarns was analyzed using energy-dispersive X-ray spectroscopy (EDX), with the results presented in Fig. 4 and Table 1 . The EDX spectra confirmed the presence of carbon (C), oxygen (O), aluminum (Al), strontium (Sr), europium (Eu), and dysprosium (Dy). As expected, C and O were the dominant elements in the neat PLLA/PET electrospun yarn, reflecting the polyester-based composition of both PLLA and PET. In contrast, the EDX spectrum of the luminous (PLLA–SAOED)/PET electrospun yarn displayed pronounced peaks corresponding to Al, Sr, Eu, and Dy, providing direct evidence of the successful incorporation of SAOED particles within the electrospun nanofiber matrix. Table 1 The elements (wt.%) of neat PLLA/PET and luminous (PLLA-SAOED)/PET electrospun yarns were determined by EDX SAOED particle content (wt.%) C O Al Sr Eu Dy Neat PLLA/PET (0%) 49.99 50.01 --- --- --- --- 2 48.22 49.62 0.88 0.68 0.35 0.28 3.5 43.62 53.73 1.03 0.83 0.46 0.33 5 44.93 51.73 1.24 1.05 0.57 0.48 3.2. Crystalline structure The wide-angle X-ray diffraction (WAXD) profiles of the neat PLLA/PET and luminous (PLLA–SAOED)/PET electrospun yarns are shown in Fig. 5 . As observed, none of the samples exhibited sharp diffraction peaks, indicating a predominantly amorphous structure. However, a broader diffraction peak was recorded for the luminous (PLLA–SAOED)/PET samples compared to the neat PLLA/PET yarn. Specifically, the peak intensity at 2θ = 16.9°, corresponding to the α-crystalline form of PLLA and assigned to the (200)/(110) diffraction planes [ 31 ], decreased with the incorporation of SAOED particles into the PLA matrix. The broad nature of the peak centered at 2θ = 16.9° is commonly attributed to the rapid solvent evaporation during the electrospinning process, which limits the time available for molecular chains to arrange into well-defined crystalline domains [ 29 ]. Additionally, previous studies have suggested that electrospun PLA fibers may contain a mesophase characterized by highly oriented chains lacking a fully developed crystalline structure. Importantly, the diffraction patterns of the (PLLA–SAOED)/PET electrospun yarns reveal that the crystalline structure of PLLA remains largely unaffected by the addition of SAOED at concentrations ranging from 2 to 5 wt.%. This observation is consistent with the thermal analysis results (Table 2 ), which show a slight decrease in crystallinity in the SAOED-loaded samples, thereby corroborating the WAXD findings. 3.3. Thermal analysis Figure 6 shows DSC thermograms of neat PLLA/PET and luminous (PLLA-SAOED)/PET electrospun yarns. The glass transition temperature (T g ), cold crystallization temperature (T cc ), cold crystallization enthalpy (∆H cc ), melting temperature (T m ), melting enthalpy (∆H m ), crystallization temperature (T c ), crystallization enthalpy (∆H c ), and degree of crystallinity (X c ) of the samples were obtained from DSC analysis and summarized in Table 2 . Figure 6 indicates that neat neat PLLA/PET and luminous (PLLA-SAOED)/PET electrospun yarns have the same thermal trend; the T g followed by the T cc and T m peaks, which are common for heating curves of PLA (Fig. 6 a). It can be observed from Table 2 that the T g of the luminous (PLLA-SAOED)/PET electrospun yarns changed remarkably compared with that of the neat PLLA/PET electrospun yarn. A similar trend was also recorded for the T cc , in which T cc for neat PLLA/PET electrospun yarn increased from 73.49 to 80.81 for the luminous (PLLA-SAOED)/PET electrospun yarn containing 5 wt.% SAOED. This may be related to molecular chain restriction in the presence of SAOED particles. In contrast, T m of PLLA/PET electrospun yarns did not change upon incorporation of SAOED particles. Data in Table 2 reveals that melting enthalpy and crystallinity of neat PLLA/PET decreased with addition of SAOED particles in the luminous (PLLA-SAOED)/PET electrospun yarns, suggesting that SAOED particles play an obstacle role to PLA crystallization, mainly due to the restriction in the molecular chain movements. It should be noted that although PLA crystallinity decreased in the presence of SAOED particles, the crystallinity of luminous (PLLA-SAOED)/PET samples did not change significantly when the content of SAOED increased. Table 2 Thermal characteristics of neat PLLA/PET and luminous (PLLA-SAOED)/PET electrospun yarns with 2–5 wt.% SAOED SAOED particle content (wt.%) T g T cc ∆H cc T m ∆H m T c ∆H c Crystallinity Neat PLLA/PET (0%) 62.62 73.49 10.00 182.26 29.49 104.14 8.87 20.80 2 65.51 78.26 6.58 182.31 22.74 106.04 14.07 17.24 3.5 68.83 79.74 6.88 183.09 21.66 107.34 14.46 15.77 5 70.07 80.81 6.25 182.68 21.56 111.28 11.87 16.33 3.4. Spectroscopy Figure 7 Shows FTIR spectra of neat PLLA/PET electrospun yarn and luminous (PLLA-SAOED)/PET electrospun yarns containing different amounts of SAOED particles. As can be observed in Fig. 7 , these particles show a characteristic peak at 420 cm − 1 which could correspond to O-Al-O symmetric stretching. This peak was not detectable in the neat PLLA/PET electrospun yarn and became more intense when the content of SAOED particles increased, confirming the presence of SAOED particles in the luminous (PLLA-SAOED)/PET electrospun yarns. 3.5. Afterglow characteristics Figure 8 presents the emission spectra of luminous (PLLA–SAOED)/PET electrospun yarns. All samples exhibited a broad and intense emission band within the visible region, with a maximum emission peak centered at 526 nm, corresponding to green light. The intensity of the afterglow emission increased with rising SAOED content, with the sample containing 5 wt.% SAOED demonstrating the most pronounced green afterglow. This emission is attributed to two distinct strontium sites within the SrAl₂O₄ crystal lattice, which are known to contribute to persistent luminescence in the green region [ 32 , 33 ]. A comparison of afterglow behavior among (PLLA–SAOED)/PET electrospun yarns with different twist levels revealed that the sample twisted at 7000 TPM exhibited lower afterglow intensity compared to those twisted at 2000 TPM and 4000 TPM. This reduction in luminescence may result from a more compact yarn structure at higher twist levels, which could hinder the effective excitation of embedded SAOED particles under UV irradiation. Additionally, the yarn formation process at elevated twist levels may lead to the partial expulsion of SAOED particles from the fiber surface, thereby reducing the overall SAOED content and consequently diminishing the afterglow intensity. Visual evidence supporting this explanation is provided in Fig. 9 , where the yarn twisted at 4000 TPM displays a visibly more intense green luminescence than the yarn twisted at 7000 TPM. These results suggest that an optimal twist level is critical to balancing mechanical integrity and luminescent performance in (PLLA–SAOED)/PET electrospun yarns. Figure 10 displays fluorescence microscopy and confocal microscopy images of the luminous (PLLA–SAOED)/PET electrospun yarn containing 5 wt.% SAOED, captured after excitation under UV irradiation. As evident, the fibers emitted a strong green luminescence, consistent with the emission peak observed at 526 nm in the photoluminescence spectra (Fig. 8 ). The uniform green color throughout the image suggests a homogeneous dispersion of SAOED particles within the PLA matrix, indicating effective incorporation during electrospinning. Additionally, the images confirm that the luminous (PLLA–SAOED) nanofiber sheath was uniformly and securely wrapped around the PET multifilament core, supporting the structural integrity of the sheath/core configuration. 3.6. Tensile Properties The tenacity and elongation at break of neat PLLA/PET and luminous (PLLA–SAOED)/PET electrospun yarns are presented in Fig. 11 . A primary objective of this study was to fabricate luminous PLLA-based nanofiber yarns without compromising their mechanical performance. As shown in Fig. 11 , the incorporation of SAOED particles into the PLLA matrix did not result in significant changes to the tensile properties. The mechanical performance of the luminous (PLLA–SAOED)/PET electrospun yarns remained within acceptable limits, demonstrating that the addition of luminescent fillers did not substantially weaken the structure. This finding contrasts with previous reports on PLLA–SAOED composites, where a notable reduction in tensile strength, elastic modulus, and elongation at break was observed upon SAOED incorporation [ 34 ]. For instance, Ni et al. [ 27 ] attributed these declines in mechanical properties to reduced crystallinity and poor interfacial compatibility between the inorganic SAOED particles and the organic PLLA matrix. Although the crystallinity of the PLLA component decreased with increasing SAOED content (as shown in Table 2 ), the anticipated deterioration in tensile performance was not observed in this study. This discrepancy is likely due to the structural support provided by the PET multifilament core in the sheath/core electrospun yarn configuration, which effectively compensates for the mechanical limitations of the PLLA/SAOED sheath. Furthermore, it is worth noting that the inherent incompatibility between inorganic SAOED particles and the PLLA polymer matrix may still negatively influence the mechanical behavior of PLLA/SAOED nanofibers; however, this effect appears to be mitigated in the composite yarn due to the reinforcing role of the PET core. 4. Conclusion In this study, luminous (PLLA–SAOED)/PET electrospun nanofiber yarns were successfully fabricated using a sheath/core electrospinning approach to preserve the mechanical integrity of the resulting yarns. Based on SEM images, significant decrease in electrospun nanofiber yarn diameter is attributed to the combined effects of reduced fiber diameters and enhanced fiber compaction, promoted by the twisting mechanism during the electrospinning of sheath/core yarns. The luminescent fibers exhibited strong green emission under UV excitation, with a broad emission band in the visible range and a maximum peak at 615 nm upon 380 nm excitation, confirming the effective luminescent performance of SAOED. The results showed that more twists have a negative effect on the afterglow characteristics of electrospun nanofiber yarns. This finding suggests that twist-induced compactness and potential particle ejection can impact photoluminescent efficiency. Although SAOED incorporation may lead to reduced tenacity and elongation in pure PLA-based nanofiber systems due to poor interfacial compatibility, the mechanical properties of the luminous electrospun yarns in this work remained within acceptable limits. This is attributed to the reinforcement provided by the PET multifilament core. Future work could explore the use of biodegradable alternatives such as polycaprolactone (PCL) or poly(lactic-co-glycolic acid) (PLGA) as core materials, enabling the development of fully biodegradable, multifunctional nanofiber yarns. Such structures hold significant promise for applications in tissue engineering, wound healing, and smart biomedical textiles. Statement During the preparation of this work the authors used ChatGPT in order to improve the readability and language of the manuscript. After using this tool, the authors reviewed and edited the content as needed and take full responsibility for the content of the published article. 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Wang, Fabrication and characterization of long-persistent luminescence/polymer (Ca2MgSi2O7:Eu2+, Dy3+/PLA) composite fibers by electrospinning, Optical Materials 45 (2015) 64-68. M. Mondragón, G. Trujillo, I. Moggio, E. Arias, Luminescent polylactic acid and polysulfone electrospun fibers containing europium (III) complexes, European Polymer Journal 80 (2016) 126-133. Z. Ni, T. Fan, S. Bai, S. Zhou, Y. Lv, Y. Ni, B. Xu, Effect of the Concentration of SrAl2O4: Eu2+and Dy3+ (SAO) on Characteristics and Properties of Environment-Friendly Long-Persistent Luminescence Composites from Polylactic Acid and SAO, Scanning 2021(1) (2021) 6337768. K. Sukthavorn, N. Nootsuwan, C. Veranitisagul, A. Laobuthee, Development of luminescence composite materials from poly(lactic acid) and europium-doped magnesium aluminate for textile applications and 3D printing process, Polymer Composites 43(9) (2022) 6637-6646. H. Maleki, R. Semnani Rahbar, M.M. Saadatmand, H. Barani, Physical and morphological characterisation of poly(L-lactide) acid-based electrospun fibrous structures: tunning solution properties, Plastics, Rubber and Composites 47(10) (2018) 438-446. H. Maleki, A.A. Gharehaghaji, T. Toliyat, P.J. Dijkstra, Drug release behavior of electrospun twisted yarns as implantable medical devices, Biofabrication 8(3) (2016) 035019. H. Maleki, R. Semnani Rahbar, A. Nazir, Improvement of physical and mechanical properties of electrospun poly(lactic acid) nanofibrous structures, Iranian Polymer Journal 29(9) (2020) 841-851. K. Abou-Melha, Preparation of photoluminescent nanocomposite ink toward dual-mode secure anti-counterfeiting stamps, Arabian Journal of Chemistry 15(2) (2022) 103604. M.E. El-Hefnawy, A.I. Ismail, S. Alhayyani, S.T. Al-Goul, M.M. Zayed, M. Abou Taleb, Immobilization of Strontium Aluminate into Recycled Polycarbonate Plastics towards an Afterglow and Photochromic Smart Window, Polymers 15(1) (2023) 119. M. Tayebi, S. Ostad Movahed, A. Ahmadpour, The effect of the surface coating of a strontium mono-aluminate europium dysprosium-based (SrAl2O4:Eu2+,Dy3+) phosphor by polyethylene (PE), polystyrene (PS) and their dual system on the photoluminescence properties of the pigment, RSC Advances 9 (2019) 38703 - 38712. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 27 Apr, 2026 Reviews received at journal 19 Apr, 2026 Reviews received at journal 11 Apr, 2026 Reviewers agreed at journal 06 Apr, 2026 Reviewers agreed at journal 02 Apr, 2026 Reviewers agreed at journal 15 Feb, 2026 Reviewers invited by journal 06 Sep, 2025 Editor assigned by journal 06 Sep, 2025 Submission checks completed at journal 30 Aug, 2025 First submitted to journal 24 Aug, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7447165","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":511304210,"identity":"971780e4-4051-496a-8088-b4f2a53c7768","order_by":0,"name":"Rouhollah Semnani Rahbar","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA6klEQVRIiWNgGAWjYPACCTkwxcPAwNgAYiQQocWYgY1ELQyJDSha8AH59u60Bz93WKTPn9/87MGbmnuyDeyHHzA83INbi8GZs9sNe89I5G44xmZuOOdYsXEDT5oBQ8IzPFokcrdJ8LYBtbAxmEnzsCUkNjDkAP1yAI/D5r/dJvm3TSJdvo39mzTPP6AW/jf4tTDc4N0mDbQlgeEYjxmQAdQiQcAWgzO526Rl2yQMNxzLKZOc25dg3CbxzOAAXoe1n90m+batTl6++fg2iTffEmT7+ZMfPvyBz2EYABQ/JGkYBaNgFIyCUYAJAKTMTr9eloJJAAAAAElFTkSuQmCC","orcid":"","institution":"Standard Research Institute (SRI)","correspondingAuthor":true,"prefix":"","firstName":"Rouhollah","middleName":"Semnani","lastName":"Rahbar","suffix":""},{"id":511304211,"identity":"66b9df87-70be-480c-a7ff-0242fb894ae9","order_by":1,"name":"Homa Maleki","email":"","orcid":"","institution":"University of Birjand","correspondingAuthor":false,"prefix":"","firstName":"Homa","middleName":"","lastName":"Maleki","suffix":""}],"badges":[],"createdAt":"2025-08-24 15:38:16","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7447165/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7447165/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":91196530,"identity":"cb5788d2-9bdd-40f6-a4c3-4b675c3e6c59","added_by":"auto","created_at":"2025-09-12 15:02:54","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":175762,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic of the preparation of luminous (PLLA-SAOED)/PET electrospun nanofiber yarn\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-7447165/v1/edf9eda830b76ea318a52b90.png"},{"id":91200500,"identity":"1dafcef8-080d-4f13-9fc3-736e705b07d4","added_by":"auto","created_at":"2025-09-12 15:26:54","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":489259,"visible":true,"origin":"","legend":"\u003cp\u003eSEM micrographs of electrospun (PLLA-SAOED)/PET sheath/core yarns with varying concentrations of SAOED: (a) 0 wt.% SAOED (neat PLLA/PET), (b) 2 wt.% SAOED, (c) 3.5 wt.% SAOED, and (d) 5 wt.% SAOED.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-7447165/v1/aa7041aaa6163b2d7eab80f3.png"},{"id":91196527,"identity":"1f8169e3-3b23-487e-99a5-b95f96090b8c","added_by":"auto","created_at":"2025-09-12 15:02:54","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":280537,"visible":true,"origin":"","legend":"\u003cp\u003eSEM image of the fractured end of electrospun (PLLA-SAOED)/PET sheath/core yarn\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-7447165/v1/ad5de0d09cce4f208d740616.png"},{"id":91197862,"identity":"12d954e9-a801-4873-be23-85000d351dd5","added_by":"auto","created_at":"2025-09-12 15:10:54","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":80627,"visible":true,"origin":"","legend":"\u003cp\u003eEDX diagrams of (a) neat PLLA/PET and (b) luminous (PLLA-SAOED)/PET electrospun yarn containing 5 wt.% SAOED particles\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-7447165/v1/d877f2593a97acb38202f0ed.png"},{"id":91196540,"identity":"c2ecf3ac-7010-42bb-8d49-6de429dfb50a","added_by":"auto","created_at":"2025-09-12 15:02:54","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":137026,"visible":true,"origin":"","legend":"\u003cp\u003eWAXD patterns of neat PLLA/PET and luminous (PLLA-SAOED)/PET electrospun yarns with 2-5 wt.% SAOED.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-7447165/v1/bcf96a8d422e899ccdb6566d.png"},{"id":91197865,"identity":"4cfb9399-92e6-4bed-9018-2b087404f967","added_by":"auto","created_at":"2025-09-12 15:10:54","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":168961,"visible":true,"origin":"","legend":"\u003cp\u003eDSC heating (a) and cooling (b) curves of neat PLLA/PET and luminous (PLLA-SAOED)/PET electrospun yarns containing different amounts of SAOED particles\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-7447165/v1/398f054394693203edb0f6c6.png"},{"id":91196534,"identity":"9b7470df-d53b-419d-aaea-4a6f1c18a916","added_by":"auto","created_at":"2025-09-12 15:02:54","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":135097,"visible":true,"origin":"","legend":"\u003cp\u003eFTIR spectra of neat PLLA/PET and luminous (PLLA-SAOED)/PET electrospun nanofiber yarns containing different amounts of SAOED particles\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-7447165/v1/7e06c8a34a1fa7a1d52a9817.png"},{"id":91196541,"identity":"59117596-f4d7-4785-869e-d825a28a6a9c","added_by":"auto","created_at":"2025-09-12 15:02:54","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":154482,"visible":true,"origin":"","legend":"\u003cp\u003eAfterglow intensity of luminous (PLLA-SAOED)/PET electrospun yarns containing different amounts of SAOED, excited at 380 nm wavelength radiation\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-7447165/v1/30944034447f27219711c2a5.png"},{"id":91197867,"identity":"4f81b8f1-d421-40c4-9f8f-0d1d6e29071a","added_by":"auto","created_at":"2025-09-12 15:10:54","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":195363,"visible":true,"origin":"","legend":"\u003cp\u003eLuminous (PLLA-SAOED)/PET electrospun yarn prepared with twist level of 4000 TPM and 7000 TPM. More twists have a negative effect on the afterglow characteristics of electrospun nanofiber yarns\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-7447165/v1/1f9f41f45e2a259aee510aae.png"},{"id":91196546,"identity":"46231f34-59ba-48ec-bba8-dffe21b0d905","added_by":"auto","created_at":"2025-09-12 15:02:54","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":506552,"visible":true,"origin":"","legend":"\u003cp\u003eFluorescent optical microscope image (a) and confocal microscope photo (b) for luminous (PLLA-SAOED)/PET electrospun yarn containing 5 wt.% SAOED.\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-7447165/v1/e04f37c0d3e8a0a3f0e04953.png"},{"id":91197868,"identity":"a067d42e-0808-4902-9dc6-cf196c488c40","added_by":"auto","created_at":"2025-09-12 15:10:54","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":194260,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of SAOED loading on the tenacity and elongation at break of luminous (PLLA-SAOED)/PET electrospun yarn. The tensile properties of the luminous (PLLA–SAOED)/PET electrospun yarns are within the acceptable limits.\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-7447165/v1/c77ce2e85b8442c8319a8938.png"},{"id":91200845,"identity":"725490c6-29aa-4075-b493-4e83f38d21fc","added_by":"auto","created_at":"2025-09-12 15:35:00","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2970103,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7447165/v1/4655bb16-d2f9-40d0-b95c-523f0d6ce6a9.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Photoluminescent PLLA/PET Electrospun Nanofiber Yarns with Sheath/Core Architecture: A Strategy to Preserve Tensile Properties","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eLuminous nanofibers have attracted increasing interest in recent years due to their potential applications in a wide range of fields, including lighting, nerve regeneration, tissue engineering, anti-counterfeiting technologies, optoelectronics, catalysis, and wearable electronics [\u003cspan additionalcitationids=\"CR2 CR3 CR4\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. These nanofibers can be fabricated using various techniques such as electrospinning, centrifugal spinning, and sol-gel modification [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e].\u003c/p\u003e\u003cp\u003ePolylactic acid (PLA) is a widely used biodegradable polymer that has been extensively investigated for biomedical applications due to its biocompatibility, renewability, and processability [\u003cspan additionalcitationids=\"CR9\" citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. PLA nanofibers, particularly those produced via electrospinning, have garnered attention because of their high surface area, porosity, and potential for functionalization [\u003cspan additionalcitationids=\"CR12\" citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. A promising strategy to enhance the functionality of PLA nanofibers is the incorporation of luminescent additives. Photoluminescent materials such as carbon quantum dots [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e], CdTe quantum dots [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e], and alkaline-earth metal aluminates [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e] have been incorporated into PLA matrices to create photoluminescent nanofibers with potential applications in lighting, bioimaging, biosensing, drug delivery, and tracking [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eRecent studies have investigated various luminescent materials-including perovskite quantum dots, lanthanide-based compounds, and organic-inorganic hybrids-for the fabrication of luminous nanofibers [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. Among them, strontium aluminate doped with europium and dysprosium (SrAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e: Eu\u0026sup2;⁺, Dy\u0026sup3;⁺, abbreviated as SAOED) has received considerable attention due to its high luminous efficiency, color tunability, long afterglow, stability, and environmental safety [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. SAOED can be excited by visible or ultraviolet light and continues to emit light in the dark for an extended period after excitation. These particles have been incorporated into various polymer matrices to develop luminescent fibers, fabrics, and composites [\u003cspan additionalcitationids=\"CR21 CR22 CR23\" citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eYe et al. [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e] fabricated long-persistent luminescent PLA nanofibers via electrospinning using Sr\u003csub\u003e2\u003c/sub\u003eMgSi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e: Eu\u0026sup2;, Dy\u0026sup3;⁺ and Ca\u003csub\u003e2\u003c/sub\u003eMgSi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e: Eu\u0026sup2;⁺, Dy\u0026sup3;⁺, reporting uniform dispersion of the luminescent particles in the PLA matrix. Although the luminescent fibers exhibited similar decay behavior to that of the pure luminescent powders, the emission intensity was somewhat reduced. However, these studies did not evaluate the impact of luminescent particle incorporation on the mechanical properties of the PLA fibers. In another study, composite fibers containing europium complexes were fabricated via electrospinning, and the europium complexes were found to be distributed as irregular crystalline domains (150\u0026ndash;300 nm), resulting in bright red fluorescence under UV illumination [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eNi et al. [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e] prepared PLA/SAOED composites using a solvent casting method. To improve interfacial compatibility, a silane coupling agent was used. While composites containing 15 wt.% SAOED exhibited optimal luminescent performance, mechanical properties deteriorated with increasing SAOED content. The most favorable balance of mechanical and optical properties was achieved at 5 wt.% SAOED. Similar surface modification strategies have been employed with other luminescent fillers, such as MgAl₂O₄: Eu, to enhance mechanical performance in PLA-based systems [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eTo the best of our knowledge, no prior studies have reported the fabrication of PLLA/SAOED electrospun yarns. The present work aims to fill this gap by developing and characterizing luminescent PLLA/SAOED electrospun nanofiber yarns. One of the key challenges in incorporating inorganic fillers into PLLA nanofibers is the associated decline in mechanical performance. To address this, we employed a sheath/core electrospinning configuration, in which the PLLA/SAOED nanofibers serve as the sheath (the luminescent component), while a microfilament poly(ethylene terephthalate) (PET) yarn functions as the core to maintain the mechanical integrity of the composite yarn.\u003c/p\u003e"},{"header":"2. Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n \u003ch2\u003e2.1. Materials\u003c/h2\u003e\n \u003cp\u003ePhosphor strontium aluminate (SrAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e: Eu\u0026sup2;⁺, Dy\u0026sup3;⁺) particles (SAOED) were purchased from Sigma-Aldrich Ltd. (product code: 756539). Poly(l-lactide) (intrinsic viscosity of 2.51 dL/g) was supplied from Purac Biomaterials, Netherlands. 2,2,2-Trifluoroethanol (TFE) (Merck, Germany) was selected as a solvent and used without subsequent purification. PET microfilament yarn (100 den/144 filaments) was kindly provided by Behkoosh Co., Iran.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\n \u003ch2\u003e2.2. Preparation of Polymer Solutions and Electrospinning Process\u003c/h2\u003e\n \u003cp\u003eThe detailed procedures for the preparation of polymer solutions and the electrospinning process parameters have been previously reported in our earlier publication [\u003cspan class=\"CitationRef\"\u003e29\u003c/span\u003e]. In this study, electrospun PLLA/SAOED nanofibers were fabricated with varying SAOED concentrations of 2 wt.%, 3.5 wt.%, and 5 wt.%. For all these samples, the twist level was constant at 4000 turns per meter (TPM). Additionally, to investigate the effect of twist on photoluminescence properties of yarns, (PLLA\u0026ndash;SAOED)/PET electrospun nanofiber yarns containing 5 wt.% SAOED were also produced with two other twist levels: 2000 TPM and 7000 TPM. A schematic of the production of luminous fiber and fabric is shown in Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\n \u003ch2\u003e2.3. Characterization\u003c/h2\u003e\n \u003cp\u003eThe morphology and chemical compositions of nanofibers and electrospun nanofiber yarn surfaces were studied using a scanning electron microscope with an energy-dispersive X-ray spectroscopy (EDX) (SEM; TESCAN VEGA, TESCAN Ltd., Czech Republic). The samples were coated with a thin layer of gold under vacuum before SEM observation at an acceleration voltage of 30 kV. From at least 5 SEM images of each sample, nanofiber and yarn diameters were determined using Digimizer 4.1.1.0 software.\u003c/p\u003e\n \u003cp\u003eConfocal Laser Scanning Microscopy (CLSM) was performed by Leica, TCS SPE (Leica Microsystems Inc.) equipped with LAS X Software program. The samples were excited by solid state laser and high-resolution images were obtained.\u003c/p\u003e\n \u003cp\u003eFluorescent optical microscopy images were taken using a BK-FL4 microscope (Drawell, China). The irradiation source was a UV fluorescence illuminator.\u003c/p\u003e\n \u003cp\u003eThermal characteristics of electrospun nanofiber yarns were analyzed by differential scanning calorimetry (DSC; DSC 2010 machine, TA Instruments, New Castle, DE). The heating and cooling rates were 10 \u0026deg;C/min under nitrogen atmosphere. The crystallinity of samples (Xc) was calculated using the following equation:\u003c/p\u003e\n \u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\n \u003cdiv class=\"EquationNumber\"\u003e\u003cimg src=\"data:image/png;base64,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\"\u003e\u003c/div\u003e\n \u003c/div\u003e\n \u003cp\u003eWhere ∆H\u003csub\u003ef\u003c/sub\u003e is the heat of fusion of the analyzed sample (J/g), \u0026Delta;Hcc is the cold crystallization enthalpy induced during DSC test, and ∆H\u003csub\u003ef\u003c/sub\u003e\u003csup\u003e0\u003c/sup\u003e is the heat of fusion for a 100% crystalline PLLA polymer, it was taken as 93.7 J/g [\u003cspan class=\"CitationRef\"\u003e30\u003c/span\u003e].\u003c/p\u003e\n \u003cp\u003eThe wide angle X-ray diffraction (WAXD) patterns of the fibers were collected at a voltage of 40 kV and current of 30 mA using EQUINOX 3000 X-ray diffractometer (Inel, France, Cu K\u0026alpha; \u0026lambda;\u0026thinsp;=\u0026thinsp;0.1540 nm). The scattering intensities were recorded every 0.04\u003csup\u003e◦\u003c/sup\u003e in the 2\u0026theta; of 5-110\u003csup\u003e◦\u003c/sup\u003e.\u003c/p\u003e\n \u003cp\u003eTensile properties of electrospun yarns were examined using a universal testing machine (Gotech Co.). From stress-strain curves, tenacity and breaking elongation were evaluated. The cross-head speed of 50 mm/min and initial length of 50 mm were fixed for all samples. At least 10 specimens from each sample were tested, and the values were averaged.\u003c/p\u003e\n \u003cp\u003eFourier Transform Infrared (FTIR) analysis of electrospun nanofiber yarns was carried out using VERTEX 70 (Bruker, Germany) in the wavenumber range of 4000\u0026thinsp;\u0026minus;\u0026thinsp;400 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. An average of 40 scans was recorded in the transmission mode.\u003c/p\u003e\n \u003cp\u003ePhotoluminescence spectroscopy (PL) was conducted to investigate the luminescence properties of luminous electrospun nanofiber yarns using a Perkin Elmer fluorescence spectrophotometer (model LS55). The samples were excited under ultraviolet light (UV) at 380 nm, and emission spectra representing the amount of reflection were plotted in the range of 400\u0026ndash;700 nm.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"3. Results and discussion","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\n \u003ch2\u003e3.1. Surface morphology\u003c/h2\u003e\n \u003cp\u003eThe surface morphology of photoluminescent nanofiber yarns-comprising a conventional PET core enveloped by electrospun (PLLA-SAOED) nanofibers with varying SAOED concentrations was examined using scanning electron microscopy (SEM). Representative SEM micrographs of both individual nanofibers and twisted yarn configurations are presented in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e. Across all samples, regardless of SAOED content, the nanofibers exhibited continuous, bead-free, and uniform structures, indicating that the electrospinning parameters were effectively optimized. Pure PLLA nanofibers (0% SAOED) displayed a smooth, cylindrical morphology (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ea). As the SAOED concentration increased, crystalline SAOED particles became progressively more evident on or near the fiber surfaces, as observed in the SEM images. Importantly, no fiber breakage, discontinuities, or substantial particle agglomeration were detected, suggesting effective dispersion of the SAOED particles and favorable compatibility within the PLLA matrix (Figs.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eb\u0026ndash;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ed). Additionally, the absence of defects such as fiber fusion or localized thickening further supports the conclusion that particle distribution remained uniform and stable throughout the electrospinning process.\u003c/p\u003e\n \u003cp\u003eThe twisted yarn configurations exhibited coherent and uniform structures, characterized by consistent fiber alignment and evenly distributed twists across all SAOED concentrations. SEM analysis revealed that the majority of nanofibers were oriented at an angle relative to the yarn axis, reflecting the directional alignment induced by the applied twist during yarn formation (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ec). This organized fiber orientation contributes to both the structural integrity and the uniform visual appearance of the electrospun yarns.\u003c/p\u003e\n \u003cp\u003eQuantitative analysis of the fiber diameters indicated a statistically significant decrease with increasing SAOED concentration (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). The average fiber diameter decreased from (661.26\u0026thinsp;\u0026plusmn;\u0026thinsp;96.10) nm for pure PLLA to (419.18\u0026thinsp;\u0026plusmn;\u0026thinsp;65.39) nm for PLLA containing 5 wt.% SAOED. Intermediate values were recorded for PLLA with 2 wt.% SAOED (521.75\u0026thinsp;\u0026plusmn;\u0026thinsp;78.82 nm) and 3.5 wt.% SAOED (505.16\u0026thinsp;\u0026plusmn;\u0026thinsp;69.47 nm). Correspondingly, the overall yarn diameter also decreased as the SAOED concentration increased. Specifically, the average yarn diameter reduced from (1447.91\u0026thinsp;\u0026plusmn;\u0026thinsp;25.94) \u0026micro;m at 0 wt.% SAOED to (906.01\u0026thinsp;\u0026plusmn;\u0026thinsp;10.22) \u0026micro;m at 5 wt.% SAOED, representing an approximate 37% reduction. This significant decrease in bulk yarn size is attributed to the combined effects of reduced fiber diameters and enhanced fiber compaction, promoted by the twisting mechanism during the electrospinning of sheath/core yarns. The twisting process likely contributes to this trend by applying axial tension, thereby increasing fiber packing density.\u003c/p\u003e\n \u003cp\u003eFurther SEM analysis of the fractured ends of the electrospun sheath/core yarns distinctly revealed the coexistence of PET microfilaments and PLLA nanofibers within the same structure (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e). The preserved integrity of both individual fibers and twisted yarns across all SAOED concentrations is particularly advantageous for applications requiring both photoluminescence and mechanical durability. The consistent sheath/core configuration ensures that the PET microfilament provides mechanical reinforcement, while the outer (PLLA-SAOED) layer imparts photoluminescent functionality. This robust interface between the core and sheath components is critical for maintaining the overall yarn strength while enabling multifunctional performance.\u003c/p\u003e\n \u003cp\u003eThe elemental composition of SAOED in the luminous (PLLA\u0026ndash;SAOED)/PET electrospun yarns was analyzed using energy-dispersive X-ray spectroscopy (EDX), with the results presented in Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e and Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e. The EDX spectra confirmed the presence of carbon (C), oxygen (O), aluminum (Al), strontium (Sr), europium (Eu), and dysprosium (Dy). As expected, C and O were the dominant elements in the neat PLLA/PET electrospun yarn, reflecting the polyester-based composition of both PLLA and PET. In contrast, the EDX spectrum of the luminous (PLLA\u0026ndash;SAOED)/PET electrospun yarn displayed pronounced peaks corresponding to Al, Sr, Eu, and Dy, providing direct evidence of the successful incorporation of SAOED particles within the electrospun nanofiber matrix.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eThe elements (wt.%) of neat PLLA/PET and luminous (PLLA-SAOED)/PET electrospun yarns were determined by EDX\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSAOED particle content\u003c/p\u003e\n \u003cp\u003e(wt.%)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eC\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eO\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eAl\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSr\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eEu\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eDy\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNeat PLLA/PET (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e49.99\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e50.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e---\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e---\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e---\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e---\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e48.22\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e49.62\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.88\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.68\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.35\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.28\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e43.62\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e53.73\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.83\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.46\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.33\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e44.93\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e51.73\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.05\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.57\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.48\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\n \u003ch2\u003e3.2. Crystalline structure\u003c/h2\u003e\n \u003cp\u003eThe wide-angle X-ray diffraction (WAXD) profiles of the neat PLLA/PET and luminous (PLLA\u0026ndash;SAOED)/PET electrospun yarns are shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e. As observed, none of the samples exhibited sharp diffraction peaks, indicating a predominantly amorphous structure. However, a broader diffraction peak was recorded for the luminous (PLLA\u0026ndash;SAOED)/PET samples compared to the neat PLLA/PET yarn. Specifically, the peak intensity at 2\u0026theta;\u0026thinsp;=\u0026thinsp;16.9\u0026deg;, corresponding to the \u0026alpha;-crystalline form of PLLA and assigned to the (200)/(110) diffraction planes [\u003cspan class=\"CitationRef\"\u003e31\u003c/span\u003e], decreased with the incorporation of SAOED particles into the PLA matrix.\u003c/p\u003e\n \u003cp\u003eThe broad nature of the peak centered at 2\u0026theta;\u0026thinsp;=\u0026thinsp;16.9\u0026deg; is commonly attributed to the rapid solvent evaporation during the electrospinning process, which limits the time available for molecular chains to arrange into well-defined crystalline domains [\u003cspan class=\"CitationRef\"\u003e29\u003c/span\u003e]. Additionally, previous studies have suggested that electrospun PLA fibers may contain a mesophase characterized by highly oriented chains lacking a fully developed crystalline structure.\u003c/p\u003e\n \u003cp\u003eImportantly, the diffraction patterns of the (PLLA\u0026ndash;SAOED)/PET electrospun yarns reveal that the crystalline structure of PLLA remains largely unaffected by the addition of SAOED at concentrations ranging from 2 to 5 wt.%. This observation is consistent with the thermal analysis results (Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e), which show a slight decrease in crystallinity in the SAOED-loaded samples, thereby corroborating the WAXD findings.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\n \u003ch2\u003e3.3. Thermal analysis\u003c/h2\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e shows DSC thermograms of neat PLLA/PET and luminous (PLLA-SAOED)/PET electrospun yarns. The glass transition temperature (T\u003csub\u003eg\u003c/sub\u003e), cold crystallization temperature (T\u003csub\u003ecc\u003c/sub\u003e), cold crystallization enthalpy (∆H\u003csub\u003ecc\u003c/sub\u003e), melting temperature (T\u003csub\u003em\u003c/sub\u003e), melting enthalpy (∆H\u003csub\u003em\u003c/sub\u003e), crystallization temperature (T\u003csub\u003ec\u003c/sub\u003e), crystallization enthalpy (∆H\u003csub\u003ec\u003c/sub\u003e), and degree of crystallinity (X\u003csub\u003ec\u003c/sub\u003e) of the samples were obtained from DSC analysis and summarized in Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e. Figure \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e indicates that neat neat PLLA/PET and luminous (PLLA-SAOED)/PET electrospun yarns have the same thermal trend; the T\u003csub\u003eg\u003c/sub\u003e followed by the T\u003csub\u003ecc\u003c/sub\u003e and T\u003csub\u003em\u003c/sub\u003e peaks, which are common for heating curves of PLA (Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003ea).\u003c/p\u003e\n \u003cp\u003eIt can be observed from Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e that the T\u003csub\u003eg\u003c/sub\u003e of the luminous (PLLA-SAOED)/PET electrospun yarns changed remarkably compared with that of the neat PLLA/PET electrospun yarn. A similar trend was also recorded for the T\u003csub\u003ecc\u003c/sub\u003e, in which T\u003csub\u003ecc\u003c/sub\u003e for neat PLLA/PET electrospun yarn increased from 73.49 to 80.81 for the luminous (PLLA-SAOED)/PET electrospun yarn containing 5 wt.% SAOED. This may be related to molecular chain restriction in the presence of SAOED particles. In contrast, T\u003csub\u003em\u003c/sub\u003e of PLLA/PET electrospun yarns did not change upon incorporation of SAOED particles. Data in Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e reveals that melting enthalpy and crystallinity of neat PLLA/PET decreased with addition of SAOED particles in the luminous (PLLA-SAOED)/PET electrospun yarns, suggesting that SAOED particles play an obstacle role to PLA crystallization, mainly due to the restriction in the molecular chain movements. It should be noted that although PLA crystallinity decreased in the presence of SAOED particles, the crystallinity of luminous (PLLA-SAOED)/PET samples did not change significantly when the content of SAOED increased.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab2\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eThermal characteristics of neat PLLA/PET and luminous (PLLA-SAOED)/PET electrospun yarns with 2\u0026ndash;5 wt.% SAOED\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSAOED particle content\u003c/p\u003e\n \u003cp\u003e(wt.%)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eT\u003csub\u003eg\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eT\u003csub\u003ecc\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e∆H\u003csub\u003ecc\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eT\u003csub\u003em\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e∆H\u003csub\u003em\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eT\u003csub\u003ec\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e∆H\u003csub\u003ec\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCrystallinity\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNeat PLLA/PET (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e62.62\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e73.49\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e10.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e182.26\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e29.49\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e104.14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e8.87\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e20.80\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e65.51\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e78.26\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6.58\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e182.31\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e22.74\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e106.04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e14.07\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e17.24\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e68.83\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e79.74\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6.88\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e183.09\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e21.66\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e107.34\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e14.46\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e15.77\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e70.07\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e80.81\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6.25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e182.68\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e21.56\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e111.28\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e11.87\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e16.33\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\n \u003ch2\u003e3.4. Spectroscopy\u003c/h2\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e Shows FTIR spectra of neat PLLA/PET electrospun yarn and luminous (PLLA-SAOED)/PET electrospun yarns containing different amounts of SAOED particles. As can be observed in Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e, these particles show a characteristic peak at 420 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e which could correspond to O-Al-O symmetric stretching. This peak was not detectable in the neat PLLA/PET electrospun yarn and became more intense when the content of SAOED particles increased, confirming the presence of SAOED particles in the luminous (PLLA-SAOED)/PET electrospun yarns.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\n \u003ch2\u003e3.5. Afterglow characteristics\u003c/h2\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e presents the emission spectra of luminous (PLLA\u0026ndash;SAOED)/PET electrospun yarns. All samples exhibited a broad and intense emission band within the visible region, with a maximum emission peak centered at 526 nm, corresponding to green light. The intensity of the afterglow emission increased with rising SAOED content, with the sample containing 5 wt.% SAOED demonstrating the most pronounced green afterglow. This emission is attributed to two distinct strontium sites within the SrAl₂O₄ crystal lattice, which are known to contribute to persistent luminescence in the green region [\u003cspan class=\"CitationRef\"\u003e32\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e33\u003c/span\u003e].\u003c/p\u003e\n \u003cp\u003eA comparison of afterglow behavior among (PLLA\u0026ndash;SAOED)/PET electrospun yarns with different twist levels revealed that the sample twisted at 7000 TPM exhibited lower afterglow intensity compared to those twisted at 2000 TPM and 4000 TPM. This reduction in luminescence may result from a more compact yarn structure at higher twist levels, which could hinder the effective excitation of embedded SAOED particles under UV irradiation. Additionally, the yarn formation process at elevated twist levels may lead to the partial expulsion of SAOED particles from the fiber surface, thereby reducing the overall SAOED content and consequently diminishing the afterglow intensity.\u003c/p\u003e\n \u003cp\u003eVisual evidence supporting this explanation is provided in Fig. \u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e, where the yarn twisted at 4000 TPM displays a visibly more intense green luminescence than the yarn twisted at 7000 TPM. These results suggest that an optimal twist level is critical to balancing mechanical integrity and luminescent performance in (PLLA\u0026ndash;SAOED)/PET electrospun yarns.\u003c/p\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e10\u003c/span\u003e displays fluorescence microscopy and confocal microscopy images of the luminous (PLLA\u0026ndash;SAOED)/PET electrospun yarn containing 5 wt.% SAOED, captured after excitation under UV irradiation. As evident, the fibers emitted a strong green luminescence, consistent with the emission peak observed at 526 nm in the photoluminescence spectra (Fig. \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e). The uniform green color throughout the image suggests a homogeneous dispersion of SAOED particles within the PLA matrix, indicating effective incorporation during electrospinning. Additionally, the images confirm that the luminous (PLLA\u0026ndash;SAOED) nanofiber sheath was uniformly and securely wrapped around the PET multifilament core, supporting the structural integrity of the sheath/core configuration.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\n \u003ch2\u003e3.6. Tensile Properties\u003c/h2\u003e\n \u003cp\u003eThe tenacity and elongation at break of neat PLLA/PET and luminous (PLLA\u0026ndash;SAOED)/PET electrospun yarns are presented in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e11\u003c/span\u003e. A primary objective of this study was to fabricate luminous PLLA-based nanofiber yarns without compromising their mechanical performance. As shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e11\u003c/span\u003e, the incorporation of SAOED particles into the PLLA matrix did not result in significant changes to the tensile properties. The mechanical performance of the luminous (PLLA\u0026ndash;SAOED)/PET electrospun yarns remained within acceptable limits, demonstrating that the addition of luminescent fillers did not substantially weaken the structure.\u003c/p\u003e\n \u003cp\u003eThis finding contrasts with previous reports on PLLA\u0026ndash;SAOED composites, where a notable reduction in tensile strength, elastic modulus, and elongation at break was observed upon SAOED incorporation [\u003cspan class=\"CitationRef\"\u003e34\u003c/span\u003e]. For instance, Ni et al. [\u003cspan class=\"CitationRef\"\u003e27\u003c/span\u003e] attributed these declines in mechanical properties to reduced crystallinity and poor interfacial compatibility between the inorganic SAOED particles and the organic PLLA matrix.\u003c/p\u003e\n \u003cp\u003eAlthough the crystallinity of the PLLA component decreased with increasing SAOED content (as shown in Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e), the anticipated deterioration in tensile performance was not observed in this study. This discrepancy is likely due to the structural support provided by the PET multifilament core in the sheath/core electrospun yarn configuration, which effectively compensates for the mechanical limitations of the PLLA/SAOED sheath. Furthermore, it is worth noting that the inherent incompatibility between inorganic SAOED particles and the PLLA polymer matrix may still negatively influence the mechanical behavior of PLLA/SAOED nanofibers; however, this effect appears to be mitigated in the composite yarn due to the reinforcing role of the PET core.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eIn this study, luminous (PLLA\u0026ndash;SAOED)/PET electrospun nanofiber yarns were successfully fabricated using a sheath/core electrospinning approach to preserve the mechanical integrity of the resulting yarns. Based on SEM images, significant decrease in electrospun nanofiber yarn diameter is attributed to the combined effects of reduced fiber diameters and enhanced fiber compaction, promoted by the twisting mechanism during the electrospinning of sheath/core yarns. The luminescent fibers exhibited strong green emission under UV excitation, with a broad emission band in the visible range and a maximum peak at 615 nm upon 380 nm excitation, confirming the effective luminescent performance of SAOED. The results showed that more twists have a negative effect on the afterglow characteristics of electrospun nanofiber yarns. This finding suggests that twist-induced compactness and potential particle ejection can impact photoluminescent efficiency. Although SAOED incorporation may lead to reduced tenacity and elongation in pure PLA-based nanofiber systems due to poor interfacial compatibility, the mechanical properties of the luminous electrospun yarns in this work remained within acceptable limits. This is attributed to the reinforcement provided by the PET multifilament core. Future work could explore the use of biodegradable alternatives such as polycaprolactone (PCL) or poly(lactic-co-glycolic acid) (PLGA) as core materials, enabling the development of fully biodegradable, multifunctional nanofiber yarns. Such structures hold significant promise for applications in tissue engineering, wound healing, and smart biomedical textiles.\u003c/p\u003e\u003cp\u003e\u003cstrong\u003eStatement\u003c/strong\u003e\u003cp\u003eDuring the preparation of this work the authors used ChatGPT in order to improve the readability and language of the manuscript. After using this tool, the authors reviewed and edited the content as needed and take full responsibility for the content of the published article.\u003c/p\u003e\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eRouhollah Semnani Rahbar: Conceptualization, Methodology, Investigation, Supervision, Writing - Original Draft, Writing - review \u0026amp; editing. Homa Maleki: Methodology, Investigation, Validation, Writing - Original Draft; All authors read and approved the final manuscript.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eI. Antony K. J, D. Jana, Stable Mn-Doped CsPbCl3 Nanocrystals inside Mesoporous Alumina Films for Display and Catalytic Applications, ACS Applied Nano Materials 3(3) (2020) 2941-2951.\u003c/li\u003e\n \u003cli\u003eA. 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Ahmadpour, The effect of the surface coating of a strontium mono-aluminate europium dysprosium-based (SrAl2O4:Eu2+,Dy3+) phosphor by polyethylene (PE), polystyrene (PS) and their dual system on the photoluminescence properties of the pigment, RSC Advances 9 (2019) 38703 - 38712.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"polymer-bulletin","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"pobu","sideBox":"Learn more about [Polymer Bulletin](http://link.springer.com/journal/289)","snPcode":"289","submissionUrl":"https://submission.nature.com/new-submission/289/3","title":"Polymer Bulletin","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Sheath/core electrospinning system, Luminescent characteristics, Tensile properties, Poly(L-lactic acid)","lastPublishedDoi":"10.21203/rs.3.rs-7447165/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7447165/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eA sheath/core electrospinning system was employed to fabricate luminescent poly(L-lactic acid) (PLLA) electrospun nanofiber yarns as the sheath, with microfilament poly(ethylene terephthalate) (PET) yarns serving as the core. To achieve this, varying amounts of strontium aluminate (SrAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e: Eu²⁺, Dy³⁺) phosphorescent particles (SAOED) were incorporated into the PLLA matrix. Additionally, (PLLA–SAOED)/PET electrospun nanofiber yarns with different twist levels were also produced. The morphology, crystalline structure, thermal behavior, tensile properties, and luminescent characteristics of the resulting yarns were systematically investigated. SEM images showed that average nanofiber diameter decreased from (661.26±96.10) nm for pure PLLA electrospun nanofiber yarns to (419.18±65.39) nm for PLLA containing 5% SAOED. Correspondingly, the overall yarn diameter also decreased as the SAOED concentration increased, showing a maximum 37% reduction. Thermal analysis revealed that increasing the SAOED content had negligible effects on the thermal properties of the fibers. Tensile tests demonstrated that the incorporation of SAOED particles did not significantly compromise the tensile properties of the (PLLA–SAOED)/PET yarns, with values comparable to those of the non-loaded samples. Moreover, Upon UV light exposure, all luminescent yarn samples emitted a strong green phosphorescent band. The afterglow intensity of the yarns was significantly influenced by both SAOED content and twist level, with higher luminescence observed at increased SAOED loading and lower twist levels. These results suggest that luminescent PLLA nanofiber yarns can be successfully fabricated via sheath/core electrospinning strategy without sacrificing mechanical integrity, highlighting their potential for applications in biomedical engineering, smart textiles, and other advanced functional materials.\u003c/p\u003e","manuscriptTitle":"Photoluminescent PLLA/PET Electrospun Nanofiber Yarns with Sheath/Core Architecture: A Strategy to Preserve Tensile Properties","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-09-12 15:02:49","doi":"10.21203/rs.3.rs-7447165/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-04-27T06:29:40+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-19T15:51:15+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-11T10:50:44+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"37088770455569801294453740324402211582","date":"2026-04-06T12:04:56+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"338477670829095606250243804090150136994","date":"2026-04-02T07:55:46+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"334856673443699870519038024744133086","date":"2026-02-16T04:13:51+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-09-07T02:36:04+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-09-07T00:25:04+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-08-30T09:30:58+00:00","index":"","fulltext":""},{"type":"submitted","content":"Polymer Bulletin","date":"2025-08-24T15:35:20+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"polymer-bulletin","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"pobu","sideBox":"Learn more about [Polymer Bulletin](http://link.springer.com/journal/289)","snPcode":"289","submissionUrl":"https://submission.nature.com/new-submission/289/3","title":"Polymer Bulletin","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"26c9b84f-2e89-4d7d-a3d0-32f02d42ef79","owner":[],"postedDate":"September 12th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-05-17T07:08:06+00:00","versionOfRecord":[],"versionCreatedAt":"2025-09-12 15:02:49","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7447165","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7447165","identity":"rs-7447165","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}