Citation: Gicheha, D.; Cisse, A.N.; Bhuiyan, A.; Shamim, N. Non-Isothermal Crystallization Kinetics of Poly (ε-Caprolactone) (PCL) and MgO Incorporated PCL Nanofibers. Polymers 2023, 15, 3013. https://doi.org/10.3390/ polym15143013 Academic Editor: Francisco Javier Espinach Orús Received: 18 April 2023 Revised: 1 July 2023 Accepted: 4 July 2023 Published: 12 July 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). polymers Article Non-Isothermal Crystallization Kinetics of Poly (ε-Caprolactone) (PCL) and MgO Incorporated PCL Nanofibers Daisaku Gicheha 1 , Aicha Noura Cisse 1 , Ariful Bhuiyan 2 and Nabila Shamim 1, * 1 Department of Chemical Engineering, Prairie View A & M University, Prairie View, TX 77446, USA; dgicheha@pvamu.edu (D.G.); acisse1@pvamu.edu (A.N.C.) 2 Mechanical Engineering Program, University of Houston Clear Lake, Houston, TX 77058, USA; bhuiyan@uhcl.edu * Correspondence: nashamim@pvamu.edu Abstract: The study delves into the kinetics of non-isothermal crystallization of Poly (ε-caprolactone) (PCL) and MgO-incorporated PCL nanofibers with varying cooling rates. Differential Scanning Calorimetry (DSC-3) was used to acquire crystallization information and investigate the kinetics behavior of the two types of nanofibers under different cooling rates ranging from 0.5–5 K/min. The results show that the crystallization rate decreases at higher crystallization temperatures. Furthermore, the parameters of non-isothermal crystallization kinetics were investigated via several mathematical models, including Jeziorny and Mo’s models. Mo’s approach was suitable to describe the nanofibers’ overall non-isothermal crystallization process. In addition, the Kissinger and Friedman methods were used to calculate the activation energy of bulk-PCL, PCL, and MgO-PCL nanofibers. The result showed that the activation energy of bulk-PCL was comparatively lower than that of nanofibers. The investigation of the kinetics of crystallization plays a crucial role in optimizing manufacturing processes and enhancing the overall performance of nanofibers. Keywords: nanofibers; electrospinning; non-isothermal crystallization 1. Introduction Polymer nanofibers are gaining significant attention due to their potential for develop- ing materials with tailored properties for various applications, including but not limited to oral drug delivery [1], wound healing [2], fine particle filtration [3], tissue engineering [4], optoelectronics [5], and sensor technology [6]. The efficacy of nanofibers in scaffold fabrica- tion is contingent upon their surface-to-volume ratio, the porosity of the nanofiber mesh, and distinctive physicochemical characteristics [7]. Electrospinning has been the most prevalent technique for producing nanofibers. Due to the rapid stretching of the electrical jet and evaporation of the solvent during the electrospinning process, a portion of the polymer remains non-crystalline. The non-crystalline polymer chain eventually becomes entrapped between the growing crystals [8]. Recent research by Soleimani et al. [9] on the structure-property relationship of randomly aligned polylactide revealed that spun fibers consist of crystalline and mesomorphic phases as well as oriented but mobile amorphous chain segments. According to Dimitry et al. [10], the mechanical properties significantly influences the practical applications of nanofibers. These properties can be modified by manipulating their internal structure, which includes their nanoscopic and substructural characteristics. The microstructure and characteristics of fibers and the scaffold they form are directly influenced by the molecular alignment of nanofibers produced through electro- spinning. The size of electrospun fibers is limited by the interaction between electrical and mechanical forces that cause polymer chains to align [11]. However, several aspects of the relationship between structure and property still require further investigation. Therefore, it is crucial to comprehensively examine the internal structure of polymeric nanofibers to enhance their efficiency, a domain that has yet to be extensively explored. Polymers 2023, 15, 3013. https://doi.org/10.3390/polym15143013 https://www.mdpi.com/journal/polymers