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1. Role of Draw Rate and Molecular Weight when Electrospun Nanofibers are Post‐Drawn with Residual Solvent

   https://doi.org/10.1002/mame.202200475  

   Conte, Adriano A.; Hu, Xiao; Beachley, Vince (October 2022, Macromolecular Materials and Engineering)

   Abstract The postdrawing process is poorly understood for polymer nanofibers due to the difficulty of manipulating nanofiber structures. Here, an angled track system facilitates postdrawing of individual nanofibers with control of parameters including molecular weight, draw rate, draw ratio, and solvent evaporation time. In this study, the effects of molecular weight, draw rate, and relative residual solvent content on final nanofiber properties are investigated. Molecular weight is first investigated to clarify any influence polymer chain length can have on drawing in facilitating or hindering chain extensibility. Polyacrylonitrile nanofibers with 50 and 150 kDa molecular weights behave similarly with postdrawing resulting in reduced diameters and enhanced mechanics. Since solvent quantity during drawing is a time sensitive component it is meaningful to assess the impact of draw rate on the chemical and structural makeup of postdrawn fibers. Chemical bond vibrations and chain orientation are sensitive to draw rate when polycaprolactone nanofibers are dried for 3 minutes prior to postdrawing, but this dependency to draw rate is not observed when fibers are postdrawn immediately upon collection. These findings demonstrate that the amount of retained solvent at collection is relevant to this postprocessing approach, and highlights the dynamics of solvent evaporation during postdrawing. 

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2. Charting the envelope of mechanical properties of synthetic silk fibers through predictive modeling of the drawing process

   https://doi.org/10.1126/sciadv.adr3833  

   Graham, Jacob J; Subramani, Shri V; Yang, Xinyan; Russell, Timothy M; Zhang, Fuzhong; Keten, Sinan (March 2025, Science Advances)

   A major challenge in synthesizing strong and tough protein fibers based on spider silk motifs is understanding the coupling between protein sequence and the postspin drawing process. We clarify how drawing-induced elongational force affects ordering, chain extension, interchain contacts, and molecular mobility through mesoscale simulations of silk-based fibers. We show that these emergent features can be used to predict mechanical property enhancements arising from postspin drawing. Simulations recapitulate a purely process-dependent mechanical property envelope in which order enhances fiber strength while preserving toughness. The relationship between chain extension and crystalline domain alignment observed in simulations is validated by Raman spectroscopy of wet-spun fibers. Property enhancements attributed to the progression of anisotropic extension are verified by mechanical tests of drawn silk fibers and justified by theory. These findings elucidate how drawing enhances properties of protein-based fibers and shed light on how to incorporate this effect into predictive models. 

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3. Laser Processing Technology for PAN Fiber Carbonization

   Xie, Jianxin; Zhang, Mei (October 2018, The Composites and Advanced Materials Expo. CAMX Conference Proceedings)

   Carbon fibers (CFs) are an important engineering material due to their superior mechanical, electrical, and thermal properties. Majority of them are produced from the thermal conversion of polyacrylonitrile (PAN)-based fibers. In order to promote the CF manufacturing speed and offer the possibility to control the microstructure of the fibers, an alternative technology for carbonization of stabilized PAN fiber are explored by laser processing technology. In this work, we investigated the relationship between the laser process and the properties of fibers. Laser irradiation introduces the structural changes in the stabilized PAN fibers. The appearance of D band and G band in Raman spectrum verifies the existence of graphite structures in the laser scanned fibers. The characteristic peaks in FTIR disappear when the high laser energy condition is engaged, which indicates diminishing of non-carbon bonds. Laser treatment also introduces an obvious shrinkage in fiber diameter. The condition of laser irradiation could influence the electrical and mechanical properties of fibers. A new approach to convert stabilized PAN fiber into carbon fiber was demonstrated. 

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4. Annealing post-drawn polycaprolactone (PCL) nanofibers optimizes crystallinity and molecular alignment and enhances mechanical properties and drug release profiles

   https://doi.org/10.1039/D1MA01183A  

   Flamini, Matthew D.; Lima, Thamires; Corkum, Kerri; Alvarez, Nicolas J.; Beachley, Vince (April 2022, Materials Advances)

   Post-drawn PCL nanofibers can be molecularly tuned to have a variety of mechanical properties and drug release profiles depending on the temperature and time of annealing, which has implications for regenerative medicine and drug delivery applications. Post-drawing polycaprolactone (PCL) nanofibers has previously been demonstrated to drastically increase their mechanical properties. Here the effects of annealing on post-drawn PCL nanofibers are characterized. It is shown that room temperature storage and in vivo temperatures increase crystallinity significantly on the order of weeks, and that high temperature annealing near melt significantly increases crystallinity and molecular orientation on the order of minutes. The kinetics of crystallization were assessed using an anneal and quench approach. High temperature annealing also increased the ultimate tensile strength and toughness of the fibers and changed the release profile of a model drug absorbed in PCL nanofibers from first-order to zero-order kinetics. 

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5. Hierarchically Structured Composite Fibers for Real Nanoscale Manipulation of Carbon Nanotubes

   https://doi.org/10.1002/adfm.202009311  

   Xu, Weiheng; Ravichandran, Dharneedar; Jambhulkar, Sayli; Zhu, Yuxiang; Song, Kenan (January 2021, Advanced Functional Materials)

   Abstract Carbon nanotube (CNT)‐reinforced polymer fibers have broad applications in electrical, thermal, optical, and smart applications. The key for mechanically robust fibers is the precise microstructural control of these CNTs, including their location, dispersion, and orientation. A new methodology is presented here that combines dry‐jet‐wet spinning and forced assembly for scalable fabrication of fiber composites, consisting of alternating layers of polyacrylonitrile (PAN) and CNT/PAN. The thickness of each layer is controlled during the multiplication process, with resolutions down to the nanometer scale. The introduction of alternating layers facilitates the quality of CNT dispersion due to nanoscale confinement, and at the same time, enhances their orientation due to shear stress generated at each layer interface. In a demonstration example, with 0.5 wt% CNTs loading and the inclusion of 170 nm thick layers, a composite fiber shows a significant mechanical enhancement, namely, a 46.4% increase in modulus and a 39.5% increase in strength compared to a pure PAN fiber. Beyond mechanical reinforcement, the presented fabrication method is expected to have enormous potential for scalable fabrication of polymer nanocomposites with complex structural features for versatile applications. 

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