This work aims to provide effective strategies and practical tools to control the diameter of fibers, a long-lasting challenge in the application of free surface melt electrospinning, mainly by hig...

The mechanical properties of electrospun fibers play an important role in determining their applications. Most of the reported literature measures the mechanical properties of electrospun mats, scaffolds, or films instead of single fibers; however, a basic understanding of the relationship between the mechanical properties of the single fiber and that of the mat is critical to obtain precise information for choosing their application. This Review aims to evaluate the reported mechanical properties of electrospun fibers and the variables that influence those properties. An overview on the recent inputs in the development of mechanical properties of electrospun fibers is given, illustrating attempts to tailor mechanical properties of the fibers and/or mats. The necessity of determining flexible and reliable testing methods to establish testing standards for obtaining consistent and reliable data for both electrospun fibers and mats is also highlighted.

The covid-19 pandemic has revealed the need for alternative production approaches with low startup costs like electrospinning for filter needs, the most imperative element of the personal protective equipment (PPE) Current attempts in advancing melt electrospinning deal with developing strategies for fiber diameter attenuation toward sub-micron scale Here, the attunement in the spinning-zone temperature known as ''spin-line temperature profile'' was utilized as a baseline for fiber diameter reduction The mechanical performance of the melt-electrospun linear low-density polyethylene (LLDPE) fibers is reported to characterize their structural transformation with respect to various spin-line temperature profiles With an increase in the spin-line temperature to above 100°C in the area of cone formation, an increased tensile and yield strength along with fiber diameter reduction by four-folds was demonstrated A significant increase in toughness, by almost three times, without compromising the stiffness and Young's modulus was observed The dynamic mechanical analysis revealed that spinning in high temperatures produces changes in the alpha (α) relaxation, contributing to the significant increase in strain at break These results are significant because polyolefin fibers are an imperative element of medical textiles and PPE Therefore, developing a correlation for process-structure-properties for emerging production techniques like melt electrospinning becomes critical © 2021 Wiley Periodicals LLC

Many laboratory experimental techniques used for investigating fine fluid structure, such as fiber spinning, microfluidic flow, and electrospinning, require high quality images with good contrast. Common processes of observation and image recording rely heavily on highly technical light and camera setups which can be difficult to operate in some processing conditions and expensive as well. Here, we report a facile technique using LED backlight imaging to investigate ultrathin fluid profile in two different processes, melt electrospinning and tubeless siphoning. The setup comprises of a simple LED light source facing toward the camera, directly shining into the camera lens. The object under investigation was placed between the camera and the light source. The high-quality captured images and video recordings enable the precise analysis of the cone diameter and jet solidification in case of melt electrospinning, and extensional behavior profiles for tubeless siphoning. The LED backlight setup with high resolution camera is a useful tool to investigate sub-micron scale dimensions in fiber spinning, microfluidic flow, solution electrospinning, contact angle measurement for surface properties analysis, etc.

A novel modacrylic fiber with the capability to absorb ∼80% of all infrared radiation was evaluated for use in personal thermal comfort applications. Using an infrared (IR) imaging camera to monitor optical changes over time and heat flux measurements, it was concluded that this altered modacrylic fiber possesses both a unique thermal signature as well as increased heat flux compared to 100% cotton. A design of experiments (DOE) was conducted to determine if blending this material with other fibers would result in a fabric with a higher thermal conductivity. It was observed that blends of nylon and the altered modacrylic tended to have the highest conductivity and would provide a cooling effect if used in a garment.

Photothermal heating via metal nanoparticles is utilized to degrade polyethylcyanoacrylate (PECA), which undergoes a thermally-driven depolymerization process, resulting in (i) monomer loss from the sample, (ii) repolymerization to form shorter chains (oligomer), and (iii) formation of carbonaceous by-products which are graphene-like and luminescent. These unique PECA properties are used to demonstrate the heterogeneous temperature distribution present during photothermal processing and the results are compared to degradation via conventional methods where a uniform temperature is present. Photothermal heating results in formation of pockets of depolymerized material around each nanoscale heating site. The characteristic size of these photothermally-generated mechanical defects is determined from changes in the material's tensile strength. Changes in mass loss and molecular weight are utilized to determine the fraction of the sample that has depolymerized: distributing this volume equally to each heating site (based on the nanoparticle concentration) results in a volume that matches the defect size from independent mechanical measurements. In this way, macroscopic measurements elucidate the mesoscopic pattern of photothermal degradation. Sample morphology on scales from millimeters to nanometers is assessed via optical and electron microscopy. The carbonaceous by-products of degradation form in the hot region around each nanoparticle during photothermal heating, as revealed by transmission electron microscopy studies. Heterogeneous heating is also evident from optical images where starch granules, employed as an inert dilute additive to enhance PECA mechanical properties, also become luminescent due to degradation in "hot spots" created by the overlap of warm regions from nearby nanoparticle sites. Beyond the fundamental knowledge gained by these studies, the results demonstrate the ability to manipulate the connection between mechanical properties and chemical degradation which is important for developing new strategies for management of polymeric waste.

Photothermal heating via metal nanoparticles is utilized to degrade polyethylcyanoacrylate (PECA), which undergoes a thermally-driven depolymerization process, resulting in (i) monomer loss from the sample, (ii) repolymerization to form shorter chains (oligomer), and (iii) formation of carbonaceous by-products which are graphene-like and luminescent. These unique PECA properties are used to demonstrate the heterogeneous temperature distribution present during photothermal processing and the results are compared to degradation via conventional methods where a uniform temperature is present. Photothermal heating results in formation of pockets of depolymerized material around each nanoscale heating site. The characteristic size of these photothermally-generated mechanical defects is determined from changes in the material’s tensile strength. Changes in mass loss and molecular weight are utilized to determine the fraction of the sample that has depolymerized: distributing this volume equally to each heating site (based on the nanoparticle concentration) results in a volume that matches the defect size from independent mechanical measurements. In this way, macroscopic measurements elucidate the mesoscopic pattern of photothermal degradation. Sample morphology on scales from millimeters to nanometers is assessed via optical and electron microscopy. The carbonaceous by-products of degradation form in the hot region around each nanoparticle during photothermal heating, as revealed by transmission electron microscopy studies. Heterogeneous heating is also evident from optical images where starch granules, employed as an inert dilute additive to enhance PECA mechanical properties, also become luminescent due to degradation in “hot spots” created by the overlap of warm regions from nearby nanoparticle sites. Beyond the fundamental knowledge gained by these studies, the results demonstrate the ability to manipulate the connection between mechanical properties and chemical degradation which is important for developing new strategies for management of polymeric waste.

There is significant interest in biodegradable and transparent UV protection films from renewable resources for many different applications. Herein, the preparation and characterization of semitransparent flexible cellulose films containing low amounts of covalently bonded lignin with UV-blocking properties are described. Azide modified cellulose dissolved in dimethylacetamide/lithium chloride (DMAc/LiCl) was reacted with propargylated lignin to produce 0.5%, 1%, and 2% by weight lignin containing materials. Cellulose-lignin films were prepared by regeneration in acetone. These covalently bonded cellulose-lignin films were homogeneous, unlike the simple blends of cellulose and lignin. Prepared films showed high UV protection ability. Cellulose film containing 2% lignin showed 100% protection of UV-B (280–320 nm) and more than 90% of UV-A (320–400 nm). The UV protection of prepared films was persistent when exposed to thermal treatment at 120 °C and UV irradiation. Thermogravimetric analysis of the films s...

Metal nanoparticles incorporated at low concentration into epoxy systems enable in situ curing via photothermal heating. In the process of nanoparticle-mediated photothermal heating, light interacts specifically with particles embedded within a liquid or solid material and this energy is transformed into heat, resulting in significant temperature increase local to each particle with minimal warming of surroundings. The ability to use such internal heating to transform the mechanical properties of a material (e.g., from liquid to rigid solid) without application of damaging heat to the surrounding environment represents a powerful tool for a variety of scientific applications, particularly within the biomedical sector. Uniform particle dispersion is achieved by placing the nanoparticles within solvent miscible with the desired epoxy resin, demonstrating a strategy utilizable for a wide range of materials without requiring chemical modification of the particles or epoxy. Mechanical and thermal properties (storage modulus, Tg, and degradation behavior) of the cured epoxy are equivalent to those obtained under traditional heating methods. Selective curing of a shape is demonstrated within a liquid bath of epoxy, where the solid form is generated by rastering a spatially confined, photothermal-driving light beam. The non-irradiated regions are largely unaffected and the solid part is easily removed from the remaining liquid. Temperature profiles showing minimal heating outside the irradiated zone are presented and discussed.

Poly(ethylene oxide) electrospun nanofibers with a low concentration of embedded gold nanoparticles (AuNP) were subjected to postfabrication annealing via photothermal heating from the nanoparticles. The results, including nano fibrous mat morphology, crystallinity fraction as a function of annealing time and modality, and average crystallite size, were compared with that for conventional heating at the same average temperature. Maximum crystallinity is achieved more quickly under photothermal heating, and higher maximum crystallinity values, approaching the theoretical maxima for an entangled polymer (similar to 80%), are obtained. Photothermal heating better preserves the unique nanostructured morphology of the nano fibrous mat whereas significant fiber thickening and loss of porosity occur under conventional annealing treatment. With photothermal heating, heat may be predominantly applied within amorphous material within the fiber, which provides energy for the amorphous chains to reorient and then possibly crystallize but while preserving existing crystalline regions as well as the temperature-fragile nanofiber surface. This occurs because nanoparticles are spontaneously segregated within amorphous material due to their characteristic size. In the complex environment of a polymeric nanofiber where crystalline, aligned amorphous, and random amorphous material are all present, further spontaneous segregation of the AuNP to the random amorphous material may occur which enables targeting of this higher barrier to crystallization population, leading to very high final crystallinity fractions.