Due to this bottleneck, 3D printing may never offer a feasible alternative to mass-production polymer processing methods such as extrusion or injection molding. Electrospun nanofibers might never ...have the desired precise geometry, high strength, or resistance to abrasion or tearing, but the 3D-printed layers have, and they protect the nano fibers at a macro-scale. 3Dprinted layers do not have that small pore size or high specific surface area, but nanofibers do. ...these hierarchical structures offer a challenging research area; therefore, various new processing approaches and applications will arise in the near future. * Corresponding author, e-mail: molnarUpt.bme.hu
Protective masks – worn properly - have become the key to wither away the COVID-19 pandemic. Nowadays, the vast majority of these masks are made of nonwoven fabrics. High-quality products have mainly ...melt-blown filtering layers of nano/microfiber. Melt blowing produces very fine synthetic nonwovens from a wide range of polymers and allows a fair control of the fiber structure and morphology that makes it ideal for filtration purposes. Melt blowing has a high throughput, and the low price of the filter makes these products widely available for civil use. Although melt-blown fiber applications were rapidly growing in the last three decades, we still have limited knowledge on the processing parameters. In this regard, we detailed the melt blowing parameters to obtain a filter media with high particle capturing efficiency and a low-pressure drop. We summarized the melt-blown fiber mat characteristics with specific attention to the pore size, the porosity, the fiber diameter, the fiber packing density and the air permeability desired for highly efficient filtration. Even though we cannot estimate the future social effects and the trauma caused by the current pandemic, and protective masks might remain a part of everyday life for a long while. That also implies that near-future investments in wider manufacturing capacities seem inevitable. This paper also aims to facilitate masks' production with improved filtration efficiency by reviewing the recent developments in melt blowing, the related applications, the effects of processing parameters on the structure and performance of the nonwoven products focusing on the filtration efficiency via knowledge.
When it comes to a gig, the venue generates income from selling tickets and drinks, but do not give the musicians a single penny (subscription model). Besides that, the 'pay to play' model also ...exists, in which the band takes the risk of selling tickets (see APC model). Let us track how many people streamed the band's songs (number of reads) and how many other musicians mentioned their works (number of citations). ...let's say the 'b-index' means there are a number of B other bands, each mentioned at least B number of songs of the actual band as their influence.
This study introduces systematic and comparative investigations of various PLA fine fiber mats prepared by melt blowing. A series of PLLA and PDLA melt-blown fibers from various L and D enantiomers ...blends were produced. Their morphological, mechanical, and thermal properties were studied, and their decomposition in water and compost was investigated. It was found that the 1:1 ratio blend with stereocomplex crystals had an 80% lower average fiber diameter, 60% higher specific strength and better thermal stability than the PLLA and PDLA fiber mats. In the case of composting, the crystalline peak melting temperature, crystallinity, and thermogravimetric decomposition temperatures marginally decreased after 14 days. The high surface of the fine fiber mats played a crucial role in fast decomposition, as they entirely disintegrated in less than only 40 days. In the case of water, the homocrystalline domains were more susceptible to hydrolysis than the stereocomplex ones. All the PLA fiber mats underwent decomposition and extensive disintegration for 70 days in water. Hydrolysis reduced the amorphous and crystalline fraction of the fibers via surface and bulk erosion, while the decomposition of stereocomplex-crystalline-rich domains mainly exhibited surface erosion. Findings revealed that high porosity and the high surface area of PLA melt-blown fine fiber mats undergo fast decomposition in compost and in water.
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In this study, we presented systematic and comparative investigations on the structure of polypropylene fibers generated using different processing conditions via melt blowing. Increasing air ...pressure, die‐to‐collector distance, and air temperature reduced the average fiber diameter nearly 3‐fold, 2‐fold, and 1.75‐fold, respectively. An average of 1.4 μm Feret‐diameter was observed as the smallest pore size, while the fiber mat solidities ranged from 8 to 13%. Differential scanning calorimetry results showed single melting peaks in the 1st heating cycle and double melting peaks in the second one, due to the phase transition at melt blowing. The fiber crystallinities varied between 43 and 52% by changing the processing conditions. The X‐ray diffraction study revealed that the MB fibers exhibited α and mesomorphic crystals depending on the processing parameters. The reference polypropylene sheet made of the same fiber grade polypropylene resin, on the other hand, exhibited a mix of α and γ crystalline forms. The polypropylene fiber mat tensile strength improved by 48% and by 13% with increasing air pressure and air temperature, respectively. Decreasing fiber collection distances resulted in 2.5‐fold higher tensile strength while strain at break reduced eightfold. A new factor, mat consolidation coefficient, was introduced and used to efficiently summarize melt‐blown fiber mats' process–property–structure relationships. This study details how to control the melt blowing parameters to tailor the polypropylene fiber mat features for the respective application field. It also presents an insight into fiber formation mechanisms during melt blowing for generating self‐bonded, defect‐free, fine fiber mats.
In this study, we demonstrate that integrating melt-blown fiber mat interleaves into single-polypropylene composites enhances several mechanical properties and influences the morphology positively. ...Polypropylene veils were generated by melt blowing. We then created single-polypropylene composites by film-stacking in which we applied a film as a matrix, a woven fabric as primary reinforcement, and the melt-blown fiber mats as interleaves. The tensile modulus was improved in the range of 20%–46%, and the interlaminar shear strength and the perforation energy at impact were increased by 17% and 14%, respectively, due to interleaving. Master curves were constructed from dynamic mechanical analysis frequency sweep tests based on the time–temperature superposition principle. The storage modulus significantly increased while the tanδ decreased. The interleaving considerably reduced the delamination by creating a net-like structure leading to superior interfacial adhesion. The interleaving demonstrated in this study can promote single-polymer composites’ utilization in various engineering applications where high toughness and impact resistance are required.
We briefly introduce a new approach for electrospinning in this paper. The novel high-speed electrospinning setup we invented involves a spinneret consisting of a cylindrical rotor placed within a ...concentric stator, both having a sharp metal edge. The solution gets out of the spinneret at the annular orifice in between these two edges forming a narrow liquid meniscus from which electrospinning jets are initiated. The setup applies mechanical shearing on the electrospinning solution. As the shear rate is increased (via the rotation speed) the viscosity of the shear-thinning solution decreases leading to enhanced Taylor-cone formation and the initiation of multiple jets. The throughput can be several orders of magnitude higher than that of the single capillary method and seems to be limited mainly by the evaporation rate of the solvent. With the small spinneret we reached 20 ml h−1 throughput for poly(ethyle oxide) solutions. The average fiber diameters decreased from 297 nm to 202 nm by applying shearing within the annulus.
In this article, we introduce a novel high productivity electrospinning setup for scaling up the classical method. We propose a new spinneret concept, which allows the shearing of the polymer ...solution prior to electrospinning. Most of the solutions used in electrospinning are shear‐thinning, that is, as they are sheared, they show smaller resistance against the deformations caused by the electrostatic field. Therefore, enhanced Taylor‐cone formation can be achieved, and it also gives a hand in controlling the nanofiber morphology easily, even during operation. In this study, we investigated the influence of shearing on the electrospinning process and the fiber morphology. When shearing was applied by rotation, the operation became more stable and the fiber morphology improved. Multiple jets were observed along the circular edges of the spinneret, also became thinner as an effect of the shearing rotation. The average diameter of the electrospun nanofibers was decreased by 18% with rotation speed applied, compared to those of the nonrotating condition (0 rpm). Besides that, we found that the electrospun nanofiber diameter distribution was significantly different for the various rotation speeds for which we found an applicable explanation with the aid of high‐speed camera recordings.
The incorporation of nanomaterials into polymer melts has been widely studied in recent years with the aim of improving the mechanical properties of 3D printed products. But it is still challenging, ...due to the poor dispersion of additives and the difficult processability of the resulting high-viscosity material. Here, we propose a novel fabrication process to enhance the mechanical properties of the 3D printed structure, and to overcome the above-mentioned issues. It is a method based on fused filament fabrication 3D printing with the application of nanofiber interleaves. We used poly (lactide acid) (PLA) both for producing nanofibers by electrospinning and for preparing 3D printing filaments by extrusion. The nanofiber mat (interleave) was placed between two printed layers during the printing process. We systematically studied the morphology of nanofibers at the interlaminar interface and found that nozzle temperature was the essential parameter that affected the adhesion between the nanofiber interleaves and the printed layers. We varied nanofiber content to study its effect on the mechanical properties of nanocomposites. With the integration of nanofibers, nanocomposites obtained improvements in storage modulus and tensile strength.
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In this article, we demonstrate fabricating polypropylene (PP)/multiwalled carbon nanotube (MWCNT) nanocomposite fiber veils and use them as interleaves in single‐polymer composites (SPCs) to enhance ...their thermal and mechanical properties. With this regard, we produced a hierarchical composite structure made of a film, a woven fabric and a fine fiber mat made of the same polymer. The nanocomposite fiber mats were generated by melt‐blowing. Results implied that incorporating MWCNT increased the viscosity of the melt blowing grade PP resin. Increasing MWCNT content increased the average fiber diameter and pore size by 2.1‐fold and 2.5‐fold, respectively. Incorporating MWCNT enhanced the melt‐blown (MB) fiber mat's specific strength by 78% and improved the thermal stability. We generated multiscale SPCs by film‐stacking, for which we applied a PP film as a matrix, a PP‐woven fabric as the primary reinforcement, and the MB fiber mats as interleaves. The SPC's tensile modulus was improved by 37% by the interleaving. Our findings implied that the MWCNT‐doped PP fiber mat interleaving provides a robust interfacial adhesion and higher damage tolerance under tensile load. Master curves were constructed from dynamic mechanical analysis frequency sweep tests based on the time–temperature superposition principle. The storage modulus increased by 33%, while the tanδ decreased around 10% with PP/MWCNT fiber mat interleaving. The developed multiscale SPC with MWCNT fiber mat interleaving veils may be easily integrated into engineering composite applications due to its cost‐efficiency, fair recycling, straightforward processing, enhanced stiffness, and interfacial adhesion.
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