Fiber Breakup Research Articles

Mechanical recycling of biobased polyethylene-agave fiber composites

Biobased polymers have emerged as a promising alternative to petroleum-based polymers in terms of lower environmental impact. However, to improve their carbon footprint, it is important to study strategies, such as recycling, extending the useful life of these biopolymers, and mitigate their higher costs compared to petroleum-based polymers. Adding agro-industrial wastes as fillers or reinforcements is another option to reduce the cost and increase the biobased content to produce composites. This study aimed to evaluate the addition of agave fibers to biobased linear low-density polyethylene (bio-LLDPE) and their effect on its reprocessing by extrusion, i.e., close-loop mechanical recycling. The results revealed that it was possible to reprocess the bio-LLDPE alone as limited changes in their physical properties were observed up to 34 cycles. However, for the composites, the viscosity changed in the first eight cycles mainly due to fiber break-up (lower aspect ratio). The dimensions of the agave fibers are modified by reprocessing. In the initial 8 cycles, there is a notable decrease in fiber dimensions, affecting the tensile, flexural, and impact properties of the composites. The water uptake was found to decrease with each cycle due to better fiber dispersion and the reduction of interfacial voids/defects. Nevertheless, the color of the bio-LLDPE and its composites showed significant changes by reprocessing, which is associated with thermal and oxidation degradation. Despite minor property losses, the study reveals that bio-LLDPE/agave fiber composites exhibit a commendable level of sustainability. This characteristic enables their extended reuse and reprocessing over a prolonged duration.

Non-circular pressure swirl nozzles injecting into stagnant air

As far as we are aware, all the previous studies have focused on circular injectors. Here, the effect of non-circular orifice shape on pressure swirl injector was investigated experimentally. For this purpose, three injectors; circular, square and rectangular were manufactured. The nozzles had the same cross-sectional area. Water was used as the working fluid and tests were conducted at room temperature and pressure. The Weber number varied from 484 to 1936. Flow parameters of the swirl jets were obtained by an in-house image processing code. The measured parameters were: discharge coefficient, spray angle, breakup length, lateral spread, SMD of drops and wavelength of surface waves formed on the cone. The influence of nozzle shape on all these parameters are discussed.A new breakup regime morphology for non-circular pressure swirl nozzles was defined. At lower Weber numbers, the air core was trapped inside the liquid sheet and relatively large ligaments were formed and separated from the edges (fiber breakup regime). As the Weber number was increased Rayleigh-Taylor instability produced cell-like structures near the nozzle exit. These cell-like structures eventually broke up at the thickened edges of the cells and formed Christmas tree like structures (Christmas tree regime). We found that all the measured flow parameters can best be correlated as a function of Reynolds number and Weber number based on liquid sheet thickness at nozzle exit. All these correlations were reported. Breakup length and lateral spread were heavily influenced by the breakup regime. In fiber breakup regime the breakup length and lateral spread increased with increasing Weber number. However, in Christmas tree (cellular) breakup regime, breakup length and lateral spread decreased with increasing Weber number.

Primary and secondary breakup of molten Ti64 in an EIGA atomizer for metal powder production

Electrode Induction melting Gas Atomization (EIGA) is a free-fall gas atomization process used to produce metal powders, where a swirling supersonic gas jet hits a molten metal stream atomizing it into droplets through various fragmentation mechanisms. Fragmentation mechanisms of molten Ti64 are investigated by high-speed video visualization. The role of gas pressure and melting chamber overpressure on the fragmentation mechanisms and on the particle size distribution is determined. The mechanisms observed are fiber breakup, bag breakup and Rayleigh breakup for primary fragmentation and bag breakup and shear breakup for secondary fragmentation. Increasing the gas pressure promotes shear breakup and creates finer droplets. A model based on log-stable law is proposed to fit the mass distribution according to the dominant fragmentation regime. A good agreement is observed between the different analysis (dominant atomization regime, mass cumulative distribution evolution, parameters of log-stable law). A criterion for prediction of nozzle clogging is devised.

Influence of PMMA brushes grafted from GO on rheological properties of PMMA/SAN immiscible blend in shear and elongation flow

In real technological processes, both shear and elongational flow is present. The material properties may differ significantly under both types of flow. Hence, they both define the final morphology and thus properties of the materials. In this work, the morphology of immiscible blends containing polymer hybrid particles was related to extensional rheological properties for the first time. The effect of various lengths of polymer brushes grafted from graphene oxide particles (GO) surface was investigated. As a polymer matrix the immiscible blend of poly(methyl methacrylate)/styrene-co-acrylonitrile (PMMA/SAN) was used. Thus the poly(methyl methacrylate) (PMMA) brushes grafted from GO (GO-g-PMMA) with various number average molar masses (Mn) of PMMA brushes with respect to chain entanglement limit of freely dispersed PMMA were prepared. The extensional rheological properties were affected by Mn of PMMA brushes, while the rheological properties in shear were unchanged. Transmission electron microscopy revealed the compatibilization effect for short densely grafted brushes with Mn of 10,300 g/mol, as smaller domains were observed. On the contrary, the higher Mn PMMA brushes facilitated coalescence. With increasing length of brushes, the elongational viscosity at low elongation rates (∼< 0.1 s−1) decreased, which facilitated the coalescence. The increase of viscosity at higher elongation rates (∼> 0.1 s−1) was not sufficient enough to cause fiber breakup and thus elongated domains were formed.

Cell-Incorporated Bioactive Tissue Engineering Scaffolds made by Concurrent Cell Electrospinning and Emulsion Electrospinning

Electrospun fibrous scaffolds attract great attention in tissue engineering owing to their high similarity in architecture to the extracellular matrix (ECM) that support cell attachment and growth in human bodies. Although they have shown superiority in promoting cell attachment and proliferation on their surfaces and hence, hold great promise for the regeneration of body tissues, the research still faces a great challenge of three-dimensional (3D) cell incorporation in electrospun scaffolds to form thick and cell-dense constructs because deep cell infiltration is hard to achieve in conventional electrospun scaffolds that normally have very small diameters of interconnected pores. Such hindrance has severely limited the clinical application of electrospun fibrous scaffolds to repair/regenerate various body tissues, particularly those with complex anatomies. To address this challenge, we have developed a concurrent cell electrospinning and emulsion electrospinning technique for fabricating bioactive bio-hybrid scaffolds with 3D and high-density cell incorporation. Through concurrent electrospinning, cell-encapsulated hydrogel fibers (“cell fibers”) and growth factor-containing ultrafine fibers are simultaneously deposited to form two-component scaffolds (i.e., scaffolds composed of two types of fibers) according to the design. With the breakup of cell fibers, live cells with well-preserved cell viability are released in situ inside the scaffolds, resulting in the creation of cell-incorporated bioactive scaffolds with ECM-mimicking fibrous architectures and 3D and high-density incorporation of cells. The growth and functions of incorporated cells in the scaffolds can be enhanced by the released growth factor from the emulsion electrospun fibrous component. The bioactive bio-hybrid scaffolds fabricated via concurrent electrospinning mimic the cell-matrix organization of body tissues and therefore have great potential for regenerating body tissues such as tendon and ligament.

Fiber Length Distribution in Twin-Screw Extrusion of Fiber-Reinforced Polymer Composites: A Comparison between Shear and Extensional Mixing

Abstract New extensional mixing elements (EME) for twin-screw extrusion were applied to compound glass fibers (GF), carbon fibers (CF) or polyethylene terephthalate fibers (PETF) reinforced polymer composites with polymer matrix of polypropylene (PP) or polyethylene oxide (PEO) and the resulting fiber degradation upon processing was evaluated and compared with compounding via shear flow-dominated kneading blocks (KB). Composites structures were characterized in terms of fiber length and distribution, and cumulative length ratio, at five locations along the mixing zone. Although significant fiber breakage was achieved for both configurations, it was markedly lower in composites processed using the EME, because whereas the high shear stress kneading motion in the KB degrades fibers significantly, fiber breakup is significantly minimized by the alignment induced by the EME prior to flow in the high-stress regions.

In-situ nano-fibrillation of poly(butylene succinate-co-adipate) in isosorbide-based polycarbonate matrix. Relationship between rheological parameters and induced morphological and mechanical properties

Multiphase systems in which 30 wt% of ductile semi-crystalline polymer, namely poly(butylene succinate-co-adipate) (PBSA), was homogeneously dispersed at the melt state in an amorphous bio-based poly(isosorbide carbonate co-cyclohexanedimethanol) (named PIC). Usually, for the manufacturing of in situ microfiber reinforced polymer composite (MFCs), the melting temperature of the reinforcing polymer must exceed that of the matrix by at least 30 °C, to allow fibril preservation during matrix consolidation step. Then, the blend is drawn at temperatures equal or slightly above the glass transition temperatures (Tg) of both components. Surprisingly, in our case, despite the low melting temperature of PBSA with respect to the (Tg) of PIC, it was demonstrated for the first time, the feasibility to create a nanosized fibrillar PBSA phase in the continuous PIC matrix. The development of a stable nanofibrillar morphology was promoted by controlling the viscosity and elasticity ratios between the dispersed and continuous phases as well as the time required for fiber breakup during processing. Interestingly, compared to the PIC matrix, the nanofibrillar PIC/PBSA composites exhibited outstanding mechanical and rheological properties. The elongation at break of the blend was increased by about 670% compared to that of the neat matrix without sacrificing the tensile strength. On the other hand, the energy to break of blends was found to be almost ten times greater than that of pure PIC matrix. Therefore, the methodology for the rheological and morphological control developed in the present study could find interesting applications in the design of novel bio-based polymer composites thin films dedicated for green packaging.

Simulation of Breakup Process of Polymer Jet during Melt Blowing

A Level- set method coupled with the Navier-Stokes equations was applied to simulate the breakup process of polymer jet during melt blowing. The initial perturbation was represented by a trigonometric function. The theory of the polymer jet breakup process driven by surface tension was explained and the breakup process was illustrated visually by simulation results. By varying the parameter values in the model, the effects of viscosity, diameter, surface tension, and surrounding perturbation on the fiber breakup process were discussed. Experiments were conducted to explore the effects of processing conditions on the fiber breakup process and validate the simulation results. It is suggested that lowering the surface tension of polymer through physical and chemical modification can help to reduce the possibility of polymer jet breakup and produce melt blown nonwovens with better quality.

Meltblown technology for production of polymeric microfibers/nanofibers: A review

This work summarizes the current state of knowledge in the area of meltblown technology for production of polymeric nonwovens with specific attention to utilized polymers, die design, production of nanofibers, the effect of process variables (such as the throughput rate, melt rheology, melt temperature, die temperature, air temperature/velocity/pressure, die-to-collector distance, and speed) with relation to nonwoven characteristics as well as to typical flow instabilities such as whipping, die drool, fiber breakup, melt spraying, flies, generation of small isolated spherical particles, shots, jam, and generation of nonuniform fiber diameters.

Visual analysis of plastication of long‐glass fiber‐reinforced resins using a glass‐insert heating cylinder

The fiber‐reinforced plastication processes during the injection molding of reinforced resins with long fibers are difficult to observe through visualization cylinders because of possible obstacles, such as (1) opacification of melts, (2) abrasion on the inner surface of glass windows, and (3) breakage of glass windows under high pressures. In this study, we visualized the plastication process of long‐glass fiber‐reinforced resins containing 50 wt% fibers. In plastication experiments using three full‐flight screws with different compression ratios, we observed the instability of the melting process, the generation of solid beds and melt pools, and the breakup of melted segments. We demonstrated that the plastication process depends considerably on the compression ratio and clarified the characteristic molding phenomena related to fiber breakup. Based on our observations, we proposed a model that explains the different fiber breakage distributions at different compression ratios during the melting process of long‐glass fiber‐reinforced resins. POLYM. ENG. SCI., 59:1300–1309 2019. © 2019 Society of Plastics Engineers

Liquid jet breakup unsteadiness in a coaxial air-blast atomizer

The aim of this paper is to experimentally characterize the liquid jet breakup unsteadiness in a coaxial air-blast atomizer. The current research focuses on the measurement of the fluctuations of the jet breakup length and the flapping instability of the liquid jet, which contribute to the downstream fluctuations of the spray characteristics. The optical connectivity technique was used to measure the instantaneous breakup length of the water jet. Also, time resolved shadowgraph images of the primary jet breakup process were captured by high-speed imaging to characterize the jet instabilities at different axial locations from the atomizer exit. Experiments were performed for a wide range of air-to-liquid momentum flux ratio ( M) and aerodynamic Weber number ( Weg) corresponding to membrane- and/or fiber breakup mode of the jet disintegration process. The mean jet breakup length was found to vary inversely with M through a power law relation in agreement with the literature, while the breakup length fluctuations were found to first decrease and then increase with M. In order to capture the unsteady dynamics of the jet breakup process, the proper orthogonal decomposition analysis of the optical connectivity images was performed. The jet flapping and the fluctuations of the jet breakup length were identified as the second and the third spatial proper orthogonal decomposition modes, respectively, for all operating conditions of the atomizer. The amplitude and the frequency of the instabilities were measured by temporal tracking of the liquid–air interface on the shadowgraph images. The disturbance close to the injector exit corresponds to the Kelvin–Helmholtz instability, while close to the jet breakup point the jet exhibits the flapping instability, which is characterized by lateral oscillation of the jet about the atomizer axis. The influence of the liquid jet Reynolds number and momentum flux ratio on the KH and the flapping instabilities are examined.

Easy Printing of High Viscous Microdots by Spontaneous Breakup of Thin Fibers.

Electrohydrodynamic jetting is emerging as a successful technique for printing inks with resolutions well beyond those offered by conventional inkjet printers. However, the variety of printable inks is still limited to those with relatively low viscosities (typically <20 mPa s) due to nozzle clogging problems. Here, we show the possibility of printing ordered microdots of high viscous inks such as poly(lactic-co-glycolic acid) (PLGA) by exploiting the spontaneous breakup of a thin fiber generated through nozzle-free pyro-electrospinning. The PLGA fiber is deposited onto a partially wetting surface, and the breakup is achieved simply by applying an appropriate thermal stimulation, which is able to induce polymer melting and hence a mechanism of surface area minimization due to the Plateau-Rayleigh instability. The results show that this technique is a good candidate for extending the printability at the microscale to high viscous inks, thus extending their applicability to additional applications, such as cell behavior under controlled morphological constraints.

Interfacial activity of reactive compatibilizers in polymer blends

The influence of a reactive block copolymer compatibilizer on the breakup of polymer fibers in the quiescent conditions is investigated using the breaking thread method (BTM). The compatibilizer is either localized at the interface of two polymers or incorporated in the bulk of thread phase. Moreover, the nominal interfacial tension between two polymers is estimated as a function of compatibilizer concentration for both types of samples using Tomotika theory. It is shown that assembling of compatibilizer molecules at the interface of two immiscible polymers can result in very different dynamic of thread breakup compared to samples containing the compatibilizer in the bulk phase. We observe a reduction in the rate of thread breakup (kinetic of stabilization) when compatibilizer is incorporated in the bulk of thread phase. Such effect is more significant when compatibilizer is localized at the interface of two fluids. Additionally, the mode of thread breakup is sensitive to the compatibilizer location since a beads-on-a-string (BOAS) morphology is observed when compatibilizer is localized at the interface. In conclusion, the usual attribution of interfacial activity of compatibilizer in polymer blends may be originated from their random presence at the interface rather than thermodynamically favored diffusion to the interface.

Microscopy Study of Morphology of Electrospun Fiber-MOF Composites with Secondary Growth

ABSTRACTMicroscopy studies were performed over a series of metal-organic-framework (MOF) imbedded electrospun fibers. Analysis of as-spun fibers revealed five different MOF particle-fiber imbedded morphologies including complete particle encasement, over-filled, surface-bound, welded, and agglomerated. To mitigate issues with fiber breakup during electrospinning (ES) due to MOF particle incorporation, secondary growth method was used. Secondary growth was performed on both Matrimid and polysulfone fibers impregnated with a MOF, ZIF-8, in either water or methanol solvents. Results show that when water was used, crystal formation was limited to formation on the top layer of the fiber mat due to hydrophobicity. When methanol was used in place of water, MOF crystal growth occurred in a patchwise manner, where crystals grow across fibers and span the entire fiber mat. From this work, it was determined that successful secondary growth of MOF imbedded electrospun fibers can be accomplished when particles are either highly exposed along the fiber surface for adequate exposure to solvent, or the solvent used promotes reactant penetration into the polymer to allow access to the seeded MOF crystals.

Surface free energy analysis of electrospun fibers based on Rayleigh-Plateau/Weber instabilities

Electrospinning is an increasingly common technique used to produce fibers with a range of diameters. These electrospun fibers are used extensively in applications that exploit the material’s high surface area to volume ratio, thus requiring detailed knowledge of the surface properties of the fibers. The surface free energy of individual free standing electrospun styrene-butadiene rubber (SBR) fibers was determined here from the time-dependent break-up of long fibers driven initially by Rayleigh-Plateau/Weber instabilities. Individual free standing electrospun rubber fibers were observed to change from a cylindrical fibrous geometry to semi-spherical droplets during a time period of several days when above the glass transition temperature of the polymer. A wave-like transition from fiber to droplet was attributed to a surface tension driven break-up process occurring over a time strongly influenced by the rubber's viscosity. The surface free energy for an electrospun rubber fiber was found using a Weber approach for the free standing fibers and Diez et al theory for dynamic fluid instability of fluid ridges. Both methods lead to similar values of fiber surface free energy and were confirmed from bulk measurements exploiting Owens-Wend theory. The approach presented here is powerful as the surface free energy, indicative of the physical and chemical behavior of the fiber surface, can be determined for any fiber diameter provided the geometric break-up of the fiber is observed.

Investigation of Nanofiber Breakup in the Melt-Blowing Process

Nanofibers definitely hold a great advantage and can be applied in many areas because they have very high specific surface area. Recently, great attention is being paid to fabricate nanofiber nonwoven webs using melt-blowing technology. In this paper, melt-blown nanofibers have been produced by multihole dies using two kinds of commercial polymers under different processing conditions. The average nanofiber diameters achieved were 780 and 810 nm, respectively. The fiber breakup, which was driven by surface tension when fiber diameters approached nanoscale, was investigated. The Rayleigh instability theory for a melt-blowing fiber was introduced and illustrated as the reason for fiber breakup. Both theory and experimental results reveal that the surface tension, polymer viscosity, fiber diameter, and melt-blowing-process conditions, such as air pressure and temperature, significantly influence the fiber breakup. This research gives a useful understanding for the formation of melt-blown nanofibers and provi...

Effect of extensional viscosity on cocontinuity of immiscible polymer blends

Cocontinuous blends were prepared from polyethylene (PE) and polylactic acid (PLA). The extensional and shear rheological properties of PE and PLA were independently tuned by varying long chain branching architecture. Shear rheological properties of the blend components were characterized by capillary and oscillatory rheometry. Extensional rheological properties were characterized by orifice entrance pressure drop and sheet wind-up. It was found that branching significantly increased zero-shear viscosity and extensional viscosity, but did not alter the shear viscosity at the shear rates typically observed in mixing flows. Adding a branched polymer to the blend allowed the other blend component to percolate into a continuous network with less material. Blending with two branched materials significantly broadened the range of cocontinuous compositions from 39–59 vol. % with a linear/linear blend to 25–76 vol. % for a branched/branched blend. This was attributed to the ability of a strain hardening matrix to promote elongation, and hence percolation, of the minor phase. Domain size was minimized when a slight amount of strain hardening was introduced, as this allowed formation of narrow features while stabilizing them against fiber breakup. All blends showed a rate of morphological coarsening during annealing inversely proportional to zero-shear rate viscosity, suggesting that quiescent coarsening flows are dictated by low-rate shear flow properties and not extensional properties. We find that our results and coarsening rates in the literature show the same linear dependence on the ratio of interfacial tension to log volume average zero-shear viscosity with a coefficient of ∼0.03, indicating a simple universal relation.

Manipulating characteristic timescales and fiber morphology in simultaneous centrifugal spinning and photopolymerization

In this study, the fabrication of crosslinked nonwoven fibers via simultaneous thiol-ene photopolymerization and spinning of monomer jets has been demonstrated in centrifugal Forcespinning for the first time. We observed that simultaneous Forcespinning and photopolymerization resulted in a wide variety of fiber morphologies including beads, beads-on-string, uniform fiber, fused fibers, and well-cured fibers. To elucidate the underlying mechanisms and parameter interactions that give rise to these morphologies, we systematically varied the light intensity, solution elasticity, and spin speed of the Forcespinning process. From these experimental results, an operating diagram was constructed based on the measured process parameters, their respective timescales, and observed effects on fiber morphology. While numerous parameters can individually affect fiber formation and morphology, the interplay between curing kinetics, solution viscoelasticity, and orifice-to-collector processing time window is also crucial in this process. Smooth and well-cured fibers were formed only when the photopolymerization occurred sufficiently quickly, before both the breakup of fibers into droplets due to a surface tension driven Rayleigh instability and the deposition of fibers on the collector. Our findings can serve as a predictive guideline for the fabrication of crosslinked fibers with desired morphology, the implementation of the in-situ polymerization and spinning concept into other commercial fiber manufacturing technologies, and the adaptation of other functional or high performance monomer systems.

Breakup morphology of annular liquid sheet with an inner round air stream

Experiments were performed on the deformation and breakup of annular liquid sheet of nine coaxial twin-fluid air-blast atomizers with water–air systems by using a high speed camera. Due to the morphological difference, the annular sheet breakup could be classified into three regimes, which were bubble (shell) breakup, Christmas tree (cellular) breakup and fiber breakup. The roles of atomizer size and Rayleigh–Taylor instability in the annular sheet breakup were studied. The correlations on the instability wavelength and the size of cellular structure were deduced. The results showed that the dimensionless cellular size was proportional to We−0.5, which were in good agreement with the experimental results. In order to have an overview of the different breakup mechanisms taking place over the wide range, we suggested categorizing these breakup regimes in a Weber number and dimensionless sheet thickness map.

Effect of local stress concentration near the rib edge on water and electron transport phenomena in polymer electrolyte fuel cell

The performance of polymer electrolyte fuel cell (PEFC) depends on transport phenomena in the gas diffusion layer (GDL). To elucidate the relationship between the local stress concentration near the rib edge and current density distribution, contact stress analysis and charge transport calculations were performed. Subsequently, the effect of GDL deformation caused by the local stress concentration on water transport was investigated. As a result, contact stress analysis showed that through-plane stress in GDL was concentrated near the rib edge. However, the stress was not concentrated on the catalyst layer even when the compression ratio and curvature radius of the rib were varied over a wide range. By solving the charge conservation equation, the potential and current density distribution were obtained. The current density, although not concentrated on the catalyst layer, was concentrated in GDL near the rib edge because the GDL conductivity near the rib edge increased locally from the stress concentration. Calculation showed that to decrease the effect of local stress, rounding off the rib is more effective than decreasing the compression ratio. From scanning electron microscopy (SEM) images of the GDL after clamping, the stress concentration caused the breakup of fibers and polytetrafluoroethylene (PTFE), which caused the hydrophobicity to deteriorate. Therefore, the preferential pathways of water behavior were observed near the rib edge. It was shown that local stress concentration near the rib edge affected the water behavior and GDL characteristics although it did not affect the catalyst layer.