Fiber Extrusion Research Articles

Effect of Single Wall Carbon Nanotubes on the Conformation of Poly(vinylidene fluoride)

Structures consisting of single Poly(vinylidene fluoride) (PVDF) chains, single wall carbon nanotubes (SWCNTs), a PVDF chain interacting with a SWCNT and of five PVDF chains arranged to resemble the α and β crystal structures of PVDF were evaluated using geometry optimizations and single point energy calculations. Density functional theory with dispersion correction was used for all calculations. The conformer of PVDF is the lowest energy structure, irrespective of whether the SWCNT is present or not. Interaction with the SWCNT reduces the energy difference between the β and α conformers by approximately 30%, indicating that SWCNTs can increase the relative amount of the β conformers at higher temperatures. However, even in the presence of the SWCNT this energy difference is approximately 1.67 kcal/mol per –CH2CF2– repeat unit, which is larger than kT at 300 K (0.6 kcal/mol). Hence, the presence of the SWCNTs is not expected to substantially increase the relative amount of the β conformers at these conditions. Compression of the α and β crystal structures, which occurs during fibre extrusion, and which may be increased if nanoparticles are present in the polymer matrix, further decreases the energy difference between the β and α conformers but only to a very small extent at pressures relevant to fibre extrusion.

Microstructure, texture evolution, mechanical properties and corrosion behavior of ECAP processed ZK60 magnesium alloy for biodegradable applications

Ultra-fine grained ZK60 Mg alloy was obtained by multi-pass equal-channel angular pressing at different temperatures of 250°C, 200°C and 150°C. Microstructural observations showed a significant grain refinement after ECAP, leading to an equiaxed and ultrafine grain (UFG) structure with average size of 600nm. The original extrusion fiber texture with planes oriented parallel to extrusion direction was gradually undermined during ECAP process and eventually it was substituted by a newly stronger texture component with considerably higher intensity, coinciding with ECAP shear plane. A combination of texture modification and grain refinement in UFG samples led to a marked reduction in mechanical asymmetric behavior compared to the as-received alloy, as well as adequate mechanical properties with about 100% improvement in elongation to failure while keeping relatively high tensile strength. Open circuit potential, potentiodynamic and weight loss measurements in a phosphate buffer solution electrolyte revealed an improved corrosion resistance of UFG alloy compared to the extruded one, stemming from a shift of corrosion regime from localized pitting in the as-received sample to a more uniform corrosion mode with reduced localized attack in ECAP processed alloy. Compression tests on immersed samples showed that the rate of loss of mechanical integrity in the UFG sample was lower than that in the as-received sample.

Water dependent structural changes of silk from Bombyx mori gland to fibre as evidenced by Raman and IR spectroscopies

DSC, attenuated total reflexion infrared (ATR-FTIR), and Raman microspectroscopy were used for the first time in a close to in vivo environment to study ready-to-spin Bombyx mori silkworms. The aim was to understand the change of the fibroin backbone organisation from the gland to the fibre. Raman shifts of the Amide I components reveal a strong change of organisation in the middle part of the hydrated gland, as anticipated previously measured modifications of salts concentrations and pH. Series of bands characteristics of the fully hydrated silk disappear, as observed for spider silk, despite the different aminoacid sequence. Confirmation is obtained from IR spectra taking into account the superimposed water component. The change of the silk–water interaction in the central part of the gland, from a hydrophobic to hydrophilic behaviour, is related to the water content decrease along the gland. pH sensitive carboxylate side chains markers confirm the modification. Fibroin organisation was also studied in the dried gland and in the spun fibre. The fibre extrusion by orients the fibroin chains along the fibre axis, with intercalated water molecules, leading to a material with specific mechanical properties, compared to the amorphous dried gland.

UNSTEADY BOUNDARY LAYER FLOW ALONG A STRETCHING CYLINDER AN ANALYTICAL SOLUTION

The axisymetric laminar boundary layer unsteady flo w along a continuously stretching cylinder immersed in a viscous and incompressible fluid is studied. T he governing partial boundary layer equations in cylindrical form are first transformed into ordinar y differential equations these equations are solved analytically using the optimal modified Homotopy Asymptotic method in order to get a closed form solution for the dimensionless functions f and e. The main object of this study is to investigate the effect of an unsteady motion of a stretching cylinder on the flow and hea t transfer characteristics such as surface skin friction and surface heat flux. These characteristi cs have a direct effect on the quality of the final product of the fiber manufacturing and extrusion processes. Co nsiderable effects were found for the dynamic parameter (γ), the curvature parameter ( ρ) and the prandtl number (pr) on the velocity and t he heat transfer.

Effect of fibre spinning conditions on the electrical properties of cellulose and carbon nanotube composite fibres spun using ionic liquid as a benign solvent

The aim of this study was to develop electrically conductive fibres from cellulose. To achieve this, the effect of fibre extrusion speed and fibre winding speed on the degree of alignment of multiwall carbon nanotubes (MWNTs), as well as the resulting electrical properties of the cellulose/MWNTs composite fibres were systematically studied. 1-Ethyl-3- Methylimidazolium Acetate (EMIMAc) was used as an environmentally benign solvent for dissolution of cellulose as well as for dispersion of MWNTs in the solution dope. To achieve good dispersion of MWNTs in the cellulose solution dope, MWNTs were non-covalently functionalized using carboxymethyl cellulose (CMC). This significantly improved the dis- persion of MWNTs in the solution dope. The degree of alignment of MWNTs after both fibre extrusion and winding, was studied using scanning electron microscopy (SEM) and wide angle X-ray diffraction (WAXD). The degree of alignment of MWNTs was correlated with the electrical properties. A significant decrease in electrical conductivity accompanied the increase in degree of alignment of MWNTs when fibres were spun with higher extrusion speed. The decrease was also measured when fibres were spun with higher winding speed using a constant extrusion speed. However, the decrease in conductivity due to winding was low relative to fibres spun at highest extrusion speed.

Synthesis and characterization of lignin-based carbon materials with tunable microstructure

Lignin-based carbons can be used as a low-cost alternative to graphite and petroleum-based carbons enabling the production of sustainable, functional carbon materials for various applications. The microstructure development of these carbons can be controlled through chemical modification of the lignin precursor and choice of carbonization parameters. In this work, microstructured carbon materials are synthesized from lignin using a combination of chemical modification and carbon fiber processing techniques. Lignin is modified by incorporating different ester groups which results in a precursor highly compatible with melt processing using the fiber extrusion technique and conversion into microstructured carbons by oxidative stabilization and subsequent carbonization. Furthermore, the impact of esterifications on precursor chemistry and carbonizations is investigated. A nuclear magnetic resonance study of modified lignins shows characteristic spectral changes as a result of esterifications. Ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry shows the modification process does not affect the polymeric character of the lignin backbone. Esterifications result in moderate shifts in O : C and H : C ratios. Thermogravimetric analysis of lignins reveals distinct differences in mass loss trends during oxidations and carbonizations.

D-Penicillamine induced elastosis perforans serpiginosa with involvement of glans penis

Elastosis perforans serpiginosa (EPS) is an unusual perforating disorder characterized by extrusion of altered elastic fibers through the epidermis. Clinically, it presents as keratotic papules with a tendency for serpiginous or annular distribution that most commonly involves the sides of the neck and the back. However, involvement of the penis has rarely been reported. We present a case of EPS involving the neck, axilla, and glans penis in a 42-year-old man who had received long-term d -penicillamine treatment for Wilson disease. Skin biopsy revealed perforating channels containing numerous altered elastic fibers, with a characteristic “bramble brush” or “lumpy-bumpy” appearance as demonstrated by an elastin stain. The latter is thought to be pathognomonic for penicillamine-induced degenerative elastosis. These degenerative changes occurring in glans penis have rarely been described in the literature. Prompt recognition of the rare presentation could lead to early discontinuation of the offending drug, to prevent further sequelae.

Development of polyethersulfone and polyacrylonitrile hollow fiber membranes for clarification of surface water and fungal enzyme broth

Hollow fiber membranes are of great commercial interest with several applications at the forefront of research to carryout bioseparations, drinking water purification, wastewater treatment besides liquid phase separations and gaseous separations. An experimental study was carried out to synthesize hollow fiber membranes from polyethersulfone (PES) and polyacrylonitrile (PAN) polymers to fabricate modules for surface water treatment and clarification of fungal enzyme broth. Design drawings of a manual hollow fiber spinning machine and spinneret were prepared to fabricate the necessary equipment for extrusion of hollow fibers. Effect of various spinning conditions on specific macroscopic fiber properties, such as outer diameter and wall thickness and membrane pore structure was studied. Concentrations of 15–20 wt% PES in n-methylpyrrolidone (NMP) and PAN in dimethyl formamide (DMF) solvents with important additives and pore formers were prepared. These polymer solutions were extruded through the spinneret and subjected to phase inversion in a water bath. The membranes were characterized by scanning electron microscopy (SEM) and pure water flux studies. PAN and PES exhibited 99.8 and 95.4% turbidity rejection. PAN exhibited a 5 log reduction of Escherichia coli bacteria for surface water treatment at a low hydraulic pressure of 1 bar with a flux of 54.2 L/m2 h at a water recovery of 80% whereas PES gave a flux of 36.6 L/m2 h with 4 log reduction of E. coli. PAN and PES membranes exhibited 54.9 and 69.3% xylanase enzyme recoveries from fungal broth at reasonable flux with turbidity rejection of 94.8 and 95.7% respectively.

A matricial approach of fibre breakage in twin-screw extrusion of glass fibres reinforced thermoplastics

Limiting fibre breakage during composite processing is a crucial issue. The purpose of this paper is to predict the evolution of the fibre-length distribution along a twin-screw extruder. This approach relies on using a fragmentation matrix to describe changes in the fibre-length distribution. The flow parameters in the screw elements are obtained using the simulation software Ludovic®. Evolution of an initial fibre-length distribution for several processing conditions was computed and the results were compared with experimental values. The computation gives satisfying results, even though more comparisons with experiments would be necessary.

German collaboration develops natural fibre pellets for injection moulding and extrusion

In Germany, a collaborative project led by the nova-Institut GmbH claims to have resolved the feeding and dosing problems typically encountered in the injection moulding and extrusion of natural fibres though the development of hemp fibre pellets. The pellets are manufactured by Badische Naturfaseraufbereitung GmbH (BaFa), and have been evaluated by Bremen's University of Applied Sciences (HS Bremen, Bionik) and trialled by a number of industry partners.

Extrusion‐based differences in two types of nylon 6 capillary‐channeled polymer (C‐CP) fiber stationary phases as applied to the separation of proteins via ion exchange chromatography

AbstractNylon 6 capillary‐channeled polymer (C‐CP) fibers used as the stationary phase in high‐performance liquid chromatography protein separations have been investigated. A difference in chromatographic behavior between two (presumably identical) nylon 6 C‐CP fibers, designated simply as nylon 6A and nylon 6B, reveals unknown differences in their chemical and physical nature as proteins are less retained on the latter. The possible differences are evaluated through several test methods, including Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), mechanical testing, MALDI‐TOF mass spectrometry, an organic reaction with ninhydrin, and dilute solution viscometry. Nylon 6B is shown to be a larger perimeter, stronger fiber, yet in a 200 mm, 0.8 mm i.d. column having an interstitial fraction of ∼0.6, it has an available surface area of ∼189 cm2, while nylon 6A is almost double that at ∼374 cm2. It is revealed that when in amorphous form, the base polymers have very comparable FTIR and DSC characteristics. When in their solid, extruded fiber form there are significant differences found in crystallinity, tensile strength, molecular weight distribution, and end group density. Nylon 6A is a lower molecular weight fiber, which results in ∼1.3× more amine end groups than nylon 6B. It is the end group density that ultimately determines the separation qualities. These results imply that both a difference in base nylon 6 molecular weight and also the fiber extrusion process have a significant influence on the performance of nylon 6 C‐CP fiber separation of proteins via ion exchange chromatography. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Synthetic Spider Silk Production on a Laboratory Scale

As society progresses and resources become scarcer, it is becoming increasingly important to cultivate new technologies that engineer next generation biomaterials with high performance properties. The development of these new structural materials must be rapid, cost-efficient and involve processing methodologies and products that are environmentally friendly and sustainable. Spiders spin a multitude of different fiber types with diverse mechanical properties, offering a rich source of next generation engineering materials for biomimicry that rival the best manmade and natural materials. Since the collection of large quantities of natural spider silk is impractical, synthetic silk production has the ability to provide scientists with access to an unlimited supply of threads. Therefore, if the spinning process can be streamlined and perfected, artificial spider fibers have the potential use for a broad range of applications ranging from body armor, surgical sutures, ropes and cables, tires, strings for musical instruments, and composites for aviation and aerospace technology. In order to advance the synthetic silk production process and to yield fibers that display low variance in their material properties from spin to spin, we developed a wet-spinning protocol that integrates expression of recombinant spider silk proteins in bacteria, purification and concentration of the proteins, followed by fiber extrusion and a mechanical post-spin treatment. This is the first visual representation that reveals a step-by-step process to spin and analyze artificial silk fibers on a laboratory scale. It also provides details to minimize the introduction of variability among fibers spun from the same spinning dope. Collectively, these methods will propel the process of artificial silk production, leading to higher quality fibers that surpass natural spider silks.

Synthetic Spider Silk Production on a Laboratory Scale

As society progresses and resources become scarcer, it is becoming increasingly important to cultivate new technologies that engineer next generation biomaterials with high performance properties. The development of these new structural materials must be rapid, cost-efficient and involve processing methodologies and products that are environmentally friendly and sustainable. Spiders spin a multitude of different fiber types with diverse mechanical properties, offering a rich source of next generation engineering materials for biomimicry that rival the best manmade and natural materials. Since the collection of large quantities of natural spider silk is impractical, synthetic silk production has the ability to provide scientists with access to an unlimited supply of threads. Therefore, if the spinning process can be streamlined and perfected, artificial spider fibers have the potential use for a broad range of applications ranging from body armor, surgical sutures, ropes and cables, tires, strings for musical instruments, and composites for aviation and aerospace technology. In order to advance the synthetic silk production process and to yield fibers that display low variance in their material properties from spin to spin, we developed a wet-spinning protocol that integrates expression of recombinant spider silk proteins in bacteria, purification and concentration of the proteins, followed by fiber extrusion and a mechanical post-spin treatment. This is the first visual representation that reveals a step-by-step process to spin and analyze artificial silk fibers on a laboratory scale. It also provides details to minimize the introduction of variability among fibers spun from the same spinning dope. Collectively, these methods will propel the process of artificial silk production, leading to higher quality fibers that surpass natural spider silks.

Directionally reflective fiber from multicomponent fiber extrusion

Directionally reflective fiber from multicomponent fiber extrusion

Extrusion Compounding of Flax-Fiber-Reinforced Polyethylene Composites: Effects of Fiber Content and Extrusion Parameters

The objectives of this study were to examine the effects of fiber content and extrusion parameters on flax-fiber-reinforced polyethylene composites and to determine the optimum values for the same. The flax fibers were chemically pretreated, ground, and mixed with powdered polyethylene. The mixture was extruded, pelletized, ground, rotationally molded, and cut into test specimens for testing and characterization. Superposition surface methodology was then applied as optimization technique. Optimum values were fiber content = 6.25%, barrel zone temperatures = 75, 117, 127, 137, and 147 °C, and screw speed = 118 rpm for linear low-density polyethylene (LLDPE) composites; and fiber content = 5.02%, barrel zone temperatures = 75, 118, 128, 138, and 148°C, and screw speed = 126 rpm for high-density polyethylene (HDPE) composites.

Recrystallization and texture evolution of Mg–3%Al–1%Zn–(0.4–0.8)%Sr alloys during extrusion

Microstructure and texture evolution during the extrusion of AZ31 magnesium alloy containing 0.4 and 0.8wt%Sr has been investigated. Following extrusion at 250°C, the microstructure consists of fine recrystallized and large elongated grains along with Al4Sr stringer precipitates. Extrusion at 350°C results in larger and more uniform grain size. Grain refinement and nucleation of new grains were associated with sub-grain formation in the elongated grains, grain boundary bulging, and nucleation at the particle interfaces. Texture measurements in the extrusion deformation zone show an increase in the basal ring fiber-texture from the undeformed zone toward the die opening. Compared to AZ31 without Sr, the texture intensity increases with increasing Sr at 250°C, whereas the strength of extrusion fiber texture decreases at 350°C. The Al solubility in the α-Mg matrix decreases with increasing the Sr and the Al solute atmosphere around the dislocations weakens. Due to the reduction of the solute drag effect, dislocation movement is facilitated and dynamic recrystallization becomes more intensive resulting in strengthening the texture during extrusion at 250°C. The decrease in texture intensity at 350°C extrusion is attributed to the activation of particle-stimulated nucleation (PSN) that leads to the nucleation of new grains with high orientation mismatch to the parent grains.

Elastose perfurante serpiginosa em portadora da síndrome de Down

Elastosis perforans serpiginosa is a rare, primary perforating dermatosis, frequently associated with certain genetic diseases and characterized by the transepidermal extrusion of elastic fibers. The present case report describes this dermatosis in a 19-year old female patient with Down's syndrome, who presented with asymptomatic erythematous, keratotic papules in an arciform pattern, located on her right forearm and knee, which had been present for five years. Following histopathological confirmation, treatment with cryotherapy was initiated, resulting in partial remission of the lesions.

Microstructure and mechanical properties of differently extruded AZ31 magnesium alloy

Abstract Profiles of the magnesium alloy AZ31 were produced by conventional indirect extrusion and by indirect extrusion into counterpressure with variations of the billet temperature TB from 200 °C up to 350 °C. Microstructural examination by optical microscopy showed that for extrusion trials carried out with billet temperatures TB ≤ 250 °C fine dynamically recrystallized grains are found while elongated grains of the former cast structure remain. Above TB ≥ 300 °C most grains show higher dynamic recrystallization kinetics and additional static recrystallization and increase to grain sizes of d = 30 – 50 μm. At TB ≤ 250 °C the typical extrusion fiber texture is found, at TB ≥ 300 °C a double fiber texture is formed due to static recrystallization. The results of the quasistatic mechanical tests are due to these differences in the microstructure.

Melt spun microporous fibers using poly(lactic acid) and sulfonated copolyester blends for tissue engineering applications

AbstractMicroporous fibers can potentially increase diffusional properties of three‐dimensional nonwoven scaffolds used for tissue engineering applications. We have investigated the use of a water‐dispersible copolyester, sulfonated copolyester (SP), to create micropores in composite fibers containing a blend of SP and poly(lactic acid) (PLA) at 1, 3, 5, and 10% SP content. PLA and SP were blended at 175°C in a microcompounder followed by extrusion of composite fibers and removal of SP from composite fibers by using hydrodispersion to form micropores in the composite fibers. Differential scanning calorimetric studies on unhydrolysed composite fibers showed that SP was partially miscible in PLA. Fourier transform infrared mapping of composite fiber cross sections revealed that SP was randomly dispersed throughout the cross section where the degree of dispersion depended on the SP content. As revealed by the scanning electron micrographs, the size of the micropores was dependent on the SP content. Micropores on fiber cross sections were observed in fibers above 3% SP indicating that at least 3% SP content is needed to produce droplet morphology of SP in these fibers. These results show that SP can be successfully used in a blend with PLA to produce microporous fibers to fabricate three‐dimensional nonwoven scaffolds for tissue engineering applications. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Large scale production of vesicles by hollow fiber extrusion: a novel method for generating polymersome encapsulated hemoglobin dispersions.

Vesicles, which include both liposomes and polymersomes (polymer vesicles), are being developed as therapeutic drug carriers. In this study, we present a fully scalable low pressure extrusion methodology for preparing vesicles. Vesicles were generated by continuous extrusion through a 200 nm pore diameter hollow fiber (HF) membrane. The first half of this study describes a method for generating empty polymersomes composed of different molecular weight amphiphilic poly(butadiene-b-ethylene oxide) (PBD-b-PEO) diblock copolymers on a large scale (50-100 mL) using a HF membrane. Monodisperse empty polymersomes were formed with particle diameters slightly less than 200 nm, which were close to the rated 200 nm pore size of the HF membrane. The second half of this study describes the successful encapsulation of hemoglobin (Hb) inside the aqueous core of polymersomes using the HF extrusion methodology. We demonstrate that polymersome encapsulated hemoglobin (PEH) particles formed by this technique had similar oxygen affinity, cooperativity coefficient, and methemoglobin (metHb) level compared to PEH particles formed by the 1 mL volume small scale manual extrusion method. Most notably, Hb encapsulation inside the polymer vesicles formed by the HF extrusion method increased 2-fold compared to the manual extrusion method. This work is important, since it will enable facile scale-up of homogeneous vesicle dispersions that are typically required for preclinical and clinical studies as well as industrial use.