Fiber spinning of anisotropic polymers

Yang, H. H.; Allen, Steven R.

doi:10.1533/9781845693213.130

Cited by 10 publications

(11 citation statements)

References 23 publications

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“…block copolymers | microfluidics | small-angle X-ray scattering T he flow orientation of anisotropic particles in narrow channels is relevant in many fields, ranging from the spinning and molding of fibers to the flow of cells or proteins through thin capillaries (1)(2)(3)(4). It is commonly assumed that anisotropic particles align parallel to the flow direction (5).…”

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confidence: 99%

Anisotropic particles align perpendicular to the flow direction in narrow microchannels

Trebbin¹,

Steinhauser

Perlich³

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

162

147

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The flow orientation of anisotropic particles through narrow channels is of importance in many fields, ranging from the spinning and molding of fibers to the flow of cells and proteins through thin capillaries. It is commonly assumed that anisotropic particles align parallel to the flow direction. When flowing through narrowed channel sections, one expects the increased flow rate to improve the parallel alignment. Here, we show by microfocus synchrotron X-ray scattering and polarized optical microscopy that anisotropic colloidal particles align perpendicular to the flow direction after passing a narrow channel section. We find this to be a general behavior of anisotropic colloids, which is also observed for disk-like particles. This perpendicular particle alignment is stable, extending downstream throughout the remaining part of the channel. We show by microparticle image velocimetry that the particle reorientation in the expansion zone after a narrow channel section occurs in a region with considerable extensional flow. This extensional flow is promoted by shear thinning, a typical property of complex fluids. Our discovery has important consequences when considering the flow orientation of polymers, micelles, fibers, proteins, or cells through narrow channels, pipes, or capillary sections. An immediate consequence for the production of fibers is the necessity for realignment by extension in the flow direction. For fibrous proteins, reorientation and stable plug flow are likely mechanisms for protein coagulation.block copolymers | microfluidics | small-angle X-ray scattering T he flow orientation of anisotropic particles in narrow channels is relevant in many fields, ranging from the spinning and molding of fibers to the flow of cells or proteins through thin capillaries (1-4). It is commonly assumed that anisotropic particles align parallel to the flow direction (5). When flowing through thin channel sections, one expects the increased flow rate to improve the alignment. We investigated the alignment of anisotropic colloids (i.e., cylindrical micelles) flowing through thin sections of microchannels using synchrotron microfocus small-angle X-ray diffraction and polarized optical microscopy. Surprisingly, we find that anisotropic colloids orient perpendicular to the flow direction after passing through narrow channel sections. The perpendicular alignment is surprisingly stable, extending throughout the remaining part downstream of the channel. Ongoing experimental studies indicate that this observation holds for other anisotropic cylindrical or disk-like colloids as well. We show by microparticle image velocimetry and finite element fluid dynamics simulations that the perpendicular flow orientation is induced by perpendicular extensional flow in the expansion zone after the narrow section. Only close to the channel walls does shear flow dominate, leading to parallel flow orientation of anisotropic particles.In situ investigations of the flow orientation of colloids in solution under very well-defined flow conditi...

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mentioning

confidence: 99%

Anisotropic particles align perpendicular to the flow direction in narrow microchannels

Trebbin¹,

Steinhauser

Perlich³

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

162

147

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“…Indicative ranges for the tensile properties of as-spun fibre are 42-650 gpd for the modulus, 1-12 gpd for the tenaticity and 1-3% for the elongation at break. After heat treatment, these values generally increase to 480-1200 gpd for the tensile modulus, 3-35 gpd for tenacity and 2-5% for the strain to failure (Yang and Allen, 1994). For these polymers the theoretical crystal modulus is in the range of 180-250 GPa (i.e.…”

Section: Mechanical Propertiesmentioning

confidence: 99%

“…Consequently, typical spinning processes are conducted at extrusion temperatures of 280-400 °C for polymer with inherent viscosities of 1.5-5 dL/g. The fibres are collected from spinneret holes with diameters of 0.127-0.254 mm at a draw speed of 90-1800 m/min in air or in an inert atmosphere (Pletcher, 1976;Adams and Farrow, 1993;Yang and Allen, 1994;Clements, 1998). The mechanical properties of as-spun fibre strongly depend on the polymer molecular weight.…”

Section: Fibre Spinningmentioning

confidence: 99%

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Liquid crystalline organic fibres and their mechanical behaviour

Pegoretti

Traina

2009

Handbook of Tensile Properties of Textile and Technical Fibres

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“…Thermotropic liquid crystalline polymers (TLCPs), which exhibit liquid crystal behavior at adequate temperature, is one of the typical anisotropic polymers and represented almost exclusively by aromatic copolyesters [ 1 , 2 , 3 ]. Especially, TLCP resins such as the copolymers, composed of 4-hydroxybenzoic acid (HBA) and 2-hydroxy-6-napthoic acid (HNA) in a molar ratio of 73/27, has attracted attention as one of the commercially available resins, because it possesses excellent melt processability to manufacture technical fibers, films and injected parts through the conventional melt processes [ 4 , 5 , 6 , 7 ].…”

Section: Introductionmentioning

confidence: 99%

Fiber Formation and Structural Development of HBA/HNA Thermotropic Liquid Crystalline Polymer in High-Speed Melt Spinning

Song

Lee

Jang³

et al. 2021

Polymers

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High-speed melt spinning of thermotropic liquid crystalline polymer (TLCP) resin composed of 4-hydroxybenzoic acid (HBA) and 2-hydroxy-6-napthoic acid (HNA) monomers in a molar ratio of 73/27 was conducted to investigate the characteristic structure development of the fibers under industrial spinning conditions, and the obtained as-spun TLCP fibers were analyzed in detail. The tensile strength and modulus of the fibers increased with shear rate in nozzle hole, draft in spin-line and spinning temperature and exhibited the high values of approximately 1.1 and 63 GPa, respectively, comparable to those of industrial as-spun TLCP fibers, at a shear rate of 70,000 s−1 and a draft of 25. X-ray diffraction demonstrated that the mechanical properties of the fibers increased with the crystalline orientation factor (fc) and the fractions of highly oriented crystalline and non-crystalline anisotropic phases. The results of structure analysis indicated that a characteristic skin–core structure developed at high drafts (i.e., spinning velocity) and low spinning temperatures, which contributed to weakening the mechanical properties of the TLCP fibers. It is supposed that this heterogeneous structure in the cross-section of the fibers was induced by differences in the cooling rates of the skin and core of the fiber in the spin-line.

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Fiber spinning of anisotropic polymers

Cited by 10 publications

References 23 publications

Anisotropic particles align perpendicular to the flow direction in narrow microchannels

Anisotropic particles align perpendicular to the flow direction in narrow microchannels

Liquid crystalline organic fibres and their mechanical behaviour

Fiber Formation and Structural Development of HBA/HNA Thermotropic Liquid Crystalline Polymer in High-Speed Melt Spinning

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