Gel-spinning

Gel spitming enables the production of high-performance fibers from polymers with flexible polymer chains, such as ultra-high molecular weight polyethylene (UHMW-PE). To form gel filaments, the concentration of polymer solution is typically low, e.g., 1-2% for UHMW-PE. The maximum attainable draw ratio is related to the initial polymer concentration (c) by  

Therefore, lower polymer concentration leads to higher draw ratio, which is beneficial for achieving ultra-high molecular orientation. 

FIGURE 3.67 Stress-strain curves for gel spun-drawn polyethylene fibers. Draw ratios (A) 2.8x (B) 8.4x (C) 15.7x (D) 31.7x. (From Smith, P. Lemstra, P.J. J. Mater. ScL, 1980, 75, 505. With permission.) 

The technology of gel spinning has not been successful with polypropylene. Unlike polyethylene with a simple linear chain conformation, the hehcal chain conformation of polypropylene can conceivably forfeit a tight crystal packing required for a high-strength, 

Smith and Lemstra (DSM, The Netherlands) combined the ideas of superdraw-ability and working with dilute solutions of (ultra-)high molecular weight polyethylene, and added the essential function of a continuous spinning process [18]. Gel spinning was born. 

A high molecular weight is required for an eventually high draw ratio. Draw ratio scales as DR MW°. In gel spinning the molecular weight is higher than in 

Gel crystals are melted and rebuilt, entanglements give coherence 

Gel-spun polyethylene is produced by DSM in cooperation with Toyobo (Dyneema) and Honeywell, formerly Allied Signal (Spectra). From the relevant patents it is fairly obvious that different solvents are used a volatile solvent in the Dyneema process and a nonvolatile solvent in the Spectra process. 

A nonvolatile solvent must be completely removed before drawing, by extraction with a volatile solvent. The dried filaments have a xerogef structure, a dry, porous structure which collapses during drawing. A volatile solvent can be partly removed in the spinning step, but may well be further removed by evaporation and squeezing out in the drawing step. 

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GELSIL Gel, silicone Gel spinning Gel spun fibers Geltabs... 

Rotations around torsional barriers induce changes in chain conformation. For conjugated systems like polydiacetylenes, flow-induced changes in chain conformation can have a profound influence on the photon absorption and electronic conductivity properties of the material [73]. Flow-induced changes in molecular conformation form the basis for several technically important processes, the best known examples are the production of oriented fibers by gel spinning [74], the compatibility enhancement [75] and the shear-induced modification of polymer morphology [76]. 

Fig. 28 The observed strength as a function of the initial modulus for a series of POK yarns made by melt spinning and by gel spinning compared with the calculated curves...

FIGURE 5.10 (a) Prototype CARS endoscope image of 0.75-(xmpolystyrene beads embedded in agarose gel spin-coated on a coverslip (Ar = 2845 cm ). The image dimension is 29 (xm x 29 Xm (128 x 128 pixels). The pump and Stokes powers at the sample were 80 mW each, with a pixel dwell time of 1 ms. (b) CARS intensity profile along the white line in (a). The CARS contrast decreased when the system was tuned off the resonance maximum. 

A conventional <111> oriented Pb(Zro.45Tio.55)03 (pzt) ferroelectric film, deposited on Pt/Ti02/Si02/Si substrate by sol-gel spin casting and Pt-sputter top electrodes, was used in this study [24], The pzt film thickness was 175 nm. The experimental set-up used for the afm assisted piezoresponse imaging study of the pzt film consisted of a Park Scientific Instrument Autoprobe cp afm combined with a lock-in amplifier to excite and collect the piezoelectric vibration response amplitude and phase. 

In 4.3 we have already seen that polymers, in the rubber or fluid condition, crystallize much more rapidly when their chains are oriented. Therefore a stretched rubber, if stereospecific in its molecular structure, is able to crystallize at a temperature considerably above its equilibrium thermodynamic melting point. Also a thermoplast such as polyethylene, when in the molten state or in solution, can crystallize spontaneously when the chains are being orientated in elongational flow. The latter case is utilized when polyethylene is spun from a diluted solution (gel spinning process), resulting in fibres of super-high strength and stiffness ( Dyneema fibres). 

De Gennes scaling concepts for polymer solutions and melts and the concept of reptation movement of polymer chains in melts Pennings discovery of chain extension and shish-kebab formation in stirred solutions of very high MW polyethylene this eventually led to the ultra-high modulus gel-spinning process of polyethylene... 

The next major development was the "gel-spinning" by Smith and Lemstra (1979), where a "gel fibre" is first produced by spinning a dilute solution of very high molecular weight polyethylene into cold water after drying this "gel fibre" is drawn in a hot oven at... 

For successful gel-spinning/ultra-drawing two requirements must be fulfilled ... 

For an interesting review concerning gel-spinning the reader is referred to the paper by Van Dingenen (2001). 

The typically high-crystalline polymers, such as polyethylene and polypropylene here high natural draw ratios (5-10) are found in combination with gel-spinning they may be as high as 50... 

Gel-permeation chromatography (GPC), 19 Gel-spinning, 730 Gel-spun yams, 735 General correlation of aesthetic properties, 876 maintenance properties, 883 use (performance) properties, 878 General description of polymer-penetrant system, 695... 

Extended-chain polyethylene fiber became available commercially in 1984 when DSM, a Dutch firm in the Netherlands, introduced Dyneema , and Mitsui Petrochemicals in Japan announced Tekmilon . Allied Signal of the United States entered the field in 1985 when it introduced Spectra fibers. These materials are characterized by very high strength and modulus, which are achieved by the use of ultrahigh molecular weight polyethylene spun by the gel spinning method into fibers having extended-chain structures and near perfect orientation. 

Gel Spinning. In general, the purpose for which the gel spinning method is used is to produce an as-spun fiber that contains a loose... 

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