Undrawn Fibers Research Articles

THz spectra of drawn and undrawn fibers measured on fiber shape samples

This paper describes how to measure THz spectrum of a filament shape sample without freeze-crushing chemical fiber. The filament yarn was installed in parallel on a stainless-steel O-ring. The fiber axis direction of this O-ring was installed in parallel to THz polarization direction. THz spectrum measured by this pre-treatment method was measured at a high S/N ratio than THz spectrum of the freeze-crushing sample. Next, THz spectra of drawn and undrawn fibers, which were confirmed to have different internal structure of the fibers by wide-angle X-ray images, were measured. THz spectra of these samples were measured with different yarn spacings and at different angles (at regular angle intervals of 30°) between the polarization direction of THz light and the fiber axis direction. When the fiber molecules were oriented along the axis by the drawing process, THz spectrum shape changed with the polarization angle, but it did not when the fiber orientations were random. This pre-treatment method avoids freeze-crushing, so the raw molecular structure inside the fiber was not altered thermally or mechanically and could be measured directly.

The Importance of Long-Term Observations in Assessing the Strength of Polycaproamide Fibre

According to long-term observations, rewinding and slubbing operations have almost no effect on the unit strength of complex and slubbed polycaproamide fibres but affect the relative elongation at break. The stability of the deformation-strength properties of the fibres in time, assessed with the values of the coefficients of variation, during the manufacturing process, including slubbing, improves significantly. The fibre strength is not a function of fluctuations in the content of low-molecular-weight compounds in the initial polymer and its relative viscosity, spinning temperature, and elementary fibre thickness in the undrawn fibre in contrast to the moisture content of polymer going to spinning and the degree of orientational drawing of the fibre.

Study on fiber structure formation in wet spinning of aliphatic polyketone using aqueous solution of complex metal salts?Characteristics of solid structure formation in drying step and its effects on superdrawing step

Solid structure formation in the drying step for wet spinning of poly(1-oxotrimethylene) using as a solvent an aqueous solution of complex metal salts of calcium chloride/zinc chloride was studied. Because the degree of structural densification and the crystal structure both differ depending on the drying temperature, the drying temperature had a major effect on the drawing behavior and the strength achieved after drawing. With higher drying temperature, the denseness increased due to smaller voids in the dried undrawn fiber, while there was also a tendency toward higher strength with respect to the draw ratio. However, an excessively high drying temperature altered the crystal structure from a rough crystalline form to a dense crystalline form and reduced both the maximum draw ratio and strength. Mechanical cleavage of the molecular chains occurred between the ethylene groups and carbonyl groups of the main chains in the drawing step. This cleavage made it possible to suppress the inhibition of drawing due to entanglement of the molecular chains, thereby enabling superdrawing to afford a high performance fiber. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 446–452, 2004

Density determination and the related parameters for drawn polymeric textile fibers

The problem of determining the density of drawn polyethylene and nylon 66 fibers has been investigated. With knowledge of the density and the refractive indices of the undrawn fibers, the density for the drawn fibers can easily be calculated. The values obtained for densities were used to calculate the related parameters such as the crystallinity, the mean square density fluctuation, the number of monomer units per unit volume, the polarizability of monomer unit, the specific refractivity of isotropic dielectric and others. In addition, the molar refractivity, the segment anisotropy and the number of chains between cross links per unit volume were calculated. Microinterferograms, and relationships between the parameters obtained are given for illustration.

In-Situ Simultaneous Synchrotron Small- and Wide-Angle X-ray Scattering Measurement of Poly(vinylidene fluoride) Fibers under Deformation

Poly(vinylidene fluoride) (PVDF) fibers spun at different take-up speeds (10.6−61.0 m/min) were subjected to stretch−hold deformation at room temperature and in-situ simultaneous synchrotron small- and wide-angle X-ray scattering measurements. Crystal transformation from α to β form and morphological changes in lamellar and fibrillar structures were analyzed in detail. All fibers were found to yield at an early stage of deformation, resulting in alternating necked and unnecked regions along the fiber. From the two-dimensional (2-D) wide-angle X-ray diffraction (WAXD) patterns, mixed α and β (minor fraction) forms were found to coexist in the undrawn fibers. Deformation assisted in the conversion from the α-form into the β-form. In necked regions, more α to β transformation took place than in unnecked regions. The overall crystallinity index and unit cell parameters of the α form did not change significantly prior to necking. From the 2-D small-angle X-ray scattering (SAXS) patterns, two kinds of equatorial streaks were observed. The first kind originated from fiber of high take-up speed (61.0 m/min) under zero or small strain, and the second kind came from highly deformed fibers (all take-up speeds) in both necked and unnecked regions. These two kinds of equatorial streaks were attributed to the formation of microfibrils and microvoids, respectively. The dimensions of the lengths of microfibrils and microvoids were estimated by Ruland's method. Meridianal scattering maxima from a lamellar morphology were observed in the SAXS patterns in fibers under zero or low strain. The long period of the lamellar structure, estimated using correlation function analysis, increased with strain. Results from SAXS and WAXD analysis suggest that the formation of defects during yielding and plastic flow facilitates the α to β crystal phase transformation, and a phase, similar to conformationally disordered phase, whose density is close to that of crystal, is induced out of the amorphous phase in lamellar structure with application of strain.

Composites based on poly(ethylene terephthalate) fibers with polyaniline. II. The effect of the growth of the polyaniline molecules during the polymerization in the morphology of the PET substrate

PET fibers of different drawn ratios were used as substrates to produce composites with PANi. The influence of the growth of the polyaniline molecules in the structure of the fibers previously pretreated in the presence of aniline at different conditions were studied by different characterization techniques (differential scanning calorimetry, X-ray scattering, dynamic and mechanical thermal analysis, sonic modu- lus, and scanning electron microscopy). The polymerization of the aniline inside the fiber substrates modified the structure of the fibers. In the case of the drawn fiber substrates the growth of the PANi molecules occurred mainly in the interfibrillar regions, which promoted reorganization of the preexisting crystals such as defect elimination (mainly in the interface of these regions with the lamellar regions) and at same time reorientation of their amorphous and crystalline regions. Also, due to this reorientation process the crystals became not only bigger and more perfect, but also they became more homogeneous. In the case of the undrawn fiber substrates, due to the lack of previous orientation, the growth of the PANi molecules would be occurring in the amorphous interlamellar regions only. Finally, the use of fibers with different drawn ratios as substrates for the composites was essential to reach such conclusions. © 2000

Comparative Structural Characterization of Naturally- and Synthetically-Spun Fibers of Bombyx mori Fibroin

This investigation describes the comparative structural characterization of naturally- and synthetically-spun fibers of Bombyx mori fibroin. Wet spinning from 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) solutions was used to spin fibroin fibers with varying degrees of postspinning draw. Quantitative Raman spectroscopy showed that the secondary structure of fibroin changed dramatically from predominantly α-helical in HFIP solution to principally β-sheet in the undrawn synthetically-spun fiber. X-ray fiber diffraction showed that the undrawn fibers were highly crystalline (>50%) with little or no preferential crystalline alignment. The addition of a postspinning draw caused the polypeptide backbone and β-sheet crystals, which were formed largely by a methanol coagulation bath, to align with the fiber axis. The molecular and crystalline structures most similar to those of naturally-spun fibers were reproduced in synthetically-spun fibers with a minimum draw ratio of 2.5.

Hydrolysis of polycaprolactone fibers by lipase: Effects of draw ratio on enzymatic degradation

AbstractUsing polycaprolactone (PCL) fibers drawn with various draw ratios, the effects of draw ratio on enzymatic degradation were studied in order to understand the influence of fine structure on biodegradation. Degradability of PCL fibers as monitored by total organic carbon (TOC) formation or weight loss decreased with increase in draw ratio due to higher crystalline content. There were some distinct features of degradation behavior among the fibers, because the fibers underwent significant change in molecular organization of the polymer, such as crystallinity and orientation, during drawing processes. From scanning electron microscopy (SEM) photographs showing that the enzyme preferentially attacked amorphous or less ordered regions rather than crystalline or more ordered regions of the fiber, spherulites were observed in the undrawn fiber, and on the other hand, fibrillar stripes along the fiber axis were observed in the drawn fibers, which suggest that the spherulites in the undrawn fiber were extended to be broken, and fibril structures were formed during the drawing processes. These SEM photographs suggest that there are differences of crystal structures in addition to crystallinity among the fibers with different draw ratio, which significantly affects the enzymatic degradation behavior of the fibers. The diameter of the fibers became gradually slim, macroscopically uniform, as enzymatic degradation proceeded although it was dependent on draw ratio. It is evident that the degradation proceeded in the crystalline regions as well as the amorphous regions. © 1995 John Wiley & Sons, Inc.

Drawing and annealing of nylon-6 fibres: studies of crystal growth, orientation of amorphous and crystalline domains and their influence on properties

Structural changes in nylon-6 fibres that occur during processing are analysed using X-ray diffraction (X.r.d.), optical birefringence, density and infra-red (i.r.) spectroscopy methods. Amorphous orientation is described completely by a single parameter, degree of orientation, on the basis of i.r. and optical birefringence measurements. But an additional parameter, the fraction of oriented or anisotropic amorphous component, was necessary to fully interpret the X.r.d. data. The amorphous orientation increases as expected upon drawing, but decreases upon annealing at all temperatures. Crystalline orientation increases rapidly at small draw ratios (<3) and reaches a plateau at higher draw ratios. Crystalline orientation decreases upon annealing in highly drawn fibres but increases in others. The crystallinity is ∼15% in the undrawn fibre, and continues to increase beyond the ∼50% value measured for the fibre with the highest (4.5x) draw ratios used here. Secondary crystallization during drawing occurs at the expense of unoriented amorphous fraction, and in the initial stages of drawing (3x) is accompanied by the transformation of the γ into the α crystalline form. Secondary crystallization during annealing occurs at the expense of the oriented amorphous fraction. The ease of γ to α conversion during annealing depends on the initial state of the γ form. The glass transition temperature ( T g) appears to be determined solely by the amorphous orientation, being higher in fibres with a higher anisotropic component. The improved mechanical properties observed at higher draw ratios are attributed to higher crystallinity and lower fraction of the unoriented amorphous component. The shrinkage observed upon annealing of fibres with smaller draw ratios (∼3) is likely to be the result of the crystallization of the oriented amorphous chain segments.

Characterization of the Viscoelastic Behavior of Polyaniline Solutions for Fiber Spinning

ABSTRACTSolutions of emeraldine base(EB) in DMPU have been successfully spun into fibers and characterized according to their morphology, mechanical and electrical properties. This study presents results for as-spun (undrawn) fibers. The viscoelastic behavior of EB spin solutions have been investigated with dynamic measurements of the complex moduli, first normal stress coefficient, and complex viscosity. A knowledge of the viscoelastic behavior of emeraldine base solutions is crucial for effective processing into fibers and films.

Hydration in semicrystalline polymers: Small‐angle neutron scattering studies of the effect of drawing in nylon‐6 fibers

AbstractWater absorbed by nylons appears to be partitioned into interlamellar and interfibrillar spaces. The amount of water in the interfibrillar region remains essentially unchanged with increasing draw ratio, whereas that in the interlamellar regions decreases with draw ratio; the latter accounts for the decrease in the water uptake in the drawn fibers. These results suggest that the amount of the amorphous material in the interfibrillar regions remains unchanged during drawing, and the increase in the crystallinity during drawing results from the incorporation of the amorphous chain segments in the interlamellar regions into the crystalline lamellae. Further, the interfibrillar water is more tightly bound than the interlamellar water. The length of the longitudinal channels into which water diffuses is about the same as that of the fibrils, and increases from ca. 1500 to 2000 Å upon drawing. The longitudinal channels are highly oriented even in undrawn fibers, and their misorientation increases from 5° to 15° upon drawing. These channels can be described as surface fractals of dimension 3.4–3.6. © 1994 John Wiley &amp; Sons, Inc.

The Use of Sodium Hydroxide Hydrolysis to Study the Fine Structure of Undrawn and Drawn High-Speed Spun Polyethylene Terephthalate) Fibers

Abstract The fine structures of undrawn and drawn high-speed spun poly-(ethylene terephthalate) (PET) fibers, 0.86 dL/g intrinsic viscosity, formed at speeds from 1615 to 3329 m/min, were investigated. Increasing the spinning speed and drawing resulted in greater levels of orientation and crystallinity in the untreated fibers. The relatively high molecular weight of the PET yielded undrawn products of higher orientation and crystallinity than those obtained by workers using PET of lower molecular weight but spun at similar speeds. A linear relationship between cohesive and optical anisotropy was found for the undrawn and drawn fibers. Aqueous sodium hydroxide hydrolysis was utilized to reveal the presence of any radial variations in structure. In the undrawn fibers, hydrolysis revealed that a more oriented layer was present very near the fiber periphery at higher spinning speeds. In the drawn samples a small but significant progressive decrease in birefringence was generally observed as the center of the fiber was approached. The drawing process appears to produce fibers without a skin-core structure and less susceptible to tenacity loss due to surface defects.

The microstructure and macrostructure of sulfonated poly(ethylene terethphalate) fibers

AbstractThe effects of fiber‐forming processes on the microstructure and macrostructure and overall orientation in sulfonated poly(ethylene terephthalate) (SPET) fibers are reported. The processing parameters examined include drawing, crimping, relaxing, and annealing. Drawing and annealing cause changes in both the crystalline structure and molecular packing in the noncrystalline regions, while crimping and relaxing appear to affect only the noncrystalline regions. A bimodal melting endotherm was observed for the SPET fibers. Experimental data suggest the low‐temperature endotherm of the SPET fibers originates from melting of the crystalline structure formed on drawing, and that the high‐temperature endotherm results from melting the heat‐induced crystals formed during fiber processing and/or thermal analysis. Compared to the PET fibers, the SPET chains in the undrawn fibers appear to have higher mobility, are easier to crystallize, and form smaller crystals upon drawing as well as DTA heating. At the crimped stage, the SPET fibers have higher overall molecular packing but lower overall orientation than the PET fibers. The differences in physical and thermal properties between the analogous SPET and PET fibers are related to their different responses to processing variations because of molecular weight and sidegroup effects. © 1993 John Wiley &amp; Sons, Inc.

Surface Change of Aramid Fiber by Laser Ablation.

Excimer laser irradiation was applied to aramid fibers (PPODPTA fiber, PPTA fiber), A micro-structure of unevenness was formed, perpendicular to the fiber axis, and this structure became larger with the laser wavelength. Even in undrawn fiber, a slight structure of unevenness was formed perpendicular to the fiber axis, just as in drawn fiber. This was thought to be due to the high orientation of undrawn aramid fiber. It was found by XPS analysis that the atomic ratio of O/C in the PPODPTA fiber declines and the ratio of oxygen present is lower. For PPTA fiber, however, this ratio showed almost no change and stayed at a set value. It is considered that the difference in the above results is caused by the difference in chemical structures between PPODPTA fiber and PPTA fiber (difference in the bond energy of the ether and amide bond).

Influence of an interfacial agent on the structure of polypropylene-polyamide fibres

In this paper the structure and properties of fibres prepared from the polypropylene/polyamide (PP/PA6) blend have been studied as a function of the interfacial-agent (IFA) content. For this purpose the grafted polypropylene-maleic anhydride copolymer was used. Fibres containing 20% of PA6 and 80% of PP possess the phase matrix-fibril structure. The size and distribution of fibres in the dispersed PA6 phase in the PP matrix depend on the interfacial-agent amount. Due to the indirect nucleating effect the PA6 phase has been found to act, in the presence of the interfacial agent, on the PP crystallization during fibre formation. As a result, undrawn fibres have the more pre-oriented and crystalline PP matrix with the morphological rod-like structure. The pre-orientation of the dispersed fibrilar PA6 phase is minimum. Mechanical properties of the drawn blended fibres are favourably influenced provided that the interfacial-agent concentration is higher than 1%. The growing rate of the mutual interaction between the components was mostly reflected in the increased values of Young's modulus.

SAXS investigations of isotactic polypropylene (IPP) fibres mass coloured with organic pigments

The effect of selected organic pigments on the supermolecular structure of isotactic polypropylene (IPP) fibre has been investigated. For the present work, three organic pigments of different molecular and supermolecular constitution were selected. Undrawn fibres with a minimal technological degree of drawing and fibres at draw ratios of 2, 4 and 5 were examined. The supermolecular structure was explored using small-angle X-ray scattering (SAXS). From the SAXS patterns the one-dimensional intensity function and the correlation function were determined. The parameters characterizing the supermolecular structure of the fibre, i.e. long period and invariant, were assessed. It was found that a lamellar structure develops during fibre formation. A regular lamellar structure is formed irrespective of the presence of pigments. On drawing fibres the high regularity of the lamellar structure decreases. In the drawing process the pigments are at the origin of micropore formation.

Structure of fibres prepared from polypropylene‐polycaproamide mixture. 1. Undrawn fibres

AbstractThe structure of fibres prepared from a polypropylene‐polycaproamide mixture is studied. The blend fibres possess a matrix‐fibril structure. The presence of a dispersed polycaproamide component in the form of fibrils in the polypropylene matrix, affects the macrostructure created inthe fibres under the dynamic fibre‐forming conditions.

Effect of moisture content on the physicomechanical properties of polyamide yarns

The effect of small amounts of moisture during a short interaction time (not over 2 sec) with undrawn Kapron fibre on its ability to undergo deformation and its structure is discussed.

Effect of a mechanical stress on the crystallization of undrawn polyethylene terephtalate fibres

It has been shown that the intensity of the mechanical field accelerates crystallization to a varying degree in the samples of undrawn polyethyleneterephthalate (PET) fibres investigated. The relation was non-linear. This phenomenon is explained by metastability of the texture in the amorphous PET formed during the spinning to undrawn fibres. The applied mechanical field impedes the destruction of the latter during the passage of the polymer from the glass to the rubber state up until beginning of crystallization.

Copolyester studies. VII. The dyeing behavior of undrawn fibers derived from tetramethylene terephthalate: Poly(tetramethylene oxide) random block copolymers

AbstractA series of copolymers based on poly(tetramethylene terephthalate) containing poly(tetramethylene oxide) blocks whose molecular weights ranged from 1000 to 5000 in concentrations from 10 to 30% by weight was prepared. The polymers were melt spun into fibers and the undrawn fibers dyed with a disperse dye at three temperatures. The equibrium adsorption and diffusion coefficient of the dye increased with both the molecular weight and concentration of the polyether. The equilibrium adsorption varied linearly with both the molecular weight and concentration. It has been assumed that the equilibrium dye partition coefficient KM gives a parameter of the accessibility, V, of the fiber for dye. If the diffusion coefficient DM is given by DM = VDo/τ, where Do is the diffusion coefficient of the dye in the amorphous regions and τ is a tortuosity factor, a good correlation can be obtained between KM and DM, suggesting that changes in Do/τ vary in a systematic fashion.