High-strength poly(L-lactide) fibers by a dry-spinning/hot-drawing process. II. Influence of the extrusion speed and winding speed on the dry-spinning process

This paper is concerned with the influences of the extrusion speed and the winding speed during dry spinning of 4 wt % solutions of poly(L -lactide) (PLLA) in mixtures of chloroform and toluene, on the ultimate fiber tenacities after hot drawing. It was found that high-strength PLLA fibers (1.5 GPa) can be produced at high spinning rates (> 180 m/min) if rupturing of the entanglement network and oriented crystallization during spinning is suppressed. This could be accomplished by avoiding spinline stretching and applying low elongational deformation rates in the spinneret during spinning.     

Resorbable materials of poly(L-lactide). II. Fibers spun from solutions of poly(L-lactide) in good solvents

Fibers of poly(L -lactide) (PLLA) with a tensile strength up to 1.2 GPa and Young's modulus in the range of 12–15 GPA were obtained by a hot drawing of fibers spun from solution of PLLA in good solvents such as dichloromethane and trichloromethane. The tensile strength of fibers was strongly dependent on the molecular weight of PLLA and on polymer concentrations in the spinning solution. Changing of the polymer concentration in the spinning solution gives rise to formation of fibers with different shape and porosity. Fibers spun from 10–20% solutions at room temperature exhibit a regular structurization, due to the melt fracture. These fibers had knot strengths up to 0.6 GPa, whereas fibers with a smooth surface spun from more dilute solutions had weaker square knots up to 0.3 GPa.     

Biodegradable materials of poly(l-lactic acid): 1. Melt-spun and solution-spun fibres

Poly(l-lactic) PLLA fibres with a high degree of molecular orientation and crystallinity were produced by hot-drawing of the melt-spun and solution-spun fibres. Solution-spun fibres show better tensile properties as compared with those of the melt-spun fibres. This may be caused by a lower number of entanglements trapped in the solution-spun fibres. The highest values of the tensile strength found for PLLA fibres in the present study were 0.5 and 1.0 GPa for the melt-spun and solution-spun fibres, respectively. Tensile strength of PLLA fibres increases with the draw ratio, and above a certain molecular weight, also with molecular weight of the polymer. Tensile strength was found to be strongly dependent on the drawing temperature which may be associated with the occurrence of two crystal modifications.     

Melt spinning of nylon 6: Structure development and mechanical properties of as-spun filaments

The structure of melt-spun nylon 6 filaments was studied using on-line x-ray diffraction and birefringence measurements. Measurements were also made on as-spun and treated filaments. On-line wide-angle x-ray scattering measurements indicated that crystallization did not occur on the nylon 6 spinline at spinning rates up to 1000 m/min when spinning was done into either ambient air of 60% relative humidity or into wet saturated air. The filaments did crystalline gradually on the bobbin to a paracrystalline pseudohexagonal (γ) form. The rate of crystallization was dependent on the molecular orientation developed in the spun filaments. Crystalline orientation factors based on hexagonal symmetry were computed as a function of take-up velocity for fibers which were conditioned 24 hr in air at 65% relative humidity. Annealing in air or treatment in water or 20% formic acid solution causes a transformation from the pseudohexagonal form to the α monoclinic form. The tangent modulus of elasticity and tensile strength of spun and conditioned filaments increase with increasing take-up velocity and spinline stress, while elongation to break decreases with these variables.     

The effect of diameter on the mechanical properties of amorphous carbon fibres from linear low density polyethylene

Summary The mechanical properties of amorphous carbon fibres, derived from linear low density polyethylene strongly depend on the fibre diameter, which may be attributed to the presence of a skin/core structure in these fibres. High strength carbon fibres could thus be prepared by using thin precursor filaments, that are obtained by a melt-spinning process, in which the spinline is stretched at an elevated surrounding temperature. Careful carbonization of these precursors gives carbon fibres with a strength of 2.16 GPa, a modulus of 130 GPa and a high strain at break of 3%.     

Morphology development from rod-like to nanofibrillar structures of dispersed poly (lactic acid) phase in a binary blend with poly (vinyl alcohol) matrix along the spinline

The morphological evolution of thermoplastic poly (vinyl alcohol) (PVA) and poly (lactic acid) (PLA) blend filaments along the spinline is investigated for the first time. Emphasis of the study is given on considering the axial velocity gradient and tensile stress that influence the final state of deformation of the dispersed PLA phase. In this study, pieces of the PVA/PLA blend filaments at different locations along the spinline are collected by using a special self-constructed fiber-capturing device. This fiber-capturing device allows closer off-line study of the morphological properties of PVA/PLA blend filaments. The axial velocity gradient at different zones along the spinline is calculated from velocity data using Laser Doppler Velocimetry (LDV) technique. The tensile stress is determined from the momentum balance equation. It is observed that the fibrillation process takes place up to a certain distance from the die exit, where the polymeric PVA/PLA blend filament reaches its glass transition temperature. In this region, the axial velocity and tensile stress undergoes major changes. A phase inversion of dispersed PLA phase from rod-like structures to continuous long thin fibrils has been found at the point in which the axial velocity gradient reaches a maximum value.     

Structure development in melt‐spinning syndiotactic polystyrene and comparison to atactic polystyrene

Syndiotactic polystyrene (s‐PS) and atactic polystyrene (a‐PS) were melt‐spun into filaments. The s‐PS filaments exhibited increasing amounts of crystallinity and orientation with increasing drawdown ratio and spinline stress. The a‐PS filaments were amorphous but exhibited birefringence. The birefringence and Hermans orientation factors for a‐PS were proportional to this spinline stress. In ice water and at low drawdown ratios, the s‐PS is glassy or mesomorphic. At higher drawdown ratios and spinline stresses, it crystallized. The crystalline form was the zigzag TTTT hexagonal α‐form. The birefringence and orientation factors of the s‐PS filaments were higher than those of the a‐PS filaments and the difference of the birefringence increased with increasing spinline stress. Mechanical testing results showed that the Young's modulus and tensile strength generally increased with increasing spinline drawdown ratio for both a‐PS and s‐PS filaments. The elongation to break was enhanced for both materials by increased chain orientation. Polym. Eng. Sci. 44:2141–2147, 2004. © 2004 Society of Plastics Engineers.     

High modulus/tenacity filaments from blends of different molecular weights of polypropylene

Polypropylene (PP) filaments are prepared by blending two different molecular weight components of PP. A melt‐spinning process to produce filaments includes mixing of components, extrusion, and two‐stage drawing, followed by a unique Gradient Drawing? process. Blending results in highly deformable as‐spun filaments with high draw ratios. For 90:10 blends of PP samples with melt flow indexes of 35 and 3, a high level of crystallinity and crystalline and amorphous orientations are obtained. A sonic modulus of 28 GPa, dynamic modulus of 20 GPa, tensile modulus of 16 GPa, and tenacity of 667 MPa are achieved. These samples are dimensionally stable up to ～100°C. All steps in the production of the filaments are continuous. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1021–1028, 2005     

Melt spinning of poly(L‐lactic acid) and its biodegradability

The melt spinning and melt drawing of poly(L ‐lactic acid) (PLLA) were carried out with a melt‐spinning machine, and the mechanical properties, structure, and biodegradability of PLLA fiber were investigated. PLLA fiber with a tensile strength of 0.81 GPa was successfully obtained through two steps of drawing at a draw ratio of 18 in hot water. This fiber had enough tensile strength for common engineering use. The fiber could be degraded under controlled composting conditions at 70°C for 1 week. In scanning electron microscopy observations of the fiber, a regular pattern of cracks running along the vertical direction to the fiber axis was clearly observed. This suggested that the PLLA fiber built up a highly ordered structure arranged along the direction of the fiber axis. After the fiber was left to lie in the ground for 1 year, however, the surface of the fiber was still smooth, and the tensile strength did not decrease much. This PLLA fiber could not be hydrolyzed after 1 month of steeping in a buffer solution at 37°C, but it was rapidly hydrolyzed at more than 60°C. It was suggested that the degradation (hydrolysis) rate of PLLA depended on the glass‐transition temperature. Upon hydrolysis at 80°C for 48 h, a regular crack along the vertical direction to the fiber axis was found that was very similar to that observed in degradation under composting conditions. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2118–2124, 2005     

High-modulus fibres of nylon-6 prepared by a dry-spinning method

Nylon-6 filaments with tensile strengths at break up to 1 GPa and initial moduli in the range of 16 to 19 GPa have been produced by dry-spinning of solutions of nylon-6 in cosolvent mixtures of formic acid and chloroform followed by hot-drawing at 200°C–240°C. Tensile strengths and elastic moduli of the nylon-6 fibres were strongly dependent on the draw ratio, on the molecular weight of the polymer, on the polymer concentration in the spinning solution and on concentration of nonsolvent in the spinning solution. At high concentrations of nonsolvent in the spinning solution, the as-spun fibres of nylon-6 were composed of ball-like structural units, formed possibly due to the liquid-liquid phase separation in the polymer/solvent/nonsolvent ternary system. Formation of ball-like structures reduced the ultimate mechanical properties of hot-drawn fibres of nylon-6.     

Production of ultrahigh modulus polyoxymethylene by drawing under dielectric heating

A tensile drawing process under dielectric heating has been developed for polyoxymethylene. The influence of ambient temperature, electric field strength, and strain rate on the maximum draw ratio and the tensile modulus has been examined. Tubes possessing tensile moduli up to 63GPa were produced by the new drawing technique. It is speculated that the achievement of such ultrahigh moduli is due to the fact that the stress by drawing is used effectively to orient the molecular chains in the noncrystalline regions and at defect regions within the crystal lamellae. This is because these regions are heated to higher temperatures than the crystalline regions during dielectric heating.     

Radial temperature differences during the melt spinning of fibers

In this investigation, a numerical model was developed to predict the temperature distribution in a fiber during melt spinning. This model uses the implicit Crank–Nicolson method to solve the governing differential equation for the problem. The model was applied to a series of numerical experiments on a liquid crystalline fiber which is melt-spun. These simulations used typical sets of operating conditions to determine the effect of various operating parameters on the predicted radius profile, spinline tension, and temperature distribution. The effects of spinneret capillary diameter, mass flow rate, ambient air temperature, spinning temperature, and elongational viscosity were investigated. The results of the various runs showed that ambient air temperature and mass flow rate had a significant effect on the predicted radius profile, spinline tension, and temperature distribution. The spinning temperature was an important parameter, but its only significant effect was on the spinline tension. Spinneret capillary diameter and elongational viscosity had little effect on the predicted results.     

Polylactide. III. Fiber preparation by spinning in precipitant vapor

The mechanical properties and morphologies of poly(L-lactide) (PLLA) fibers, prepared by spinning in different vapor precipitants and hot drawing afterward, were studied in relation to fiber in vitro degradability. Petrolether, methanol, and ethanol were employed as precipitants. PLLA was used as-polymerized, i.e., with 10% of residual L-lactide. The tensile strength, structure, and degradability of obtained fibers were mainly governed by the nonsolvent concentration in the vapor phase. Using methanol as the precipitant for the fiber preparation, total tensile strength loss was achieved during 12 wk of in vitro degradation. © 1994 John Wiley & Sons, Inc.     

Preparation of poly(lactic acid) fiber by dry‐jet‐wet‐spinning. I. Influence of draw ratio on fiber properties

Poly(lactic acid) fiber was prepared by dry‐jet‐wet spinning of the polymer from chloroform solution and with methanol as the precipitating medium. The as‐spun fiber was subsequently made into high strength fiber by two‐step process of drawing at a temperature of 90°C and subsequent heat setting in the temperature range of 120°C. The draw ratio had significant influence on the crystallinity and the tensile strength of the fiber. The fiber with the tenacity of 0.6 GPa and modulus of 8.2 GPa was achieved at a draw ratio of 8. The differential scanning calorimetry revealed an increase in the glass‐transition temperature with the increase in the draw ratio, which suggests the orientation of chains during the drawing process. The surface morphology of the filament as revealed by scanning electron microscopy shows that fibers are porous in nature, but a significant reduction in the porosity and pore size of the fiber was observed with the increase in the draw ratio. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1239–1246, 2006     

Study on the drawing behavior of poly(L-lactide) to obtain high-strength fibers

The tensile drawing behavior of poly(L -lactide) has been studied in order to obtain high strength fibers. Elongational viscosity measurements indicated that the hot drawing can take place in two temperature regions with different activation energies. Up to 180°C, the deformation proceeds in the semicrystalline state of the polymer having an activation energy of 15–28 kJ/mol, presumably by shear deformation. In the range of 180–190°C, the deformation proceeds in the liquid state of the polymer having an activation energy of 145–165 kJ/mol, leading to a semicrystalline state by strain hardening after displacement of topological defects. By using high deformation rates during drawing in a temperature gradient (tube drawing), the deformation will principally proceed in the semicrystalline region and inhomogeneous draw will take place leading to inferior fiber properties, unless the deformation rate and drawing temperature are strictly adjusted. Homogeneous drawing can be achieved by applying low deformation rates so that the deformation may take place in the liquid state of the polymer in which individual chains can be easily aligned and topological defects can be removed. Poly(L -lactide) fibers with tensile strengths of 2.3 GPa have been produced in this way.     

Ultra-high strength and ultra-high modulus fibers from polyethylene

Summary Using the method of hot drawing developed earlier, an attempt has been made to obtain ultra-high modulus and ultrahigh strength PE filaments from original filaments produced by the surface growth technique. The average tensile strength of the drawn fibers reaches 5.5 GPa and the value of modulus measured in a dead loading creep experiment is estimated to be 44 GPa. 13 % of the drawn specimens had extremely high tensile strength close to theoretical estimates. The great scatter of the tensile strength data is attributed to the kink-band formation in the specimens due to their bending during preparation or during drawing.     

Melt spinning and draw resonance studies on a poly (α-methyl styrene/silicone) block copolymer

Fiber spinning experiments were carried out with an α-methyl styrene/silicone block copolymer under various sets of spinning conditions. The behavior observed was very sensitive to the ambient axial temperature profile employed along the spinline and to the initial melt temperature at the die. By optimizing these parameters, very high draw ratios (>400 to 1) could be achieved. Under less optimum conditions, filament rupture and instabilities such as draw resonance, accompanied by periodic diameter and spinline tension fluctuations, were noted. Tensile stress and axial velocity gradient profiles were obtained along the spinline under a variety of spinning conditions. These profiles, together with an independent: rheological characterization of the polymer, provide insights into the mechanisms giving rise to the various types of behavior observed.     

Melt spinning and drawing of 2‐methyl‐1,3‐propanediol‐substituted poly(ethylene terephthalate)

The structure and properties of fibers prepared from copolymers of poly(ethylene terephthalate) (PET) in which 2‐methyl‐1,3‐propanediol (MPDiol® Glycol is a registered trademark of Lyondell Chemical Company) at 4, 7, 10, and 25 mol% was substituted for ethylene glycol were studied and compared with those of PET homopolymer. Filaments were melt spun over a range of spinning conditions, and some filaments that were spun at relatively low spinning speeds were subjected to hot drawing. The filaments were characterized by measurements of birefringence, differential scanning calorimetry (DSC) crystallinity, melting point, glass transition temperature, wide‐angle X‐ray diffraction patterns, boiling water shrinkage, tenacity, and elongation to break. Filaments containing 25 mol% MPDiol did not crystallize in the spinline at any spinning speed investigated, whereas the other resins did crystallize in the spinline at high spinning speeds. However, compared with PET homopolymer, increasing substitution of MPDiol reduced the rate at which the crystallinity of the melt spun filaments increased with spinning speed and reduced the ultimate crystallinity that could be achieved by high‐speed spinning. The rate of development of molecular orientation, as measured by birefringence, also decreased somewhat with increasing MPDiol content. Shrinkage in boiling water decreased at high spinning speeds as the amount of crystallinity increased; however, the shrinkage decreased more slowly with increase in spinning speed as MPDiol content increased. Tenacity also decreased slightly at any given spinning speed as MPDiol content increased, but there was no significant effect on elongation to break. The addition of MPDiol in amounts up to 7 mol% increased the maximum take‐up velocity that could be achieved at a given mass throughput. This result indicates that the use of higher spinning speeds could potentially increase the productivity of melt spun yarns. Copolymer filaments spun at low speeds were readily drawn to produce highly oriented fibers with slightly less birefringence, crystallinity, and tenacity than similarly processed PET homopolymer. Preliminary dyeing experiments showed that the incorporation of MPDiol improved the dyeability of the filaments. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2598–2606, 2003     

Effects of water on drawability,structure, and mechanical properties of poly(vinyl alcohol) melt‐spun fibers

Poly(vinyl alcohol) (PVA) melt‐spun fibers with circular cross‐section and uniform structure, which could support high stretching, were prepared by using water as plasticizer. The effects of water content on drawability, crystallization structure, and mechanical properties of the fibers were studied. The results showed that the maximum draw ratio of PVA fibers decreased with the increase of water content due to the intensive evaporation of excessive water in PVA fibers at high drawing temperature. Hot drying could remove partially the water content in PVA as‐spun fibers, thus reducing the defects caused by the rapid evaporation of water and enhancing the drawability of PVA fibers at high drawing temperature. The decreased water content also improved the orientation and crystallization structure of PVA, thus producing a corresponding enhancement in the mechanical properties of the fibers. When PVA as‐spun fibers with 5 wt % water were drawn at 180 °C, the maximum draw ratio of 11 was obtained and the corresponding tensile strength and modulus reached ～0.9 GPa and 24 GPa, respectively. Further drawing these fibers at 215 °C and thermal treating them at 220 °C for 1.5 min, drawing ratio of 16 times, tensile strength of 1.9 GPa, and modulus of 39.5 GPa were achieved. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45436.     

Morphological changes of wide polyoxymethylene rod during a microwave heating drawing process

The microwave heating drawing process for producing a polyoxymethylene (POM) rod (2.5 mm in diameter) with a sonic modulus of 40 GPa has been analysed by investigating the changes in both orientation and thermal properties during drawing. During the initial crystalline deformation in the necking region, the lamellae are oriented perpendicular to the draw direction and are then unfolded into microfibrils. The crystalline orientation function reaches a high value (0.988) at a draw ratio of 6 immediately after necking. In the advanced ultra-drawing stage, the Young modulus increases gradually with increasing amorphous orientation. At the same time, the orientation distribution in the radial direction is caused by the temperature distribution induced in the radial direction of the rod. It is noted that fine adjustments of ambient temperature and microwave power are required to get ultra-high-modulus POM rods over 40 GPa with large crosssections.