Preparation of high-modulus nylon 6 fibers by vibrating hot drawing and zone annealing

To prepare high-modulus fibers, the vibrating hot-drawing and zone-annealing methods have been applied to nylon 6. The vibrating hot drawing was repeated two times, increasing the applied tension; further, the zone annealing was superposed on the vibrating hot-drawn fibers. The superstructure and mechanical properties of each step fiber were investigated. The vibration under a cooperation of heating and tension was very useful for increasing the draw ratio, birefringence, and orientation factor of the amorphous chains. Consequently, the obtained fiber indicated high moduli, namely, Young's modulus of 23 GPa and the dynamic storage modulus at room temperature of 25.3 GPa. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1993–2000, 1998     

Preparation of high-modulus and high-strength poly(ethylene terephthalate) film by zone-annealing method

The zone-annealing method was attempted to prepare high-modulus and high-strength poly(ethylene terephthalate) (PET) film. The film having Young′s modulus of 14.5 × 10¹⁰ dyn/cm² and a tensile strength of 86.9 kg/mm² in the drawing direction was obtained. These values correspond to four times those of a biaxial-stretched PET film available commercially. The dyanmic viscoelastic properties also were measured. The dynamic storage modulus was 15.4 × 10¹⁰ dyn/cm² at room temperature, and a high value of 3.6 × 10¹⁰ dyn/cm² even at 200°C. The latter value is slightly higher than the room temperature modulus of the commercially available film. From the intensity and temperature position of α-dispersion E″ peak, it was suggested that the amorphous chains in the zone-annealed film was densely packed in a highly oriented state. Furthermore, the crystallinity, orientation, especially double orientation, and molecular chain conformation of the films in the zone-annealing process are discussed in the present paper.     

Preparation of high-modulus and high-strength poly(ethylene terephthalate) fiber by zone annealing

To prepare high-modulus and high-strength PET fiber, a new method using zone drawing and zone annealing has been studied. The apparatus used for this method is the usual tensile tester equipped with a band heater 2 mm wide and a sample holder which can apply a high tension to the fiber. The experimental procedure consists of two stages: zone drawing and zone annealing. The zone drawing was done on the original as-spun fiber in order to produce a fiber with as high an orientation and as low a crystallinity as possible. The zone-drawn fiber was subsequently zone annealed under high tension by moving the band heater from one end to the other of the fiber at a temperature above the crystallization temperature at a considerably low moving speed. In spite of the simple apparatus and procedure, Young's modulus of the fiber obtained was 19.4 × 10¹⁰ dyn/cm², which is comparable to the maximum value of the high-tenacity PET filament commercially available. In order to elucidate the change in the superstructure with zone drawing or zone annealing, optical, x-ray, IR, DSC, and dynamic mechanical measurements were performed. It is suggested that the zone-annealed fiber consists of almost perfectly oriented crystallites and fully extended amorphous chains.     

Mechanism of cold drawing in melt-spun poly(ethylene terephthalate) fibers

An investigation has been made into the mechanism of cold drawing in melt-spun poly(ethylene terephthalate) (PET) fibers. An analysis of the cold-drawing behavior using wide-angle x-ray diffraction, orientation measurements, calorimetric and mechanical techniques was performed. The evidence suggests that the cold-drawing process involes stress-enhanced crystallization which occurs in conjuction with incresing orientation of the crystalline and amorphous regions. A degradation in the fiber properties after cold drawing was observed for fibers spun below 1,000 m/min while fibers spun above 1,000 m/min exhibited an improvement in fiber properties with cold drawing. This behavior was explained by the existence of two distinct irreversible deformation micromechanisms for fibers spun below and above 1,000 m/min.     

Tensile drawing behaviour of poly(ethylene terephthalate)

A detailed study has been undertaken of the drawing behaviour of poly(ethylene terephthalate) over the temperature range 20° to 80°C. Cold drawing behaviour was observed at the lower temperatures and homogeneous deformation at 80°C. Samples were also subjected to two-stage drawing: homogeneous draw at 80°C followed by cold drawing at 20°C. In all cases the geometry of the deformation was monitored by measuring the changes in macroscopic dimensions. In addition, measurements were made of the final birefringence, and the shrinkage force developed when the drawn samples were heated to a temperature above T_g. The results are discussed in terms of continuum models for the deformation of polymers. In particular, the relevance of a simple molecular network model is considered. It is shown that many of the observations are consistent with the deformation of a molecular network, although our understanding of the molecular processes involved in cold drawing is still incomplete.     

Preparation of high-strength and high-modulus poly(vinyl alcohol) fibers by crosslinking wet spinning/multistep drawing method

This study is mainly focused on the preparation of high-strength and high-modulus poly(vinyl alcohol) (PVA) fibers by crosslinking wet spinning and multistep drawing. High strength as well as high modulus can be achieved by introduction of the crosslinks into the oriented chains to reduce entanglement degree and slippage between chains. The relationships between mechanical properties and fine structure of the drawn fibers were examined based on results of measurements of tensile property, thermal property, dynamic viscoelasticity, crystallinity, and orientation. The strength and Young's modulus of the drawn fibers are approximated to 1.82 and 51.76 GPa, respectively. The fiber has a sharp melting peak temperature that appeared at 236.7°C in the differential scanning calorimeter (DSC) curve. Our results indicate the multistep drawing procedure is superior to the conventional one-step drawing procedure. These excellent mechanical properties can be directly attributed to their high orientation of the amorphous chains. © 1994 John Wiley & Sons, Inc.     

Heat generation associated with drawing of poly(ethylene terephthalate)

The heat associated with drawing of poly(ethylene terephthalate) fiber is estimated on the basis of equations developed in the literature on films undergoing deformation by neck propagation. The deformation process is divided into two steps: neck propagation or drawing to the natural draw ratio and uniform deformation accompanied by crystallization. The results show that heat loss is negligible during deformation by necking and the temperature rise is estimated to be about 60K in yarns with a spun birefringence of 0.011. The heat released in step 2 is sufficient to raise the fiber temperature about 55K under adiabatic conditions, of free air convection, the temperature rise is estimated to be only about 5–1 0K.     

Preparation of poly(ethylene terephthalate) nanocomposite fibers incorporating a thermally stable organoclay

Summary A series of poly(ethylene terephthalate) (PET) nanocomposites containing organically-modified mica (HB-Mica) were prepared by in-situ interlayer polymerization of dimethyl terephthalate and ethylene glycol. The PET nanocomposites, which contained organoclay loadings of 0 to 2 wt %, were melt-spun to produce monofilaments with various draw ratios. Some of the clay particles appeared well dispersed within the PET matrix, while others were found to form agglomerates with sizes greater than 20 nm. The addition of a small amount of organoclay was sufficient to improve the thermo-mechanical properties of the PET hybrid fibers. Both the thermal stability and the mechanical tensile properties increased with increasing clay content for draw ratios of 1–16.     

Preparation and property of poly(ethylene terephthalate) fibers providing ultraviolet radiation protection

Interest in protection against solar ultraviolet radiation (UVR) among the general public in the world has been increasing steadily. Poly(ethylene terephthalate) (PET) was blended with UVR‐protection agents and was spun into modified fibers to provide the property of UVR protection. Investigation of this property using a UV spectrophotometer showed that the modified PET fabrics could be resistant to UVR more than 90% in the UV‐B band. The treatment of aqueous alkali on the surface of the fibers to improve the comfortable feel had little influence on the property of UVR protection. Scanning electron microscopy was employed to observe the surface morphology of the fibers. Also, the modified fibers had good heat insulation property and the mechanical properties of the fibers were measured. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1180–1185, 2003     

A study of the drawing behavior of poly(ethylene terephthalate)

Cold-drawn and hot-drawn samples of poly(ethylene terephthalate) were studied by means of measurements of shrinkage stress, birefringence and differential scanning calorimetry (DSC). The values of shrinkage stress were comparable for both types of sample, implying that the deformation of a molecular network is important for both cold drawing and hot drawing. The DSC results indicate that substantial crystallization occurs in hot drawing for other than the lowest draw ratios, and this crystallization gives rise to an additional peak in the shrinkage stress measurements. In addition to temperature, strain rate is also an important variable, and changes in strain rate caused significant changes in both hot-drawn and cold-drawn samples.     

Improved mechanical properties of poly(ethylene terephthalate) nanocomposite fibers

Improvements in Young's modulus and strength (tenacity) of poly(ethylene terephthalate) (PET) fibers were obtained by drawing unoriented nanocomposite filaments containing low concentrations (<3 wt%) of various organically modified montmorillonites (MMTs) in a second step at temperatures above the glass transition. Prior to melt spinning, solid‐state polymerization was used to rebuild lost molecular weight, due to MMT‐induced degradation, to a level suitable for producing high strength fibers. Greater improvements in mechanical properties occurred when the MMT stacks were intercalated with PET. A nominal 1 wt% loading of dimethyl‐dehydrogenated tallow quaternary ammonium surface modified MMT in drawn PET fiber showed a 28% and 63% increase in Young's modulus and strength, respectively. Relative to an unfilled PET fiber, these results surpassed the upper bound of the rule of mixtures estimate and suggested that both the type of surface modification and concentration of MMT affect the degree of PET orientation and crystallinity. Furthermore, drawability above T_g and elongation at break increased upon the addition of organically modified MMT to unoriented PET fibers, which was a key distinction of this work from others examining similar systems. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers     

Composition depth profiles of plasma-fluorinated poly(ethylene terephthalate) fibers

Composition depth profiles of the outer 50 Å of plasma-fluorinated poly(ethylene terephthalate) fibers were obtained by angle-dependent X-ray photoelectron spectroscopy (XPS). The effect of sample geometry on XPS sampling depth and the depth distribution function (DDF) was determined theoretically for cylindrical and hemispherical surfaces. The theoretical DDFs are nonexponential. For cylindrical surfaces, the effect is small, a 22% increase in surface sensitivity. The average XPS sampling depth for smooth, properly oriented fibers is shown to vary, as it does for a planar surface, as the sine of the nominal takeoff angle. The DDF appropriate for cylindrical surfaces was incorporated into a computer program for inversion of angle-dependent XPS data to obtain composition depth profiles of the fibers. Plasma-fluorinated PET fibers were used to demonstrate the use of angle-dependent XPS on fibers. XPS results indicate that most fluorination occurs within the top few “monolayers,” attack is preferentially at the phenyl ring, both ? CHF? and ? CF₂ ? moieties are formed, and fluorination causes partial loss of aromaticity. © 1994 John Wiley & Sons, Inc.     

Lamellar structure and properties in poly(ethylene terephthalate) fibers

The fibrillar and the lamellar structures in a range of poly(ethylene terephthalate) fibers were studied by small-angle X-ray scattering. The intensity maxima in the lamellar peaks lie on a curve that can be described as an ellipse. Therefore, the two-dimensional images were analyzed in elliptical coordinates. The dimensions of the coherently diffracting lamellar stack, the dimensions of the fibrils, the interfibrillar spacing, and the orientation of the lamellar surfaces were measured in addition to the lamellar spacing. The orientation of the lamellar planes and the size of the lamellar stacks had a better correlation with mechanical properties of the fibers than did the lamellar spacing. In particular, longer and wider lamellar stacks reduced fiber shrinkage, as did the closer alignment of the lamellar normal to the fiber axis. These structural features were also associated with lower tenacity. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2527–2538, 1998     

Studies of post drawing relaxation phenomena in poly(ethylene terephthalate) by infrared spectroscopy

In this paper, we study the relaxation behavior of initially amorphous poly(ethylene terephthalate) (PET) films drawn, at 80°C using a draw rate of 2 cm/min, to a draw ratio (λ) from 1 to 5 and then quenched to room temperature. These films were then heated at different temperatures from 68 to 80°C for different times and their orientation determined. The orientation measurements were performed by transmission infrared spectroscopy and the bands used for the determination of orientation were those at 1340 and 970 cm^?1 for the trans conformers, normalized using the 1410 cm^?1 benzene ring vibration. The crystallinity was determined by thermal analysis. It is shown that when PET is drawn to λ values up to 2–2.5 (before stress-induced crystallization), the orientation relaxes rapidly at temperatures close to the glass transition temperature of PET. For λ values of 3 or higher, the orientational relaxation of the amorphous regions is hindered. This effect is ascribed to the development of strain-induced crystallites, which are believed to act as pseudo-crosslinks.     

Molar mass of poly (ethylene terephthalate) (PET) during ultimate uniaxial drawing

The changes of the average molar mass M_w, M_n, M_z, and molar mass distributions during multistep uniaxial drawing of poly(ethylene terephthalate) (PET) to achieve ultimate mechanical properties have been studied in detail by means of size exclusion chromatography (SEC) with triple detection: concentration, viscosimetry, and light scattering, using HFIP as solvent. An increase in molar mass of PET due to post‐polycondensation and/or transesterfication during drawing at a high temperature of 160 to 230°C was found. Moreover, drawing leads to crystallization and large orientation in the amorphous phase, which results in lower molecular mobility and prevents a further growth in chain length. Crazing under extreme drawing conditions occurs and affects a decrease in molar mass.     

Aspects of the yield behavior in poly(ethylene terephthalate) fibers

The yield behavior during cold drawing of commercially spun poly(ethylene terephthalate) (PET) filament yarn was investigated. Microscopic examination revealed the presence of inherent flaws within the spun filaments; these act as points for localized stress concentration. These inhomogeneities appear to be either internal cracks or crazes developed during the fiber melt spinning process. During elongation, stress magnification at these flaws results in shear band formation, indicating the onset of inhomogeneous yielding. At the yield bend in the load-elongation curve a circumferential crack propagates within these shear band regions. This yield crack develops into the classical neck geometry which further localizes additional plastic deformation within the sample at the neck.     

Benzoyl-peroxide-initiated graft copolymerization of poly(ethylene terephthalate) fibers with acrylamide

In this study the grafting of acrylamide onto poly(ethylene terephthalate) fibers with the help of benzoyl peroxide and the effects of the temperature and the concentrations of initiator and monomer were investigated. Some of the experiments were repeated several times in order to check the reproducibility. The optimum temperature for grafting was found to be 75°C. The graft yield was observed to increase with the monomer concentrations examined. The graft yield increased up to the benzoyl peroxide concentration approximately 0.05 g/50 mL, and then passed a plateau, before showing a decrease. The fiber diameter, intrinsic viscosity, and the moisture regain increased while the fiber density decreased with the graft yield.     

Superstructure in ultrahigh speed spun fibers of poly(ethylene terephthalate)

Ultrahigh speed spinning of poly(ethylene terephthalate) (PET) was carried out at various take-up velocities from 5 to 10 km/min. The superstructure of as-spun fibers was characterized by small-angle X-ray scattering (SAXS), wide-angle X-ray diffraction (WAXD), viscoelastic properties, and scanning electron microscopy (SEM). Above 6 km/min the peaks or shoulders that are due to the interference between microfibrils appear on the equatorial SAXS intensity curves. The interfibrillar spacing estimated from the peak position increases with increasing take-up velocity. Comparison of the spacing with the lateral crystal sizes estimated from the broadness of the crystal (hk0) WAXD peaks indicates that the microfibril diameter becomes thick with increasing take-up velocity. Although the orientation and density in amorphous region for high-speed spun fibers are very low on the average, it can be seen that a few highly extended tie molecules exist in that region, and the number of these molecules increases with increasing take-up velocity. The modes and mechanisms of fibrillation induced by a rubbing test are discussed relating to these results.     

Orientation and crystallisation mechanisms during fast drawing of poly(ethylene terephthalate)

Summary Synchrotron radiation has been used to record the diffraction patterns from Poly(ethylene terephthalate) for a range of draw rates (0.1 to 10sec⁻¹) and temperatures (90 to 120°C). The patterns were analysed to derive the development of the <P ₂(cosθ)> order parameter and the rates of crystallisation. The effects of temperature and draw rate can be unified with a WLF time-temperature shift factor. Comparison with estimates of chain relaxation processes show that, when the draw rate is faster than the chain retraction process, the onset of crystallisation is delayed until the end of drawing. Crystallisation is very sensitive to both temperature and orientation and has an approximate 4th power dependence on <P₂(cosθ)>. Received: 26 October 1998/Accepted: 12 February 1999