Critical stress for crystallization in the threadline during high-speed spinning of poly(ethylene terephthalate)

The development of structure during steady-state high-speed spinning of poly(ethylene terephthalate) has been correlated with the stress on the threadline. In particular, it is shown that a critical stress at the freeze point of 0.08–0.09 g/denier (9.5–10.6 MPa) is necessary for the occurrence of threadline crystallization independent of polymer molecular weight or process variables such as windup speed or filament character.     

Dyeing behaviour of poly(ethylene terephthalate) fibres spun by high-speed melt spinning

Poly(ethylene terephthalate) (polyester) fibres were spun using a high-speed melt spinning method. By changing the spinning conditions, polyester fibres with differences in crystallinity, birefringence and melting point were obtained. The dyeing behaviour of these fibres was investigated using CI Disperse Red 1. The degree of crystallisation of polyester lowered the dyeability. The fibres with lower molecular orientation and larger crystallite size showed better dyeability.     

Necking behavior in high‐speed melt spinning of poly(ethylene terephthalate)

The necking behavior in the high‐speed melt‐spinning process of poly(ethylene terephthalate) (PET) was analyzed using a mathematical simulation under a nonisothermal condition. A constitutive model into which the strain‐rate dependence of viscosity and the strain‐hardening effect are incorporated was used. Based on the simulated results, the cause of a local reduction of apparent viscosity was found to be due mainly to high strain rate. Also the onset of crystallization, if it occurred, was found to happen near the end of the neck. In addition, with no crystallization involved, the necking can still occur. The deformation process in high‐speed spinning of PET was found to consist of two regions along the spin line: a Newtonian flow region and a rubberlike deformation region. The necking behavior is discussed here in terms of strain‐rate sensitivity and strain‐hardening parameter. As a result, a criterion for the onset of stable necking has been obtained. The necking behavior does not seem to be essentially different from that in cold drawing. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 446–456, 2000     

Influence of melt spinning conditions on dye uptake of poly(ethylene terephthalate) fibres

The effects of quenching air temperature, quenching air speed and winding speed in the melt spinning process of poly(ethylene terephthalate) fibres with a titre of 147 dtex and 96 filaments on dye uptake were investigated. The ranges used for quenching air temperature, quenching air speed and winding speed were 17–27 °C, 0.3–0.7 m/s and 2600–3800 m/min, respectively. Specimens were dyed and their colour strengths (K/S values) were measured using a spectrophotometer. The results were statistically analysed.     

Effect of metallic wire inserted in nozzle in high-speed melt spinning of poly(ethylene terephthalate)

High-speed melt spinning of poly(ethylene terephthalate) was performed using a spinning nozzle with an inserted metallic wire of various lengths (0, 8, 30, and 45 mm). The molecular orientation of as-spun fibers increased with the increase in the wire length at all the take-up velocities examined. Along with the enhanced molecular orientation, the longer wire length led to the starting of orientation-induced crystallization at lower take-up velocities. The structure of crystallized fibers obtained at low speeds can be characterized by high crystallinity and relatively low molecular orientation. From the on-line measurement of the diameter and temperature profiles of the spin line with the 30-mm metallic wire, it was revealed that the spin-line had a maximum diameter of about 6 mm at the wire end. The spin-line temperature at this position was about 190°C. The solidification of the spin-line occurred at positions much closer to the spinneret in comparison with ordinary high-speed spinning. These results show that high-speed spinning with a wire inserted in the nozzle corresponds to a spinning process operated at extremely low extrusion temperature using a nozzle with an extremely large diameter. From the starting of orientation-induced crystallization at lower levels of birefringence in comparison with ordinary high-speed spinning, the alteration of the inherent fiber structure that cannot be represented by birefringence was also suggested. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 665–674, 1998     

Organoclays assisted vat and disperse dyeing of poly(ethylene terephthalate) nanocomposite fabrics via melt spinning

Polyethylene terephthalate nanocomposites containing six modified montmorillonite nanoclays were prepared by a melt compounding technique. The effect of intercalated compounds of montmorillonite on textile mechanical properties of resultant polyethylene terephthalate nanocomposite fabrics was investigated. Winding was not possible, when the polymers were first compounded with the desired amount of montmorillonite and then spun, as filament breakage occurred. Spinable polymer were only obtained by mixing polyethylene terephthalate master batches with 4 wt% montmorillonite, which contained tallow intercalating compound with pure untreated polyethylene terephthalate to a montmorillonite content of 0.5 wt%, thus decreasing the concentration of thermally degraded polymer chains. After spinning the fibres were drawn and knitted into fabric samples for further testing. The prepared polyethylene terephthalate nanocomposite fabrics using montmorillonite exhibited higher colour strength using vat and disperse dyes compared with those of the reference fabrics made from fibres spun without montmorillonite clay content and regular fabrics. The carbocyclic‐based vat dyes have higher colour strength values on polyethylene terephthalate nanocomposite fabrics if compared with heterocyclic‐based vat dyes. The colour fastness ratings for both vat and disperse dyeings secured very good to excellent washing and perspiration fastness on polyethylene terephthalate nanocomposite fabrics. All dyed fabrics showed excellent light fastness using vat and disperse dyes. The preparation of polyethylene terephthalate nanocomposite fabrics with improved textile mechanical and vat dyeing properties needs further investigations.     

Dynamics of the threadline in melt spinning

In the nylon 6 melt spinning process at speeds of 900 and 1200 m/min the quenching is done in a stepwise manner. The effect on physical data of the drawn yarn is investigated and correlation between quench height, water takeup, and boiloff shrinkage discussed. Length changes across the takeup machine are also measured as function of quench height and seem to correlate with physical data. The speed of length changes for both finished and unfinished yarn as a function of quench height suggests a molecular oscillation along the spinning line rather than a continuous orientation of the molecular structures. A secondary disorientation zone is defined.     

Film reaction kinetics for melt postpolycondensation of poly(ethylene terephthalate)

Melt polycondensation has recently been reported to prepare high-viscosity poly(ethylene terephthalate) (PET), the reaction efficiency is greatly improved in over 10-folds compared with conventional solid state polycondensation (SSP). Melt postpolycondensation of common PET chips was conducted in specified film thickness to obtain industrial PET. Based on the investigation of reaction conditions, film reaction kinetics were determined in the principle of end groups analysis. It was positively regulated that the intrinsic viscosity of PET could be achieved in condition of high vacuum, thin melt film and proper temperature, degradation reaction would be increased at exorbitant temperature. An apparent reaction kinetic model was proposed and was verified by experiments. Results indicated the activation energy of melt postpolycondensation of PET was 88.22 kJ/mol and the reaction rate constant was significant higher than that of solid state polycondensation.     

Blends of poly(ethylene terephthalate) and poly(butylene terephthalate)

Commercial grade poly(ethylene terephthalate), (PET, intrinsic viscosity = 0.80 dL/g) and poly(butylene terephthalate), (PBT, intrinsic viscosity = 1.00 dL/g) were melt blended over the entire composition range using a counterrotating twin‐screw extruder. The mechanical, thermal, electrical, and rheological properties of the blends were studied. All of the blends showed higher impact properties than that of PET or PBT. The 50:50 blend composition exhibited the highest impact value. Other mechanical properties also showed similar trends for blends of this composition. The addition of PBT increased the processability of PET. Differential scanning calorimetry data showed the presence of both phases. For all blends, only a single glass‐transition temperature was observed. The melting characteristics of one phase were influenced by the presence of the other. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 75–82, 2005     

Orientation of poly(ethylene terephthalate) in high-speed spinning using a heating zone

Data on high-speed spinning using a heating zone were analyzed. It was shown that in spinning at a speed of 3500–4000 m/min using a heating zone, it is possible to attain high orientation corresponding to the level of ultrahigh-speed spinning at 7000 m/min.All-Russian Scientific-Research Institute of Synthetic Fibres. Tver' Translated from Khimicheskie Volokna No. 3. pp. 4–6. May–June. 1966.     

On-line studies of structure development during melt spinning of poly(butylene terephthalate)

An on-line study of structure development during poly(butylene terephthalate) melt spinning was carried out. Two polymers with different molecular weights (intrinsic viscosities of 0.75 and 1.0 dL/g) were used. The range of take-up velocities studied was 1500 to 4500 m/min. On-line measurements included diameter, temperature, birefringence, and tension. The phenomenon of diameter thinning (necking) was observed for both polymers at take-up velocities of 3500 and 4500 m/min with a mass throughput of 4 g/min. At a constant mass throughput, the distance from the spinneret at which the necking occurred varied with take-up velocity and molecular weight of the polymer. Increasing the take-up velocity at constant mass throughput caused an increase in cooling rate and a slight increase in the rate at which the temperature decreased with distance from teh spinneret. A small but detectable change in the rate of temperature decrease was observed at a position near or just beyond the formation of the neck. It is suggested that this effect is due to the increased heat transfer caused by the rapid increase in filament velocity and increased surface to volume ration in the neck. Increased take-up velocity also caused necking to occur at higher temperature, as did an increase of polymer molecular weight. Birefringence increased with distance from the spinneret and indicated substantial molecular orientation was developed in the filament prior to the necking zone. A sharp increase of birefringence in the necking zone was observed for take-up velocities of 3500 and 4500 m/min. A discussion of the mechanism of neck formation is presented, and it was concluded that necking is intimately associated with stress-induced crystallization in PBT. An increase of spinline stress resulting from either an increase of take-up velocity or an increase of molecular weight can cause stress-induced crystallization and, hence, necking to occur nearer the spinneret and at higher temperature. For a given polymer this leads to filaments with higher levels of crystallinity, crystalline orientation, and crystalline perfection (greater crystal size). These changes in morphology result in changes in the filament mechanical properties. The effect of molecular weight change on the structure and properties is complicated by the fact that the development of crystallinity seems to be affected by the molecular weight independent of the spinline stress.     

Crystallization in blends of poly(ethylene terephthalate) and poly(butylene terephthalate)

Blends composed of poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT) were melt-mixed in a Brabender cam mixer at different mixing speeds. The glass transition (T_g) and the crystallization behavior of the blends from glassy state were studied using DSC. It was found that although the blends had the same composition and exhibited the similar T_g, their properties of crystallization could be different; some exhibited a single crystallization peak and some exhibited multiple crystallization peaks depending upon experimental conditions. Results indicated that the behavior of crystallization from glassy state were influenced by entanglement and transesterification of chains. The crystallization time values were obtained over a wide range of crystallization temperature. From curve fitting, the crystallization time values and the temperature, at which the crystallization rate reaches the maximum, were found.     

Powdered poly(ethylene terephthalate)

The influence of the conditions of preparation on the properties of powdered poly(ethylene terephthalate) was followed from the point of view of its specific surface. The powdered poly(ethylene terephthalate) prepared by reprecipitation from the melt of 6-caprolactam has a porous and structured surface, and consequently, also a large specific surface in comparison with the powedered poly(ethylene terephthalate) prepared by mechanical milling. The specific surface value is influenced by the cooling rate of the initial homogeneous melt of poly(ethylene terephthalate)-6-caprolactam, by the concentration of poly(ethylene terephthalate) in this melt and by its molecular weight, by the water temperature at the extraction of 6-caprolactam from the tough mixed melt, by the drying temperature of the powdered poly(ethylene terephthalate), and by the content of residual 6-caprolactam in the powdered product. In the examined area, the specific surface value of the powdered poly(ethylene terephthalate) prepared by reprecipitation from the melt of 6-caprolactam ranged from 10 to 110 m²·g^?1.     

Flame-retardant poly(ethylene terephthalate)

Poly(ethylene terephthalate) containing hexabromobenzene, tricresyl phosphate, or a combination of triphenyl phosphate and hexabromobenzene, pentabromotoluene, or octabromobiphenyl was extruded or spun at 280°C into monofilaments or low-denier yarn, respectively. Only combinations of the phosphorus- and halogen-containing compounds resulted in flame-retardant poly(ethylene terephthalate) systems, without depreciating their degree of luster and color quality. The melting temperature, the reduced viscosity, and the thermal stability above 400°C of these flame-retardant systems were in most cases comparable to those of poly(ethylene terephthalate) itself. Phosphorus-bromine synergism was proposed with flame inhibition occurring mostly in the gas phase.     

Melt spinning of (multifilament) poly(ethylene terephthalate) fibers: A simulation approach

An approach for modeling and simulation of multifilament melt spinning of poly(ethylene terephthalate) fibers is presented. It is shown that the quench conditions seen by the filaments within a bundle are not identical but differ for different rows of filaments. This, in turn, affects the spun fiber properties and introduces a degree of variability in the properties. The proposed approach allows determination of both the average properties and their variability for a given set of spinning conditions, spinneret geometry, and quench details.     

High-speed melt spinning of bicomponent fibers: Mechanism of fiber structure development in poly(ethylene terephthalate)/polypropylene system

High-speed bicomponent spinning of poly(ethylene terephthalate)(PET)(core) and poly-propylene (PP) (sheath) was carried out and the structure development in the individual components, PET and PP, was investigated. The orientation and crystallinity development in the PET component was enhanced as compared to that of the single-component spinning while the PP component remained in a low orientation state and had a pseudohexagonal crystal structure even at high take-up speeds. To clarify the mutual interaction between the two components in bicomponent spinning, a semiquantitative numerical simulation was performed. The simulation results obtained using the Newtonian fluid model showed that the solidification stress in the PET component was enhanced while that of the PP component was decreased in comparison with the corresponding single-component spinning. This is due to the difference in the temperature dependence of their elongational viscosity. Simulation with an upper-convected Maxwell model as the constitutive equation suggested that significant stress relaxation of the PP component can occur in the spinline if the PET component solidifies earlier than does PP. Based on the structural characterization results, and the simulation results, it was concluded that the difference in the activation energy of the elongational viscosity and solidification temperature between the two polymers are the main factors influencing the mutual interaction in the bicomponent spinning process. © 1996 John Wiley & Sons, Inc.     

Role of 2‐hydroxyethyl end group on the thermal degradation of poly(ethylene terephthalate) and reactive melt mixing of poly(ethylene terephthalate)/poly(ethylene naphthalate) blends

In an attempt to minimize the acetaldehyde formation at the processing temperatures (280–300°C) and the outer–inner transesterification reactions in the poly (ethylene terephthalate) (PET)–poly(ethylene naphthalate) (PEN) melt‐mixed blends, the hydroxyl chain ends of PET were capped using benzoyl chloride. The thermal characterization of the melt‐mixed PET–PEN blends at 300°C, as well as that of the corresponding homopolymers, was performed. Degradations were carried out under dynamic heating and isothermal conditions in both flowing nitrogen and static air atmosphere. The initial decomposition temperatures (T_i) were determined to draw useful information about the overall thermal stability of the studied compounds. Also, the glass transition temperature (T_g) was determined by finding data, indicating that the end‐capped copolymers showed a higher degradation stability compared to the unmodified PET and, when blended with PEN, seemed to be efficient in slowing the kinetic of transesterification leading to, for a finite time, the formation of block copolymers, as determined by ¹H‐NMR analysis. This is strong and direct evidence that the end‐capping of the ? OH chain ends influences the mechanism and the kinetic of transesterification. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Finite strain behavior of poly(ethylene terephthalate) (PET) and poly(ethylene terephthalate)-glycol (PETG)

Uniaxial and plane strain compression experiments are conducted on amorphous poly(ethylene terephthalate) (PET) and poly(ethylene terephthalate)-glycol (PETG) over a wide range of temperatures (25-110 °C) and strain rates (.005-1.0 s⁻¹). The stress-strain behavior of each material is presented and the results for the two materials are found to be remarkably similar over the investigated range of rates, temperatures, and strain levels. Below the glass transition temperature (θ_g=80 °C), the materials exhibit a distinct yield stress, followed by strain softening then moderate strain hardening at moderate strain levels and dramatic strain hardening at large strains. Above the glass transition temperature, the stress-strain curves exhibit the classic trends of a rubbery material during loading, albeit with a strong temperature and time dependence. Instead of a distinct yield stress, the curve transitions gradually, or rolls over, to flow. As in the sub-θ_g range, this is followed by moderate strain hardening and stiffening, and subsequent dramatic hardening. The exhibition of dramatic hardening in PETG, a copolymer of PET which does not undergo strain-induced crystallization, indicates that crystallization may not be the source of the dramatic hardening and stiffening in PET and, instead molecular orientation is the primary hardening and stiffening mechanism in both PET and PETG. Indeed, it is only in cases of deformation which result in highly uniaxial network orientation that the stress-strain behavior of PET differs significantly from that of PETG, suggesting the influence of a meso-ordered structure or crystallization in these instances. During unloading, PETG exhibits extensive elastic recovery, whereas PET exhibits relatively little recovery, suggesting that crystallization occurs (or continues to develop) after active loading ceases and unloading has commenced, locking in much of the deformation in PET.     

Melt spinning of poly(ethylene terephthalate)—structural transitions in a range of spinning speeds

The transitions which occur in the structural state of poly(ethylene terephthalate) filaments in the range of spinning speeds, 1600–4500m/min, have been studied. Thermal annealing of as-spunfilaments has been shown to provide useful indirect evidence for the structural states of these filaments. The results have been explained with a simple model of orientation distributions arising from crystallization in an oriented precursor.     

Fiber structure formation in ultra-high-speed melt spinning of poly(ethylene 2,6-naphthalene dicarboxylate)

The high-speed melt spinning of poly(ethylene 2,6-naphthalene dicarboxylate) (PEN) was performed up to the take-up velocity of the ultra-high-speed region, 9 km/min. From the investigations of the structure and physical properties of the as-spun fibers, the high-speed spinning of PEN was divided into three regions in terms of the mechanism of fiber structure formation. The first region is the take-up velocity of up to 2.5 km/min and the birefringence of up to 0.08 where only a slight increase in molecular orientation was attained. At the take-up velocity of 2.5–4.5 km/min and the birefringence of 0.08–0.25, although some experimental evidences indicated that the orientation-induced crystallization did not occur, there was an increase in the fiber density which suggested the formation of some ordered structure. At the take-up velocity > 4.5 km/min and birefringence > 0.25, the orientation-induced crystallization occurred. The fibers obtained in this region were characterized by the formation of the crystalline structure dominated by the β form. The presence of the necklike deformation in the spinning line was also confirmed. The solidification temperature of the spinning line analyzed from the diameter profile suggested that the formation of β modification crystals occurred at relatively low crystallization temperatures in comparison with that in an isotropic state. Therefore it was indicated that the presence of elongational stress in the spinning line promoted the formation of the β modification crystals. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 1415–1427, 1997