Comparison of the structure-property relationships for PTT and PET fibers spun at various take-up speeds

A comparison of poly(trimethylene terephthalate)(PTT) and poly(ethlene terephthalate)(PET) fibers spun at various take-up speeds was presented. Fiber characterization included tensile and thermal properties, optical birefringence, density, sonic modulus, boil-off shrinkage, and wide-angle X-ray diffraction. The phenomenon of stress-induced crystallization was inferred from the X-ray diffraction diagrams for fibers spun with take-up speeds over 4000 m/min. The tenacity and elongation of PTT and PET fiber showed typical results, but the initial modulus of PTT fiber was nearly unchanged over the entire take-up speed range (2000–7000 m/min), whereas that of PET, as expected, increased monotonically with increasing take-up speed. This divergent behavior could be explained by the different molecular deformations in the c-axis as determined from X-ray diffraction patterns. The fiber crystallinity, density, and heat of fusion of both polymers increased with take-up speed. The boil-off shrinkage decreased with increasing take-up speed. The optical birefringence of the two fiber types showed a maximum level at a take-up speed of ca. 5000 m/min. The melting temperature behavior of PTT fiber was different from that of PET fibers. It was found that PTT is less sensitive to stress induced changes at high spinning speeds than is PET.     

Structure development and dynamic properties in high-speed spinning of high molecular weight PEN/PET copolyester fibers

The structure development and dynamic properties of fibers produced by high-speed spinning of P(EN-ET) random copolymers were investigated. The as-spun fibers were found to remain amorphous up to the spinning speed of 1500 m/min, and subsequent increases in speed resulted in the crystalline domains containing primarilyα crystalline modification of PEN. Theβ modification was not found up to spinning speeds of 4500 m/min. On the other hand, annealing of constrained fibers spun at the 2100 m/min at 180, 200, and 240°C exhibitedβ-form crystalline structure, while the annealed fibers spun in 600–1500 m/min range exhibited dominantlyα-form. Howeverβ-form crystals disappeared above the spinning speed of 3000 m/min. With increasing spinning speeds from 600 to 4500 m/min, the storage modulus of as-spun fibers increased continuously and reached a value of about 10.4 Gpa at room temperature. The tanδ curves showed theα-relaxation peak at about 155–165°C, which is considered to correspond to the glass transition. Theα-relaxation peaks became smaller and broader, and shift to higher temperatures as the spinning speed increases, meaning that molecular mobility in the amorphous region is restricted by increased crystalline domain.     

Structure and properties of syndiotactic polystyrene fibers prepared in high-speed melt spinning process

High-speed melt spinning of syndiotactic polystyrene was carried out using high and low molecular weight polymers, HMs-PS and LMs-PS, at the throughput rates of 3 and 6 g/min. The effect of take-up velocity on the structure and properties of as-spun fibers was investigated. Wide angle X-ray diffraction (WAXD) patterns of the as-spun fibers revealed that the orientation-induced crystallization started to occur at the take-up velocities of 2–3 km/min. The crystal modification wasα-form. Birefringence of as-spun fibers showed negative value, and the absolute value of birefringence increased with an increase in the take-up velocity. The cold crystallization temperature analyzed through the differential scanning calorimetry (DSC) decreased with an increase in the take-up velocity in the low speed region, whereas as the melting temperature increased after the on-set of orientation-induced crystallization. It was found that the fiber structure development proceeded from lower take-up velocities when the spinning conditions of higher molecular weight and lower throughput rate were adopted. The highest tensile modulus of 6.5 GPa was obtained for the fibers prepared at the spinning conditions of LMs-PS, 6 g/min and 5 km/min, whereas the highest tensile strength of 160 MPa was obtained for the HMs-PS fibers at the take-up velocity of 2 km/min. Elongation at break of as-spun fibers showed an abrupt increase, which was regarded as the brittle-ductile transition, in the low speed region, and subsequently decreased with an increase in the take-up velocity. There was a universal relation between the thermal and mechanical properties of as-spun fibers and the birefringence of as-spun fibers when the fibers were still amorphous. The orientation-induced crystallization was found to start when the birefringence reached — 0.02. After the starting of the orientation-induced crystallization, thermal and mechanical properties of as-spun fibers with similar level of birefringence varied significantly depending on the processing conditions.     

Theoretical analysis of the melt spinning process of poly(trimethylene terephthalate) fibers

Profiles development of the melt spinning process of poly(trimethylene terephthalate) (PTT) was simulated by a numerical method. The spinning speed of 3 km/min to 5 km/min was analyzed and the characteristic of PTT spinning process was compared with that of poly(ethylene terephthalate) (PET). Velocity development of PTT was slower than that of PET. Although PTT’s spinning temperature was lower than PET’s, the PTT solidified slower because of a smaller super-cooling and the large specific heat capacity. The diameter profile of PTT decreases gradually in comparison with that of PET. PTT’s strain rate has a broader distribution than PET’s and its maximum ranged from 541 to 570 s⁻¹ for PET and 136 to 149 s⁻¹ for PTT. PTT’s tensile stress was smaller than PET’s.     

Preparation of regenerated cellulose fiber via carbonation (II)

Sodium cellulose carbonate (CC-Na) dissolved in 8.5 wt% NaOH/ZnO (100/2–3, w/w) aqueous solution was spun into some acidic coagulant systems. Diameter of regenerated cellulose fibers obtained was in the range of 15–50μm. Serrated or circular cross sectional views were obtained by controlling salt concentration or acidity in the acid/salt/water coagulant systems. Velocity ratio of take-up to spinning was controlled up to 4/1 with increasing spinning velocity from 5 to 40 m/min. Skin structure of was developed at lower acidity or higher concentration of coagulants. Fineness, tenacity and elongation of the regenerated cellulose fibers were in the range of 1.5–27 denier, 1.2–2.2 g/d, and 8–11.3%, respectively. All of CC-Na and cellulose fibers spun from CC-Na exhibited cellulose II crystalline structure. Crystallinity index was increased with increasing take-up speed.     

Effect of multi walled carbon nanotube on the crystalline structure of polypropylene fibers

Polypropylene fibers containing varying amounts of multi walled carbon nanotube (MWCNT) have been spun using a conventional melt spinning and drawing apparatus. Changes in morphology and crystalline structure of composite fibers induced by addition of MWCNT were studied by small angle X-ray scattering (SAXS), wide angle X-ray scattering (WAXS), Fourier transform infrared spectroscopy (FTIR) and birefringence measurements. The results of SAXS experiments showed an increase in lamellar thickness, long period and crystallinity of the composite fibers in comparison to pure polypropylene fibers. Molecular orientation and helical content of the fibers were increased due to the addition of MWCNT to the polypropylene matrix. WAXS results, being in agreement with the SAXS results, also showed an increase in crystallinity of the composite fibers due to the increase in MWCNT content. This is probably because of nucleating effect of nanotubes in the fiber matrix, causing more crystallization and orientation of molecules to take place around them.     

Processing parameters optimization of multiple quality characteristics of open-end rotor spinning process for Bamboo charcoal and CVC blended fibers

In the field of yarn spinning engineering, the importance of the processing parameters taken depends directly on the quality characteristics of the yarn. This study aimed to find the optimal processing parameters for an open-end rotor spinning frame at work to identify its multiple quality characteristics for yarn. In this study, Bamboo charcoal and cotton 70 %/polyester 30 % (CVC) blended fibers were adopted as the materials, and the open-end rotor spinning frame was used to spin the yarn. In order to identify optimal conditions of an open-end rotor spinning frame, the Taguchi experimental method was applied to design open-end rotor spinning experiments, and the L₉ orthogonal array was chosen in accordance with nine sets of experiments and contained four control factors and three levels. Furthermore, a response surface methodology (RSM) was used to obtain the models of significant processing parameters for the strength, unevenness, I.P.I, and hairiness. Based on experiments designed to obtain an open-end rotor spun yarn Ne 30, the strength, unevenness, imperfection indicator/km (I.P.I) and hairiness were then chosen as the quality characteristics. In addition, grey relational analysis integrated the optimal processing parameter of multiple quality characteristics, and a confirmation experiment was performed. In conclusion, the optimal processing parameters under steady spinning conditions were a rotor speed of 88000 rpm, a feed speed of 0.392 m/min, and a winding speed of 39.466 m/min.     

Study on the matrix-fibril morphologies of polypropylene/polystyrene blends under non-isothermal uniaxial elongational flow

Polypropylene/polystyrene blends with different viscosity ratios, p, ranging from 1.6×10^?2 to 10.8, were prepared by using textile-grade isotactic polypropylene (iPP) and five kinds of atactic polystyrene (aPS), named PS1, PS2, PS3, PS31 and PS46 with different molecular weight, and then melt-spun into composite fibers with matrix-fibril morphology at different take-up velocities, v _L , ranging from 125 to 1000 m/min. The effects of p on the diameters and quantities of dispersed droplets in extrudate fibers, and the effects of p and v _L on the size and quantities of fibrils in take-up fibers were discussed, respectively. Based on a quantitatively characterization for the coalescence and deformation of droplets during melt spinning, a theoretical analysis based on Newtonian fluids simplification and the deformation theory was presented to predict the deformation and breakup of droplets during melt spinning. It is found that there is a good fit between theoretical and observed experimental results at most discussed take-up velocities. Furthermore, the uncertainties of Newtonian fluids simplification and a hypothesis of local energy dissipation from migration and coalescence were noted to explain the deviations between predicted and experimental data.     

The effects of UV irradiation exposure on the structure and properties of polypropylene/ZnO nanocamposite fibers

Unfilled polypropylene and polyropylene/ZnO nanocomposite fibers were produced using a melt spinning apparatus; then the fibers were exposed to UV irradiation. The structure and properties of the fibers were examined using scanning electron microscopy, tensile measurements, wide angle X-ray diffraction (WAXD), Fourier transform infrared (FTIR) spectroscopy, birefringence measurements and differential scanning calorimetry (DSC). Following 150 hours of exposure to UV irradiation, some transverse cracks on the surface of unfilled polypropylene fibers were observed. It was observed that both carbonyl and hydroperoxide indexes, which are the criteria for the detection of UV degradation of the fibers, were increased due to the increase in the UV irradiation exposure time and the increase in these indexes was smaller for nanocomposite fibers than those of unfilled Polypropylene fibers. It was also observed that crystallinity, crystallite size and total molecular orientation of UV irradiated nanocomposite fibers were increased in comparison with non-irradiated nanocomposite fibers. It was also found that the extent of increase in molecular orientation of the fibers was higher comparing to that for the nanocomposite fibers due to the UV irradiation exposure for the unfilled polypropylene fibers. Tensile properties of both unfilled and nanocomposite fibers were decreased after UV irradiation; this reduction correlated with the extent of the increase in molecular degradation of the fibers, as determined by measuring carbonyl and hydroperoxide indexes.     

The non-uniform phase structure in blend fiber. II. The migration phenomenon in melt spinning

The migration phenomenon was investigated in polypropylene/polystyrene (PP/PS) blend fiber and low density polyethylene/polyamide 6 (LDPE/PA6) blend fiber. The migration of fibrils in melt spinning was evaluated by the variation of fibrils’ area ratio over the cross section of blend fiber. In PP/PS blend fiber, the dispersed PS deformed into many highly oriented fibrils in the PP matrix, and PS fibrils migrated towards the surface of the take-up fiber in the fiber spinning process. On the contrary, PA6 fibrils migrated into the core of the take-up fiber, while the dispersed PA6 deformed into many highly oriented fibrils in the LDPE matrix for LDPE/PA6 blend fiber. Otherwise, no migration phenomenon was observed in the special fiber that was prepared without any drawing, neither in PP/PS nor in LDPE/PA6. Therefore, in the fiber spinning process, the migration phenomenon actually occurred mainly in the drawing process, which is the non-isothermal uniaxial extensional flow. Comparing with migration mechanisms in the shear flow, the migration phenomenon in melt spinning was probably due to the radial non-uniform extensional stress, the extensional viscosity.     

Spinnability in pre-gelled gel spinning of polyacrylonitrile precursor fibers

The spinnability in pre-gelled gel spinning of polyacrylonitrile (PAN) precursor fibers was investigated. The spinning solutions were aged at 25 °C for different times prior to fiber spinning. The pre-gelled spinning solution aged for 2.5 h was much more strain hardening than the ungelled one, which can increase the spinnability of the solution. The maximum take-up velocity of the first winding roller V _1m, which reflects the spinnability of the spinning solutions, was found to be largest when the aging time was 1.5 h. The spinnability increased with the increase of the air gap length and the lengthdiameter ratio L/D of the spinnerette. Once the L/D increased beyond 15, the spinnability hardly changed. The fibers spun from the spinning solution aged for 1.5 h had the best mechanical properties and favorable structure, showing that good spinnability favors the performance increase of resultant PAN precursor fibers.     

Effects of the reaction degree of melamine-formaldehyde resin on the structures and properties of melamine-formaldehyde/polyvinyl alcohol composite fiber

Composite fibers made of polyvinyl alcohol (PVA) and melamine-formaldehyde (MF) resins with different reaction degrees were prepared by wet spinning. The phase structures of MF/PVA spinning dopes and composite fibers were observed by using optical microscope (OM) and scanning electron microscope with energy-dispersive X-ray spetroscopy (SEM-EDS). Crystal structures of composite fibers were studied by X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The loss of MF resins in the spinning process was calculated by using Kjeldahl. The mechanical properties, the flame retardant property, the water resistant property, and the thermal stability of composite fibers were also tested. Results show that with an increase in the reaction degree of MF resin, the phase separation degrees of spinning dopes and composite fibers rise up, the size of MF microphase grows larger, and the loss of MF resin diminishes; consequently, the hot water resistance and the flame retardancy of the fiber ameliorate while the tensile strength and the thermal stability perform a tendency of dropping after rising.     

Effects ofIn Vitro degradation on the weight loss and tensile properties of PLA/LPCL/HPCL blend fibers

PLA/LPCL/HPCL blend fibers composed of poly (lactic acid) (PLA), low molecular weight poly (ɛ-caprolactone) (LPCL), and high molecular weight poly (ɛ-caprolactone) (HPCL) were prepared by melt blending and spinning for bioabsorbable filament sutures. The effects of blending time and blend composition on the X-ray diffraction patterns and tensile properties of PLA/LPCL/HPCL blend fibers were characterized by WAXD and UTM. In addition, the effect ofin vitro degradation on the weight loss and tensile properties of the blend fibers hydrolyzed during immersion in a phosphate buffer solution at pH 7.4 and 37°C for 1–8 weeks was investigated. The peak intensities of PLA/LPCL/HPCL blend fibers in X-ray diffraction patterns decreased with an increase of blending time and LPCL contents in the blend fibers. The weight loss of PLA/LPCL/HPCL blend fibers increased with an increase of blending time, LPCL contents, and hydrolysis time while the tensile strength and modulus of the blend fibers decreased. The tensile strength and modulus of the blend fibers were also found to be increased with an increase of HPCL contents in the blend fibers. The optimum conditions to prepare PLA/LPCL/HPCL blend fibers for bioabsorbable sutures are LPCL contents of 5 wt%, HPCL contents of 35 wt%, and blending time of 30 min. The strength retention of the PLA/LPCL/HPCL blend fiber prepared under optimum conditions was about 93.5% even at hydrolysis time of 2 weeks.     

Deformation of dispersed polystyrene droplets in immiscible polypropylene/polystyrene blend fibers under uniaxial elongational flow

The deformation of dispersed polystyrene (PS) droplets in immiscible polypropylene (PP) matrices during melt spinning of blend fibers were simulated by adopting the droplet deformation criteria. The ratios of number-average length to diameter were measured through morphology analysis, and compared with the simulated values. It was found that the adopted deformation models described the deformation behavior of the dispersed droplets during melt spinning very well. Dispersed droplets in the center of the fiber tend to be stretched longer than those of near to the surface, due to the radial temperature gradient during fiber formation. Moreover, combining with the rheological studies of raw materials, a theoretical relation between temperature and deformation was established and used to determine the radial temperature differences along the spinning line. It was found that the radial temperature gradients vary from 0.22 to 0.35 °C/μm at 40 cm beneath to the spinneret at the discussed take-up velocities.     

Uniaxially well-aligned nanofiber arrays fabricated by electrospinning with a stable and low moving velocity jet

Aligned fibers in micro-/nano-scale have attracted more attention especially in tissue engineering field because cells can orientation growth along the fiber. However, it is still a huge technological challenge in achieving it as a result of the inherent bending instability of an electrospinning jet. Herein, we report a novel and simple spinning approach, in which low dielectric constant of dioxane was judiciously used as solvent for spinning dope, to obtain electrospinning jet with low induced charge, therefore eliminating electrically and aerodynamically driven bending instability, and forming a stable and low forward-moving velocity jet longer than 100 cm. This consequently allows for readily collecting and fabricating individual fibers, well-aligned ultrafine fiber arrays over large areas. Our approach has proved to be effective in preparing well-aligned ultrafine fibers from biodegradable poly(D, L-lactic acid) with different molecular mass, natural polymer acetyl cellulose and synthesized non-biodegradable polymer polystyrene.     

Matrix-fibril morphology development of polypropylene/poly(butylenes terephthalate) blend fibers at different zones of melt spinning process and its relation to mechanical properties

Different shapes of dispersed phase such as sphere, laminar and fibrillar can form in the matrix phase of polymer blends. Production of blend fibers in melt spinning process can result more effective in fibrillar phase morphology formation than in other processes. In this research, the matrix-fibril morphology development during the melt spinning of polypropylene/poly(butylenes terephthalate) was studied. The shapes of blend dispersed phase collected from different zones of the melt spinning line were evaluated by scanning electron micrographs (SEM) and rheological mechanical spectra (RMS). The results showed that fibrillar shape could not be created in the PP/PBT blend fiber samples exited from the spinneret orifice (gravity spun fibers) at low contents (5 percent) of the PBT dispersed phase. However, a complete fibrillar structure was formed in all the as-spun PP/PBT blend fiber samples (melt drawn). The rheological evaluations confirmed a network structure resulting from fibril formation for the samples with high contents (20–40 %) of the PBT dispersed phase and the formation of spherical shape with low contents (5–10 %) of the PBT dispersed phase in matrix of the blend fibers. It was observed that the flow fields of processing zones and blend ratio, in producing the blend fibers, have intensive effects on morphological variations; besides there was a strong relation between the mechanical and morphological properties.     

Enzyme-modified casein fibers and their potential application in drug delivery

Enzymatic crosslinking of casein fibers was done using Transglutaminase (TGase) to improve the mechanical properties, particularly the stability in aqueous conditions and make them suitable for controlled drug release application. Crosslinking casein with 5 U/g of TGase in the spinning dope for 60 min at 25 °C increased the tenacity and tensile strain of the fibers from 0.40 g/den and 4.2 % to 0.70 g/den and 23.1 %, respectively. The stability of the fibers in water at different pH levels was considerably improved after the enzymatic crosslinking. The SDS-PAGE electrophoresis confirmed that higher molecular weight proteins were formed in TGase-crosslinked fibers. Thermogravimetric analysis (TGA) showed that TGase treated fibers also had a higher thermal degradation temperature than the non-crosslinked fibers. Crosslinked fibers exhibited delayed and lower rate of drug release from the fibers suggesting their suitability for controlled drug release.     

Studies on melt spinning of sea-island fibers. I. morphology evolution of polypropylene/polystyrene blend fibers

Isotactic polypropylene/atactic polystyrene (iPP/aPS) immiscible polymer blends are prepared and are melt-spun to prepare blend fibers with matrix-fibril morphologies. The running fibers are captured at different positions of the spinning line, and the morphologies including dispersions of aPS droplets in iPP matrix fibers, droplets diameter and their distributions, as well as the radial gradients on counts and diameter of droplets are analyzed. The effect of take-up velocity on the morphology of take-up fibers is discussed by comparing with that of extrudate fibers. At low take-up velocities, the enhanced radial gradients are attributed to shrinking of matrix fibers on the elongation of spinning stress. While the effects of non-uniform deformation, coalescence and migration of droplets play a role to resist the effects of shrinking of matrix fibers at high take-up velocities. Based on morphology analysis, the mechanisms of compression from the shrinking of matrix fibers, non-uniform deformation, coalescence and migration of droplets are presented to explain why and how the radial gradients form.     

The non-uniform phase structure in blend fiber. I. Non-uniform deformation of the dispersed phase in melt spinning

By melt spinning of incompatible polymer blends, the deformation of the dispersed phase was investigated in the fiber spinning process, for polypropylene/polystyrene (PP/PS) blend fiber and low density polyethylene/polyamide 6 (LDPE/PA6) blend fiber, respectively. Two kinds of the take-up fiber all exhibit the matrix fibrillar morphology, but with the opposite morphology. For PP/PS take-up fiber, the dispersed PS fibrils were finer in the core than near the surface. On the contrary, the dispersed PA6 fibrils were finer near the surface than in the core for LDPE/PA6 take-up fiber. However, for the special fiber in which the extensional flow was absent, there was the uniform morphology in either PP/PS or LDPE/PA6. Thus, fibrils’ non-uniform deformation, occurred in the drawing process, was considered to be due to the radial non-uniform processing conditions across the spin-line cross-section. The distribution of fibrils’ diameter was also investigated on the whole cross section. Rheological properties of each component were measured by the capillary rheometer. The non-uniform phase structure in blend fiber is a new phenomenon in the extensional flow.