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For different heat treatments, the changes in overall performance features such as tenacity, modulus, load at 5% strain and elongation at a load of 4.0 cN/dtex of high modulus low shrinkage poly (ethylene terephthalate) industrial fibers were compared. The variations in the mechanical behavior were linked to adjustments in the microstructure, as determined by Fourier transform infrared spectroscopy, wide-angle X-ray diffraction and small-angle X-ray scattering. The results confirmed that the tenacity of the fibers is less dependent on the heat treatment conditions, whereas the modulus, load at 5% strain and elongation at a load of 4.0 cN/dtex differ significantly, which could reflect the stability of the fibers in use. The intact crystal structure and the constrained conformation adjustment of molecular chains in amorphous after heat treatment are responsible for the excellent tenacity retention of high modulus low shrinkage poly (ethylene terephthalate) fibers. With a low pre-tension and a higher heating temperature, the molecular chains in the amorphous region relax and disorient, resulting in a lower modulus and load at 5% strain. Instead, in the case of high pre-tension, heat treatment prolongation or temperature increase helps to rearrange the amorphous region into an ordered structure, which can improve the initial modulus and load at 5% strain of the fibers.

Stretchable conductive fibers offer unparalleled advantages in the development of wearable strain sensors for smart textiles due to their excellent flexibility and weaveability. However, the practical applications of these fibers in wearable devices are hindered by either contradictory properties of conductive fibers (high stretchability versus high sensing stability), or lack of manufacturing scalability. Herein, we present a facile approach for highly stretchable self-crimping fiber strain sensors based on a polyether-ester (TPEE) elastomer matrix using a side-by-side bicomponent melt-spinning process involving two parallel but attached components with different shrinkage properties. The TPEE component serves as a highly elastic mechanical support layer within the bicomponent fibers, while the conductive component (E-TPEE) of carbon black (CB), multiwalled carbon nanotubes (MCNTs) and TPEE works as a strain-sensitive layer. In addition to the intrinsic elasticity of the matrix, the TPEE/E-TPEE bicomponent fibers present an excellent form of elasticity due to self-crimping. The self-crimping elongation of the fibers can provide a large deformation, and after the crimp disappears, the intrinsic elastic deformation is responsible for monitoring the strain sensing. The reliable strain sensing range of the TPEE/E-TPEE composite fibers was 160%–270% and could be regulated by adjusting the crimp structure. More importantly, the TPEE/E-TPEE fibers had a diameter of 30–40 µm and tenacity of 40–50 MPa, showing the necessary practicality. This work introduces new possibilities for fiber strain sensors produced in standard industrial spinning machines.

To explore the feasibility of developing bio-based elastic fibers, bio-based polylactide (PLA) and polytrimethylene terephthalate (PTT) were selected for fabrication of side-by-side bicomponent fibers using bi-constituent melt-spinning technology. The structure development and performance of PLA/PTT bicomponent fibers was investigated using thermal mechanical analysis, differential scanning calorimetry, and wide-angle X-ray diffraction in order to evaluate the crimp formability of PLA/PTT bicomponent fibers. The PLA and PTT components could form regular boundary structure and exhibit excellent interface compatibility by regulation of the rheological behavior of the two melts. In the fiber forming process, the PTT component in PLA/PTT bicomponent fibers experienced higher tensile stress, and thereby enhanced the crystal and oriented structure development, while the structural evolution of the PLA component was inhibited. The difference in the structure of the two components causes the imbalance force existence in the PLA/PTT fibers, which is the main reason of fiber crimp. In addition, the crimp formability of the PLA/PTT fibers could be enhanced by expanding the shrinkage stress difference between the two components, which could be realized by increasing the PTT ratio in PLA/PTT bicomponent fiber or draw ratio. The maximum crimp extension that could be achieved was 85% for the bicomponent fibers with PLA30/PTT70 ratio at a draw ratio of 4.2.

In situ studies of structure and performance changes in aromatic copolysulfonamide (co-PSA) fibers during stretching at different thermal exposure temperature range from room temperature to 300 °C were carried out using synchrotron small angle X-ray scattering and wide angle X-ray scattering techniques. Results showed that the optimum microstructure and mechanical property of co-PSA fibers were achieved when stretched at 200 °C, the fibril length, fibril misorientation, crystal sizes L002 reached minimum, the long period became maximum at the same strain indicating that lamella and fibrils aligned perfectly, fiber structure compactness at 200 °C. During stretching at RT to 200 °C, at low strain, fibril length, crystal size L002 increased, fibrils oriented along stretching direction, the long period was enlarged; the opposite trend evolution of structure appeared under high strain. But stretching at 300 °C, L002 increased, fibril orientation became poor, the lamellae destroyed easily resulting in the decreasing strength. It can be concluded that co-PSA fibers remain good property under thermal at 200 °C, external force use environment.

Cellulose/aromatic polysulfonamide (PSA) alloy fibers with good flame retardant properties were successfully prepared by changing the viscosity ratio of cellulose and PSA solutions. To reduce the content of PSA in the alloy fibers, cellulose and PSA with different molecular weight were adopted to prepare the alloy fibers. From the results of the limiting oxygen index(LOI) and the self-extinguishing time away from the flame, it was shown that the flame retardant properties of the alloy fibers were improved as the viscosity of PSA/[BMIM]Cl solution was lowered. The contact angle and the water retention values of the alloy fibers showed that the moisture absorption was strengthened with the addition of cellulose. To verify the properties of the alloy fiber, phase morphologies were characterized by laser scanning confocal microscope (LSCM). An analogous “sheath-core” structure in the cross section of the alloy fibers was shown when the viscosity of PSA/[BMIM]Cl solution was lower enough than that of cellulose/[BMIM]Cl solution. The lower viscosity PSA component was observed to migrate to the outer layer of the fiber, while the higher viscosity cellulose remained within the inner core of the fiber during the spinning process. This behavior improved the flame retardant properties of the alloy fibers at certain weight ratios. This work provides an effective way to prepare cellulose/PSA alloy fibers with improved flame retardancy, hygroscopic behavior, and mechanical strength by the regulating the phase morphology.

1-Butyl-3-methylimidazolium chloride ([BMIM]Cl) was selected as co-solvent to dissolve cellulose and silk fibroin and the cellulose/silk fibroin blend fibers were fabricated with dry-jet wet spinning technology. The phase morphology of cellulose and silk fibroin in the blend fibers was studied by scanning electron microcopy and laser scanning confocal microscope. It is shown that the cellulose is in the continuous phase and silk fibroin exists as “fibril-like” in cellulose, in which the radial dimension of silk fibroin phase is 0.5–1.0 μm. The phase size of silk fibroin along the fiber axis increased with the increase of silk fibroin content and draw ratio. From the wide-angle X-ray scattering, it is found that the total crystallinity of the blend fibers decreased with increasing silk fibroin content. The hydrogen bond between cellulose and silk fibroin was observed from Fourier transform infrared spectra. Although the tensile strength and initial modulus of blend fibers decreased with increasing silk fibroin content, the tensile strength of blend fibers contain 35 wt% silk fibroin was up to 191 MPa.

Pre-drawn aromatic copolysulfonamide (co-PSA) fibers were prepared by wet spinning and then heat drawing at temperatures varying from 350 to 390 degrees C, which are below the decomposition temperature. The fibers were then characterized using tensile testing, dynamic mechanical analysis, wide-angle X-ray diffraction and small-angle X-ray scattering. The relationship between structure and properties of the co-PSA fibers drawn at different temperatures was investigated. The heat-drawn co-PSA fibers displayed similar glass transition temperature of about 355 degrees C, which was higher than that of pre-drawn co-PSA fibers of 345 degrees C. The crystal orientation was high as a crystalline structure formed during heat drawing and the crystallinity increased with the heat-drawing temperature. However, the tenacity of the co-PSA fibers did not increase linearly with the draw temperature. When the drawing temperature was higher than the glass transition temperature, a decrease in tenacity was observed, which could be attributed to an increase of crystallite size of the (100) plane and a decrease of the long period of the lamellar structure. (c) 2014 Society of Chemical Industry

In order to verify the elastic response of copolyether-ester (PEE) fibers on their phase morphology and structure, the PEE fibers based on poly(butylene terephthalate) (PBT) as hard segments and poly(terramethylene glycol) (PTMG) as soft segments were prepared by melt spinning, the as-spun fibers were then heat-drawn and heat-set at different conditions. From the analysis of the mechanical properties, it is shown that the tenacity as well as elastic recovery of the fibers increased with the increasing heat-draw ratios, the elongation at break decreased. The morphological and structural were evaluated by small angle X-ray scattering (SAXS), wide angle X-ray scattering (WAXS) and birefringence. When the melt-spun PEE fibers were heat-drawn, higher crystallinity and orientation, larger size of lamellae structure was formed within the fibers, it is also much easier to form higher phase separation. This structure will contribute to better elastic performances of PEE fibers.

The changes in performance during thermal-oxidative aging process of the aromatic co-polysulfonamide (co-PSA) fibers over a broad temperature range from 250 °C to 320 °C have been investigated. In addition, the mechanism of thermal-oxidative aging process has been studied by using structural information obtained from the fibers at varying length scales. The results showed that a significant reduction in tensile strength was observed compared with that of initial modulus during aging process. Macroscopically, thermal-oxidative aging mainly causes color changes of fibers and thermally induced macro defects begin to appear only at 320 °C for 100 h. On a micro level, the crystal structure of fibers remained stable and did not show significant changes expect that aging at 320 °C. In addition, thermo-degradation as well as crosslinking has been observed primarily in amorphous region. With the increase of temperature and time duration, the crosslinking became more dominant and crosslinking density increases. Correspondingly, the fibril length decreases due to degradation and then increases due to the formation of crosslinked structures within the fibers. The results suggest that molecular degradation is the main cause of strength loss and the formation of crosslinking structure within the fibers contributes to the retention of modulus and improvement of creep resistance. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44078.

The structure and performance changes of aromatic copolysulfonamide (co-PSA) fibers that occurred during wet spinning process have been studied. While using different length scale characterization, including scan electron microscopy (SEM), wide-angle X-ray scattering (WAXS), and small-angle X-ray scattering (SAXS), it was found that the molecular chains of co-PSA formed an isotropic network during coagulation which further lead to extension and orientation of these chains during the subsequent stretching. As a result, only after heat stretching and heat setting the molecular chains tended to pack into crystal lattice in the fibrils. This gave rise to a much denser structure along the spinning line and the glass transition temperature of co-PSA fibers increased a little after heat setting. Before heat stretching, the co-PSA fibers were in amorphous state, and only the amorphous orientation was observed within the fibers. After heat stretching at the temperature higher than T-g, the fraction of amorphous region decreased, and the crystal structure formed in the fibers, which became more perfect during heat setting. The structure development during spinning process contributed toward the improvement of thermo-mechanical stability, tenacity and modulus of the co-PSA fibers. (c) 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42343.