Properties of PP/PET bicomponent melt blown microfiber nonwovens after heat‐treatment

Polypropylene (PP)/poly(ethylene terephthalate) (PET) bicomponent (bico) fibres are successfully melt blown in the Reicofil® meltblown (MB) pilot line commissioned at the Textiles and Nonwovens Development Center (TANDEC), the University of Tennessee, Knoxville. The bico fibers possess a cross‐sectional side‐by‐side configuration. The originally expected greater fiber crimp due to density and fine structure gradients on the different sides of the bico fibers was not commonly observed in the normal MB webs. These fabrics were exposed to dry heat for a period of time. The properties before and after the heat treatment were determined and compared to investigate the effects of heat on their properties. It was found that the bico webs are thermal dimensionally stable and many of their properties were not significantly affected. A mechanism is suggested on the thermal dimensional stability of the PP/PET bico MB webs. © 2003 Society of Chemical Industry     

Structure modification of isotactic polypropylene by bi‐component nucleating systems

The efficiency of heterogeneous nucleation of isotactic polypropylenes (iPP) with various isotacticity and MWD is estimated by an increase of the crystallization temperature (T_cr). A bi‐component nucleating system, composed of a pimelic acid and a calcium stearate, was added to the polymeric matrix in the molten state. The relative increase of T_cr is found to be independent on the structure stereo‐regularity of iPP. On the contrary, dependent on the polymer structure, the investigated nucleating system influences in a different way the creation of the β‐phase. The form of the DSC melting curves, for the β‐phase rich iPP samples, is discussed in terms of various preliminary cooling conditions. The transformation from a multi‐modal form of the DSC melting peak to a simple one is related to the lowering of the cooling rate and to the increase of the heating rate.     

Electrically conductive polymeric bi‐component fibers containing a high load of low‐structured carbon black

Melt spinning at semi‐industrial conditions of carbon black (CB) containing textiles fibers with enhanced electrical conductivity suitable for heating applications is described. A conductive compound of CB and high density polyethylene (HDPE) was incorporated into the core of bi‐component fibers which had a sheath of polyamide 6 (PA6). The rheological and fiber‐forming properties of a low‐structured and a high‐structured CB/HDPE composite were compared in terms of their conductivity. The low‐structured CB gave the best trade‐off between processability and final conductivity. This was discussed in terms of the strength of the resulting percolated network of carbon particles and its effect on the spin line stability during melt spinning. The conductivity was found to be further enhanced with maintained mechanical properties by an in line thermal annealing of the fibers at temperatures in the vicinity of the melting point of HDPE. By an adequate choice of CB and annealing conditions a conductivity of 1.5 S/cm of the core material was obtained. The usefulness of the fibers for heating applications was demonstrated by means of a woven fabric containing the conductive fibers in the warp direction. By applying a voltage of 48 V the surface temperature of the fabric rose from 20 to 30°C. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42255.     

复合超细纤维水刺非织造布多次水洗后的性能初探

复合超细纤维水刺非织造布经过多次水洗后,对其收缩率、力学性能的分析测试及外观评价,研究了复合超细纤维水刺非织造布原白坯和色布水洗后的性能。结果表明:随着水洗次数的增加,复合超细纤维水刺非织造布收缩率增加并且在5次后趋于稳定;复合超细纤维水刺非织造布的尺寸、强度及外观与水洗次数、烘干方式和水刺工艺设备相关;进口设备生产的超细纤维水刺非织造布,采用正确的染色后整理工艺,可以提高产品尺寸的稳定性,其收缩率小于5%,并保持产品的强度和有助于保持产品外观,满足多次使用的要求;复合超细纤维水刺非织造布经过多次水洗后分纤率提高,产品强度提高,手感更加接近丝感。     

Polymer adhesion in heat‐treated nonwovens

Polymer adhesion and sintering in compound nonwovens was studied. Nonwovens containing a mixture of binding bi‐component (BICO) fibers embedded in a fibrous matrix were heated to melt the outer shell of BICO fibers and interlock the matrix to create stiff load‐bearing surfaces. It was found that stiffness depends on heat‐treatment regimes. In low‐temperature regimes, BICO fibers melt, but do not fully flow and encase the surrounding filler matrix. At sufficiently high temperatures, the shells of BICO fibers melt and flow which results in encasing the neighboring filler fibers. This results in an abrupt increase in the nonwoven stiffness which is independent of heat‐treatment temperature. At significantly high temperatures, the filler matrix fibers sinter to each other leading to a further increase in stiffness. The experiments were conducted with co‐polymers frequently used in the shells of BICO to demonstrate the interlocking mechanism characteristic of these compound nonwovens. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46165.     

Frictional properties of thermally bonded 3D nonwoven fabrics prepared from polypropylene/polyester bi‐component staple fiber

The frictional properties of the three‐dimensional nonwoven samples produced using the recently developed air laying and through‐air thermal bonding system are evaluated. The samples were made from commercially available polypropylene (PP)/polyester (PET) (sheath/core) bi‐component staple fiber. In particular, the effects of the process parameters on the frictional properties were investigated by employing a statistical approach involving the uniform design of experiments and regression analysis. Stick‐slip frictional traces were obtained as a result of the presence of fiber loops, overlapping of fibers at bonding points, and deformation of fibers due to melting. The effect of normal load on both the static and dynamic friction forces can be described using the power‐law relationship. Both the static and dynamic friction factors increase with increase of the thermal bonding temperature and the dwell time. POLYM. ENG. SCI., 46:853–863, 2006. © 2006 Society of Plastics Engineers     

An investigation of fiber splitting of bicomponent meltblown/microfiber nonwovens by water treatment

Meltblowing is a most versatile and cost‐effective process commercially available worldwide to produce microfiber nonwovens directly from thermoplastic resins. The new bicomponent (bico) meltblown technology opens a great possibility to make even finer microfibers by subsequently fiber splitting. Water‐dispersive Eastman AQ polymers were initially introduced to the meltblown process to make the mono‐ and bicomponent meltblown webs at Textiles and Nonwovens Development Center (TANDEC), University of Tennessee, Knoxville. The postwater treatment was performed on the fabrics, which resulted in the dispersive part (AQ polymer) being dispersed in water and only the other part remaining in the bico web. A process–structure–property study is provided toward the research reported in this article. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1218–1226, 2004     

Dynamic wetting of plasma‐treated polypropylene nonwovens

Various techniques have been employed to improve the wettability of polypropylene materials for a wide range of applications. In this study, polypropylene nonwovens were treated in oxygen plasma for improving water adsorption properties. The effects of plasma treatment on wetting and water adsorption behavior were characterized using dynamic contact angle measurements and dynamic sorption measurements. The introduction of hydrophilic groups was detected by attenuated total reflection–Fourier transform infrared spectroscopy. The plasma treatment roughened the fiber surface revealed by atomic force microscopy. The roughened and hydrophilic surface resulted in the change in advancing and receding contact angles. The dynamic sorption measurements also examined the water adsorption behavior of the materials. The investigation revealed that plasma treatment could significantly improve the water adsorption properties of polypropylene nonwovens. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2157–2160, 2007     

Isotactic polypropylene microfiber prepared by carbon dioxide laser‐heating

An isotactic polypropylene (i‐PP) microfiber was obtained by irradiating a carbon dioxide laser to previously drawn fibers. To prepare the thinner i‐PP microfiber, it is necessary to previously draw original i‐PP fibers under an applied tension of 7.8 MPa at a drawing temperature of 140°C. The drawn fiber was heated under an applied tension of 0.3 MPa using the laser operated at a power density of 39.6 W cm^?2. The thinnest i‐PP microfiber obtained under optimum conditions had a diameter of 1.8 μm and a birefringence of 30 × 10^?3. Its draw ratio estimated from the diameter reached 51,630. It is so far impossible to achieve such a high draw ratio by any drawing. The wide‐angle X‐ray diffraction photograph of the microfiber shows the existence of the oriented crystallites. Laser‐heating allows easier fabrication of microfibers compared with the conventional technology such as the conjugate spinning. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1534–1539, 2004     

Isotactic polypropylene microfiber prepared by continuous laser‐thinning method

An isotactic polypropylene (i‐PP) microfiber was continuously produced by using a carbon dioxide (CO₂) laser‐thinning apparatus developed in our laboratory. The CO₂ laser‐thinning apparatus could wind up the obtained microfiber in the range of 100 m min^?1 to 2500 m min^?1. The diameter of the microfiber decreased and its birefringence increased with increasing winding speed. When the microfiber obtained by irradiating the CO₂ laser operated at a power density of 31.8 W cm^?2 to the original fiber supplied at 0.30 m min^?1 was wound at 1,387 m min^?1, the obtained microfiber had a diameter of 3.5 μm and a birefringence of 25 × 10^?3. The draw ratio calculated from the supplying and the winding speeds was 4,623‐fold. The SEM photographs showed that the obtained microfibers had a smooth surface without a surface roughened by a laser‐ablation and were uniform in diameter. The wide‐angle X‐ray diffraction photographs of the microfibers wound at 848 and 1,387 m min^?1 showed the existence of the oriented crystallites. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 27–31, 2006     

Characterization of mechanically reinforced electrospun dextrin‐polyethylene oxide sub‐microfiber mats

Dextrin and dextrin‐polyethylene oxide (DEX/PEO) fibers in the submicron range were produced by electrospinning of single and blend polymer solutions. The morphology, intermolecular interactions, and mechanical properties of dextrin microfibers with and without PEO were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, X‐ray diffraction, nuclear magnetic resonance spectroscopy, and uniaxial tensile testing. Spectroscopic results confirmed hydrogen bond formation, evidencing dextrin as a molecular entanglement source for fiber mechanical reinforcement. The uniaxial tensile tests demonstrated a synergistic mechanical reinforcement effect that varied with blend composition. Equal weight ratio blends supported a maximum tensile strength with a high elastic modulus and demonstrated to be more elastic and resistant to breaking, even than pristine PEO fibers. Moreover, elastic moduli of blend fiber mats were found to lie within the value range for human skin, thus providing the DEX/PEO meshes with potential applicability as skin tissue scaffolds. This synthesis approach proved the feasible and inexpensive fabrication process of natural‐synthetic polymer hybrid fibers that combine the biocompatibility, biodegradability, and encapsulating capability of dextrin with the mechanical strength and flexibility of PEO for the development of scaffolds for tissue engineering and topical drug delivery applications in skin wound healing. POLYM. ENG. SCI., 59:1778–1786, 2019. © 2019 Society of Plastics Engineers     

Steady bi‐directional drag flow of non‐newtonian liquids in shallow channels

This paper reexamines the analytical framework for the steady, fully developed two‐dimensional flow in shallow channels, typical of screw extruders, and provides comprehensive solution sets for the Carreau‐Yasuda and the Ostwald‐deWaele model fluids. An application example for polymethylmethacrylate (PMMA) is included to compare the relative merits of the two models under specific extrusion conditions. The Ostwald‐deWaele model, standard in engineering practice, can produce gross misrepresentations of the flow in extruder channels. Particularly, when dealing with highly shear‐sensitive polymers, n < 0.3, or polymers with extended Newtonian plateau, ∧ ～ 1, the Carreau‐Yasuda model becomes preferable. The inclusion of the Carreau model does not necessarily add to the complexity of the analysis.     

Fiber diameter of polybutylene terephthalate melt‐blown nonwovens

A polymer air‐drawing model of Polybutylene Terephthalate (PBT) melt‐blown nonwovens has been established. The predicted fiber diameter coincides with the experimental data. The effects of the processing parameters on the fiber diameter have been investigated. A lower polymer flow rate, a higher initial air velocity, and a larger die‐to‐collector distance can all produce finer fibers, whereas too high an initial air velocity and too large a die‐to‐collector distance contribute little to the polymer drawing of PBT melt‐blown nonwovens. The results show the great potential of this research for the computer‐assisted design of melt‐blowing technology. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1750–1752, 2005     

Tensile behavior of PVC‐coated woven membrane materials under uni‐ and bi‐axial loads

Tensile characteristics are the most significant mechanical properties for coated woven fabrics as membrane materials used in lightweight constructions. Factors that might affect test results of the material under uni‐ and bi‐axial tensile loads are examined. After series of tensile tests on PVC‐coated membrane materials, it is demonstrated that (1) to measure the strains in the two perpendicular directions, the contact method by the needle extensometer does not interfere the correct data recording; (2) the positions where the strains are measured on specimens have a great influence on the test results of the stiffness and Poisson's ratio in warp direction under uni‐axial load; (3) to perform bi‐axial tensile tests the size of the cruciform specimen in bi‐axial tensile test can be much smaller than those suggested in the literature. The tensile behavior of coated membrane materials under bi‐axial loads are affected dramatically by the stress ratio in the warp and fill directions. Besides the residual strains of coated membrane materials are affected not only by the properties of the constituent yarns and woven structure but also by loading conditions during the coating process. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Electrospun nonwovens of shape‐memory polyurethane block copolymers

Synthesized shape‐memory polyurethane (PU) block copolymers were used to prepare electrospun nonwovens via electrospinning. PU solutions were prepared with a mixed solvent of N,N‐dimethylformamide and tetrahydrofuran. The electrospun PU nonwovens were prepared with hard‐segment concentrations of 40 and 50 wt %. The morphology of the electrospun fibers was investigated with scanning electron microscopy. The average diameter of low‐viscosity (ca. 130–180 cPs) electrospun fibers was about 800 nm, and the morphology of the electrospun nonwovens was beaded‐on fibers. In contrast, the average diameter of high‐viscosity (ca. 530–570 cPs) electrospun fibers was about 1300 nm. In an investigation of the mechanical properties of the electrospun PU nonwovens, it was found that the tensile strength increased as the hard‐segment concentration increased within a similar range of viscosities. Also, the tensile strength of the electrospun PU nonwovens in the machine direction was higher than that in the transverse direction because of a difference in the velocities of the drum collectors. The electrospun PU nonwovens with hard‐segment concentrations of 40 and 50 wt % were found to have a shape recovery of more than 80%. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 460–465, 2005     

Electrochemical characterization of laser‐carbonized polyacrylonitrile nanofiber nonwovens

Porous carbon materials represent prospective materials for absorbers, filters, and electronic applications. Carbon fibers with high surface areas can be produced from polyacrylonitrile and spun as thin fibers from solution. The resulting polymer fibers are first stabilized to obtain conjugated ribbons and then carbonized to graphitic structures in a second high‐temperature step in an inert atmosphere. In this study, we investigated a previously described fast laser‐heating process that delivered fibers with a higher crystallinity and surface area compared to the thermally carbonized fibers. In a subsequent KOH‐activation step, the crystalline domains were exfoliated, and the surface of the fibers became macroporous. This led to a reduced specific surface area but a higher capacitance compared to thermally carbonized nanofibers. We report the electrochemical properties of the electrochemical cells and discuss their potential applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46398.     

Dielectric features of two grades of bi‐oriented isotactic polypropylene

The dielectric properties of two grades of bi‐oriented isotactic polypropylene were studied with a variety of techniques: breakdown field measurements, dielectric spectroscopy, thermally stimulated depolarization currents (Is), and direct‐current (dc) conduction I values. Standard polypropylene (STPP) and high‐crystallinity polypropylene (HCPP) films were investigated. Measurements were carried out over a wide temperature range (?150°C/+125°C). The breakdown fields in both materials showed a very small difference. On the other hand, the dielectric losses and dc conduction I values were significantly lower in HCPP. Both materials showed a decrease in the dielectric loss versus temperature in the range 20–90°C; this is favorable for application in alternating‐current power capacitors. The analysis of the dc I value allowed us to find evidence of two main conduction mechanisms: (1) below 80°C in both materials, a hopping mechanism due to the motion of electrons occurred in the amorphous phase, and (2) above 80°C, ionic conduction occurred in HCPP, and hopping conduction occurred in STPP. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42224.