Fiber packing density in the cross-section of low torque ring spun yarn

Fiber packing density in the yarn cross-section is one of the major parameters that reflect the yarn internal structure and its final properties. Taking the novel low torque ring spun yarn as the object, this work studied the fiber packing density of low torque ring spun yarns and conventional ring spun yarns under various axial tensions. With the increase of tension, the change of fiber packing state in low torque ring spun yarns and conventional ring spun yarns was compared qualitatively. In this study, fiber distribution in the cross-section of both Tencel yarns and wool yarns was carried out. The results show that, under the same axial tension, the packing density of fibers of low torque ring spun yarn is much higher than that of conventional ring spun yarn. The axial tension has greater influence on the fiber packing density for the conventional ring spun yarn. From the experimental results, in low torque Tencel yarn, the fiber packing density nearly reaches 0.9, which is the maximum value for close-packed yarn. Due to different fiber properties and yarn structure, it is difficult to form a close packing for fibers in low torque ring wool yarns. The current results indicate that low torque ring spun yarn has a more compact structure than conventional ring spun yarn. Compared with conventional ring spun yarns with the same count and twist levels, in low torque ring spun yarns, more fibers contribute to the yarn breaking strength.

Continuous measurement of apparent Poisson’s ratio for yarn based on omni-directional diameters

We proposed a new method for measuring apparent Poisson’s ratio for yarn and developed a new tensile tester equipped with a digital micrometer that can measure the omni-directional diameter of the yarn annularly while the yarn is elongated. Values of apparent Poisson’s ratio were obtained from the longitudinal and transverse strains continuously. The mean diameter measured omni-directionally was used to calculate the transverse strain for each longitudinal strain. We tested five spun yarns, one monofilament yarn and two filament yarns and obtained values of apparent Poisson’s ratio against longitudinal strain for all samples. Apparent Poisson’s ratio was not constant for spun and filament yarns, while it was constant for monofilament yarn. When the longitudinal strain was low, apparent Poisson’s ratios of ring spun yarns and filament yarns were large, owing to the fiber packing density. As the longitudinal strain increased, apparent Poisson’s ratio gradually decreased. Furthermore, we approximated the relationship between apparent Poisson’s ratio and the longitudinal strain using a power function. The apparent Poisson values can be used in the simulation of fabrics.

Numerical Study of Boiler Feed Water Deoxygenation Using Hollow Fiber Membrane Contactor

Removal of dissolved oxygen from feed water is a necessary process in power industry. The hollow fiber membrane contactor is more efficient and pollution-free compared with some traditional methods. In this paper, hollow fiber is modeled by random distribution, and Gaussian function N(R, sigma) was used to model the polydisperse out radii of hollow fiber. This paper discussed the influence of different sigma on mass transfer coefficient with fiber packing density ranging from 0.1 to 0.4. It was found that, the effect of different sigma on the logarithmic mean Sherwood number decreased with increasing fiber packing density. When the packing density increased to 0.4, the removal of dissolved oxygen could meet the requirement of power industry, no matter how much value the sigma was. With the sigma increasing, the deviation of max and min Sherwood number from the average value increased gradually, except when the sigma was 0.05. This paper deduces there is a best value of sigma for membrane contactor when the fiber distribution is randomly distributed.

Optical Properties of Electrospun Nanofiber Substrates

Light impinging upon electrospun nanofiber substrates encounters a complex media where a multitude of factors controls the transmittance and reflectance of light through the structure. The chemical composition of the nanofiber plays a significant role in that it determines the index of refraction of individual fibers. However, the surrounding media (e.g., air, encapsulating polymer, etc.) also plays an equally important role. In addition, physical effects such as fiber diameter, fiber morphology, fiber packing density (i.e., structure void volume), and substrate thickness play a large role in determining the light management properties of nanofibers. Our research has demonstrated that the transmittance and reflectance of undoped nanofibers can be adjusted through proper manipulation of these factors. For example, similar electrospinning formulations can produce either highly transmitting or highly reflecting light structures depending upon fabrication parameters that impact the final properties of the nanofiber substrates. In addition, a degree of wavelength dependent reflectance and transmittance can be imparted simply by adjusting the physical properties of the nanofibers to promote preferential light scattering below selected frequencies. This paper provides an overview of various factors impacting the light management properties of nanofiber substrates and the importance of controlling these factors to meet end-use applications.

Compression and Packing Density of Fibrous Assemblies

This paper presents a generalization of the unidimensional deformation equation based on the van Wyk theory. The derivation considers the effect of uncompressed areas between contacting fibers. Theoretical results are verified by the experimental work of Baljasov. The solution is extended to cover bidimensional deformation of an oriented fibrous assembly. The work also proves the importance of using fiber packing density as the argument in the compression equation.

Optimal Fiber Spacing in Externally Pressurized Hollow Fiber Module for Solid Liquid Separation

Flux decline and clogging mechanism in hollow fiber bundle by activated sludge and kaolin clay suspensions were investigated experimentally. Filtration characteristics of hollow fiber bundles consisting of 10 fiber threads but different in packing density were observed. The main reason for severe flux decline was due to the accumulation of particles at the space in between fibers. The results showed that there was no particle accumulation when fiber packing density β was lower than a critical value βa. Maximum filtration flux and maximum membrane productivity Q/Vr,which is defined as the filtration rate per unit volume of bundle, were obtained below and at this point, respectively. When fiber packing density β was increased, accumulation of particles happened and flux declined rapidly to a minimum, then increased to a maximum and then decreased when surface clogging predominated in the case of activated sludge filtration, but remained almost constant for the case of kaolin clay suspensions. The critical point where accumulation of particles started was related to cross flow velocity. The higher the cross flow velocity, the higher the value of βa obtained.

Air-Jet Texturing of Spun Cotton Yarns for Improved Comfort

We have studied the importance of yarn structural variants such as fiber packing density, fiber fineness and length distribution, mean fiber extent, and migration parameters in deciding the bulking potential of a spun yarn structure with air-jet texturing. Three variants of carded yarns, combed yarns, and yarns made from combed sliver which is again carded in both 100% spun and composite spun forms with three different twist levels show that fiber-to-fiber distance and frictional hindrance may have a significant influence on the relative local velocities of the fibers in the turbulent air stream, which would affect the texturing behavior. We have observed that spun yarns with uniform fiber length distribution, higher fiber extent, and more fiber parallelization, such as combed yarns, have less bulk during texturing. Yarns with higher packing and migration have higher frictional hindrance with less fiber-to-fiber distance. They are therefore subjected to reduced flow asymmetry and produce yarns with reduced bulk.