Nagendra Anantharamaiah

Influence of polymer type, composition, and interface on the structural and mechanical properties of core/sheath type bicomponent nonwoven fibers

In this study, we investigated the effect of polymer type, composition, and interface on the structural and mechanical properties of core–sheath type bicomponent nonwoven fibers. These fibers were produced using poly(ethylene terephthalate)/polyethylene (PET/PE), polyamide 6/polyethylene (PA6/PE), polyamide 6/polypropylene (PA6/PP), polypropylene/polyethylene (PP/PE) polymer configurations at varying compositions. The crystallinity, crystalline structure, and thermal behavior of each component in bicomponent fibers were studied and compared with their homocomponent counterparts. We found that the fiber structure of the core component was enhanced in PET/PE, PA6/PE, and PA6/PP whereas that of the sheath component was degraded in all polymer combinations compared to corresponding single component fibers. The degrees of these changes were also shown to be composition dependent. These results were attributed to the mutual interaction between two components and its effect on the thermal and stress histories experienced by polymers during bicomponent fiber spinning. For the interface study, the polymer–polymer compatibility and the interfacial adhesion for the laminates of corresponding polymeric films were determined. It was shown that PP/PE was the most compatible polymer pairing with the highest interfacial adhesion value. On the other hand, PET/PE was found to be the most incompatible polymer pairings followed by PA6/PP and PA6/PE. Accordingly, the tensile strength values of the bicomponent fibers deviated from the theoretically estimated values depending on core–sheath compatibility. Thus, while PP/PE yielded a higher tensile strength value than estimated, other polymer combinations showed lower values in accordance with their degree of incompatibility and interfacial adhesion. These results unveiled the direct relation between interface and tensile response of the bicomponent fiber.

A simple expression for predicting the inlet roundness of micro-nozzles

The inlet roundness of micro-nozzles can directly influence properties of the liquid jets conducted through them. Obtaining accurate information regarding the inlet roundness of such tiny nozzles, however, is not easy. This is mainly due to the minute dimensions of these nozzles which render most nondestructive examination methods ineffective. In this study, a series of steady-state two-phase computational fluid dynamics simulations is performed to predict the inlet roundness of micro-nozzles used for producing constricted waterjets, i.e., waterjets resulting from a detached nozzle flow. Different micro-nozzles with inlet roundness ranging from r/d = 0 to 0.18 (where r and d are the inlet radius of curvature and the capillary diameter, respectively) were considered to obtain an expression for predicting the nozzles inlet roundness as a function of its discharge coefficient. It is demonstrated that the discharge coefficient of nozzles conducting a detached flow increases with increasing inlet roundness. The inlet roundness predicted by our expression is in good agreement with the actual roundness determined by sectioning the nozzle and imaging its cross-section. Our expression is believed to be useful for manufacturers and users of capillary micro-nozzles for producing liquid micro-jets.

Focused ion beam characterization of bicomponent polymer fibers.

Previous work has shown that focused ion beam (FIB) nanomachining can be effectively utilized for the cross-sectional analysis of polymers such as core-shell solid microspheres and hollow latex nanospheres. While these studies have clearly demonstrated the precise location selection and nanomachining control provided by the FIB technique, the samples studied consisted of only a single polymer. In this work, FIB is used to investigate bicomponent polymeric fiber systems by taking advantage of the components differing sputter rates that result from their differing physical properties. An approach for cross sectioning and thus revealing the cross-sectional morphology of the polymeric components in a bicomponent polymeric fiber with the island-in-the-sea (I/S) structure is presented. The two I/S fibers investigated were fabricated using the melt spinning process and are composed of bicomponent combinations of linear low density polyethylene (LLDPE) and nylon 6 (PA6) or polylactic acid (PLA) and an EastONE proprietary polymer. Topographical contrast as a result of differential sputtering and the high surface specificity and high signal-to-noise obtained using FIB-induced secondary electron imaging is shown to provide a useful approach for the rapid characterization of the cross-sectional morphology of bicomponent polymeric fibers without the necessity of staining or other sample preparation.

Three-Dimensional Structural Characterization of Nonwoven Fabrics

Nonwoven materials are found in a gamut of critical applications. This is partly due to the fact that these structures can be produced at high speed and engineered to deliver unique functionality at low cost. The behavior of these materials is highly dependent on alignment of fibers within the structure. The ability to characterize and also to control the structure is important, but very challenging due to the complex nature of the structures. Thus, to date, focus has been placed mainly on two-dimensional analysis techniques for describing the behavior of nonwovens. This article demonstrates the utility of three-dimensional (3D) digital volumetric imaging technique for visualizing and characterizing a complex 3D class of nonwoven structures produced by hydroentanglement.

Impacts of high-speed waterjets on web structures

Hydroentangling, where a fabric is formed by striking of fine, closely spaced, high speed waterjets, is one of the fastest growing bonding methods in the nonwoven industry. Softness, drape, conformability, and relatively high strength are the major characteristics that make this bonding technology unique. Despite the method appeal, few understand the impact of waterjet on fabric structures. The primary function of waterjet is to produce fiber entangling, which induces web integrity. In this paper, we have analyzed the interaction of waterjets on web structures to provide a better understanding of the hydroentangling mechanism. We have successfully visualized and analyzed structures of entangled regions through 2D and 3D imaging techniques. The influence of water-jet pressure, jet diameter, and number of jets on hydroentangled web structures is reported.

Hybrid mixed media nonwovens composed of macrofibers and microfibers. Part I: three-layer segmented pie configuration

Nonwoven fabrics, composed of microdenier fibers, can be easily created by using splittable bicomponents such as segmented pie. Hydroentangling has been shown as a very effective method for mechanically splitting these fibers. Such structures are known to form a densely packed nonwoven fabric with concomitant consequences in low porosity and tear strength. It is not, therefore, uncommon to insert a reinforcing scrim as a “rip-stop” mechanism in the middle of such structures to improve their properties, especially tear resistance. Instead, we propose a hybrid structure where the middle portion consists of solid homocomponent fibers, made from the same polymer as one of the components used in the bicomponent fibers, produced simultaneously during web formation, without causing noticeable changes in the fabrics’ overall texture. We report on the production and properties of fabrics composed entirely of bicomponent segmented pie fibers as well as our hybrid fabrics arranged in a three-layer configuration.

Structures and properties of hydroentangled nonwovens: effect of number of manifolds

Hydroentangling is a process in which fibers are entangled by impinging of a curtain of high-speed water jets to form mechanically strong, soft, and textile-like fabrics. Hydroentangled nonwovens are finding a gamut of applications without knowing the entangling mechanisms. In most applications, hydroentangling is carried out using multiple manifolds. This study focuses on the formation of hydroentangled web structures with multiple manifolds and their properties. The 3D analysis revealed the internal structures of hydroentangled nonwovens disclosing formation of fiber loops at jet impact regions. We also report changes of fiber orientations and fiber interlocking within web structures in nonwovens hydroentanged with multiple manifolds.