The meltblowing process employs high-speed hot air jets to attenuate polymer streams injected from a die head. In this study, we examine design strategies to control the air flow field below the polymer injection point to achieve higher fiber attenuation and meltblown webs with smaller fiber diameters. Computational fluid dynamics (CFD) simulations for new die configurations show that vertical or inclined air constrictors around the primary air jets keep the centerline air velocity and temperature at their maximum values for 10–15 mm longer below the die face than the reference die. Polymer streams are kept near their melting temperatures at higher air velocities for a longer period, resulting in higher fiber attenuation. The underlying mechanisms leading to such behavior are discussed. Experimental results show reduction in fiber diameter and pore size, validating the simulation. Improved filtration properties are also obtained from the nonwovens webs.

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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.

This paper deals in general with fabrics consisting of bicomponent fibers that are fractured/fibrillated and bonded using mechanical and/or thermal means to form micro-denier fibers. Bicomponent filaments produced by the spunbonding process, where two polymers are co-extruded to form a fiber are used to demonstrate the feasibility of fracturing bicomponents. This process of nonwoven fabric manufacture combined with the fiber-fracturing process is discussed. These fabrics are processed using commercially accepted practices. Differences in the physical properties due to the different polymer ratios and cross-sections produced are discussed. In particular, this paper deals with the production of modified 'Islands-in-the-Sea' filament cross-sections that enhance the fracturing of such filaments to produce micro-fiber webs that have considerably higher surface area compared to their conventional counterparts. Point-bond calendered bicomponent samples were also tested for their mechanical properties with different island counts and polymer compositions. The optimal bonding techniques for the fabrics were identified. The role of the Islandsin-the-Sea fiber cross-section was demonstrated for optimizing the fabric strength and enhancement of surface area.

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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.

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