Bimodal Nanofiber and Microfiber Nonwovens by Melt-Blowing Immiscible Ternary Polymer Blends

Abstract

Most nonwoven fiber mats are produced with a uniform, narrow fiber diameter distribution. However, building evidence suggests that a bimodal diameter distribution (i.e., comprised of two populations of fibers, one with a smaller average diameter (d av), d, and the other with a larger d av, D, where D ≥ 5d), has certain advantages in applications such as filtration media. To the best of our knowledge, all previous reports describing production of bimodal fiber diameter distributions have relied on solution-based electrospinning, a much less common fiber-spinning technique, compared to melt blowing, which currently produces more than 10% of nonwovens globally (an approximately $50 billion market). In this study, we demonstrate a facile method for producing bimodal fiber diameter distributions by melt blowing immiscible ternary polymer blends, with the two minority blend components being randomly dispersed as isolated, bimodally sized particles within the continuous matrix. Such a ternary blend can be obtained by selecting a matrix phase that preferentially wets/encapsulates both dispersed phases having vastly different viscosity ratios. Specifically, two model immiscible ternary blends comprised of polystyrene/polyethylene/Nylon-6 (PS/PE/Nylon) and poly­(ethylene oxide)/polyethylene/Nylon-6 (PEO/PE/Nylon) with the desired morphologies and PS or PEO as the matrix were examined. During melt blowing of the blends, the PE minority domains (∼8 μm in diameter) and Nylon minority domains (∼70 μm in diameter) dispersed within the matrix were transformed to PE nanofibers (d av ≈ 560 nm) and Nylon microfibers (d av ≈ 8 μm) embedded in the elongated PS matrix fibers, and similarly for fibers made with a PEO matrix. Subsequent removal of the matrix polymer with an appropriate solvent (tetrahydrofuran for PS or water for PEO) produced a macroscopic mat of randomly distributed, bimodal nanofibers and microfibers. The nanofiber and microfiber compositions of the bimodal-diameter fiber mats were effectively tuned by varying the composition of the minority components of the original ternary polymer blends. Interestingly, the resulting bimodal-diameter fiber mats possessed few nanofiber bundles; we hypothesize that this is due to the presence of Nylon microfibers that are intrinsically intermixed among the PE nanofibers that physically restrict the formation of nanofiber bundles. Overall, this versatile method could provide a high-throughput route to scalable quantities of fiber mats with a bimodal distribution of fiber diameters, thus promoting the application of hierarchically structured nonwovens.

Tailoring the softness performance of polyethylene/polypropylene micro‐nanofibrous fabrics for skin contacts

“…34,35 For the blended melts that contained two incompatible components, a breakup would occur in the zone between the two components under the external forces from the high-speed hot air, due to their weak interactions. 19,36 Figures 5(a)-(h) show the SEM images and fiber diameter distributions of the samples with PE mass ratios of 50% at die temperatures of 260, 270, 280, and 290 C, respectively. It was visible that smaller average fiber diameters and a narrower distribution were observed for samples fabricated at the 280 C die temperature compared to the samples fabricated at 260 C and 270 C. An increase in die temperature from 260 to 290 C resulted in a reduction of the average fiber diameter from 3.2 to 1.3 μm (displayed in Figure S3b).…”

“…17,18 Generally, adding functional polymers during the meltblowing process has been an effective and facile strategy to improve the performance of PP micro-nanofibrous fabrics. 19 Adding elastic polymers to create the blend, for example, propylene-based elastomer 20 and thermoplastic polyurethane, 21 can improve the elasticity performance of PP fabrics. Immiscible polymers, for example, polystyrene, 22 polyethylene glycol, 23 and polyester, 24 can improve the distribution of blend fiber diameters.…”

Mathematical Modelling and Software Development to Optimize the Composition of Four-Component Nanofilled Systems

“…Today, one of the most effective ways to obtain ultrathin fibres is to process melts of thermodynamically incompatible polymer mixtures. The formation in situ micro-or nanofibrils of one component in the matrix of another has been implemented for many pairs of polymers by extrusion methods [1-7], blow-out [8,9], uniaxial stretching [10][11][12], and 3D-forming (fused deposition modelling) [13]. In this case, diameter of the microfibrils is largely determined by the rheological characteristics of the components of mixture and the degree of their compatibility at the interphase.…”

Porous Fibers Templated by Melt Blowing Cocontinuous Immiscible Polymer Blends

“…Melt blown nonwovens with average fiber diameters ranging from ∼2–30 μm are widely employed in applications where a high specific surface area ( i.e ., surface-to-volume ratio) and interconnected pores between fibers are of critical importance. For example, air filtration modules require high surface area and significant interconnected pore space to effectively capture particulates with a low pressure drop. − Fiber-based lithium-ion battery separators also benefit from higher surface areas and interconnected pore structures, which facilitate greater electrolyte penetration for improved power performance. , Since the specific surface area of a fiber scales inversely with diameter, significant research efforts have been dedicated to reducing fiber diameters, usually with the goal of producing nanofibers. ,− For instance, a reduction in average fiber diameter from 5 μm to 500 nm results in 10-fold increase in the specific surface area. Most of these efforts for producing nanofibers focus on electrospinning and centrifugal spinning, with significantly less emphasis on melt blowing …”

“…Selective extraction of the sacrificial polymer component yielded interconnected porous channels across the entire fiber cross-section with pore sizes as small as ∼100 nm, suggesting the ability to produce porous nonwovens with hierarchical pore structures within and between fibers. While we chose the PS/HDPE model blend out of convenience, one can envision that porous fibers could also be obtained using a binary blend comprising a water-soluble polymer where the pore structures can be revealed by washing with water instead of organic solvents. , Significant research opportunities exist to fully understand and exploit the potentially unique capabilities of these nonwovens for numerous applications. For example, we anticipate that the hierarchical porosity of the fiber mats may offer improved performance as active layers in biofiltration, air filtration, and fuel/oil filtration modules.…”