Fluorine-Enriched Melt-Blown Fibers from Polymer Blends of Poly(butylene terephthalate) and a Fluorinated Multiblock Copolyester

Influence of a Meltblown Die with a Laval Airstream Channel on the Manufacturing Process of a Polymer Fiber Based on an Orthogonal Test and Simulation Analysis

A Laval nozzle is a device that accelerates a low-speed airstream to form a high-speed airstream. In this work, we use a Laval nozzle in the airstream channel design of a meltblown die to improve the tensile properties of the fiber in the airstream field of the meltblown die. The features of the airstream field of the meltblown die are analyzed by numerical simulation. For a given parametrization, six factors may be tuned to optimize the performance of the Laval airstream channel of the meltblown die. We thus use a five-level, six-factor orthogonal test method to optimize the airstream channel of the meltblown die to determine the various factors that influence the airstream field beneath the meltblown die. The results show that the optimized Laval meltblown die performs better than the traditional die and that the widths of the larynx and expansion segment most strongly affect the airstream velocity beneath the Laval meltblown die. Compared with a traditional die, the Laval die optimized by orthogonal testing increases the peak airstream velocity by 17.54%, average velocity by 96.81%, average temperature by 12.32%, and peak pressure by 14.61% and produces weaker turbulence intensity near the spinneret. These characteristics make the airstream beneath the die more stable and uniform and accelerate the attenuation of the fiber diameter, producing more polymer nanofibers. These results demonstrate a valuable approach to the design and optimization of meltblown dies and provide a technical reference for the production and application of the meltblown fiber production equipment.

Towards a Long-Chain Perfluoroalkyl Replacement: Water and Oil Repellent Perfluoropolyether-Based Polyurethane Oligomers

Original perfluoropolyether (PFPE)-based oligomeric polyurethanes (FOPUs) with different macromolecular architecture were synthesized (in one step) as low-surface-energy materials. It is demonstrated that the oligomers, especially the ones terminated with CF₃ moieties, can be employed as safer replacements to long-chain perfluoroalkyl substances/additives. The FOPU macromolecules, when added to an engineering thermoplastic (polyethylene terephthalate, PET) film, readily migrate to the film surface and bring significant water and oil repellency to the thermoplastic boundary. The best performing FOPU/PET films have reached the level of oil wettability and surface energy significantly lower than that of polytetrafluoroethylene, a fully perfluorinated polymer. Specifically, the highest level of the repellency is observed with an oligomeric additive, which was made using aromatic diisocyanate as a comonomer and has CF₃ end-group. This semicrystalline oligomer has a glass transition temperature (T_g) well above room temperature, and we associate the superiority of the material in achieving low water and oil wettability with its ability to effectively retain CF₃ and CF₂ moieties in contact with the test wetting liquids.

Experimental investigation on the three-dimensional flow field from a meltblowing slot die

To investigate the distribution characteristics of the three-dimensional flow field under the slot die, an online measurement of the airflow velocity was performed using a hot wire anemometer. The experimental results show that the air-slot end faces have a great influence on the airflow distribution in its vicinity. Compared with the air velocity in the center area, the velocity below the slot end face is much lower. The distribution characteristics of the three-dimensional flow field under the slot die would cause the fibers at different positions to bear inconsistent air force. The air velocity of the spinning centerline is higher than that around it, which is more conducive to fiber diameter attenuation. The violent fluctuation of the instantaneous velocity of the airflow could easily cause the meltblowing fiber to whip in the area close to the die.

Highly Oil-Repellent Thermoplastic Boundaries via Surface Delivery of CF3 Groups by Molecular Bottlebrush Additives

We fabricated thermoplastic surfaces possessing extremely limited water and oil wettability without employment of long-chain perfluoroalkyl (LCPFA) substances. Namely, by taking advantage of the structure and behavior of original oleophobic perfluoropolyether (PFPE) methacrylate (PFM) molecular bottlebrush (MBB) additive we obtained polymeric surfaces with oil contact angles well above 80° and surface energy on the level of 10 mN/m. Those angles and surface energies are the highest and the lowest respective values reported to date for any bulk solid flat organic surface not containing LCPFA. We show experimentally and computationally that this remarkable oil repellency is attributed to migration of small quantities of the oleophobic MBB additives to the surface of the thermoplastics. Severe mismatch in the affinity between the densely grafted long side chains of MBB and a host matrix promotes stretching and densification of mobile side chains delivering the lowest surface energy functionalities (CF₃) to the materials' boundary. Our studies demonstrate that PFM can be utilized as an effective low surface energy additive to conventional thermoplastic polymers, such as poly(methyl methacrylate) and Nylon-6. We show that films containing PFM achieve the level of oil repellency significantly higher than that of polytetrafluoroethylene (PTFE), a fully perfluorinated thermoplastic. The surface energy of the films is also significantly lower than that of PTFE, even at low concentrations of PFM additives.

Migration Effects of Fluorochemical Melt Additives for Alcohol Repellency in Polypropylene Nonwoven Materials

The use of bulk polymer melt additives provides a facile, industrially relevant approach to tailor properties of polymer surfaces for many different applications. These melt additives, when blended with polymers prior to melt spinning, migrate to the fiber surface and influence surface functionality. While the use of bulk polymer melt additives to impart hydrophilicity or oleophobicity is well studied, the impact of the fiber formation process on additive migration and resultant repellency of nonwoven media products remains largely unexplored. In this study, we produce fluorochemical melt additive containing meltblown nonwovens, and establish methods for characterization of fiber mat surface composition and repellency. Repellency of low surface tension fluids is a significant challenge and is of particular importance in the creation of medical garments such as surgical gowns and masks which must perform as liquid barriers even when exposed to alcohol based solutions. Similarly, melt additives are also used in the production of electret air filtration devices. Electret filters are imbued with charges to enhance particle capture performance, but this charge can be negated through wetting by low surface tension fluids. To address this challenge, the changing composition of fiber surfaces due to the migration of additives is monitored via X-ray Photoelectron Spectroscopy, then related to repellency of alcohol solutions by contact angle analysis. We demonstrate that for the samples tested a fluorine to carbon (F/C) ratio of 0.35 is sufficient to prevent wicking of isopropanol droplets, and higher surface tension fluids could be repelled by fiber mats with lower fluorine content. Through the use of cross-sectional ToF-SIMS analysis, we find that migration of additives is key to the performance of samples with low additive loadings, and that these phenomena are heavily influenced by many nonwoven manufacturing parameters including fiber size, die-to-collector distance, and polymer resin melt flow rates.

Effect of slot end faces on the three-dimensional airflow field from the melt-blowing die

In order to investigate the effect of the slot ends of the melt-blowing die on the three-dimensional airflow field distribution and the fiber draft, the numerical calculation was carried out. The computational domain of the slot die was established with Gambit, and the flow field was calculated using FLUENT. Compared with the experimental data collected by a hot-wire anemometer, the numerical calculation results are credible. The results show that the slot end face has a certain influence on the three-dimensional flow field distribution under the melt-blowing die. The air velocity and temperature in the center region are quite different from those near the slot-end face. As the distance from the center of the flow field increases, the velocity and temperature on the spinning line begin to decrease. The velocity and temperature distributions of the spinning lines in the central area and nearby areas are almost the same; the temperature and velocity values on the spinning lines near the slot end are the lowest. The distribution characteristics of the three-dimensional airflow field could affect the uniformity of the fiber diameter and the meltblowing products.

Numerical Analysis of Airflow Fields from New Melt-Blowing Dies for Dual-Slot Jets

The melt-blowing process uses high-speed and high-temperature airflow from the die head to draw polymer melt into micron-sized fibers. In this work, to reduce the diameter of the melt-blowing fibers, three new slot dies have been designed based on the common slot die. With computational fluid dynamics technology, the two-dimensional flow fields from these new types of slot dies were numerically calculated. To verify the validity of the calculation, the simulation data was compared with the experimental data. The numerical result shows that the internal flow stabilizers could increase the velocity peak and the pressure peak on the centerline of the flow field and could reduce the reverse velocity, temperature decay, and maximum value of turbulence intensity near the die head. Compared with the common slot die, the slot dies with cuboid bosses could increase the air velocity and temperature on the spinning line in most areas and reduce the air pressure within 1.5 cm below the die. The slot dies with internal flow stabilizers and cuboid bosses have the optimal flow field performance and would be beneficial to the production of thinner fibers.

Attainment of Water and Oil Repellency for Engineering Thermoplastics without Long-Chain Perfluoroalkyls: Perfluoropolyether-Based Triblock Polyester Additives

For decades, water and oil repellency of engineering thermoplastics has been achieved with introduction of long-chain perfluoroalkyl substances and moieties (C _nF_{2 n+1}, n ≥ 7). However, their bioaccumulative and toxicological impact is now widely recognized and, consequently, the substances have been phased out of industrial production and applications. To this end, we have synthesized fluorinated oligomeric triblock polyesters (FOPBs), which do not possess the long-chain perfluoroalkyl segments and serve as effective low-surface-energy additives to engineering thermoplastics. More specifically, we obtained original perfluoropolyether (PFPE)-based triblock copolymers, in which two identical fluorinated blocks were separated by a short nonfluorinated polyester block made of poly(ethylene isophthalate) (PEI). It was found that when FOPBs were added to poly(ethylene terephthalate), nylon-6, and poly(methyl methacrylate) films they readily migrate to the film surface and in doing so imparted significant water and oil repellency to the thermoplastic boundary. The water/oil wettability of the films modified with FOPB is considerably lower than the wettability of the films modified with an analogous PFPE-based polyester, which differs from FOPB only by the absence of the short nonfluorinated PEI middle block. We associate the superiority of the triblock copolymers in terms of water and oil repellency with their ability to form brushlike structures on polymer film surfaces.

An insight into the amphiphobicity and thermal degradation behavior of PDMS-based block copolymers bearing POSS and fluorinated units

Methacryloxypropyl-polyhedral oligomeric silsesquioxane (MAPOSS) and dodecafluoroheptyl methacrylate (DFHM) are proposed to separately block-copolymerize with polydimethylsiloxane (PDMS)-based acrylate block copolymer (PDMS-b-PMMA). The syntheses of PDMS-b-PMMA-b-PMAPOSS and PDMS-b-PMMA-b-PDFHM were executed in this manner to examine the effect of PMAPOSS and PDFHM on surface amphiphobic behavior and thermal degradation behavior. PMAPOSS and PDFHM were found to both contribute towards the improvement of static hydrophobicity. However, the PMAPOSS was found to disable the dynamic hexadecane-dewetting properties because of its restriction on molecular wriggling motion and its induced high roughness. In contrast, PDFHM was found to improve the dynamic dewetting properties for oil-based ink. With regard to the thermal stability, the incorporation of either PMAPOSS or PDFHM into PDMS-b-PMMA with PDMS (Mn ∼1000 or 5000 Da) favors the increase in the original thermal-decomposition temperature. However, the presence of PMAPOSS initiates a higher degradation rate and fails to improve the thermal stability in the case of long PDMS (Mn ∼10 000 Da) due to the heterogeneous dispersion of POSS in the matrix.

Environmentally Friendly and Breathable Fluorinated Polyurethane Fibrous Membranes Exhibiting Robust Waterproof Performance

Waterproof and breathable membranes that provide a high level of protection and comfort are promising core materials for meeting the pressing demand for future upscale protective clothing. However, creating such materials that exhibit environmental protection, high performance, and ease of fabrication has proven to be a great challenge. Herein, we report a novel strategy for synthesizing fluorinated polyurethane (C6FPU) containing short perfluorohexyl (-C₆F₁₃) chains and introduced it as hydrophobic agent into a polyurethane (PU) solution for one-step electrospinning. A plausible mechanism about the dynamic behavior of fluorinated chains with an increasing C6FPU concentration was proposed. Benefiting from the utilization of magnesium chloride (MgCl₂), the fibrous membranes had dramatically decreased maximum pore sizes. Consequently, the prepared PU/C6FPU/MgCl₂ fibrous membranes exhibited an excellent hydrostatic pressure of 104 kPa, a modest water vapor transmission rate of 11.5 kg m^-2 d^-1, and a desirable tensile strength of 12.4 MPa. The facile fabrication of PU/C6FPU/MgCl₂ waterproof and breathable membranes not only matches well with the tendency to be environmentally protective but also fully meets the requirements for high performance in extremely harsh environments.

Toward a Long-Chain Perfluoroalkyl Replacement: Water and Oil Repellency of Polyethylene Terephthalate (PET) Films Modified with Perfluoropolyether-Based Polyesters

Original perfluoropolyethers (PFPE)-based oligomeric polyesters (FOPs) of different macromolecular architecture were synthesized via polycondensation as low surface energy additives to engineering thermoplastics. The oligomers do not contain long-chain perfluoroalkyl segments, which are known to yield environmentally unsafe perfluoroalkyl carboxylic acids. To improve the compatibility of the materials with polyethylene terephthalate (PET) we introduced isophthalate segments into the polyesters and targeted the synthesis of lower molecular weight oligomeric macromolecules. The surface properties such as morphology, composition, and wettability of PET/FOP films fabricated from solution were investigated using atomic force microscopy, X-ray photoelectron spectroscopy, and contact angle measurements. It was demonstrated that FOPs, when added to PET film, readily migrate to the film surface and bring significant water and oil repellency to the thermoplastic boundary. We have established that the wettability of PET/FOP films depends on three main parameters: (i) end-groups of fluorinated polyesters, (ii) the concentration of fluorinated polyesters in the films, and (iii) equilibration via annealing. The most effective water/oil repellency FOP has two C₄F₉-PFPE-tails. The addition of this oligomeric polyester to PET allows (even at relatively low concentrations) reaching a level of oil repellency and surface energy comparable to that of polytetrafluorethylene (PTFE/Teflon). Therefore, the materials can be considered suitable replacements for additives containing long-chain perfluoroalkyl substances.

Electrospinning of Nanodiamond-Modified Polysaccharide Nanofibers with Physico-Mechanical Properties Close to Natural Skins

Electrospinning of biopolymers has gained significant interest for the fabrication of fibrous mats for potential applications in tissue engineering, particularly for wound dressing and skin regeneration. In this study, for the first time, we report successful electrospinning of chitosan-based biopolymers containing bacterial cellulous (33 wt %) and medical grade nanodiamonds (MND) (3 nm; up to 3 wt %). Morphological studies by scanning electron microscopy showed that long and uniform fibers with controllable diameters from 80 to 170 nm were prepared. Introducing diamond nanoparticles facilitated the electrospinning process with a decrease in the size of fibers. Fourier transform infrared spectroscopy determined hydrogen bonding between the polymeric matrix and functional groups of MND. It was also found that beyond 1 wt % MND, percolation networks of nanoparticles were formed which affected the properties of the nanofibrous mats. Uniaxial tensile testing of the woven mats determined significant enhancement of the strength (from 13 MPa to 25 MP) by dispersion of 1 wt % MND. The hydrophilicity of the mats was also remarkably improved, which was favorable for cell attachment. The water vapor permeability was tailorable in the range of 342 to 423 µg·Pa(-1)·s(-1)·m(-1). The nanodiamond-modified mats are potentially suitable for wound healing applications.