Nano-Crystalline Sandwich Formed in Polylactic Acid Fibers.

Fibers have traditionally been made through melt or solution processes from macromolecules. Most of these fibers have crystalline domains where the segregation of different crystalline features is extremely difficult due to the statistical nature of the formation and growth of these domains. A fibrous nano-crystalline sandwich is reported where distinctly different crystalline regions are formed in layers along the continuous fiber direction during the spinning process and locked in place. This approach employs side-by-side bicomponent nanofiber electrospinning where the components are the enantiomeric pair of poly(l-lactic acid) and poly(d-lactic acid). The formation of the poly(lactic acid) (PLA) stereo-complexes at the junction interphase of the two components is demonstrated through diffusion, which subsequently crystallize into continuous sandwich domains. The stereo-complex crystalline core in the fiber possesses a melting point 50 °C higher than, and properties substantially different from, the regular PLAs at the fringe areas of the fiber. This nano-crystalline sandwich fiber structure can be scaled to the micrometers in a commercial bicomponent process.

Evaluation of Mask Performances in Filtration and Comfort in Fabric Combinations.

A systemic study on improving particulate pollutant filtration efficiency through the combination of conventional fabrics is presented with the objective of finding comfortable, yet effective airway mask materials and products. Fabrics, nonwovens, and their combinations made of cotton, silk, wool, and synthetic fibers are examined on their filtration efficiency for aerosol particles with diameters ranging from 0.225 µm to 3.750 µm under industry-standard testing conditions. It is found that composite fabrics can improve filtration efficiency more than just layers of the same fabric, and the filtration quality factor of some of the fabric combinations can exceed that of the standard melt-blown materials. In addition, fabric friction and charging between the combined layers also improve filtration efficiency substantially. With a broader understanding of the fabric characteristics, we may design mask products with reduced facial skin discomfort, better aesthetics, as well as the ability to alleviate the environmental impact of discarded protective masks in the extended period of controlling the transmission of pollutants and viruses, such as during the COVID-19 pandemic.

Enhanced stereocomplex crystalline polylactic acids in melt processed enantiomeric bicomponent fiber configurations.

The formation of stereocomplex crystalline domains in the bicomponent fiber melt spinning of enantiomeric polylactic acids (PLAs) is systematically explored and enhanced. Here we report a polycrystalline morphology where distinctly different crystalline regions are formed and aligned along the longitudinal direction of the fiber. This approach employs side-by-side and sheath-core bicomponent melt spinning configurations where the two components are the enantiomeric pairs of poly(L-lactic acid) (PLLA) and poly(D-lactic acid) (PDLA). We demonstrate the formation of the PLA stereocomplexes at the junction interphase through the melt spinning process which subsequently crystallize into a round fibers with stereocomplex and homogeneous crystal lamella morphologies. The fiber morphologies and crystallinities of the melt processed fiber are substantially different from the solution based bicomponent spinning system reported in the prior literature. Furthermore, the different molecular weight in the PLLA/PDLA pairing are found to be crucial to the structural development and properties of the PLA polycrystalline materials. The solid-state annealing does not change the crystal distribution of the crystalline domains and stereocomplex crystalline state, it just enhances the homo-crystallinity in the peripheral of the bicomponent fibers.

A Review on Nanocellulose and Superhydrophobic Features for Advanced Water Treatment.

Globally, developing countries require access to safe drinking water to support human health and facilitate long-term sustainable development, in which waste management and control are critical tasks. As the most plentiful, renewable biopolymer on earth, cellulose has significant utility in the delivery of potable water for human consumption. Herein, recent developments in the application of nanoscale cellulose and cellulose derivatives for water treatment are reviewed, with reference to the properties and structure of the material. The potential application of nanocellulose as a primary component for water treatment is linked to its high aspect ratio, high surface area, and the high number of hydroxyl groups available for molecular interaction with heavy metals, dyes, oil-water separation, and other chemical impurities. The ability of superhydrophobic nanocellulose-based textiles as functional fabrics is particularly acknowledged as designed structures for advanced water treatment systems. This review covers the adsorption of heavy metals and chemical impurities like dyes, oil-water separation, as well as nanocellulose and nanostructured derivative membranes, and superhydrophobic coatings, suitable for adsorbing chemical and biological pollutants, including microorganisms.

Bicomponent PLA Nanofiber Nonwovens as Highly Efficient Filtration Media for Particulate Pollutants and Pathogens.

Herein, a novel form of bicomponent nanofiber membrane containing stereo-complex polylactic acid (SC-PLA) was successfully produced by the side-by-side electrospinning of Poly (L-lactic acid) (PLLA) and Poly (D-lactic acid) (PDLA). We demonstrate that through these environmentally sustainable materials, highly efficient nanofiber assemblies for filtration can be constructed at very low basis weight. The physical and morphological structure, crystalline structure, hydrophobicity, porous structure, and filtration performance of the fibrous membranes were thoroughly characterized. It was shown that the fabricated polylactic acid (PLA) side-by-side fiber membrane had the advantages of excellent hydrophobicity, small average pore size, high porosity, high filtration efficiency, low pressure drop as well as superior air permeability. At the very low basis weight of 1.1 g/m2, the filtration efficiency and pressure drop of the prepared side-by-side membrane reached 96.2% and 30 Pa, respectively. Overall, this biomass-based, biodegradable filtration material has the potential to replace the fossil fuel-based polypropylene commercial meltblown materials for the design and development in filtration, separation, biomedical, personal protection and other fields.

Preparation and Performance of Ultra-Fine Polypropylene Antibacterial Fibers via Melt Electrospinning.

Polypropylene (PP) fibers are employed commonly as the raw material of technical textiles (nonwovens), and the research focuses on fine-denier fibers and their functionalities. In this work, antibacterial PP masterbatches with different dosage (1-5 wt.%) of nano-ZnO particles as the antibacterial agent were prepared via a twin-screw extruder. The as-prepared PP masterbatches were electrospun on a home-made electrospinning device to afford ultra-fine PP fibers. The morphologies of as-spun ultrathin PP fibers with 16 µm of average diameter were observed by SEM. The structure and element distribution were characterized by means of energy-dispersive spectroscopy (EDS) and Fourier-transfer infrared spectroscopy (FTIR), respectively. There was some zinc obviously distributed on the surface when a dosage of ZnO more than 1 wt.% was used, which contributed to the antibacterial activity. The crystallinity of PP fibers was not affected strongly by the dosage of ZnO based on the differential scanning calorimetry (DSC) heating curves, while thermal decomposition improved with the increase in ZnO content, and the mechanical strength decreased predictably with the increase in inorganic ZnO content.

Fabrication of Ultrafine PPS Fibers with High Strength and Tenacity via Melt Electrospinning.

Electrospinning (e-spinning) is an emerging technique to prepare ultrafine fibers. Polyphenylene sulfide (PPS) is a high-performance resin which does not dissolve in any solvent at room temperature. Commercial PPS fibers are produced mainly by meltblown or spunbonded process to give fibers ~20 µm in diameter. In this research, an in-house designed melt electrospinning device was used to fabricate ultrafine PPS fibers, and the e-spinning operation conducted under inert gas to keep PPS fibers from oxidizing. Under the optimum e-spinning conditions (3 mm of nozzle diameter, 30 kV of electrostatic voltage, and 9.5 cm of tip-to-collector distance), the as-spun fibers were less than 8.0 µm in diameter. After characterization, the resultant PPS fibers showed uniform diameter and structural stability. Compared with commercial PPS staple fibers, the obtained fibers had a cold crystallization peak and 10 times higher storage modulus, thereby offering better tensile tenacity and more than 400% elongation at break.