Experimental Study of the Airflow Field and Fiber Motion in the Melt-Blowing Process.

The melt-blowing process involves high velocity airflow and fiber motion, which have a significant effect on fiber attenuation. In this paper, the three-dimensional airflow field for a melt-blowing slot die was measured using the hot-wire anemometry in an experiment. The fiber motion was captured online using a high-speed camera. The characteristics of the airflow distribution and fiber motion were analyzed. The results show that the melt-blowing airflow field is asymmetrically distributed. The centerline air velocity is higher than that around it and decays quickly. The maximum airflow velocity exists near the die face, in the range of 130-160 m/s. In the region of -0.3 cm < y < 0.3 cm and 0 < z < 2 cm, the airflow has a high velocity (>100 m/s). As the distance of z reaches 5 cm and 7 cm, the maximum airflow velocity reduces to 70 m/s. The amplitude of fibers is calculated, and it increases with the increase in air dispersion area which has a significant influence on fiber attenuation. At z = 1.5 cm, 2.5 cm, 4 cm, and 5.5 cm, the average fiber amplitudes are 1.05 mm, 1.71 mm, 2.83 mm, and 3.97 mm, respectively. In the vicinity of the die, the fibers move vertically downward as straight segments. With the increase in distance from the spinneret, the fiber appears to bend significantly and forms a fiber loop. The fiber loop morphology affects the velocity of the fiber movement, causing crossover, folding, and bonding of the moving fiber. The study investigated the interaction between the fiber and airflow fields. It indicates that the airflow velocity, velocity difference, and dispersion area can affect the motion of fiber which plays an important role in fiber attenuation during the melt-blowing process.

Structure and thermal properties of cellulose nanofibrils extracted from alkali-ultrasound treated windmill palm fibers.

Windmill palm, a tree species that is native to China, has gained attention with regard to the production of substantial amounts of biomass fibers via yearly pruning. This study investigates the structure and thermal properties of cellulose nanofibrils (CNFs) obtained from windmill palm biomass, with the goal of promoting the usage of these CNFs. Alkali-ultrasound treatments are employed herein to prepare samples of the CNFs. The micromorphology of the prepared samples is observed using scanning electron microscopy, atomic force microscopy, and transmission electron microscopy. Furthermore, X-ray diffraction analysis is used to examine the aggregated structure of the samples, and thermogravimetric analysis is used to investigate their thermal properties. Results indicate that during alkali hydrolysis when obtaining CNFs, the fiber cell wall exhibits distinct spiral cracking. The diameter of the obtained nanocellulose is <90 nm. The removal of lignin and hemicellulose materials from the fiber cell enhances the crystallinity of CNFs to as high as 60 %, surpassing that of windmill palm single fibers. The thermal decomposition temperatures of the CNFs are found to be 469 °C and 246 °C for the crystalline and amorphous regions, respectively.

A green strategy to recycle the waste PP melt-blown materials: From 2D to 3D construction.

The demand for polypropylene (PP) melt-blown materials has dramatically increased due to the COVID-19 pandemic. It has caused serious environmental problems because of the lack of effective treatment for the waste PP melt-blown materials. In this study, we propose a green and sustainable recycling method to create PP sponges from waste PP melt-blown material for oil spill cleaning by freeze-drying and thermal treatment techniques. The recycling method is simple and without secondary pollution to the environment. The developed recycling method successfully transforms 2D laminar dispersed PP microfibers into elastic sponges with a 3D porous structure, providing the material with good mechanical properties and promotes its potential application in the field of oil spill cleaning. The morphology structure, thermal properties, mechanical properties, and oil absorption properties are tested and characterized. The PP sponges with a three-dimensional porous network structure show an exceedingly low density of >0.014 g/cm3, a high porosity of <98.77 %, and a high water contact angle range of 130.4-139.9°. Moreover, the PP sponges own a good absorption capacity of <47.61 g/g for different oil and solvents. In particular, the compressive modulus of the PP sponges is 33.59-201.21 kPa, which is higher than that of most other fiber-based porous materials, indicating that the PP sponges have better durability under the same force. The excellent comprehensive performance of the PP sponges demonstrates the method developed in this study has large application potential in the field of the recycle of waste PP melt-blown materials.

Mechanical properties of toughened windmill palm fibre with different chemical compositions.

Windmill palm fibres are well-known plant fibres exhibiting the largest elongation at break. In this study, lignin or hemicellulose was removed from windmill palm fibres in a targeted manner to prepare materials with different chemical compositions. The structure and mechanical properties of the windmill palm fibres were analysed using in situ scanning electron microscopy, Fourier transform infrared spectroscopy, thermogravimetry, X-ray diffraction analysis and tensile testing. The large elongation at break was attributed to the unwinding of the single fibre, the micro cracks and the small degree of orientation (<62 %). On a microscopic scale, the lumen shape of fibre cross section influences the local stress distribution. The hemicellulose-removed fibres exhibited a high breaking strength of 236 MPa with deterioration of the thermal property. The binding force between single fibres is the weakest after lignin removal. The removal of hard lignin softens the fibres and increases the elongation at break to >30 %.

Quantitative Determination of Airborne Redox-Active Compounds Based on Heating-Induced Reduction of Gold Nanoparticles.

Airborne redox-active compounds (ARC) account for a substantial fraction of atmospheric aerosols and play a vital role in chemical processes that influence global climate and human and ecological health. With the exception of the determination of total organic carbon by the expensive total organic carbon (TOC) analyzer, there is currently no easy-to-use method to quantify ARC. Here, we designed a method to detect the concentration of ARC by using the thermal-induced reduction and colorimetric behaviors of gold nanoparticles (AuNPs), in which the humic substances (HS) was used as a standard model of ARC to calculate the HS-equivalent concentration of ARC. Distinguished from the conventional complex methods, e.g., TOC analysis, the proposed approach measured localized surface plasmon resonance absorption of AuNPs and the target ARC concentration can be either directly quantified by the absorption spectrometer or qualitatively evaluated by the naked eyes. By using the absorption spectrometer, a limit of detection of 0.005 ppm by our AuNP sensor was achieved. To validate this sensing technique, aerosol samples collected from Basel (suburban), Bern (urban), and Rigi mountain (rural and high-altitude) sites in Switzerland were further investigated through the TOC combustion method. The results thereby substantiated that our plasmonic absorption-based AuNP sensor upholds a great promise for fast, cost-efficient total ARC detection and air quality assessment.

Development of natural fiber-based degradable nonwoven mulch from recyclable mill waste.

The extensively used agricultural polyethylene mulch is associated with serious environmental pollution because it is difficult to degrade. This study evaluated the feasibility and degradability of a new mulch that was fabricated entirely from recyclable biodegradable natural fibers. In 2018, three types of this new natural fiber-based mulch were prepared from textile mill waste using needle-punched nonwoven technology and characterized using both laboratory and field tests. Physical parameters, including air permeability, thermal insulation value, and light transmittance, were determined through laboratory tests. Other parameters, including soil moisture content, soil temperature, weed suppression, agronomic traits, cotton yield, and soil burial degradation, were investigated through field tests, with a degradable plastic film as the control. The results showed that the crop yield from the best new mulch treatment (2802.2 kg/arc) and the degradable plastic film treatment (2851.3 kg/arc) were similar. The superior thermal insulation value of the new mulch, which was at least 9.4% higher than the control, facilitated its capacity to substantially moderate soil temperature. The weed germination suppression ratio of the new mulch was 50% higher than the control because it was 100- fold thicker and showed 54.6% lower light transmittance. In addition, after 90 days in the soil, the new mulch evidently degraded. Therefore, this newly developed degradable nonwoven mulch addresses the issue of industrial waste utilization, thereby preventing agricultural pollution. In the future, enhancing the soil moisture retention capacity of the new mulch will greatly facilitate its application.

Three-Dimensional Hierarchically Porous Graphene Fiber-Shaped Supercapacitors with High Specific Capacitance and Rate Capability.

Chemically converted graphene fiber-shaped supercapacitors (FSSCs) are highly promising flexible energy storage devices for wearable electronics. However, the ultralow specific capacitance and poor rate performance severely hamper their practical applications. They are caused by severe stacking of graphene nanosheets and tortuous ion diffusion path in graphene-based electrodes; thus, the ultralow utilization of graphene has been rarely carefully considered to date. Here, we address these issues by developing three-dimensional hierarchically porous graphene fiber with the incorporation of holey graphene for efficient utilization of graphene to achieve fast charge diffusion and good charge storage capability. Without deterioration in electrical but robust mechanical properties, the optimal graphene fiber shows ultrahigh specific capacitance of 220.1 F cm-3 at current density of 0.1 A cm-3 and boosted specific capacitance of 254.3 F cm-3 at 0.1 A cm-3 after nitrogen doping. Moreover, the nitrogen-doped 40% holey graphene hybrid fiber-assembled FSSC exhibits ultrahigh rate capability (96, 91, and 87% at current density of 0.5, 1.0, and 2.0 A cm-3, respectively, and 67% even at ultrahigh current density of 10.0 A cm-3) and excellent cycle stability (95.65% capacitance retention after 10 000 cycles). The contribution of three-dimensional interconnected hierarchically porous network to the enhanced electrochemical (EC) performance is semiquantitatively elucidated by Brunauer-Emmett-Teller and energy dispersive spectroscopy mapping. Our work gives insights into the importance of fully utilizing graphene and provides an efficient strategy for high EC performance in chemically converted graphene-based FSSCs.

One-Pot Route towards Active TiO2 Doped Hierarchically Porous Cellulose: Highly Efficient Photocatalysts for Methylene Blue Degradation.

In this study, novel photocatalyst monolith materials were successfully fabricated by a non-solvent induced phase separation (NIPS) technique. By adding a certain amount of ethyl acetate (as non-solvent) into a cellulose/LiCl/N,N-dimethylacetamide (DMAc) solution, and successively adding titanium dioxide (TiO2) nanoparticles (NPs), cellulose/TiO2 composite monoliths with hierarchically porous structures were easily formed. The obtained composite monoliths possessed mesopores, and two kinds of macropores. Scanning Electron Microscope (SEM), Energy Dispersive Spectroscopy (EDS), Fourier Transform Infrared Spectroscopy (FT-IR), X-ray Diffraction (XRD), Brunauer-Emmett-Teller (BET), and Ultraviolet-visible Spectroscopy (UV-Vis) measurements were adopted to characterize the cellulose/TiO2 composite monolith. The cellulose/TiO2 composite monoliths showed high efficiency of photocatalytic activity in the decomposition of methylene blue dye, which was decomposed up to 99% within 60 min under UV light. Moreover, the composite monoliths could retain 90% of the photodegradation efficiency after 10 cycles. The novel NIPS technique has great potential for fabricating recyclable photocatalysts with highly efficiency.