Durable cellulose paper by grafting thiol groups and controlling silver deposition for ultrahigh electromagnetic interference shielding.

Electromagnetic interference (EMI) shielding paper with durability and high effectiveness is of significant importance to long-term service for preventing EMI pollution. Herein, we report a practical method for preparing cellulose paper/Ag composite with outstanding durable and ultrahigh EMI shielding performance by electroless silver plating. The silver deposition process, the surface morphology, the silver content and conductivity of the composite can be controlled by varying the amount of N-acetyl-L-cysteine (NAC) grafted onto the cellulose fibers and ammonia amount for silver-ammonia complex formation. Moreover, the grafted NAC with thiol groups on cellulose can enhance the adhesion between silver and cellulose paper, meanwhile, NAC as the reducing agent can result in a more complete flower-shaped silver structure and reducing the reflection of electromagnetic waves in silver layer. The composite exhibited excellent conductivity, EMI shielding effectiveness (SE) up to 106 dB and outstanding durability. After 10,000 bending times and 60 abrasion cycles respectively, the electrical resistance of the composite only increased from 0.030 Ω/sq. to 0.041 Ω/sq. and 0.050 Ω/sq., and the EMI SE decreased to 102 dB and 105 dB.

Pronounced Suppression and X-Pattern Merging of Equatorial Ionization Anomalies After the 2022 Tonga Volcano Eruption.

Following the 2022 Tonga Volcano eruption, dramatic suppression and deformation of the equatorial ionization anomaly (EIA) crests occurred in the American sector ∼14,000 km away from the epicenter. The EIA crests variations and associated ionosphere-thermosphere disturbances were investigated using Global Navigation Satellite System total electron content data, Global-scale Observations of the Limb and Disk ultraviolet images, Ionospheric Connection Explorer wind data, and ionosonde observations. The main results are as follows: (a) Following the eastward passage of expected eruption-induced atmospheric disturbances, daytime EIA crests, especially the southern one, showed severe suppression of more than 10 TEC Unit and collapsed equatorward over 10° latitudes, forming a single band of enhanced density near the geomagnetic equator around 14-17 UT, (b) Evening EIA crests experienced a drastic deformation around 22 UT, forming a unique X-pattern in a limited longitudinal area between 20 and 40°W. (c) Thermospheric horizontal winds, especially the zonal winds, showed long-lasting quasi-periodic fluctuations between ±200 m/s for 7-8 hr after the passage of volcano-induced Lamb waves. The EIA suppression and X-pattern merging was consistent with a westward equatorial zonal dynamo electric field induced by the strong zonal wind oscillation with a westward reversal.

Seasonal Variation of Thermospheric Composition Observed by NASA GOLD.

We examine characteristics of the seasonal variation of thermospheric composition using column number density ratio ∑O/N 2 observed by the NASA Global Observations of Limb and Disk (GOLD) mission from low-mid to mid-high latitudes. We also use ∑O/N 2 derived from the Global Ultraviolet Imager (GUVI) limb measurements onboard the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite and estimated by the NRLMSISE-00 empirical model to aid our investigation. We found that the ∑O/N 2 seasonal variation is hemispherically asymmetric: in the southern hemisphere, it exhibits the well-known annual and semiannual pattern, with highs near the equinoxes, and primary and secondary lows near the solstices. In the northern hemisphere, it is dominated by an annual variation, with a minor semiannual component with the highs shifting toward the wintertime. We also found that the durations of the December and June solstice seasons in terms of ∑O/N 2 are highly variable with longitude. Our hypothesis is that ion-neutral collisional heating in the equatorial ionization anomaly region, ion drag, and auroral Joule heating play substantial roles in this longitudinal dependency. Finally, the rate of change in ∑O/N 2 from one solstice season to the other is dependent on latitude, with more dramatic changes at higher latitudes.

Climatology of Mesosphere and Lower Thermosphere Residual Circulations and Mesopause Height Derived From SABER Observations.

In the mesosphere and lower thermosphere (MLT) region, residual circulations driven by gravity wave breaking and dissipation significantly impact constituent distribution and the height and temperature of the mesopause. The distribution of CO2 can be used as a proxy for the residual circulations. Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) CO2 volume mixing ratio (VMR) and temperature measurements from 2003 to 2020 are used to study the monthly climatology of MLT residual circulations and the mesopause height. Our analyses show that (a) mesopause height strongly correlates with the CO2 VMR vertical gradient during solstices; (b) mesopause height has a discontinuity at midlatitude in the summer hemisphere, with a lower mesopause height at mid-to-high latitudes as a result of adiabatic cooling driven by strong adiabatic upwelling; (c) the residual circulations have strong seasonal variations at mid-to-high latitudes, but they are more uniform at low latitudes; and (d) the interannual variability of the residual circulations and mesopause height is larger in the Southern Hemisphere (SH; 4-5 km) than in the Northern Hemisphere (NH; 0.5-1 km).

Mixed Solvents in Multilayer Ceramic Capacitors (MLCC) Electronic Paste and Their Effects on the Properties of Organic Vehicle.

The copper end paste used in multilayer ceramic capacitors sintered in nitrogen atmosphere leads to carbon residues of organic vehicles, which leads to a reduction in electrode conductivity and high scrap rate. With an attempt to leave no residue in the sintering, the compatibility of solvents and thickeners should be improved because it has an important influence on the hierarchical volatilization and carbon residue of organic vehicles. In this work, the volatility of different solvents was compared, and several solvents were mixed in a definite proportion to prepare an organic vehicle with polyacrylate resins. The hierarchical volatility and solubility parameters of mixed solvents were effectively adjusted by changing proportions of different components. The thermogravimetric curves of resins and organic vehicles were measured by thermogravimetric analyzer, and the effect of solubility parameter on the dissolvability of resins in the solvent and the residual of organic vehicles were studied. Results showed that the hierarchical volatilization of solvents can be obtained by mixing different solvents; the intrinsic viscosity of the organic vehicle is higher, and the thermal decomposition residue of polyacrylate resins is lower when the solubility parameters of mixed solvents and polyacrylate resins are closer. The low residual sintering of organic vehicles can be achieved by using a mixed solvent with hierarchical volatility and approximate solubility parameters as resins.

Preparation of conductive cellulose fabrics with durable antibacterial properties and their application in wearable electrodes.

Electroless silver plating on fabrics can obtain conductive and antibacterial bifunctional materials which can be used as electrodes in wearable electronic products. However, these activities are deteriorated easily after washing because of the falling off of silver coating resulted from the weak adhesion. In order to improve the binding force between silver and cellulose fabrics, 3-mercaptopropytrimethoxysilane (MPTS) was applied to modify cellulose fabrics before silver electroless plating to develop the durable conductive fabrics with excellent antibacterial. The silver nanoparticles (Ag NPs) deposition process was observed via field emission scanning electron microscopy (FESEM), thermal properties were evaluated by thermogravimetric analysis (TGA). A dense and uniform silver layer was formed on the fabric. The initial electrical resistance of the conductive fabric was 0.04 Ω/sq and lowered than 2 Ω/sq after 200 washing cycles. The antibacterial efficiency of the fabric after 200 washing cycles remained 92.82%, compared to 100% with the fabric before washing. Moreover, the inhibition rate was determined by optical density of bacteria suspension at 260 nm and further substantiated by releasing of Ag+ from the fabric. The conductive fabrics were applied as wearable electrodes to capture electrocardiogram (ECG) signals of human in static states and running states.

Comparison of different extraction methods for polysaccharides from Crataegus pinnatifida Bunge.

In this study, different extraction methods of polysaccharides from Crataegus pinnatifida Bunge (CPP) were compared by studying the extraction yield, structural characteristics and antioxidant activities. Firstly, polysaccharides were obtained using hot water extraction (CPPh), ultrasound assisted extraction (CPPu), enzyme assisted extraction (CPPe) and enzyme-ultrasound assisted extraction (CPPc), respectively. Meanwhile, the optimum extraction conditions of enzyme-ultrasonic assisted extraction were determined by response surface method (RSM). The extraction yields, structural characteristics and antioxidant activities were investigated and compared by visual photos, gas chromatography, ultraviolet-visible and Fourier-transform infrared spectroscopy. The results clearly showed that enzyme-ultrasonic assisted extraction possessed the highest extraction yield (10.39 ±â€¯0.04%). The molecular weight of CPPh was the highest while the other polysaccharides had no significant difference. Besides, the monosaccharide composition of CPPc, CPPh, CPPu and CPPe were similar but the molar percentages of monosaccharide were different. Finally, the results of antioxidant activities showed that CPPc exhibited the highest scavenging effect of superoxide radical and lipids inhibiting ability. In summary, enzyme-ultrasonic assisted extraction was a high-efficient and low-energy consumption method for CPP extraction.

Study on the Preparation of Ionic Liquid Doped Chitosan/Cellulose-Based Electroactive Composites.

Electro-actuated polymer (EAP) can change its shape or volume under the action of an external electric field and shows similar behavioral characteristics with those of biological muscles, and so it has good application prospects in aerospace, bionic robots, and other fields. The properties of cellulose-based electroactive materials are similar to ionic EAP materials, although they have higher Young's modulus and lower energy consumption. However, cellulose-based electroactive materials have a more obvious deficiency-their actuation performance is often more significantly affected by ambient humidity due to the hygroscopicity caused by the strong hydrophilic structure of cellulose itself. Compared with cellulose, chitosan has good film-forming and water retention properties, and its compatibility with cellulose is very excellent. In this study, a chitosan/cellulose composite film doped with ionic liquid, 1-ethyl-3-methylimidazolium acetate ([EMIM]Ac), was prepared by co-dissolution and regeneration process using [EMIM]Ac as the solvent. After that, a conductive polymer, poly(3,4-ethylenedioxythiophene)/poly (styrene sulfonate) (PEDOT: PSS), was deposited on the surface of the resulted composite, and then a kind of cellulose-based electroactive composites were obtained. The results showed that the end bending deformation amplitude of the resulted material was increased by 2.3 times higher than that of the pure cellulose film under the same conditions, and the maximum deformation amplitude reached 7.3 mm. The tensile strength of the chitosan/cellulose composite film was 53.68% higher than that of the cellulose film, and the Young's modulus was increased by 72.52%. Furthermore, in comparison with the pure cellulose film, the water retention of the composite film increased and the water absorption rate decreased obviously, which meant that the resistance of the material to changes in environmental humidity was greatly improved.

Novel Wearable Electrodes Based on Conductive Chitosan Fabrics and Their Application in Smart Garments.

Smart garments, which can capture electrocardiogram signals at any time or location, can alert others to the risk of heart attacks and prevent sudden cardiac death when people are sleeping, walking, or running. Novel wearable electrodes for smart garments based on conductive chitosan fabrics were fabricated by electroless plating of silver nanoparticles onto the surfaces of the fibers. The electrical resistance, which is related to the silver content of the composite fabrics, can be as low as 0.0332 ± 0.0041 Ω/sq due to the strong reactivity between amine groups and silver ions. After washing these fabrics eight times, the electrical resistance remained below 1 Ω/sq. The conductive chitosan fabrics were applied to smart garments as wearable electrodes to capture electrocardiogram signals of the human body in static state, jogging state, and running state, which showed good data acquisition ability and sensitivity.

Preparation of Novel Nano-Sized Hydrogel Microcapsules via Layer-By-Layer Assembly as Delivery Vehicles for Drugs onto Hygiene Paper.

Hydrogel microcapsules are improved transplantation delivery vehicles for pharmaceuticals by effectively segregating the active ingredients from the surroundings and delivering them to a certain target site. Layer-by-layer (LbL) assembly is an attractive process to fabricate the nano-sized hydrogel microcapsules. In this study, nano-sized hydrogel microcapsules were prepared through LbL assembly using calcium carbonate nanoparticles (CaCO3 NPs) as the sacrificial inorganic template, sodium alginate (SA) and polyethyleneimine (PEI) as the shell materials. Ciprofloxacin was used to study the encapsulation and release properties of the hydrogel microcapsules. The hydrogel microcapsules were further adsorbed onto the paper to render antimicrobial properties. The results showed that the mean size of the CaCO3 template was reduced after dispersing into sodium n-dodecyl sulfate (SDS) solution under sonication. Transmission electron microscope (TEM) and atomic force microscope (AFM) revealed that some hydrogel microcapsules had a diameter under 200 nm, typical creases and collapses were found on the surface. The nano-sized PEI/SA hydrogel microcapsules showed high loading capacity of ciprofloxacin and a sustained release. PEI/SA hydrogel microcapsules rendered good antimicrobial properties onto the paper by the adsorption of hydrogel microcapsules, however, the mechanical properties of the hygiene paper were decreased.

Microwave Assisted Preparation of Antimicrobial Chitosan with Guanidine Oligomers and Its Application in Hygiene Paper Products.

Guanidinylated chitosan (GCS) was prepared by grafting guanidine oligomers onto chitosan under microwave irradiation. The structure of GCS characterized by FT-IR and ¹H NMR verified the covalent bonding between the guanidine oligomers and chitosan; the effects of molar ratio, reaction temperature, and time were investigated and the degree of substitution of GCS reached a maximum of 25.5% under optimized conditions in this work. The resulting GCS showed significantly enhanced antimicrobial activities. The results obtained from the dynamic UV absorption of Escherichia coli (E. coli) and atomic force microscopy (AFM) revealed that the deactivation of E. coli by GCS was due to the destructing of the cell membrane and the prompt release of cytoplasm from the bacterial cells. The adsorption of GCS onto cellulose fibers and the antimicrobial efficiency of the hygiene papers with GCS were also investigated. Microwave irradiation as a green assisted method was applied to promote this reaction. This facile approach allowed chitosan to be guanidinylated without tedious preparation procedures and thus broadened its application as a biocompatible antimicrobial agent.

Enhanced water vapour barrier and grease resistance of paper bilayer-coated with chitosan and beeswax.

In order to overcome the deficiencies of single layer coating, bilayer coated papers were prepared by two separate coating procedures using various combinations of proteins or polysaccharides with beeswax. Among those combinations, chitosan-beeswax bilayer coated paper showed the best water vapour barrier property. It was observed that as the concentration of chitosan solution increased from 1.0 to 3.0 wt%, its water vapour transport rate (WVTR) decreased from 171.6 to 52.8 g/m(2)/d but using reduced beeswax coating weight (from 10.1 to 4.9 g/m(2)). It also displayed an enhanced performance of grease resistance. Scanning electron microscopy (SEM) showed that beeswax layer was fitted to chitosan layer so closely that these two layers are indistinguishable. Confocal laser scanning microscope (CLSM) further confirmed the existence of an integrated chitosan film between beeswax layer and paper base and a thin composite layer consisting of chitosan and beeswax.

Immobilization of pectinase on oxidized pulp fiber and its application in whitewater treatment.

Modified pulp fiber was originally used as a new type of carrier for pectinase immobilization. Pulp fiber was oxidized by sodium periodate to produce aldehyde groups for covalently binding with amino groups of pectinase. Results showed that the enzymatic activity of immobilized pectinase on pulp fiber reached 65 µgg(-1)min(-1) when immobilization pH value, temperature and time were of 7.0, 20 °C and 15 min, respectively. The immobilized pectinase showed higher thermo stability in a wider temperature range of 40-70 °C than its free type and its optimal pH shifted from 8.0 to 8.8. Furthermore, the immobilized pectinase exhibited good operational stability. When employed in whitewater treatment of papermaking industry, it still efficiently decreased the cationic demand after operating repeatedly for six batches. The results obtained demonstrate a promising route to prepare available, cheap and biodegradable carrier for immobilizing enzymes with potential application in wastewater treatment in papermaking industry.

Synthesis of modified guanidine-based polymers and their antimicrobial activities revealed by AFM and CLSM.

Modified guanidine-based polymers with chain extension were synthesized by condensation and cross-linking polymerizations in an attempt to increase molecular weight and charge density of the antimicrobial polymers. The antimicrobial activity and the corresponding mechanisms were investigated by several approaches. The results indicated that the antimicrobial activities of the modified guanidine-based polymer, based on the minimum inhibition concentration (MIC) against E.coli, varied with alkyl monomer ratios. UV absorption at 260 nm further quantified the amount of intracellular components leaked into bacteria suspension. The UV absorption measurements were also used to monitor inhibition processes dynamically. It was found that the modified guanidine-based polymer inhibited the growth of bacteria by causing membrane compromised and intracellular leaked. Dual fluorescent dyes were used to stain all bacteria including the dead ones, which enabled us to utilize CLSM to visualize the viability of bacteria in the presence of various modified guanidine-based polymers without causing any damage. The morphologies of bacteria untreated and treated with modified guanidine-based polymer were observed using an atomic force microscope (AFM), which further demonstrated the damage of E.coli membrane and the leakage of intracellular component induced by the modified guanidine-based polymers.

Antimicrobial/Antimold polymer-grafted starches for recycled cellulose fibers.

In this work, an antimicrobial guanidine polymer (PHGH) was grafted onto starch as a carrier to form branched or grafted chains along the starch backbone. This grafting improved the antimicrobial properties and the adsorption of the starch on recycled cellulose fibers. Similar work was also conducted on bleached sulfite fibers for comparison. The results showed that the starch, grafted with 12 wt% PHGH, adsorbed more on recycled fibers than on sulfite fibers. By applying the antimicrobial-modified starch to recycled or sulfite pulps up to 20 mg/g, both antimicrobial and antimold performances of the papers were improved substantially. Additionally, the PHGH-modified starch increased the tensile index of papers, but decreased the tear index slightly. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were employed to investigate the morphologic changes of Escherichia coli bacteria and Chaetomium globosum fungi upon exposure to the PHGH-modified starch, thus demonstrating that the antimicrobial mechanism is based on the damage of bacterial membrane.

Synergistic effects of chitosan-guanidine complexes on enhancing antimicrobial activity and wet-strength of paper.

Chitosan-guanidine complexes were prepared by reacting chitosan and polyhexamethylene guanidine hydrochloride or crosslinked polyhexamethylene guanidine hydrochloride in the presence of sodium tripolyphosphate as a crosslinking agent. The complexes, used as functional additives for paper, synergistically improved wet-strength and antimicrobial activities. In comparison with the control sample, the wet/dry strength ratio of hand-sheets treated with the complexes was increased from 2.65% up to 23.3%. The MIC values of the chitosan-PHGH and chitosan-PHGHE complexes against Escherichia coli were 15.6 and 31.2 microg mL(-1), respectively, thus demonstrating excellent antimicrobial activity. Hand-sheets treated with the complexes exhibited antibacterial activity against E. coli and Staphylococcus aureus. The release of the guanidine polymers included in the complexes was dynamically monitored using UV and the results showed the amount released exceeded 80%. Atomic force microscopy images indicated that the antimicrobial mechanism of the complexes was likely due to membrane damage.