Effect of Plasma Treatment on Bamboo Fiber-Reinforced Epoxy Composites.

Bamboo cellulose fiber (BF)-reinforced epoxy (EP) composites were fabricated with BF subjected to plasma treatment using argon (Ar), oxygen (O2), and nitrogen (N2) gases. Optimal mechanical properties of the EP/BF composites were achieved with BFs subjected to 30 min of plasma treatment using Ar. This is because Ar gas improved the plasma electron density, surface polarity, and BF roughness. Flexural strength and flexural modulus increased with O2 plasma treatment. Scanning electron microscopy images showed that the etching of the fiber surface with Ar gas improved interfacial adhesion. The water contact angle and surface tension of the EP/BF composite improved after 10 min of Ar treatment, owing to the compatibility between the BFs and the EP matrix. The Fourier transform infrared spectroscopy results confirmed a reduction in lignin after treatment and the formation of new peaks at 1736 cm-1, which indicated a reaction between epoxy groups of the EP and carbon in the BF backbone. This reaction improved the compatibility, mechanical properties, and water resistance of the composites.

Avocado seed starch utilized in eco-friendly, UV-blocking, and high-barrier polylactic acid (PLA) biocomposites for active food packaging applications.

Efficient and effective use of biopolymers, such as starch, has increasingly prompted interest due to the current environmental challenges. However, starch-based composites still show poor ductility along with water and oxygen permeability, which may not meet the requirements for food packaging standards. In this study, modified starch (m-St), isolated from the avocado seed and synthesized with tert-butyl acetoacetate (t-BAA), was embedded into polylactic acid (PLA) to design new eco-friendly composites. The developed biocomposites were found to exhibit high performance with outstanding mechanical properties in conjunction with remarkable light, water vapor, and oxygen blocking features for food packaging applications. PLA/m-St(1:6) 20 wt% composites showed a dramatic increase in elongation at break (EB%) from 3.35 to 27.80 % (about 730 % enhancement) and exhibited remarkable UV-blocking performance from 16.21 to 83.86 % for UVB, relative to pure PLA. Equally importantly, these biocomposites revealed significant improvement in oxygen and water vapor barrier performance by reducing their values from 1331 to 32.9 cc m-2 day-1 (indicating a remarkable reduction of 97.53 %) and 61.9 to 28 g m-2 day-1, respectively. This study can show the great potential of extracting starch from biowaste resources and transforming it into sustainable bio-based composites as a promising solution for food packaging applications.

Correction: Ji et al. Mesoporous Cobalt Oxide (CoOx) Nanowires with Different Aspect Ratios for High Performance Hybrid Supercapacitors. Nanomaterials 2023, 13, 749.

There was an error in the original publication [...].

Surface Modification and Mechanical Properties Improvement of Bamboo Fibers Using Dielectric Barrier Discharge Plasma Treatment.

The effect of argon (Ar) and oxygen (O2) gases as well as the treatment times on the properties of modified bamboo fibers using dielectric barrier discharge (DBD) plasma at generated power of 180 W were investigated. The plasma treatment of bamboo fibers with inert gases leads to the generation of ions and radicals on the fiber surface. Fourier transform-infrared spectroscopy (FTIR) confirmed that the functional groups of lignin and hemicellulose were reduced owing to the removal of the amorphous portion of the fibers by plasma etching. X-ray diffraction analysis (XRD) results in an increased crystallinity percentage. X-ray photoelectron spectroscopy (XPS) results showed the oxygen/carbon (O/C) atomic concentration ratio increased with increasing treatment time. The fiber weight loss percentage increased with increased treatment time. Scanning electron microscopy (SEM) images showed that partial etching of the fiber surface led to a higher surface roughness and area and that the Ar + O2 gas plasma treatment provided more surface etching than the Ar gas treatment because of the oxidation reaction of the O2 plasma. The mechanical properties of fiber-reinforced epoxy (FRE) matrix composites revealed that the F(tr)RE-Ar (30) samples showed a high tensile strength, whereas the mechanical properties of the F(tr)RE-Ar + O2 sample decreased with increased treatment time.

Pressure Sensor Based on a Lumpily Pyramidal Vertical Graphene Film with a Broad Sensing Range and High Sensitivity.

Wearable sensors are vital for the development of electronic skins to improve health monitoring, robotic tactile sensing, and artificial intelligence. Active materials and the construction of microstructures in the sensitive layer are the dominating approaches to improve the performance of pressure sensors. However, it is still a challenge to simultaneously achieve a sensor with a high sensitivity and a wide detection range. In this work, using three-dimensional (3D) vertical graphene (VG) as an active material, in combination with micropyramid arrays and lumpy holders, the stress concentration effects are generated in nano-, micro-, and macroscales. Therefore, the lumpily pyramidal VG film-based pressure sensor (LPV sensor) achieves an ultrahigh sensitivity (131.36 kPa-1) and a wide response range (0.1-100 kPa). Finite element analysis demonstrates that the stress concentration effects are enhanced by the micropyramid arrays and lumpy structures in micro- and macroscales, respectively. Finally, the LPV pressure sensors are tested in practical applications, including wearable health monitoring and force feedback of robotic tactile sensing.

Highly Sensitive and Flexible Capacitive Pressure Sensors Based on Vertical Graphene and Micro-Pyramidal Dielectric Layer.

Many practical applications require flexible high-sensitivity pressure sensors. However, such sensors are difficult to achieve using conventional materials. Engineering the morphology of the electrodes and the topography of the dielectrics has been demonstrated to be effective in boosting the sensing performance of capacitive pressure sensors. In this study, a flexible capacitive pressure sensor with high sensitivity was fabricated by using three-dimensional vertical graphene (VG) as the electrode and micro-pyramidal polydimethylsiloxane (PDMS) as the dielectric layer. The engineering of the VG morphology, size, and interval of the micro-pyramids in the PDMS dielectric layer significantly boosted the sensor sensitivity. As a result, the sensors demonstrated an exceptional sensitivity of up to 6.04 kPa-1 in the pressure range of 0-1 kPa, and 0.69 kPa-1 under 1-10 kPa. Finite element analysis revealed that the micro-pyramid structure in the dielectric layer generated a significant deformation effect under pressure, thereby ameliorating the sensing properties. Finally, the sensor was used to monitor finger joint movement, knee motion, facial expression, and pressure distribution. The results indicate that the sensor exhibits great potential in various applications, including human motion detection and human-machine interaction.

Mesoporous Cobalt Oxide (CoOx) Nanowires with Different Aspect Ratios for High Performance Hybrid Supercapacitors.

Cobalt oxide (CoOx) nanowires have been broadly explored as advanced pseudocapacitive materials owing to their impressive theoretical gravimetric capacity. However, the traditional method of compositing with conductive nanoparticles to improve their poor conductivity will unpredictably lead to a decrease in actual capacity. The amelioration of the aspect ratio of the CoOx nanowires may affect the pathway of electron conduction and ion diffusion, thereby improving the electrochemical performances. Here, CoOx nanowires with various aspect ratios were synthesized by controlling hydrothermal temperature, and the CoOx electrodes achieve a high gravimetric specific capacity (1424.8 C g-1) and rate performance (38% retention at 100 A g-1 compared to 1 A g-1). Hybrid supercapacitors (HSCs) based on activated carbon anode reach an exceptional specific energy of 61.8 Wh kg-1 and excellent cyclic performance (92.72% retention, 5000 cycles at 5 A g-1). The CoOx nanowires exhibit great promise as a favorable cathode material in the field of high-performance supercapacitors (SCs).

Thermal degradation and flame retardancy of nylon 6/aluminum methylmethoxy phosphonate composites.

An aluminum methylmethoxyphosphonate (AlPo)-based flame retardant (FR) was synthesized. Thermal degradation and flame retardancy of nylon 6 (PA6)/AlPo composites were examined and compared with PA6/commercial aluminum diethylphosphinate (AlPi) composites. The PA6/AlPo composite achieved a V-0 rating at 20 wt% loading during the UL-94 test, and it exhibited the formation of a charred layer that protected the polymer from burning and reduced the release of gases during the combustion of PA6. AlPo demonstrated exceptional performance in gaseous and condensed phases in the PA6 matrix, whereas AlPi only worked in the gaseous phase. The differences between the thermal degradation mechanisms and flame retardancies of AlPi and AlPo were investigated via Fourier-transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and cone calorimetry. A suitable degradation mechanism was proposed to aid the development of flame retardants in the future.

Optimization of 3D Printing Technology for Fabrication of Dental Crown Prototype Using Plastic Powder and Zirconia Materials.

This research was aimed at developing a dental prototype from 3D printing technology using a synthetic filament of polylactic acid (PLA) and zirconium dioxide (ZrO2) with glycerol and silane coupling agent as a binder. A face-centered central composite design was used to study the effects of the filament extrusion parameters and the 3D printing parameters. Tensile and compressive testing was conducted to determine the stress-strain relationship of the filaments. The yield strength, elongation percentage and Young's modulus were also calculated. Results showed the melting temperature of 193 °C, ZrO2 ratio of 17 wt.% and 25 rpm screw speed contributed to the highest ultimate tensile strength of the synthetic filament. A Nozzle temperature of 210 °C and an infill density of 100% had the most effect on the ultimate compressive strength whilst the printing speed had no significant effects. Differential scanning calorimetry (DSC) was used to study the thermal properties and percentage of crystallinity of PLA filaments. The addition of glycerol and a silane coupling agent increased the tensile strength and filament size. The ZrO2 particles induced the crystallization of the PLA matrix. A higher crystallization was also obtained from the annealing treatment resulting in the greater thermal resistance performance of the dental crown prototype.

Vertical Graphene Canal Mesh for Strain Sensing with a Supereminent Resolution.

The development of microstrain sensors offers significant prospects in diverse applications, such as microrobots, intelligent human-computer interaction, health monitoring, and medical rehabilitation. Among strain sensor materials, vertical graphene (VG) has demonstrated considerable potential as a resistive material; however, VG-based strain sensors with high resolution are yet to be developed. In addition, the detection mechanism of VG has not been extensively investigated. Herein, we developed a VG canal mesh (VGCM) to fabricate a flexible strain sensor for ultralow strain sensing, achieving an accurate response to strains as low as 0.1‰ within a total strain range of 0%-4%. The detection of such low strains is due to the rigorous structural design and strain concentration effect of the three-dimensional micronano structure of the VGCM. Through experimental results and theoretical simulation, the evolution of microcracks in VG and the sensing mechanism of VG and VGCM are elaborated, and the unique advantages of VGCM are revealed. Finally, the VGCM-based strain sensors are proposed as portable breathing test equipment for rapid breathing detection.

Porous Carbon Boosted Non-Enzymatic Glutamate Detection with Ultra-High Sensitivity in Broad Range Using Cu Ions.

A non-enzymatic electrochemical sensor, based on the electrode of a chitosan-derived carbon foam, has been successfully developed for the detection of glutamate. Attributed to the chelation of Cu ions and glutamate molecules, the glutamate could be detected in an amperometric way by means of the redox reactions of chelation compounds, which outperform the traditional enzymatic sensors. Moreover, due to the large electroactive surface area and effective electron transportation of the porous carbon foam, a remarkable electrochemical sensitivity up to 1.9 × 104 µA/mM∙cm2 and a broad-spectrum detection range from nM to mM scale have been achieved, which is two-orders of magnitude higher and one magnitude broader than the best reported values thus far. Furthermore, our reported glutamate detection system also demonstrates a desirable anti-interference ability as well as a durable stability. The experimental revelations show that the Cu ions chelation-assisted electrochemical sensor with carbon foam electrode has significant potential for an easy fabricating, enzyme-free, broad-spectrum, sensitive, anti-interfering, and stable glutamate-sensing platform.

Quantitative Interpretation of Electromagnetic Interference Shielding Efficiency: Is It Really a Wave Absorber or a Reflector?

As electromagnetic (EM) pollution continues to increase, electromagnetic interference (EMI) shielding materials have been intensively evaluated in terms of two main shielding mechanisms of reflection and absorption. Since the shielding effectiveness (SE) is represented in the logarithmic scale and in a coupled way of transmission (SET), absorption (SEA), and reflection (SER), often there is a misinterpretation that the EM wave reflectors are regarded as EM wave-absorbing materials. Surprisingly, we found that many materials reported as an EM wave absorber in the literature provide, in fact, less than 50% of EM wave-absorbing capability, i.e., over 50% of EM wave-reflecting feature. According to the theory and definition of EMI SE, the absorption-dominant EMI shielding materials should have the ratio of absorption to incident energy (A) as A > 0.5, which corresponds to a necessary condition that SER < 3.01 dB. The SER subsequently gives SEA in relation to SET. Using this criterion, we classified the EMI shielding materials with their shielding mechanism. The proposed methodology provides significant insight into the evaluation and development of EMI shielding materials.

Effects of functional carbon nanodots on water hyacinth response to Cd/Pb stress: Implication for phytoremediation.

Phytoremediation is one of the effective, economic and green approaches to cope with the increasing worldwide heavy metal (HM) pollution. Here, we evaluate the effects of functional carbon nanodots (FCNs) against the hyperaccumulation capacity as well as the physiological and genetic responses of water hyacinth under Pb2+ or/and Cd2+ stress. The bioaccumulation efficiency, HM content and transfer factor, biomass, root development, chlorophyll content, antioxidant system and genes expression are investigated at various concentration of HMs. Based on the excellent adsorption capacity and plant growth regulation ability, FCNs and nitrogen doped FCNs (N-FCNs) cooperate with water hyacinth to improve their HMs removal efficiencies. FCNs and N-FCNs immobilize excess HMs ions in plant, smartly regulate enzymatic levels to mitigate oxidative damage, as well as regulate the microelement uptake and related gene expression, thus improve plant tolerance against HMs stress. Although Pb and Cd have antagonistic effects on bioaccumulation of water hyacinth to the single metal, FCNs and N-FCNs can cooperate with water hyacinth to raise the removal efficiency of HMs in water, and enhance plant tolerance under Pb-Cd combined stress. The promotion effects of FCNs and N-FCNs on phytoremediation are more effective than conventional carbon nanomaterials, including carbon nanotubes and graphene oxides. These findings demonstrate that the application of FCNs or N-FCNs can improve the phytoremediation efficiency in the restoration of HMs contaminated water area. This study provides important insights into the possibility of using FCNs-based nanomaterials and water hyacinth as synergistic system for remediation of Cd-Pb contaminated water area.

A Suggested Vacuum Bagging Process for the Fabrication of Single-Walled Carbon Nanotube/Epoxy Composites That Maximize Electromagnetic Interference Shielding Effectiveness.

We designed and tested a manufacturing process that resulted in the formation of composites with maximized electrical conductivity and optimized electromagnetic interference (EMI) shielding effectiveness (SE) properties. Single-walled carbon nanotube (SWCNT) paper, which is a microscopic aggregate of van der Waals force interaction, was impregnated with semi-cured epoxy to make SWCNT prepregs. These prepregs were completely cured into SWCNT/epoxy composites. Fabricating and curing processes were executed under proper temperature cycle depending on the time. We inspected SWCNT paper and the interfacial state between the SWCNTs and epoxy in the composite with a field emission-scanning electron microscopy and calculated the SWCNT weight fraction through thermogravimetric analysis measurements. Using these observations, electrical conductivity and EMI SE were investigated according to thickness which could be controlled by the suggested manufacturing process as 1-, 5- and 10-layer composites. Finally, we determined ideal composite thickness and the associated number of prepreg layers using skin depth theory.

Heat dissipative mechanical damping properties of EPDM rubber composites including hybrid fillers of aluminium nitride and boron nitride.

As highly integrated electronic devices and automotive parts are becoming used in high-power and load-bearing systems, thermal conductivity and mechanical damping properties have become critical factors. In this study, we applied two different fillers of aluminium nitride (AlN) and boron nitride (BN), having polygonal and platelet shapes, respectively, into ethylene-propylene-diene monomer (EPDM) rubber to ensure improved thermo-mechanical properties of EPDM composites. These two different shapes are considered advantageous in providing effective pathways of phonon transfer as well as facilitating sliding movement of packed particles. When the volume ratio of AlN : BN was 1 : 1, the thermal conductivity of the hybrid-filler system (EPDM/AlN/BN) increased in comparison to that of the single-filler system (EPDM/AlN) of 3.03 to 4.76 W m-1 K-1. The coefficient of thermal expansion (CTE) and thermal distortion parameter (TDP) substantially decreased from 59.3 ppm °C-1 and 17.5 m K-1 of EPDM/AlN, to 39.7 ppm °C-1 and 8.4 m K-1 of EPDM/AlN/BN, representing reductions of 33 and 52%, respectively. Moreover, the damping coefficient of EPDM/AlN/BN was greatly increased to 0.5 of at 50 °C, compared to 0.03 of neat EPDM. These excellent performances likely stem from the effective packing of AlN/BN hybrid fillers, which could induce facile energy transfer and effective energy dissipation by the sliding movement of the adjacent hybrid fillers in the EPDM matrix.

Author Correction: Solvent-free bulk polymerization of lignin-polycaprolactone (PCL) copolymer and its thermoplastic characteristics.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Quantitative Electrode Design Modeling of an Electroadhesive Lifting Device Based on the Localized Charge Distribution and Interfacial Polarization of Different Objects.

Electroadhesive devices can lift materials of different shapes and various types using the electrostatic force developed at the interface between the device and the object. More specifically, the electrical potential generated by the device induces opposite charges on the object to give electrostatic Maxwell force. Although this technology has a great deal of potential, the key design factors based on the fundamental principles of interfacial polarization have yet to be clearly identified. In this study, we identify that the lifting force is quantitatively related to the total length of the boundary edges of the electrodes, where the induced charges are selectively concentrated. We subsequently propose a model equation that can predict the electrostatic lifting forces for different object materials as a function of the applied voltage, impedance, and electrode-boundary length. The model is based on the fact that the amount of induced charges should be concentrated where the equipotential field distance is minimal. We report that the impedance magnitude is correlated with the electroadhesive lifting forces by analyzing the impedance characteristics of objects made of different materials (e.g., paper, glass, or metal), as attached in situ to the electroadhesive device.

Non-Einstein Viscosity Phenomenon of Acrylonitrile-Butadiene-Styrene Composites Containing Lignin-Polycaprolactone Particulates Highly Dispersed by High-Shear Stress.

Lignin powder was modified via ring-opening polymerization of caprolactone to form a lignin-polycaprolactone (LPCL) particulate. The LPCL particulates were mixed with an acrylonitrile-butadiene-styrene (ABS) matrix at an extremely high rotational speed of up to 3000 rpm, which was achieved by a closed-loop screw mixer and in-line melt extruder. Using this high-shear extruding mixer, the LPCL particulate size was controlled in the range of 3395 nm (conventional twin-screw extrusion) down to 638 nm (high-shear mixer of 3000 rpm) by altering the mixing speed and time. The resulting LPCL/ABS composites clearly showed non-Einstein viscosity phenomena, exhibiting reduced viscosity (2130 Pa·s) compared to the general extruded composite one (4270 Pa·s) at 1 s-1 and 210 °C. This is due to the conformational rearrangement and the increased free volume of ABS molecular chains in the vicinity of LPCL particulates. This was supported by the decreased glass transition temperature (T g, 83.7 °C) of the LPCL/ABS composite specimens, for example, giving a 21.8% decrement compared to that (107 °C) of the neat ABS by the incorporation of 10 wt % LPCL particulates in ABS. The LPCL particulate morphology, damping characteristics, and light transmittance of the developed composites were thoroughly investigated at various levels of applied shear rates and mixing conditions. The non-Einstein rheological phenomena stemming from the incorporation of LPCL particulates suggest an interesting plasticization methodology: to improve the processability of high-loading filler/polymer composites and ultra-high molecular weight polymers that are difficult to process because of their high viscosity.

Solvent-free bulk polymerization of lignin-polycaprolactone (PCL) copolymer and its thermoplastic characteristics.

The pristine lignin molecules contain multiple reactive hydroxyl [OH] groups, some of which undergo limited polymerization depending on their configuration (aromatic or aliphatic) or conformation. The key issue in lignin-polymerization is to quantify the number of hydroxyl groups in the pristine molecules for subsequent activation to specific lignin-polymer chain lengths or degree of grafting. In this study, using ε-caprolactone (CL) as a reactive solvent, we successfully polymerized CL on the [OH] sites in the kraft lignin macromonomers (LM, Mw = 1,520 g mol-1), which resulted in a thermoplastic lignin-polycaprolactone (PCL) grafted copolymer. We found that the average number of [OH] groups in the LM was 15.3 groups mol-1, and further detected 40-71% of the [OH] groups in the CL bulk polymerization. The degree of polymerization of PCL grown on each [OH] site ranged between 7 and 26 depending on the reaction conditions ([CL]/[OH] and reaction-time) corresponding to 4,780 and 32,600 g mol-1 of PCL chains per a LM. The thermoplastic characteristics of the synthesized lignin-PCL copolymers were established by the melt viscosity exhibiting a shear-thinning behavior, e.g., 921 Pa.s at 180 °C. The thermal stability was remarkable providing a Tid (2% of weight loss) of 230 °C of the copolymers, compared with 69 °C for the pristine lignin.

Experimental Investigation on Vertically Oriented Graphene Grown in a Plasma-Enhanced Chemical Vapor Deposition Process.

Vertically oriented graphene (VG) with three-dimensional architecture has been proved to exhibit unique properties, and its particular morphology has been realized by researchers to be crucial for its performance in practical applications. In this study, we investigated the morphology evolution of VG films synthesized by the plasma-enhanced chemical vapor deposition process, including porous graphene film, graphene wall, and graphene forest. This study reveals that the morphology of VG is controlled by a combination of the deposition and etching effects and tailored by the growth conditions, such as plasma source power and growth time and temperature. The plasma source power relates to the number of branches of VG, and the growth temperature relates to the thickness of each VG flake, whereas the growth time determines the height of VG. Finally, the electrochemical properties of VG films along with morphology evolution are investigated by fabricating as VG-based supercapacitor electrodes.