High temperature oxidative resistance of polyacrylonitrile-methylmethacrylate copolymer powder converting to a carbonized monolith

Controlling the physical properties of polyacrylonitrile by strontium hexaferrite nanoparticles

The formulation of polymer with embedded magnetic nanoparticles results in promising nanocomposites for smart and analytical applications. Nanocomposites containing polyacrylonitrile (PAN) and different mass contents of strontium hexaferrite (SFO) were prepared using the casting method. The nanocomposite samples were characterized by using different techniques such as field-emission scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, differential scanning calorimetry, and thermogravimetric analysis. Dielectric investigations of SFO/PAN nanocomposites showed that the permittivity and conductivity are considerably enhanced as the content of SFO increased. Optical properties revealed that the absorption and transmittance spectra were significantly affected by adding SFO nanoparticles to the PNA polymer matrix. To investigate the magnetic properties of the nanocomposite samples, the vibrating sample magnetometer was used. The magnetic hysteresis loops illustrated the ferromagnetic nature of SFO/PAN nanocomposites. Different magnetic parameters were given, and they depend on the content of PAN in the nanocomposites.

Preparation and tribological properties of multi-layer graphene/silicon dioxide composites-based solid lubricant coatings at elevated temperatures

The solid lubricating coatings have an important role in hot metal forming. However, traditional lubricants cannot be applied to the harsh working conditions. In this investigation, the novel solid lubricant coatings including multi-layer graphene (MLG)/silicon dioxide (SiO₂) composites and sodium metaphosphate phosphate were prepared. The high-temperature tribological properties of the solid lubricant coatings were investigated by friction and wear tester. The experimental results showed that SiO₂ nanoparticles were evenly grafted by sol-gel method on the surface of MLG, forming MLG/SiO₂ composites. MLG/SiO₂ composites presented excellent thermal stability at 800°C. In the range of 400-800°C, the average coefficients of friction (COFs) were decreased from 0.3936 to 0.3663, and then increased from 0.3663 to 0.4226. Based on the analysis of wear scar, the lubrication mechanisms of the solid lubricating coatings were proposed. The low interlayer shear of MLG and the ball bearing of SiO₂ nanoparticles are the main reason for the reduction of COFs. In addition, the tribo-chemical reaction film formed on the frictional interface could protect the contact surfaces from severe damage. The findings would be beneficial for developing novel lubricants for hot metal forming process.

Dual Structure-Material Design of Separators toward Dendrite-Free Lithium Metal Anodes

The practical applications of lithium metal anodes have been severely hindered by the Li dendrite issue. Herein, a dual structure-material design strategy was developed to fabricate a new type of separator using interconnected hollow porous polyacrylonitrile (PAN) nanofibers (HPPANF), which delivered controllable and dendrite-free Li depositions. The interconnected mesopores on HPPANF bridged the hollow interiors with the outside voids among the fibers, enabling outstanding electrolyte uptake capabilities for high ion conductivity, and nano-level wetted electrolyte/anode interface for uniform Li plating/stripping. In parallel, the HPPANF separator enriched with polar groups acted as an exceptional polymer-based solid-state electrolyte, providing 3D ion channels for the transport of Li ions. Benefiting from the dual structure-material design, the HPPANF separator induced uniform Li ion flux for dendrite-free Li depositions, which caused enhanced cycling stability (1300 h, 3 mA cm^-2 ). This work demonstrates a new method to stabilize Li metal anodes through rational separator design.

Influence of various shapes of alumina nanoparticle in integrated polysulfone membrane for separation of lignin from woody biomass and salt rejection

Lignin valorization is essential in proposing an economic perspective as a raw material for valuable compounds. The bio-refineries require adequate processing to improve the high purity of lignin. Meanwhile, nanofiltration is fascinated attention to obtain high purity value-added products. The effect of alumina nanoparticles on the fabrication of mixed matrix membranes (MMM) has contributed to improvising filtration performance. However, incorporating nanoparticles is a significant issue regarding appropriate size and shape integrated into membrane for better filtration efficiency. The influence of shapes of alumina nanoparticles has been investigated into polysulfone (PSf) membranes for salt and lignin separation. The morphology of alumina was tailored with spindle, cubic, and spherical shapes synthesized at a different calcination temperature of 250, 500, 700 and 900 °C, respectively. The phase transitions were confirmed in X-ray diffraction (XRD) analysis, and the shape of the nanoparticles was observed in a high-resolution transmission electron microscope (HRTEM). The separation efficiency of membranes was tested with salt rejection using sodium sulfate, calcium chloride, potassium sulfate, and sodium chloride. The lignin was extracted from prehydrolysed sawdust, and the synthetic lignosulfonic acid sodium salt solution was separated. The higher lignin rejection of 98.6% and 97.9% were obtained for cubic shaped gamma phase alumina mixed matrix membrane. The high rejection of lignin occurred due to narrow pores channels that could resist the transfer of lignin through the membrane. The results proved that the controllable organization of PSf/alumina mixed matrix membranes could apply for lignocellulose compounds with good efficiency.

Advances in Manufacturing Composite Carbon Nanofiber-Based Aerogels

This article provides an overview on manufacturing composite carbon nanofiber-based aerogels through freeze casting technology. As known, freeze casting is a relatively new manufacturing technique for generating highly porous structures. During the process, deep cooling is used first to rapidly solidify a well-dispersed slurry. Then, vacuum drying is conducted to sublimate the solvent. This allows the creation of highly porous materials. Although the freeze casting technique was initially developed for porous ceramics processing, it has found various applications, especially for making aerogels. Aerogels are highly porous materials with extremely high volume of free spaces, which contributes to the characteristics of high porosity, ultralight, large specific surface area, huge interface area, and in addition, super low thermal conductivity. Recently, carbon nanofiber aerogels have been studied to achieve exceptional properties of high stiffness, flame-retardant and thermal-insulating. The freeze casting technology has been reported for preparing carbon nanofiber composite aerogels for energy storage, energy conversion, water purification, catalysis, fire prevention etc. This review deals with freeze casting carbon nanofiber composite materials consisting of functional nanoparticles with exceptional properties. The content of this review article is organized as follows. The first part will introduce the general freeze casting manufacturing technology of aerogels with the emphasis on how to use the technology to make nanoparticle-containing composite carbon nanofiber aerogels. Then, modeling and characterization of the freeze cast particle-containing carbon nanofibers will be presented with an emphasis on modeling the thermal conductivity and electrical conductivity of the carbon nanofiber network aerogels. After that, the applications of the carbon nanofiber aerogels will be described. Examples of energy converters, supercapacitors, secondary battery electrodes, dye absorbents, sensors, and catalysts made from composite carbon nanofiber aerogels will be shown. Finally, the perspectives to future work will be presented.

Effect of Pyrolysis Temperature on the Electrical Property and Photosensitivity of a PAN-PMMA Derived Carbon Fiber

Fibers are promising materials being utilized in electronics, principally in the areas of capacitors and sensors. In this study, we examine the effect of pyrolysis temperature on the electrical conductive behavior and photosensitivity of a carbon-based fiber, which was made by electrospinning a polymer solution containing polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), and dimethylformamide (DMF). Converting the polymeric fiber into a carbon fiber was performed through the controlled pyrolysis during which oxidation, stabilization, and carbonization happened. After oxidation at an elevated temperature, the linear polymer fiber was stabilized to have a backbone structure. Then the oxidized fiber was treated in an even higher temperature range to be partially carbonized under the protection of argon gas. We utilized multiple samples of the fibers treated at various pyrolysis temperatures inside a heat furnace and examined the effects of the temperatures on the properties. The partially carbonized fiber is highly active in view of electron generation under photon energy excitation. The unique electrical and photovoltaic property are due to their semiconducting behavior. The morphology of the specimen before and after the pyrolysis was examined using scanning electron microscopy (SEM). The SEM images displayed the shrinkage of the fiber due to the pyrolysis. There are two stages of pyrolysis kinetics. Stage I is related to the oxidation of the PAN polymer. Stage II is associated with the carbonization and the activation energy of carbonization is calculated as 118 kJ/mol.

Synthetic polymers blend used in the production of high activated carbon for pesticides removals from liquid phase

For the activated carbon (AC) production, we used the most common industrial and consumer solid waste, namely polyethyleneterephthalate (PET), alone or blended with other synthetic polymer such polyacrylonitrile (PAN). By mixing PET, with PAN, an improvement in the yield of the AC production was found and the basic character and some textural and chemical properties were enhanced. The PET-PAN mixture was subjected to carbonisation, with a pyrolysis yield of 31.9%, between that obtained with PET (16.9%) or PAN (42.6%) separately. The AC revealed a high surface area (1400, 1230 and 1117 m² g^-1) and pore volume (0.46, 0.56 and 0.50 cm³ g^-1), respectively, for PET, PAN and PET-PAN precursors. Selected ACs were successfully tested for 4-chloro-2-methylphenoxyacetic acid (MCPA) and diuron removal from the liquid phase, showing a higher adsorption capacity (1.7 and 1.2 mmol g^-1, respectively, for MCPA and diuron) and good fits with the Langmuir (PET) and Freundlich equation (PAN and PET-PAN blend). With MCPA, the controlling factor to the adsorption capacity was the porous volume and the average pore size. Concerning diuron, the adsorption was controlled essentially by the external diffusion. A remarkable result is the use of different synthetic polymers wastes, as precursors for the production of carbon materials, with high potential application on the pesticides removals from the liquid phase.

The formation of conjugated structure and its transformation to pseudo-graphite structure during thermal treatment of polyacrylonitrile

Three types of polyacrylonitrile (PAN) were considered in order to investigate the effect of molecular composition and configuration on the formation of conjugated structures during stabilization and the conversion of that to pseudo-graphite sheets after carbonization. The stabilization process was performed in an inert or oxidative atmosphere with a temperature ramp from 180°Cto 280°C. The thermal behavior was studied by differential scanning calorimetry, and the change of chemical groups and conjugated structures was detected by in situ measurement of infrared (Fourier transform infrared) and ultraviolet–visible spectroscopy, respectively. The carbonization process of the stabilized samples was performed using a thermogravimetric analyzer under nitrogen atmosphere in the temperature range of 150°C–1200°C, and Raman spectra were applied to study the pseudo-graphite sheets of the residuals. It is suggested that the introduction of comonomer or the improvement of the isotactic regularity of the polymer chain are helpful to promote the stabilization reactions and accelerate the formation of conjugated structures rather than the extent of conjugation during stabilization in nitrogen. Moreover, they are also beneficial to obtain higher degree of graphitization and larger size of the pseudo-graphite sheets with less structural defects after carbonization. While stabilization is performed in air, atactic PAN copolymer has the highest extent of stabilization among these three PAN samples, but they are extremely close. PAN samples with comonomer or higher isotacticity still show a little advantage in the formation speed of the conjugated structures. After carbonization, PAN with higher isotacticity has the highest carbon yield and graphitization degree and the largest size of pseudo-graphite sheets with least structural defects. In addition, the presence of oxygen during stabilization is contributory to increase the extent of stabilization and generate some bigger conjugated structures, which leads to obtain higher graphitization degree and larger size of pseudo-graphite sheets, but it also brings more structural defects.

High Temperature Epoxy Foam: Optimization of Process Parameters

For many years, reduction of fuel consumption has been a major aim in terms of both costs and environmental concerns. One option is to reduce the weight of fuel consumers. For this purpose, the use of a lightweight material based on rigid foams is a relevant choice. This paper deals with a new high temperature epoxy expanded material as substitution of phenolic resin, classified as potentially mutagenic by European directive Reach. The optimization of thermoset foam depends on two major parameters, the reticulation process and the expansion of the foaming agent. Controlling these two phenomena can lead to a fully expanded and cured material. The rheological behavior of epoxy resin is studied and gel time is determined at various temperatures. The expansion of foaming agent is investigated by thermomechanical analysis. Results are correlated and compared with samples foamed in the same temperature conditions. The ideal foaming/gelation temperature is then determined. The second part of this research concerns the optimization of curing cycle of a high temperature trifunctional epoxy resin. A two-step curing cycle was defined by considering the influence of different curing schedules on the glass transition temperature of the material. The final foamed material has a glass transition temperature of 270 °C.

Encapsulation of epoxy and amine curing agent in PAN nanofibers by coaxial electrospinning for self-healing purposes

Encapsulation of epoxy resin and amine based curing agent in core–shell nanofibres using coaxial electrospinning.

Design and development of a poly(acrylonitrile-co-methyl methacrylate) copolymer to improve the viscoelastic and surface properties critical to scratch resistance

The present paper reports the design, development and evaluation of methyl methacrylate (MMA) and acrylonitrile (AN) copolymers to improve viscoelastic and surface properties critical to scratch resistance.

Evidence of covalent synergy in silicon-sulfur-graphene yielding highly efficient and long-life lithium-ion batteries

Silicon has the potential to revolutionize the energy storage capacities of lithium-ion batteries to meet the ever increasing power demands of next generation technologies. To avoid the operational stability problems of silicon-based anodes, we propose synergistic physicochemical alteration of electrode structures during their design. This capitalizes on covalent interaction of Si nanoparticles with sulfur-doped graphene and with cyclized polyacrylonitrile to provide a robust nanoarchitecture. This hierarchical structure stabilized the solid electrolyte interphase leading to superior reversible capacity of over 1,000 mAh g⁻¹ for 2,275 cycles at 2 A g⁻¹. Furthermore, the nanoarchitectured design lowered the contact of the electrolyte to the electrode leading to not only high coulombic efficiency of 99.9% but also maintaining high stability even with high electrode loading associated with 3.4 mAh cm⁻². The excellent performance combined with the simplistic, scalable and non-hazardous approach render the process as a very promising candidate for Li-ion battery technology.

Silicon anodes are promising for lithium-ion battery development, but suffer from problems such as undesired volume expansion and solid-electrolyte interface formation. Here, the authors report a hierarchical silicon-sulfur-graphene composite anode which mitigates the problems leading to high performance.

Morphology and electrical properties of multi-walled carbon nanotube/carbon aerogel prepared by using polyacrylonitrile as precursor

MWCNT/PAN aerogel composites were synthesized using the Thermal Induced Phase Separation (TIPS) procedure.

Encapsulation of therapeutic lavender oil in an electrolyte assisted polyacrylonitrile nanofibres for antibacterial applications

Electrospinning, a feasible nanotechnology, has been exploited to engineer polyacrylonitrile (PAN) nanofibrous mats enclosing a representative hydrophobic drug like essential oil of lavender.