Effect of Red Mud Addition on Electrical and Magnetic Properties of Hemp-Derived-Biochar-Containing Epoxy Composites.

Waste stream valorization is a difficult task where the economic and environmental issues must be balanced. The use of complex metal-rich waste such as red mud is challenging due to the wide variety of metal oxides present such as iron, aluminum, and titanium. The simple separation of each metal is not economically feasible, so alternative routes must be implemented. In this study, we investigated the use of red mud mixed with hemp waste to produce biochar with high conductivity and good magnetic properties induced by the reduction of the metal oxides present in the red mud through carbothermal processes occurring during the co-pyrolysis. The resulting biochar enriched with thermally-reduced red mud is used for the preparation of epoxy-based composites that are tested for electric and magnetic properties. The electric properties are investigated under DC (direct current) regime with or without pressure applied and under AC (alternating current) in a frequency range from 0.5 up to 16 GHz. The magnetic measurements show the effective tailoring of hemp-derived biochar with magnetic structures during the co-pyrolytic process.

Enhancement and Evaluation of Interfacial Adhesion between Active Screen Plasma Surface-Functionalised Carbon Fibres and the Epoxy Substrate.

This paper investigated the modification of the advanced active screen plasma (ASP) technology on PAN-derived carbon fibres (CFs) with gas mixtures of N2-H2 and N2-H2-Ar, separately. A more-than-30% improvement was found in the interfacial shear strength (IFSS) between the modified CFs and the epoxy substrate in the resulting composites, as disclosed by single fibre push-out tests. Based on the study of surface morphology, surface chemistry and water-sorption behaviour, the interfacial adhesion enhancement mechanisms were attributed to (1) the increased chemical bonding between the introduced functional groups on the fibre surface and the matrix; (2) the improved surface hydrophilicity of CFs; and (3) the enhanced van der Waals bonding due to the removal of surface contaminations.

Pressure-Responsive Conductive Poly(vinyl alcohol) Composites Containing Waste Cotton Fibers Biochar.

The development of responsive composite materials is among the most interesting challenges in contemporary material science and technology. Nevertheless, the use of highly expensive nanostructured fillers has slowed down the spread of these smart materials in several key productive sectors. Here, we propose a new piezoresistive PVA composite containing a cheap, conductive, waste-derived, cotton biochar. We evaluated the electromagnetic properties of the composites under both AC and DC regimes and as a function of applied pressure, showing promisingly high conductivity values by using over 20 wt.% filler loading. We also measured the conductivity of the waste cotton biochar from 20 K up to 350 K observing, for the first time, hopping charge transport in biochar materials.

Reply to Meier, R.J. Comment on "Tagliaferro et al. Introducing the Novel Mixed Gaussian-Lorentzian Lineshape in the Analysis of the Raman Signal of Biochar. Nanomaterials 2020, 10, 1748".

First of all, we thank Dr. Meier for his thorough reading and constructive remarks [...].

Mechanical Properties, Surface Assessment, and Structural Analysis of Functionalized CFRPs after Accelerated Weathering.

The present study focuses on the effect of two novel carbon fibre surface treatments, electropolymerisation of methacrylic acid and air pressure plasma, on the mechanical properties and structural integrity of carbon-fibre-reinforced composites under operational conditions. Extensive mechanical testing was applied, both in nano- and macro-scale, to assess the performance of the composites and the interphase properties after ultraviolet/humidity weathering. The results of the mechanical assessment are supported by structure, surface, and chemistry examination in order to reveal the failure mechanism of the composites. Composites with the electropolymerisation treatment exhibited an increase of 11.8% in interlaminar shear strength, while APP treatment improved the property of 23.9%, rendering both surface treatments effective in increasing the fibre-matrix adhesion. Finally, it was proven that the developed composites can withstand operational conditions in the long term, rendering them suitable for a wide variety of structural and engineering applications.

Innovative Biochar-Based Composite Fibres from Recycled Material.

Carbon materials are becoming crucial in several industrial sectors. The drawbacks of these materials include their high cost and oil-based essence. In recent years, recycled materials have become possible alternative sources of carbon with several advantages. Firstly, the production of this alternative source of carbon may help to reduce biomass disposal, and secondly, it contributes to CO2 sequestration. The use of carbon derived from recycled materials by a pyrolysis treatment is called biochar. Here, we present composite materials based on different biochar filler contents dispersed in several thermoplastic polymer matrixes. Electrical conductivity and tensile break strength were investigated together with the material characterisation by DTA/TGA, XRD, and scanning electron microscopy (SEM) imaging. Materials with good flexibility and electrical conductivity were obtained. The local ordering in composites resembles both biochar and polymer ordering. The similarity between biochar and carbon nanotubes' (CNTs) XRD patterns may be observed. As biochar is highly cost-effective, the proposed composites could become a valid substitute for CNT composites in various applications.

High Frequency Electromagnetic Shielding by Biochar-Based Composites.

We report on the microwave shielding efficiency of non-structural composites, where inclusions of biochar-a cost effective and eco-friendly material-are dispersed in matrices of interest for building construction. We directly measured the complex permittivity of raw materials and composites, in the frequency range 100 MHz-8 GHz. A proper permittivity mixing formula allows obtaining other combinations, to enlarge the case studies. From complex permittivity, finally, we calculated the shielding efficiency, showing that tailoring the content of biochar allows obtaining a desired value of electromagnetic shielding, potentially useful for different applications. This approach represents a quick preliminary evaluation tool to design composites with desired shielding properties starting from physical parameters.

Potential natural polymer-based nanofibres for the development of facemasks in countering viral outbreaks.

The global coronavirus disease 2019 (COVID-19) pandemic has rapidly increased the demand for facemasks as a measure to reduce the rapid spread of the pathogen. Throughout the pandemic, some countries such as Italy had a monthly demand of ca. 90 million facemasks. Domestic mask manufacturers are capable of manufacturing 8 million masks each week, although the demand was 40 million per week during March 2020. This dramatic increase has contributed to a spike in the generation of facemask waste. Facemasks are often manufactured with synthetic materials that are non-biodegradable, and their increased usage and improper disposal are raising environmental concerns. Consequently, there is a strong interest for developing biodegradable facemasks made with for example, renewable nanofibres. A range of natural polymer-based nanofibres has been studied for their potential to be used in air filter applications. This review article examines potential natural polymer-based nanofibres along with their filtration and antimicrobial capabilities for developing biodegradable facemask that will promote a cleaner production.

Introducing the Novel Mixed Gaussian-Lorentzian Lineshape in the Analysis of the Raman Signal of Biochar.

In this research, an innovative procedure is proposed to elaborate Raman spectra obtained from nanostructured and disordered solids. As a challenging case study, biochar, a bio-derived carbon based material, was selected. The complex structure of biochar (i.e., channeled surface, inorganic content) represents a serious challenge for Raman characterization. As widely reported, the Raman spectra are closely linked to thermal treatments of carbon material. The individual contributions to the Raman spectra are difficult to identify due to the numerous peaks that contribute to the spectra. To tackle this problem, we propose a brand new approach based on the introduction, on sound theoretical grounds, of a mixed Gaussian--Lorentzian lineshape. As per the experimental part, biochar samples were carbonized in an inert atmosphere at various temperatures and their respective spectra were successfully decomposed using the new lineshape. The evolution of the structure with carbonization temperature was investigated by Raman and XRD analysis. The results of the two techniques fairly well agree. Compared to other approaches commonly reported in the literature this method (i) gives a sounder basis to the lineshape used in disordered materials, and (ii) appears to reduce the number of components, leading to an easier understanding of their origin.

Comparative Physical-Mechanical Properties Assessment of Tailored Surface-Treated Carbon Fibres.

Carbon Fibres (CFs) are widely used in textile-reinforced composites for the construction of lightweight, durable structures. Since their inert surface does not allow effective bonding with the matrix material, the surface treatment of fibres is suggested to improve the adhesion between the two. In the present study, different surface modifications are compared in terms of the mechanical enhancement that they can offer to the fibres. Two main advanced technologies have been investigated; namely, plasma treatment and electrochemical treatment. Specifically, active screen plasma and low-pressure plasma were compared. Regarding the electrochemical modification, electrochemical oxidation and electropolymerisation of monomer solutions of acrylic and methacrylic acids, acrylonitrile and N-vinyl pyrrolidine were tested for HTA-40 CFs. In order to assess the effects of the surface treatments, the morphology, the physicochemical properties, as well as the mechanical integrity of the fibres were investigated. The CF surface and polymeric matrix interphase adhesion in composites were also analysed. The improvement of the carbon fibre's physical-mechanical properties was evident for the case of the active screen plasma treatment and the electrochemical oxidation.

Development of Pressure-Responsive PolyPropylene and Biochar-Based Materials.

In this research paper, we reported the synthesis of biochar-based composites using biochar derived from exhausted tea leaves and polypropylene. The resulting materials were deeply characterized investigating mechanical (dynamic mechanical thermal analysis), thermal (thermogravimetrical analysis and differential scanning calorimetry), morphological (field emission scanning microscopy) and electrical properties vs. temperature. Furthermore, electrical conductivity was studied for a wide range of pressures showing an irreversible plastic deformation. An increment of one order of magnitude in the conductivity was observed in the case of 40 wt% biochar loading, reaching a value of 0.2 S/m. The material produced exhibited the properties of an irreversible pressure sensor.

A Review of Non-Soil Biochar Applications.

Biochar is the solid residue that is recovered after the thermal cracking of biomasses in an oxygen-free atmosphere. Biochar has been used for many years as a soil amendment and in general soil applications. Nonetheless, biochar is far more than a mere soil amendment. In this review, we report all the non-soil applications of biochar including environmental remediation, energy storage, composites, and catalyst production. We provide a general overview of the recent uses of biochar in material science, thus presenting this cheap and waste-derived material as a high value-added and carbonaceous source.

Development of Coffee Biochar Filler for the Production of Electrical Conductive Reinforced Plastic.

In this work we focused our attention on an innovative use of food residual biomasses. In particular, we produced biochar from coffee waste and used it as filler in epoxy resin composites with the aim to increase their electrical properties. Electrical conductivity was studied for the biochar and biochar-based composite in function of pressure applied. The results obtained were compared with carbon black and carbon black composites. We demonstrated that, even if the coffee biochar had less conductivity compared with carbon black in powder form, it created composites with better conductivity in comparison with carbon black composites. In addition, composite mechanical properties were tested and they generally improved with respect to neat epoxy resin.

X-ray Absorption and Magnetic Circular Dichroism in CVD Grown Carbon Nanotubes.

Nowadays, a deep knowledge of procedures of synthesis of nanostructured materials plays an important role in achieving nano-materials with accurate and wanted properties and performances. Carbon-based nanostructured materials continue to attract a huge amount of research efforts, because of their wide-ranging properties. Using X-ray absorption (XAS) and X-ray magnetic circular dichroism (XMCD) spectroscopy in the soft X-ray regime, by the synchrotron radiation, we studied the L3,2 absorption edges of iron (Fe) nanoparticles, when they are embedded in oriented Multi Wall Carbon Nanotube (MWCNTs) layers grown by thermal Chemical Vapor Deposition (CVD) technique catalyzed by this transition metal. This could allow us to understand the valence state and role of catalysts and thus their electronic and magnetic structures. It is important to note that the control of the size of these tethered nanoparticles is of primary importance for the purpose of tailoring the physical and chemical properties of these hierarchical materials. The MWCNTs samples used in XAS and XMCD measurements were synthesized by the CVD technique. The actual measurements were carried out by the group NEXT of the INFN- LNF with the logistic experimental support of the INFM-CNR and the Synchrotron Elettra Trieste.

Low-Cost Carbon Fillers to Improve Mechanical Properties and Conductivity of Epoxy Composites.

In recent years, low-cost carbons derived from recycled materials have been gaining attention for their potentials as filler in composites and in other applications. The electrical and mechanical properties of polymer composites can be tuned using different percentages and different kind of fillers: either low-cost (e.g., carbon black), ecofriendly (e.g., biochar), or sophisticated (e.g., carbon nanotubes). In this work, the mechanical and electrical behavior of composites with biochar and multiwall carbon nanotubes dispersed in epoxy resin are compared. Superior mechanical properties (ultimate tensile strength, strain at break) were noticed at low heat-treated biochar (concentrations 2⁻4 wt %). Furthermore, dielectric properties in the microwave range comparable to low carbon nanotubes loadings can be achieved by employing larger but manageable amounts of biochar (20 wt %), rending the production of composites for structural and functional application cost-effective.

Analysis of MWCNT/epoxy composites at microwave frequency: reproducibility investigation.

A wide-band microwave characterization of nanocomposites based on commercial multiwalled carbon nanotubes (MWCNTs) and epoxy resin is presented. The sample preparation method is discussed in detail. Field emission scanning electron microscopy is used for morphological sample analysis of nanocomposites and MWCNTs. The complex permittivity is measured in a wide frequency band (3 to 18 GHz) using a commercial dielectric probe (Agilent 85070D) and a network analyzer (E8361A). A statistical analysis based on one-way analysis of variance (ANOVA) technique is performed. The aim of this statistical analysis is to investigate the influence of concentration of nanoparticles inside the polymer matrix on the complex permittivity. This can be significantly different in nanocomposites even if the samples have similar electrical properties.

High-temperature annealing effects on multiwalled carbon nanotubes: electronic structure, field emission and magnetic behaviors.

This work elucidates the effects of high-temperature annealing on the microscopic and electronic structure of multiwalled carbon nanotubes (MWCNTs) using high-resolution transmission electron microscopy, micro-Raman spectroscopy, X-ray diffraction, X-ray absorption near-edge structure (XANES) and valence-band photoemission spectroscopy (VBPES), respectively. The field emission and magnetization behaviors are also presented. The results of annealing are as follows: (1) MWCNTs tend to align in the form of small fringes along their length, promote graphitization and be stable in air, (2) XANES indicates an enhancement in oxygen content on the sample, implying that it can be adopted for sensing and storing oxygen gas, (3) the electron field emission current density (J) is enhanced and the turn-on electric field (E(TOE)) reduced, suggesting potential use in field emission displays and as electron sources in microwave tube amplifiers and (4) as-grown MWCNTs with embedded iron nanoparticles exhibits significantly higher coercivity approximately 750 Oe than its bulk counterpart (Fe(bulk) approximately 0.9 Oe), suggesting its potential use as low-dimensional high-density magnetic recording media.

Gas chromatography study of reagent degradation during chemical vapor deposition of carbon nanotubes.

The high temperature decomposition of three types of hydrocarbons, such as ethanol, camphor and cyclohexanol has been studied in order to determine the role played by the molecular structure of the precursor during the formation of carbon nanotubes (CNTs) catalyzed by ferrocene. This investigation will help in identifying the properties of the carbon precursor crucial to obtain the highest CNT selectivity and quality. A gas chromatography mass spectrometry (GC/MS) technique was employed to monitor the evolution of the volatile thermal degradation products exhausted after a growth process of CNTs run at 900 degrees C in Ar atmosphere. The presence of ferrocene catalyst has shown negligible effect on the composition of the volatile products and the main decomposition molecule detected was benzene. Furthermore, the comparison of GC/MS results with scanning electron microscopy images and Raman spectra of the as-grown samples have suggested that the presence of benzene and its interaction with the iron clusters play a key role in the CNT formation, but only on the bare silicon wafer.

Human plasma protein adsorption on carbon-based materials.

In this study the initial reactions of different carbon-based materials with human blood were investigated by short-time exposure to platelet poor plasma (PPP). Extent of protein adsorption and conformational changes of proteins adsorbed on material surfaces are known to be keys factors affecting further biological reactions. Plasma protein adsorption on multi-walled carbon nanotubes (MWCNTs), highly oriented pyrolytic graphite (HOPG) and nanocrystalline graphite (NG) were investigated and the results obtained on these materials were compared with those obtained studying pyrolytic carbon (PyC), a material showing good anti-trombogenic properties. The quantification of adsorbed plasma proteins on sample surfaces was obtained by Micro BCA Protein Assay, while immunofluorescence analysis was employed to monitor the surface density and distribution of two selected proteins, namely fibrinogen (Fg) and Hageman factor (FXII), proteins playing a leading role in mediating platelet adhesion. The dependence of the biological response on the surface chemical and morphological properties were also investigated and data obtained using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and atomic force microscopy (AFM) are presented. After PPP incubation PyC is characterized by the presence of low level of whole proteins and FXII adsorption, in contrast to a high adhesion of Fg. Compared to PyC the analysis of the other carbon-based materials result in a higher whole protein adsorption with an increasing trend moving from MWCNTs, NG and HOPG respectively. The Fg surface density on PyC, NG and MWCNTs is about four times higher than on HOPG while only HOPG show a detectable fluorescent signal of FXII. If AFM data indicate that surface morphology does not play a crucial role in protein adhesion, XPS analysis show chemical differences that can be correlated with this biological response.