State of the art of biochar in Ethiopia. A review

Today our planet is threatened by climate change, degradation of fertile soil (food insecurity), depletion of fossil fuel a combined by greenhouse gas emissions. The persistency of these problems forces scholars finding better solutions. Biochar becomes the prominent material to secure climate change by carbon sequestering, food security by enhancing soil fertility and creates replacement of depleted fossil fuel by bio-oil and syngas. These are achieved by good of biochar in sequestration, higher in surface area, capturing pollutants and other versatile properties. The application of this imminent biochar in Ethiopia is in low level. Even researchers and the government are not evolved and payed attention to it. Generally, the fascinating properties and enormous application of this material needs serious indeed and further researches for clear impact to Ethiopia and other developing countries.

Absorption Dominated Directional Electromagnetic Interference Shielding through Asymmetry in a Multilayered Construct with an Exceptionally High Green Index

Fabricating green electromagnetic interference (EMI) shields is the need of the hour because strong secondary reflections in the vicinity of the shield adversely affect the environment and the reliability of the neighboring devices. To this end, the present work aims to maximize the absorption-based EMI shielding through a multilayered construct comprising a porous structure (pore size less than λ/5), a highly conducting entity, and a layer to match the impedance. The elements of this construct were positioned so that the incoming electromagnetic (EM) radiation interacts with the other layers of the construct before the conducting entity. This positioning of the layers in the construct offers a high green shielding index (g_s) and low reflection coefficient (R ∼ 0.1) with an exceptionally high percent absorption (up to 99%). Polyurethane (PU) foams were fabricated using the salt-leaching technique and strategically positioned with carbon nanotube (CNT) papers and polycarbonate (PC)-based films to obtain symmetric and asymmetric constructs. These structures were then employed to gain mechanistic insight into the directional dependency of shielding performance, g_s, and heat dissipation ability. Interestingly, maximum total shielding effectiveness (SE_T) of -52 dB (88% absorption @8.2 GHz) and specific shielding effectiveness/thickness (SSE_t) of -373 dB/cm²g were achieved for a symmetric construct whereas, for the asymmetric construct, the SE_T and SSE_t were -37 dB and -280 dB/cm²g, respectively, with an exceptionally high g_s of 8.6, the highest reported so far. The asymmetricity in the construct led to directional dependence of the absorption component (% SE_A, shielding effectiveness due to absorption) and heat dissipation, primarily governed by the electrical and thermal conductivity gradient, respectively. This study opens new avenues in this field and reports constructs with an exceptionally high green index.

Biomaterials Based on Carbon Nanotube Nanocomposites of Poly(styrene-b-isobutylene-b-styrene): The Effect of Nanotube Content on the Mechanical Properties, Biocompatibility and Hemocompatibility

Nanocomposites based on poly(styrene-block-isobutylene-block-styrene) (SIBS) and single-walled carbon nanotubes (CNTs) were prepared and characterized in terms of tensile strength as well as bio- and hemocompatibility. It was shown that modification of CNTs using dodecylamine (DDA), featured by a long non-polar alkane chain, provided much better dispersion of nanotubes in SIBS as compared to unmodified CNTs. As a result of such modification, the tensile strength of the nanocomposite based on SIBS with low molecular weight (M_n = 40,000 g mol^-1) containing 4% of functionalized CNTs was increased up to 5.51 ± 0.50 MPa in comparison with composites with unmodified CNTs (3.81 ± 0.11 MPa). However, the addition of CNTs had no significant effect on SIBS with high molecular weight (M_n~70,000 g mol^-1) with ultimate tensile stress of pure polymer of 11.62 MPa and 14.45 MPa in case of its modification with 1 wt% of CNT-DDA. Enhanced biocompatibility of nanocomposites as compared to neat SIBS has been demonstrated in experiment with EA.hy 926 cells. However, the platelet aggregation observed at high CNT concentrations can cause thrombosis. Therefore, SIBS with higher molecular weight (M_n~70,000 g mol^-1) reinforced by 1-2 wt% of CNTs is the most promising material for the development of cardiovascular implants such as heart valve prostheses.

Roadmap of Effects of Biowaste-Synthesized Carbon Nanomaterials on Carbon Nano-Reinforced Composites

Sustainable growth can be achieved by recycling waste material into useful resources without affecting the natural ecosystem. Among all nanomaterials, carbon nanomaterials from biowaste are used for various applications. The pyrolysis process is one of the eco-friendly ways for synthesizing such carbon nanomaterials. Recently, polymer nanocomposites (PNCs) filled with biowaste-based carbon nanomaterials attracted a lot of attention due to their enhanced mechanical properties. A variety of polymers, such as thermoplastics, thermosetting polymers, elastomers, and their blends, can be used in the formation of composite materials. This review summarizes the synthesis of carbon nanomaterials, polymer nanocomposites, and mechanical properties of PNCs. The review also focuses on various biowaste-based precursors, their nanoproperties, and turning them into proper composites. PNCs show improved mechanical properties by varying the loading percentages of carbon nanomaterials, which are vital for many defence- and aerospace-related industries. Different synthesis processes are used to achieve enhanced ultimate tensile strength and modulus. The present review summarizes the last 5 years’ work in detail on these PNCs and their applications.

High electromagnetic interference shielding of poly(ether-sulfone)/multi-walled carbon nanotube nanocomposites fabricated by an eco-friendly route

High-performance polymer matrix nanocomposites based on poly(ether-sulfone) (PES) matrix reinforced with multi-walled carbon nanotubes (MWCNTs) were fabricated using planetary ball mill followed by hot pressing. Their electrical properties and the electromagnetic interference shielding effectiveness (EMI-SE) were investigated and discussed. A percolation threshold of about 0.65 vol% MWCNT was obtained. The electrical conductivity was increased by more than ten orders of magnitude at the percolation threshold and to approximately 0.01 S cm^-1 at 6.67 vol% (or 10 wt%) MWCNT. This is a significant improvement. The highest EMI-SE of about 29-30 dB (both in the X-band and K_u-band) was obtained for the 6.67 vol% MWCNT filled nanocomposites with a thickness of 0.9 mm. The specific EMI-SE of these nanocomposites were found to be higher than the literature values. The thermal stability and the char yield (measured at 900 °C) of the nanocomposites were found to be more than 470 °C and 40.6%, respectively.

Light weight and flexible poly(ether ether ketone) based composite film with excellent thermal stability and mechanical properties for wide-band electromagnetic interference shielding

Capitalizing on wrapped MWCNTs and high-temperature lubricants produce a light weight and flexible poly(ether ether ketone) composite film with excellent thermal stability and mechanical property for wide-band electromagnetic interference shielding.

Preparation and characterization of polycarbonate/multiwalled carbon nanotube nanocomposites

A polymer nanocomposite was produced by ultrasonic-assisted dispersion of multiwalled carbon nanotubes (MWCNTs) in a polycarbonate matrix using p-xylene and dichloromethane as the solvents. The filler loading was varied from 1 to 3 wt % in order to examine the effect of MWCNTs on the structure and properties of the composites. The nanocomposites were characterized by DSC, DTA, TGA, UV-vis, FTIR and Raman spectroscopy to evaluate the changes induced by the filler in the polymer matrix. UV-vis, FTIR and Raman spectroscopy measurements confirmed the presence of the dispersed phase in the composite films, while TGA and DSC analysis of the nanocomposites revealed enhanced thermal stability and decreased crystallinity, respectively, as compared to the neat polymer. The proposed composites can find application in a number of everyday products where polycarbonate is the base polymer.

Electromagnetic shielding and mechanical properties of thermally stable poly(ether ketone)/multi-walled carbon nanotube composites prepared using a twin-screw extruder equipped with novel fractional mixing elements

A light weight, mechanically strong and thermally stable efficient EMI shielding material based on PEK/MWCNT composites prepared using a twin-screw extruder equipped with novel fractional mixing elements (for enhanced mixing) is reported.

Synergistic effect on static and dynamic mechanical properties of carbon fiber-multiwalled carbon nanotube hybrid polycarbonate composites

The synergistic effect of reinforced non-functionalized and functionalized MWCNTs accompanied by CF is observed on the mechanical properties in a polycarbonate matrix.

Dynamic mechanical properties of multiwall carbon nanotube reinforced ABS composites and their correlation with entanglement density, adhesion, reinforcement and C factor

Herein, the dynamic mechanical properties of MWCNTs reinforced ABS composites have been studied using a DMA and the results have been correlated with entanglement density, adhesion, reinforcement and C Factor.

Depression in glass transition temperature of multiwalled carbon nanotubes reinforced polycarbonate composites: effect of functionalization

Acid functionalized MWCNTs/PC composites showed significant improvement in storage modulus upto 57% in glassy and 400% in rubbery region over pure polycarbonate.

Excellent impact strength of ethylene-methyl acrylate copolymer toughened polycarbonate

The notched izod impact strength of PC/EMA blends showed a positive blending effect and increased 381% with incorporation of a very little amount of EMA (5%) with a marginal decrease in tensile strength of PC.

Polymer nanocomposite foam filled with carbon nanomaterials as an efficient electromagnetic interference shielding material

Among different carbon nanomaterial foam-filled polymer composites, graphene-based foam gives superior specific shielding effectiveness when compared to typical metals.