Showing papers on "Thermal stability published in 2021"

Effect of glycerol plasticizer loading on the physical, mechanical, thermal, and barrier properties of arrowroot (Maranta arundinacea) starch biopolymers.

Abstract: This research was set out to explore the development of arrowroot starch (AS) films using glycerol (G) as plasticizer at the ratio of 15, 30, and 45% (w/w, starch basis) using solution casting technique. The developed films were analyzed in terms of physical, structural, mechanical, thermal, environmental, and barrier properties. The incorporation of glycerol to AS film-making solution reduced the brittleness and fragility of films. An increment in glycerol concentration caused an increment in film thickness, moisture content, and solubility in water, whereas density and water absorption were reduced. The tensile strength and modulus of G-plasticized AS films were reduced significantly from 9.34 to 1.95 MPa and 620.79 to 36.08 MPa, respectively, while elongation at break was enhanced from 2.41 to 57.33%. FTIR analysis revealed that intermolecular hydrogen bonding occurred between glycerol and AS in plasticized films compared to control films. The G-plasticized films showed higher thermal stability than control films. The cross-sectional micrographs revealed that the films containing 45% glycerol concentration had higher homogeneity than 15% and 30%. Water vapour permeability of plasticized films increased by an increase in glycerol concentrations. The findings of this research provide insights into the development of bio-degradable food packaging.

Highly thermally conductive liquid metal-based composites with superior thermostability for thermal management

Abstract: Thermally conductive polymer composites (TCPCs) are highly desirable for thermal management in modern electrical systems and next-generation flexible electronic devices. However, the integration of superior thermal conductivity, good mechanical performance, and high thermostability in TCPCs remains a daunting challenge, due to the utilization of abundant rigid fillers (such as graphene, boron nitride and aluminum nitride) and the low thermal stability of polymer matrices. Herein, a highly thermally conductive film with excellent mechanical strength and toughness is developed based on soft liquid metal (LM) and rigid aramid nanofibers (ANFs), via a vacuum infiltration technique. The LM/ANF composite films possess superior in-plane and through-plane thermal conductivity (7.14 @ 1.68 W m−1 K−1) because of the formation of a tightly packed structure, in which LM droplets are randomly distributed among the well-ordered ANFs to construct efficient heat conduction networks. Meanwhile, an outstanding tensile strength of 108.5 MPa and a high toughness of 10.3 MJ m−3 are achieved in the LM/ANF composite films. Furthermore, the LM/ANF composite films also have remarkable thermostability, flexibility, and mechanical reliability, without an obvious change in the thermal conductivity even at an elevated temperature of 250 °C and after repeated folding for 1000 cycles, respectively. These admirable features shed light on the application of the LM/ANF composite films for thermal management of high-power integrated electronic devices.

A New Online Learned Interval Type-3 Fuzzy Control System for Solar Energy Management Systems

Abstract: In this article, a novel method based on interval type-3 fuzzy logic systems (IT3-FLSs) and an online learning approach is designed for power control and battery charge planing for photovoltaic (PV)/battery hybrid systems. Unlike the other methods, the dynamics of battery, PV and boost converters are considered to be fully unknown. Also, the effects of variation of temperature, radiation, and output load are taken into account. The robustness and the asymptotic stability of the proposed method is analyzed by the Lyapunov/LaSalle’s invariant set theorems, and the tuning rules are extracted for IT3-FLS. Also, the upper bound of approximation error (AE) is approximated, and then a new compensator is designed to deal with the effects of dynamic AEs. The superiority of the proposed method is examined in several conditions and is compared with some other well-known methods. It is shown that the schemed method results in high performance under difficult conditions such as variation of temperature and radiation and abruptly changing in the output load.

Effects of A/B-Site Co-Doping on Microstructure and Dielectric Thermal Stability of AgNbO3 Ceramics

Abstract: AgNbO3-based lead-free ceramics are a promising candidate material for capacitors, where thermal stability is a key property for applications in severe and complex environments. This study investigated the fabrication of Ag1-3xBixNb1-3/5x(Zn1/2Ti1/2)xO3 (ABNZT-x) (x = 0, 0.005, 0.01, 0.02, or 0.04) via a solid-state reaction under oxygen flow. The microstructure, dielectric properties, and impedance spectra of the AgNbO3 samples co-doped with Bi3+, Zn2+, and Ti4+ were systematically characterized. All samples exhibited an orthorhombic phase structure, where the average grain size decreased with increasing co-doping level, the grain growth kinetics was studied by phase-field simulation. The phase transition temperatures became lower and the maximum permittivity values decreased. These findings demonstrated that enhanced dielectric thermal stability had been achieved. The grain conduction effect was observed during the impedance spectroscopy analysis, where the calculated activation energy decreased with increasing co-doping level. This ABNZT-x ceramic system exhibited stable dielectric properties, and shows promise for use as a functional material in electronic devices.

High-Performance Supercapacitor Electrodes Prepared From Dispersions of Tetrabenzonaphthalene-Based Conjugated Microporous Polymers and Carbon Nanotubes.

Abstract: In this study, we prepared a series of conjugated microporous polymers (CMPs) through Sonogashira-Hagihara cross-couplings of a tetrabenzonaphthalene (TBN) monomer with pyrene (Py), tetraphenylethylene (TPE), and carbazole (Car) units and examined their chemical structures, thermal stabilities, morphologies, crystallinities, and porosities. TBN-TPE-CMP possessed a high surface area (1150 m2 g-1) and thermal stability (Td10 = 505 °C; char yield = 68 wt %) superior to those of TBN-Py-CMP and TBN-Car-CMP. To improve the conductivity of the TBN-CMP materials, we blended them with highly conductive single-walled carbon nanotubes (SWCNTs). Electrochemical measurements revealed that the TBN-Py-CMP/SWCNT nanocomposite had high capacitance (430 F g-1) at a current density of 0.5 A g-1 and outstanding capacitance retention (99.18%) over 2000 cycles; these characteristics were superior to those of the TBN-TPE-CMP/SWCNT and TBN-Car-CMP/SWCNT nanocomposites.

Recent advances in graphene sheets as new generation of flame retardant materials

Abstract: Polymeric and textile based materials constitute the majority of market products, however, due to their low thermal stability and high flammability hazards, their uses are limited in some applications. Therefore, flame retardant materials have to be dispersed as fillers in polymer matrix and coated on textile fabrics to enhance their fire safety and thermal stability. Graphene is two-dimensional materials and considered as a promising carbon nanomaterials with sp2-hybridization and with unique properties. In this review article conventional flame retardant and different methods of synthesis of graphene layers were summarized. Also, the possibility of use graphene sheets alone as flame retardant material for polymeric materials was reviewed and compared with other common nanofillers. Graphene sheets and their composite as flame retardant nanofillers for polymers and flame retardant coating for textiles are discussed in details. Synergistic flame retardant effect of use of nanoparticles decorated graphene sheets as flame retardant for polymer nanocomposites are discussed.

Layered double hydroxide/graphene oxide synergistically enhanced polyimide aerogels for thermal insulation and fire-retardancy

Abstract: Environmentally friendly materials with lightweight, good thermal insulation and fire-resistance are highly required for energy efficient buildings. Here, layered double hydroxide (LDH) - graphene oxide (GO) synergistically enhanced polyimide (PI) aerogels with great thermal insulation, good thermal stability and excellent flame retardancy, have been designed and synthesized through a green environmental freeze-drying method followed by thermal imidization. LDH can be uniformly dispersed in aqueous solutions by electrostatic interactions with GO, thus resulting in uniform dispersion in PI matrix. Due to the physical interaction between the two kinds of nanosheets and PI, the pore size of PI/LDH-GO (PLG) composite aerogel was significantly reduced from 20 μm to 5 μm, leading to ultralow density (52 ± 3.6 mg cm−3), low thermal conductivity (36 ± 1.7 mW m−1 K−1), and high compressive modulus (26 ± 1.8 MPa). More importantly, the addition of two pollution-free fire-retardants (LDH-GO) endows the PLG aerogels excellent fire-resistant performance with the limiting oxygen index reach up to 43 ± 1.2%, reaching the nonflammable level. Therefore, this work paves a new way for anti-flaming and heat insulating materials with great potential for practical applications in energy efficient buildings.

A Three in One Strategy to Achieve Zirconium Doping, Boron Doping, and Interfacial Coating for Stable LiNi0.8Co0.1Mn0.1O2 Cathode

Abstract: LiNi0.8Co0.1Mn0.1O2 cathodes suffer from severe bulk structural and interfacial degradation during battery operation. To address these issues, a three in one strategy using ZrB2 as the dopant is proposed for constructing a stable Ni-rich cathode. In this strategy, Zr and B are doped into the bulk of LiNi0.8Co0.1Mn0.1O2, respectively, which is beneficial to stabilize the crystal structure and mitigate the microcracks. Meanwhile, during the high-temperature calcination, some of the remaining Zr at the surface combined with the surface lithium source to form lithium zirconium coatings, which physically protect the surface and suppress the interfacial phase transition upon cycling. Thus, the 0.2 mol% ZrB2-LiNi0.8Co0.1Mn0.1O2 cathode delivers a discharge capacity of 183.1 mAh g-1 after 100 cycles at 50 °C (1C, 3.0-4.3 V), with an outstanding capacity retention of 88.1%. The cycling stability improvement is more obvious when the cut-off voltage increased to 4.4 V. Density functional theory confirms that the superior structural stability and excellent thermal stability are attributed to the higher exchange energy of Li/Ni exchange and the higher formation energy of oxygen vacancies by ZrB2 doping. The present work offers a three in one strategy to simultaneously stabilize the crystal structure and surface for the Ni-rich cathode via a facile preparation process.

Meso/Microporous Carbons from Conjugated Hyper-Crosslinked Polymers Based on Tetraphenylethene for High-Performance CO2 Capture and Supercapacitor.

Abstract: In this study, we successfully synthesized two types of meso/microporous carbon materials through the carbonization and potassium hydroxide (KOH) activation for two different kinds of hyper-crosslinked polymers of TPE-CPOP1 and TPE-CPOP2, which were synthesized by using Friedel-Crafts reaction of tetraphenylethene (TPE) monomer with or without cyanuric chloride in the presence of AlCl3 as a catalyst The resultant porous carbon materials exhibited the high specific area (up to 1100 m2 g-1), total pore volume, good thermal stability, and amorphous character based on thermogravimetric (TGA), N2 adsoprtion/desorption, and powder X-ray diffraction (PXRD) analyses The as-prepared TPE-CPOP1 after thermal treatment at 800 °C (TPE-CPOP1-800) displayed excellent CO2 uptake performance (174 mmol g-1 at 298 K and 319 mmol g-1 at 273 K) Furthermore, this material possesses a high specific capacitance of 453 F g-1 at 5 mV s-1 comparable to others porous carbon materials with excellent columbic efficiencies for 10,000 cycle at 20 A g-1

Capturing Mobile Lithium Ions in a Molecular Hole Transporter Enhances the Thermal Stability of Perovskite Solar Cells.

Abstract: A thermally stable perovskite solar cell (PSC) based on a new molecular hole transporter (MHT) of 1,3-bis(5-(4-(bis(4-methoxyphenyl) amino)phenyl)thieno[3,2-b]thiophen-2-yl)-5-octyl-4H-thieno[3,4-c]pyrrole-4,6(5H)-dione (coded HL38) is reported. Hole mobility of 1.36 × 10-3 cm2 V-1 s-1 and glass transition temperature of 92.2 °C are determined for the HL38 doped with lithium bis(trifluoromethanesulfonyl)imide and 4-tert-butylpyridine as additives. Interface engineering with 2-(2-aminoethyl)thiophene hydroiodide (2-TEAI) between the perovskite and the HL38 improves the power conversion efficiency (PCE) from 19.60% (untreated) to 21.98%, and this champion PCE is even higher than that of the additive-containing 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (spiro-MeOTAD)-based device (21.15%). Thermal stability testing at 85 °C for over 1000 h shows that the HL38-based PSC retains 85.9% of the initial PCE, while the spiro-MeOTAD-based PSC degrades unrecoverably from 21.1% to 5.8%. Time-of-flight secondary-ion mass spectrometry studies combined with Fourier transform infrared spectroscopy reveal that HL38 shows lower lithium ion diffusivity than spiro-MeOTAD due to a strong complexation of the Li+ with HL38, which is responsible for the higher degree of thermal stability. This work delivers an important message that capturing mobile Li+ in a hole-transporting layer is critical in designing novel MHTs for improving the thermal stability of PSCs. In addition, it also highlights the impact of interface design on non-conventional MHTs.

Synthesis of the SWCNTs/TiO2 nanostructure and its effect study on the thermal, optical, and conductivity properties of the CMC/PEO blend

Abstract: The TiO2 NPs have been successfully synthesized by sol-gel method and the SWCNTs/TiO2 nanostructures have been fabricated by a simple mixing technique. By a solution casting process, pure CMC/PEO and SWCNTs/TiO2 nanohybrid doped CMC/PEO polymer blend films have been prepared. The influence of SWCNTs/TiO2 nanohybrid loading on the thermal, optical, and conductivity properties of the polymer blend has been discussed. The XRD pattern shows that the average crystallite size of the nanoparticles for TiO2 and SWCNTs/TiO2 is 20 nm and 15 nm, respectively, and a change in crystallinity was observed with an increase in doping. The interaction between CMC/PEO chains and SWCNTs/TiO2 nanohybrid is confirmed by FTIR spectra. The optical absorption spectrum shows that the energy gap reduces with the dopant increase. The miscibility between the CMC and PEO was confirmed by DSC thermograms. With an increase in dopant content, the TGA study demonstrates that the system's thermal stability improves. The maximum value of the blend's AC conductivity is 4.77 10−6 S/m, and by increasing the loading of SWCNTs/TiO2 to 3.2 (wt%) increased to 9.23 10−4 S/m. The conduction mechanism changed with SWCNTs/TiO2 loading from the correlated barrier hopping, in the prepared samples. Usage of these nanocomposite films in the semiconductor industry is encouraged by the observed improvements in optical, thermal, and AC conductivity.

Extraction, characterization and chemical functionalization of phosphorylated cellulose derivatives from Giant Reed Plant

Abstract: In this work, cellulose microfibers (CMFs) and cellulose nanocrystals (P-CNCs) having phosphoric groups on their surfaces were prepared by phosphorylation of cellulose extracted from Giant Reed plant, using ammonium dihydrogen phosphate (NH4H2PO4) in a water-based urea system and phosphoric acid (H3PO4) without urea as phosphorous agents, respectively. Phosphorylated samples were studied in terms of their charge content, chemical structure, crystallinity, morphology, and thermal stability using several characterization techniques. Conductometric titration results showed higher charge content after phosphorylation with urea for P-CMFs about 3133 mmol kg−1, while without urea P-CNCs exhibited 254 mmol kg−1. FTIR analysis confirmed the total removal of non-cellulosic compounds from microfibers’ surface and their partial oxidation after phosphorylation. XRD analysis proved that the P-CMFs and P-CNCs exhibited cellulose I structure, with a crystallinity index of 70 and 83%, respectively. SEM and AFM observations showed micro-sized and needle-like morphologies for P-CMFs and P-CNCs with an average diameter of 15 µm and 20.5 nm, respectively. The thermal properties of P-CMFs indicate early dehydration with high char formation, while the high thermal stability of P-CNCs (Tmax = 352 °C) was similar to that of microcrystalline cellulose. The present work showed new routes for preparing phosphorylated micro- and nano-cellulose from a new natural source, having new functions that benefit various applications.