Characterization on mixed-crystal structure and properties of poly(butylene adipate-co-terephthalate) biodegradable fibers

Biodegradable ideal random copolymer poly(butylene adipate-co-terephthalate) (PBAT), with 44 mol% butylene terephthalate (BT), was melt-spun into fibers with take-up velocity up to 5 km/min. The structure development and properties of the as-spun fibers were investigated through birefringence, WAXD, SAXS, DSC and tensile test. Despite of the ideal randomness and composition (1:1) of PBAT copolymer, PBAT fiber showed well-developed PBT-like crystal structure, while its melting temperature (ca. 121 °C) was over 100 °C lower than that of PBT. Based on the quantitative analyses on the lattice spacing, the crystallinity and the fraction of crystallizable BT sequences, the crystal structure of PBAT was characterized to be formed by mixed-crystallization of BT and BA units, where BA units were incorporated into BT lattice. This mixed-crystal structure was found to undergo PBT-like reversible crystal modification with the application and removal of tensile stress. This crystal modification was found to occur in a higher strain region compared with that of PBT fibers.     

Film thickness dependence of the dielectric properties of SrTiO3/BaTiO3 multilayer thin films deposited by double target RF magnetron sputtering

Four-layer SrTiO₃/BaTiO₃ thin films ((ST/BT)₄) with various thicknesses deposited on Pt/Ti/SiO₂/Si substrates at 500 °C by double target RF magnetron sputtering have been investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), profilometry, capacitance-voltage and current-voltage measurements. The XRD patterns reveal the frame formation of the sputter deposited (ST/BT)₄ with controlled modulation. The adhesion between the Pt bottom electrode layer and the BT layer is excellent. The dielectric constant of the (ST/BT)₄ multilayer thin film increases with increasing film thickness. The effects of temperature, frequency, and bias voltage on the dielectric constant of the (ST/BT)₄ multilayer thin films are discussed in detail. The leakage current density of the (ST/BT)₄ multilayer with a thickness of 450.0 nm is lower than 1.0 × 10⁻⁸ A/cm² for the applied voltage of less than 5 V, showing that the multilayer thin films with such a characteristic could be applied for use in dynamic random access memory (DRAMs) capacitors.     

Electrochemical investigations of ionic liquids with vinylene carbonate for applications in rechargeable lithium ion batteries

Ionic liquids based on methylpropylpyrrolidinium (MPPY) and methylpropylpiperidinium (MPPI) cations and bis(trifluoromethanesulfonyl)imide (TFSI) anion have been synthesized and characterized by thermal analysis, cyclic voltammetry, impedance spectroscopy as well as galvanostatic charge/discharge tests. 10 wt% of vinylene carbonate (VC) was added to the electrolytes of 0.5 M LiTFSI/MPPY.TFSI and 0.5 M LiTFSI/MPPI.TFSI, which were evaluated in Li || natural graphite (NG) half cells at 25 °C and 50 °C under different current densities. At 25 °C, due to their intrinsic high viscosities, the charge/discharge capacities under the current density of 80 μA cm⁻² were much lower than those under the current density of 40 μA cm⁻². At 50 °C, with reduced viscosities, the charge/discharge capacities under both current densities were almost indistinguishable, which were also close to the typical values obtained using conventional carbonate electrolytes. In addition, the discharge capacities of the half cells were very stable with cycling, due to the effective formation of solid electrolyte interphase (SEI) on the graphite electrode. On the contrary, the charge/discharge capacities of the Li || LiCoO₂ cells using both ionic liquid electrolytes under the current density of 40 μA cm⁻² decreased continually with cycling, which were primarily due to the low oxidative stability of VC on the surface of LiCoO₂.     

Low temperature synthesis and dielectric, ferroelectric and piezoelectric study of microwave sintered BaTiO3 ceramics

Barium titanate (BaTiO₃/BT) ferroelectric system was synthesized in single perovskite phase at low temperature by using powders derived from modified solid state reaction (MSSR) and sintered by microwave (MW) processing routes. Conventional calcination temperature was optimized at 900 °C for 4 h. MW sintering of BT samples was carried out at 1100 °C for 30 min to get dense (98% density) ceramics. Room temperature (RT) dielectric constant (?_r) and dielectric loss (tan δ) at 1 kHz frequency of MW sintered BT samples was found to be ∼2500 and 0.03, respectively. Saturated polarization vs. electric field (P-E) loops with remnant polarization (P_r) ∼6 μC/cm² and coercive field (E_c) ∼1.45 kV/cm confirmed the ferroelectric nature of MW sintered BT samples. Piezoelectric coefficient from strain vs. electric field (S-E) loops study was found to be 335 pm/V.     

Effect of vibro-milling time on phase formation and particle size of barium titanate nanopowders

Barium titanate (BT) nanopowder was synthesized by a solid state reaction via a rapid vibro-milling technique. The effect of milling time on phase formation and particle size of BT powder was investigated. Powder samples were characterized using XRD (X-ray diffraction) and SEM techniques. It was found that the resulting BT powders have a range of particle size depending on milling times. Production of a single-phase BT nanopowder can be successfully achieved by employing a combination of 30 h milling time and calcination conditions of 1200 °C for 2 h.     

The effect of electrolyte temperature on the passivity of solid electrolyte interphase formed on a graphite electrode

The effect of electrolyte temperature on the passivity of solid electrolyte interphase (SEI) was investigated in 1 M LiPF₆-ethylene carbonate/diethyl carbonate (50:50 vol.%) electrolyte, using galvanostatic charge-discharge experiment, and ac-impedance spectroscopy combined with Fourier transform infra-red spectroscopy, and high resolution transmission electron microscopy (HRTEM). The galvanostatic charge-discharge curves at 20 °C evidenced that the irreversible capacity loss during electrochemical cycling was markedly increased with rising SEI formation temperature from 0 to 40 °C. This implies that the higher the SEI formation temperature, the more were the graphite electrodes exposed to structural damages. From both increase of the relative amount of Li₂CO₃ to ROCO₂Li and decrease of resistance to the lithium transport through the SEI layer with increasing SEI formation temperature, it is reasonable to claim that, due to the enhanced gas evolution reactions during transformation of ROCO₂Li to Li₂CO₃, the rising SEI formation temperature increased the number of defect sites in the SEI layer. From the analysis of HRTEM images, no significant structural destruction in bulk graphite layer was observed after charge-discharge cycles. This means that solvated lithium ions were intercalated through the defect sites in the SEI, at most, into the surface region of the graphite layer.     

Storage behavior of LiNi1/3Co1/3Mn1/3O2/artificial graphite Li-ion cells

A series of Li-ion cells containing LiNi_1/3Co_1/3Mn_1/3O₂ and artificial graphite as the active materials, have been stored at various temperatures from 0 to 70 °C. The 3-electrode impedance study shows that both the solid electrolyte interphase (SEI) film resistance and charge-transfer resistance of the negative electrode first decrease and then increase during storage at 70 °C, while both resistances for the positive electrode increase under this condition. The reversible capacity loss of the 3-electrode cell, which is possibly attributed to dissolution of SEI film, accounts for over half of the total capacity loss after 5 weeks of storage. Gases generated from the swelling aged cell at 60 °C are mainly attributed to the reduction of the electrolyte on the negative electrode. A further study on the side-reaction has been done on graphite electrodes and separators, indicating that SEI films may be rearranged and reformed on negative electrodes, and that some pores on the positive electrode side of separator are blocked due to the oxidation of electrolyte, resulting in poor Li-ion transfer and rise of the ohmic resistance during storage at elevated temperature. However, at 0 °C, this side-reaction is impeded.     

Microwave sintering of cordierite precursor green bodies prepared by starch consolidation

This paper reports on a study of the microwave sintering behavior of green disks prepared by the starch consolidation forming method to produce cordierite-based porous materials. Green disks were formed by thermogelling the aqueous suspensions of talc, kaolin and alumina (29.6 vol.%) and potato starch (11.5 vol.%) at 75 and 85 °C for 4 h, drying and calcining. They were characterized by bulk density and apparent porosity measurements, and SEM. Microwave sintering was carried out at 1300 and 1330 °C for 15, 20 and 25 min, applying 50 °C/min. For purposes of comparison, an analysis of green disks prepared and calcined in the same conditions and conventionally sintered (1330 °C for 4 h) was also made. The materials were characterized by XRD, bulk density and apparent porosity measurements, and microstructurally analyzed SEM. The results were analyzed considering the behavior of starch in aqueous suspension at varying temperatures, and the experimental conditions of consolidation and sintering.     

Property analysis of triglyceride-based thermosets

Triglycerides with acrylate functionality were prepared from various oils and model triglycerides. The triglyceride-acrylates were homopolymerized and copolymerized with styrene. The cross-link densities of the resulting polymer networks were predicted utilizing the Flory-Stockmayer theory. Although the model predictions overestimated the cross-link density, the trends in the cross-link density predictions matched the experimental results. In both cases, the cross-link density was found to increase gradually at low levels of acrylation and then linearly at higher levels of acrylation. The deviation in the experimental results and model predictions were the result of intramolecular cross-linking. Approximately 0.5 and 0.8 acrylates per triglyceride were lost to intramolecular cyclization for homopolymerized triglyceride-acrylates and triglycerides copolymerized with styrene, respectively. The glass transition temperature (T_g) increased approximately linearly with the cross-link density from as low as −50 °C to as high as 92 °C. Simple models accurately predicted the effect of cross-link density on T_g. The tensile strength and modulus of triglyceride-based polymers increased exponentially at low levels of acrylate functionality, but increased linearly at higher levels of acrylate functionality, as predicted by vector percolation theory.     

Compositional effects on the properties of high nitrogen content alkaline-earth silicon oxynitride glasses, AE = Mg, Ca, Sr, Ba

A series of alkaline-earth element containing high nitrogen content oxynitride glasses (AESiON), with AE = Mg, Ca, Sr, Ba, were prepared in order to investigate the compositional effects on the physical properties of the alkaline-earth element. The physical properties were found to change linearly with the concentration of AE elements. The density of the glasses increases substantially with an increase in the AE atomic mass and slightly with an increase in nitrogen ratio. Ba containing glasses shows the value of density 4.16 g/cm³. Glass transition temperatures are found to be higher for Mg glasses, ca. 1020 °C, in comparison with Ba glasses, ca. 895 °C. The hardness of Mg containing glasses shows high values, up to 12.2 GPa and decreases for Ca, Sr and Ba containing glasses. Ba, containing glasses shows high values of refractive index in comparison with the Sr, Ca and Mg containing glasses.     

Influence of system variables on the morphological and dynamic mechanical behavior of polydimethylsiloxane based segmented polyurethane and polyurea copolymers: a comparative perspective

The effect of the variables of polydimethylsiloxane (PDMS) soft segment (SS) length, hard segment (HS) type and content as well as choice of chain extender (its MW and symmetry) on the morphology of segmented polyurethane and polyurea copolymers was investigated. The methods of dynamic mechanic analysis, small angle X-ray scattering, atomic force microscopy, and mechanical testing were used in this analysis. Average PDMS MW of 900, 2500 or 7000 g/mol were utilized and the hard segment content ranged from 16 to 50 wt%. HMDI was used as the diisocyanate. All copolymers were synthesized via the prepolymer method. The PDMS MW had a marked effect on the morphology of the materials. Copolymers with PDMS MW of 2500 and 7000 g/mol were clearly found to be well microphase separated relative to those containing the 900 g/mol PDMS SS. The polyurea sample with a PDMS MW of 7000 and HS content of 25 wt% exhibited a remarkable service temperature window (for rubber-like behavior) of ca. 230 °C (from −55 to 175 °C) whereas it was ca. 200 °C wide (from −55 to 145 °C) for the equivalent polyurethane sample. In general, the degree of microphase separation was found to be greater in the polyurea samples due to their more cohesive bidentate hydrogen bonding.     

Electrochemical performance of pyrolytic carbon-coated natural graphite spheres

Natural graphite (NG) spheres were coated by pyrolytic carbon from the thermal decomposition of C₂H₂/Ar at 950 °C in a fluidized bed reactor. Scanning electron microscopy and secondary electron focused ion beam (FIB) images clearly showed that a pyrolytic carbon layer with a thickness of ∼250 nm was uniformly deposited on the surface of the NG spheres. Electrochemical performance measurements for the original and coated NG spheres as anode materials of a lithium-ion battery indicated that the first coulombic efficiency and cyclability were significantly improved in the coated sample. The reasons for this were investigated by analyzing structural characteristics, specific surface area, pore size distribution, and solid electrolyte interphase (SEI) film. Using a FIB workstation, we demonstrated, by cross-section imaging of a coated NG sphere that had experienced five electrochemical cycles, that the SEI film formed on the non-graphitic pyrolytic carbon surface became thinner (60-150 nm) and more uniform in composition compared with that on the surface of uncoated NG spheres; and the formation of an “internal SEI film” inside the NG spheres was also remarkably suppressed due to the uniform coating of pyrolytic carbon.     

RAFT-mediated polymerization and grafting of sodium 4-styrenesulfonate from cellulose initiated via γ-radiation

Ambient temperature (20 °C) reversible addition fragmentation chain transfer (RAFT) polymerization of sodium 4-styrenesulfonate (SS) conducted directly in aqueous media under γ-irradiation at different dose rates (0.09, 0.03 and 0.02 kGy h⁻¹) proceeds in a controlled fashion (typically, M_w/M_n < 1.25) to near quantitative conversions via 4-cyanopentanoic acid dithiobenzoate (CPADB) mediation. By applying CPADB modified cellulose as a macro chain transfer agent, a graft copolymer with SS was prepared in aqueous media under γ-irradiation. RAFT mediated graft polymerizations provided copolymers with higher graft frequencies compared to those obtained by conventional methods. Thermally initiated grafting of SS from a CPADB-functionalized cellulose surface at 70 °C was also studied which resulted in a reduced graft frequency in comparison to γ-initiated ones.     

Effect of chemical structure and crosslinking density on the thermo-mechanical properties and toughness of (meth)acrylate shape memory polymer networks

The objective of this work is to characterize and understand structure-mechanical property relationships in (meth)acrylate networks. The networks are synthesized from mono-functional (meth)acrylates with systematically varying sidegroup structure and multi-functional crosslinkers with varying mole fraction and functionality. Fundamental trends are established between the network chemical structure, crosslink density, glass transition temperature, rubbery modulus, failure strain, and toughness. The glass transition temperature of the networks ranged from −29 to 112 °C, and the rubbery modulus (E_r) ranged from 2.8 to 129.5 MPa. At low crosslink density (E_r < 10 MPa) network chemistry has a profound effect on network toughness. At high crosslink densities (E_r > 10 MPa), network chemistry has little influence on material toughness. The characteristic ratio of the mono-functional (meth)acrylates' components is unable to predict trends in network toughness as a function of chemical structure, as has been demonstrated in thermoplastics. The cohesive energy density is a better tool for relative prediction of network mechanical properties. Due to superior mechanical properties, networks with phenyl sidegroups are further investigated to understand the effect of phenyl sidegroup structure on toughness.     

Degradation of C.I. Basic Red 29 solution by combined ultrasound and Co-H2O2 system

Ultrasonic degradation of Basic Red 29 (BR29) textile dye in the presence of Co²⁺-H₂O₂ system was investigated in this study. The effects of presence of ultrasonic power, concentrations of cobalt (II) acetate (Co(II)Act) and H₂O₂, temperature and initial pH on the BR29 degradation were examined. Initial dye concentration of 20 mg/L BR29 was used in the study as a model solution. In sonication experiments, an ultrasonic bath at a frequency of 40 kHz was employed. Best experimental conditions were also obtained in the studies as follows: 1000 mg/L Co(II)Act, 1000 mg/L H₂O₂, 40 °C and original pH of 6.70.According to the results, after 30 min of sonication in the presence of Co²⁺-H₂O₂ dye removal efficiency of practically 100% was achieved. It was also found that US enhanced the degradation rate of BR29.     

Synthesis, preparation and properties of novel high-performance allyl-maleimide resins

Three novel allyl-maleimide monomers (i.e., A₂B, AB and AB₂) were designed, synthesized and thermally cured to yield a series of high-performance allyl-maleimide resins. All the monomers obtained are readily soluble in common organic solvents enabling an easy solution processing. The thermal properties of the three monomers were studied by the differential scanning calorimetry (DSC). A₂B and AB showed fairly low melting temperature (T_m < 90 °C) and wide processing window ranging from 90 °C to 260 °C. The thermal stability of the cured allyl-maleimide resins (i.e., PA₂B, PAB and PAB₂) was studied by the thermogravimetric analysis (TGA). Dynamic mechanical analysis (DMA) was used to investigate the dynamic mechanical properties of the composites based on the cured allyl-maleimide resins. PA₂B and PAB₂ showed good glass transition temperatures (T_g > 270 °C) and their corresponding composites showed high bending modulus (E′ > 1900 MPa). Allyl-compound-modified BMI resins based on AB monomer were prepared. Rheometer revealed that the processability of the prepolymer (BR-AB-pre) was improved by the addition of AB monomer. The cured BMI resins (BR and BR-AB) showed good thermal stability (T_d > 400 °C, both in nitrogen and in the air), high glass transition temperature (T_g > 320 °C), and good mechanical properties and low water uptake (<2.6%, 120 h).     

Microstructure of carbon derived from mangrove charcoal and its application in Li-ion batteries

In this study, the microstructure of mangrove-charcoal-derived carbon (MC) was studied using XRD, STM and TEM. MC was found to consist of aligned quasi-spherical structural units with diameters of around 5-20 nm. It shows typical hard carbon characteristics, including a strongly disoriented single graphene layer and BSU, formed by two or three graphene layers stacked nearly parallel. Some curved and faceted graphene layers, especially closed carbon nanoparticles with fullerene-like, were observed in the as-prepared samples. MC was also evaluated as an anodic material for Li-ion batteries. MC carbonized at 1000 °C possessed the highest available discharge capacity (below 0.5 V) of 335 mAh g⁻¹, the high first-cycle coulombic efficiency of 73.7%, good rate and cyclic capability and PC-based electrolyte compatibility. ⁷Li nuclear magnetic resonance (NMR) spectra of fully lithiated mangrove charcoal-derived carbons indicated the co-existence of three Li species.     

Optimization of Drum Drying Parameters for Low Amylose Rice (KDML105) Starch and Flour

An attempt was made to study and model the effects of drum drying process variables on the physico-chemical properties of low amylose rice (KDML105) flour and starch. Drum surface temperature, holding time and solid content of the slurry were varied at three levels: 115-135°C, 14-84 s and 20-40%, w/w, respectively. The dependent variables were moisture content (MC), degree of gelatinization (DG), water absorption index (WAI), water solubility index (WSI) and pasting property. High solid content led to a decrease in DG, WAI and initial peak viscosity (IPV) and increase in WSI of dried samples. Longer holding time resulted in increased DG while surface temperature had no significant effect on all characteristics. Predictive correlations were developed using stepwise multiple linear regression to predict MC, DG, WAI, WSI, and IPV of dried products from drum drying variables.     

Physicochemical properties of ZnCl2-NaCl-KCl eutectic melt

Physicochemical properties of ZnCl₂-NaCl-KCl eutectic melt were studied at 200-300 °C for the first time. Firstly, it was reconfirmed that the eutectic composition is ZnCl₂:NaCl:KCl = 0.6:0.2:0.2 in mole fraction, and that the eutectic temperature is 203 °C. Then, the density, viscosity, and ionic conductivity of the ZnCl₂-NaCl-KCl eutectic melt were measured at 200-300 °C. At 250 °C, the density was 2.43 g cm⁻³, the viscosity was 42.0 cP and the ionic conductivity was 8.53 S m⁻¹. The temperature dependencies of density and ionic conductivity were well fitted by the VTF equations with the same ideal glass transition temperature of 283 K (10 °C). It was found that the melt obeys the fractional Walden's rule which is explained by the decoupling effect. The electrochemical window of the melt was determined to be 1.7 V at 250 °C with the cathode limit being zinc metal deposition and the anode limit being chlorine gas evolution.     

Densification characteristics of corn cobs

Corn cobs are potential feedstocks for producing heat, power, fuels, and chemicals. Densification of corn cobs into briquettes/pellets would improve their bulk handling, transportation, and storage properties. In this study, densification characteristics of corn cobs were studied using a uniaxial piston-cylinder densification apparatus. With a maximum compression pressure of 150 MPa, effects of particle size (0.85 and 2.81 mm), moisture content (10 and 20% w.b.), and preheating temperature (25 and 85 °C) on the density and durability of the corn cob briquettes (with diameter of about 19.0 mm) were studied. It was found that the durability (measured using ASABE tumbling can method) of corn cob briquettes made at 25 °C was 0%. At both particle sizes, preheating of corn cob grinds with about 10% (w.b.) moisture content to 85 °C produced briquettes with a unit density of > 1100 kg m^-3 and durability of about 90%.