Yuezhong Meng

Thermal decomposition characteristics of poly(propylene carbonate) using TG/IR and Py-GC/MS techniques

The thermal decomposition behaviour of poly(propylene carbonate)s (PPC)s synthesized with varying molecular weights was studied at various pyrolysis temperatures by the combination of pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) and thermogravimetric analysis/infrared spectrometry (TG/IR) techniques. The pyrolysis products of PPCs with lower molecular weight of 26,900 and higher molecular weight of 144,600 at different pyrolysis temperatures were identified using Py-GC/MS. The dynamic decomposition was also explored with the TG/IR technique. The results showed that chain scission occurs at relatively lower temperature than for the unzipping reaction, and an increase in molecular weight can reduce the amount of the active terminal groups and restrict unzipping reaction to some extent. It was also observed that the backbone structure plays a great role in thermal decomposition behaviour of PPC. The same perfectly alternating structure leads to the same decomposition mechanism whereas unzipping needs a high activation energy and takes place at high decomposition temperature. The final pyrolysates are cyclic propylene carbonate, and 1,2 propanediol. Low molecular weight PPC undergoes a one-stage pyrolysis and high molecular weight PPC pyrolysis obeys two-step pyrolysis mechanism, viz. main chain random scission and unzipping. The thermal decomposition behaviour of PPC in the absence and presence of a metal complex catalyst was studied by TG/IR. It was further observed that the metal complex catalyst has little effect on the thermal decomposition of the PPC. The catalyst only slightly reduced the activation energy leading to the accelerated depolymerization reaction.

Polymer electrolytes for lithium polymer batteries

In this review, state-of-the-art polymer electrolytes are discussed with respect to their electrochemical and physical properties for their application in lithium polymer batteries. We divide polymer electrolytes into the two large categories of solid polymer electrolytes and gel polymer electrolytes (GPE). The performance requirements and ion transfer mechanisms of polymer electrolytes are presented at first. Then, solid polymer electrolyte systems, including dry solid polymer electrolytes, polymer-in-salt systems (rubbery electrolytes), and single-ion conducting polymer electrolytes, are described systematically. Solid polymer electrolytes still suffer from poor ionic conductivity, which is lower than 10−5 S cm−1. In order to further improve the ionic conductivity, numerous new types of lithium salt have been studied and inorganic fillers have been incorporated into solid polymer electrolytes. In the section on gel polymer electrolytes, the types of plasticizer and preparation methods of GPEs are summarized. Although the ionic conductivity of GPEs can reach 10−3 S cm−1, their low mechanical strength and poor interfacial properties are obstacles to their practical application. Significant attention is paid to the incorporation of inorganic fillers into GPEs to improve their mechanical strength as well as their transport properties and electrochemical properties.

Synthesis and characterization of novel sulfonated poly(arylene thioether) ionomers for vanadium redox flow battery applications

High-molecular-weight poly(arylene thioether ketone) (PTK) and poly(arylene thioether ketone ketone) (PTKK) polymers were successfully synthesized by one-pot polymerization of N,N′-dimethy-S-carbamate masked dithiols with activated dihalo compounds, followed by post-sulfonation using chlorosulfonic acid as the sulfonation agent in dichloromethane solution to give the production of sulfonated poly(arylene thioether ketone) (SPTK) and sulfonated poly(arylene thioether ketone ketone) (SPTKK) with appropriate ion-exchange capacities. The chemical structures were confirmed by 1H NMR, FT-IR and elemental analysis (EA). The thermal properties were fully investigated by TGA-IR. The synthesized SPTK and SPTKK polymers are soluble in aprotic solvents such as N,N′-dimethylacetamide (DMAc), N,N′-dimethylformamide and dimethyl sulfoxide, and can be cast into membranes on a glass plate from their DMAc solution. The proton conductivities of these membranes are comparable to Nafion117 membranes under the same conditions. Cell performance tests showed that the vanadium redox flow batteries (VRBs) assembled with SPTK and SPTKK membranes possessed higher Coulombic efficiencies than VRBs assembled with Nafion117 membranes at the current density of 50 mA cm−2, because of their one-order-of magnitude lower VO2+ permeabilities. In conclusion, these ionomers could be promising candidates as proton-exchange membranes for vanadium redox flow battery (VRB) applications.

Synthesis of novel poly(phthalazinone ether sulfone ketone)s and improvement of their melt flow properties

A series of novel poly(phthalazinone ether sulfone ketone)s was synthesized from bis(4-fluorophenyl) ketone, bis(4-chlorophenyl)sulfone, and 4-(4-hydroxybenzyl)-2,3-phthalazin-1-one through nucleophilic substitution polycondensation. The synthesized polymers exhibited surprisingly high glass transition temperatures and had excellent thermooxidative properties. The melt viscosities of these synthesized polymers are generally too high to be processed by common processing methods because of their very high glass transition temperatures and amorphous microstructure. An attempt was made to reduce their melt viscosities by solution blending the synthesized polymer with two kinds of oligomers: low molecular weight poly(phthalazinone ether sulfone ketone) and commercial poly(ether sulfone). The results proved that the addition of the oligomers to the polymers led to a marked decrease in melt viscosities. Furthermore, no obvious changes were observed in the thermal and mechanical properties of these blends after oligomer additions.

Novel Hierarchically Porous Carbon Materials Obtained from Natural Biopolymer as Host Matrixes for Lithium-Sulfur Battery Applications

Novel hierarchically porous carbon materials with very high surface areas, large pore volumes and high electron conductivities were prepared from silk cocoon by carbonization with KOH activation. The prepared novel porous carbon-encapsulated sulfur composites were fabricated by a simple melting process and used as cathodes for lithium sulfur batteries. Because of the large surface area and hierarchically porous structure of the carbon material, soluble polysulfide intermediates can be trapped within the cathode and the volume expansion can be alleviated effectively. Moreover, the electron transport properties of the carbon materials can provide an electron conductive network and promote the utilization rate of sulfur in cathode. The prepared carbon-sulfur composite exhibited a high specific capacity and excellent cycle stability. The results show a high initial discharge capacity of 1443 mAh g(-1) and retain 804 mAh g(-1) after 80 discharge/charge cycles at a rate of 0.5 C. A Coulombic efficiency retained up to 92% after 80 cycles. The prepared hierarchically porous carbon materials were proven to be an effective host matrix for sulfur encapsulation to improve the sulfur utilization rate and restrain the dissolution of polysulfides into lithium-sulfur battery electrolytes.

Microstructural and mechanical characteristics of compatibilized polypropylene hybrid composites containing potassium titanate whisker and liquid crystalline copolyester

Abstract Maleic anhydride (MA) compatibilized polypropylene (MPP) hybrid composites reinforced with potassium titanate whiskers (K2Ti6O13) and liquid crystalline polymer (LCP) were prepared in a twin-screw extruder followed by injection molding. The surface of whiskers were treated with tetrabutyl orthotitanate before blending. Scanning electron microscopic (SEM) examination showed that elongated LCP fibrils are formed in the skin section of hybrids reinforced with whiskers of various concentrations. Consequently, the hybrids reinforced with both LCP fibrils and whiskers exhibited anisotropic mechanical properties. Tensile test showed that longitudinal Young’s modulus and tensile strength of hybrids tend to increase with increasing whisker content. Moreover, the stiffness and tensile strength of hybrids were higher than those of MPP/K2Ti6O13 composites. Such enhancement in mechanical properties resulted from the compatibilizing effect of MA-grafted-PP, and from the hybrid reinforcing effect of LCP fibrils and K2Ti6O13 whiskers. Torque measurements revealed that LCP addition is beneficial in reducing the melt viscosity of MPP/K2Ti6O13/LCP hybrids. The results of SEM observations generally correlate well with the mechanical measurements. The effects of MA compatibilization on the microstructure and mechanical properties of hybrids are discussed.

Graphene-encapsulated sulfur (GES) composites with a core–shell structure as superior cathode materials for lithium–sulfur batteries

Relatively uniform sized graphene-encapsulated sulphur (GES) composites with a core (S)–shell (graphene) structure were synthesized in one pot based on a solution-chemical reaction–deposition method. These novel GES particles were characterized by XRD, Raman spectrometry, SEM, TGA, EDS and TEM. The electrochemical tests showed that the present GES composites exhibit high specific capacity, good discharge capacity retention and superior rate capability when they were employed as cathodes in rechargeable Li–S cells. A high sulphur content (83.3 wt%) was obtained in the GES composites. Stable discharge capacities of about 900, 650, 540 and 480 mA h g−1 were achieved at 0.75, 2.0, 3.0 and 6.0 C, respectively. The good electrochemical performance is attributed to the high electrical conductivity of the graphene, the reasonable particle size of sulphur particles, and the core–shell structures that have synergistic effects on facilitating good transport of electrons from the poorly conducting sulphur, preserving fast transport of lithium ions to the encapsulated sulphur particles, and alleviating the polysulfide shuttle phenomenon. The present finding may provide a significant contribution to the enhancement of cathodes for the lithium–sulphur battery technology.

Novel Quaternized Poly(arylene ether sulfone)/Nano-ZrO2 Composite Anion Exchange Membranes for Alkaline Fuel Cells

A series of composite anion exchange membranes based on novel quaternized poly(arylene ether sulfone)/nanozirconia (QPAES/nano-ZrO₂) composites are prepared using a solution casting method. The QPAES/nano-ZrO₂ composite membranes are characterized by FTIR, X-ray diffraction (XRD), and scanning electron microscopy/energy-dispersive X-ray analysis (SEM/EDX). The ion exchange capacity (IEC), water uptake, swelling ratio, hydroxide ion conductivity, mechanical properties, thermal stability, and chemical stability of the composite membranes are measured to evaluate their applicability in fuel cells. The introduction of nano-ZrO₂ induces the crystallization of the matrix and enhances the IEC of the composite membranes. The modification with nano-ZrO₂ improves water uptake, dimension stability, hydroxide ion conductivity, mechanical properties, and thermal and chemical stabilities of the composite membranes. The QPAES/nano-ZrO₂ composite membranes show hydroxide ion conductivities over 25.7 mS cm⁻¹ at a temperature above 60 °C. Especially, the QPAES/nano-ZrO₂ composite membranes with the nano-ZrO₂ content above 7.5% display hydroxide ion conductivities over 41.4 mS cm⁻¹ at 80 °C. The E(a) values of the QPAES/nano-ZrO₂ composite membranes with the nano-ZrO₂ content above 5% are lower than 11.05 kJ mol⁻¹. The QPAES/7.5% nano-ZrO₂ composite membrane displays the lowest E(a) value and the best comprehensive properties and constitutes a good potential candidate for alkaline fuel cells.

Nearly 100% internal phosphorescence efficiency in a polymer light-emitting diode using a new iridium complex phosphor

A new iridium complex with a phenylphthalazine ligand has been prepared by an unexpected method and polymer light-emitting devices doped with the complex have been achieved with nearly 100% internal phosphorescence efficiency.

Effect of reactive compatibilizers on the mechanical properties of polycarbonate/poly(acrylonitrile-butadiene-styrene) blends

Polycarbonate (PC)/poly(acrylonitrile-butadiene-styrene) (ABS) blends compatibilized with both maleic anhydride (MA)-grafted polypropylene and solid epoxy resin (bisphenol type-A) were injection molded. The effects of the compatibilizer additions on the morphology and mechanical properties of the PC/ABS blends were investigated. Tensile and Izod impact tests revealed that the addition of epoxy at 2 phr level to the MA-grafted PC/ABS 70/30 blend led to a significant increase in both tensile ductility and impact strength. Consequently, epoxy content of 2 phr level was added to all the blends investigated. Moreover, tensile tests showed that the yield strength of PC decreased almost linearly with increasing ABS content. However, the tensile modulus showed a positive deviation from the rule of mixtures. Both MA copolymer and epoxy were effective to compatibilize the PC/ABS blends containing ABS content up to 30 wt%. In this case, the impact strength of these compatibilized blends was close to that of PC. Above 40 wt% ABS content, the impact strength of the compatibilized PC/ABS blends decreased significantly. Scanning electron microscopic examination showed that the ABS tends to disperse as large domains in PC matrix of the uncompatibilized PC/ABS blends. However, the size of ABS domains of PC/ABS blends with ABS ≤ 30 wt% was reduced dramatically owing to the incorporation of both compatilizers.