TGA Result Research Articles

Preparation and Characterization of Chitosan Monomer/Organic Rectorite Nanocomposite

The nanocomposites of chitosan and its derivatives with layered silicate have gained increasing attention since they showed many attracting properties. For the first time, the present study was carried out to investigate the intercalation of chitosan monomer (Dglucosamine hydrochloride, DGH) into organic rectorite (OREC). XRD, TEM, FTIR, 13C NMR, SEM and TGA were performed to characterize the microstructure, morphology and properties of DGH/OREC nanocomposites. The results showed that DGH monosaccharide could insert into the interlayer of OREC, and intercalation result was similar to that of chitosan/OREC nanocomposites. The interlayer distance of DGH/OREC nanocomposites was not proportional to the mass ratio of DGH to OREC, it increased firstly to reach a peak value before it decreased with the increase of the DGH amount. The largest spacing of 6.13 nm was obtained when the mass ratio of DGH to OREC was at 12:1. The direct observation by TEM and SEM also confirmed the intercalated but not exfoliated DGH/OREC nanocomposites. Noteworthily, most strong crystals of DGH in DGH/OREC nanocomposites were destroyed greatly, but its two weak crystals were stronger. TGA result indicated that the thermal stability of DGH/OREC nanocomposites were higher than that of pristine DGH. Keywords: D-glucosamine hydrochloride, rectorite, nanocomposite, intercalation, crystalline, thermal stability, chitosan

Optical and electrical properties of polyaniline‐cadmium sulfide nanocomposite

AbstractPolyaniline‐cadmium sulfide nanocomposite has been synthesized by the chemical oxidative polymerization of aniline with ammonium peroxodisulfate as an initiator in presence of cadmium sulfide nanoparticles. TEM, XRD, FTIR, TGA, UV–vis spectroscopy, and photoluminescence studies were done for the structural, thermal and optical characterization of the samples. The particle size of nanocomposites lies in between 7 and 10 nm. XRD spectrum shows that polyaniline is amorphous, but peaks present in the spectrum of polymer nanocomposites are for cadmium sulfide nanoparticles. TGA result shows that nanocomposite is more thermally stable. The band gap of nanocomposite decreases with increasing content of cadmium sulfide nanoparticles. An enhancement in photoluminescence has been observed in the nanocomposite than that in pure polyaniline. The dc and ac electronic transport property of polyaniline cadmium sulfide composites has been investigated within a temperature range 77 ≤ T ≤ 300 K and in the frequency range 20 Hz–1 MHz. The dc conductivity follows variable range hopping (VRH) model. The ac conductivity follows a power law whereas the temperature dependence of frequency exponent s can be explained by correlated barrier hopping (CBH) model. The dielectric behavior of the samples has been explained in terms of the grain and grain boundary resistance and capacitance. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers

An Effective Method to Improve the Performance of Fixed Carrier Membrane via Incorporation of CO 2-selective Adsorptive Silica Nanoparticles

Fixed carrier membrane exhibits attractive CO 2 permeance and selectivity due to its transport mechanism of reaction selectivity (facilitated transport). However, its performance needs improvement to meet cost targets for CO 2 capture. This study attempts to develop membranes with multiple permselective mechanisms in order to enhance CO 2 separation performance of fixed carrier membrane. In this study, a novel membrane with multiple permselective mechanisms of solubility selectivity and reaction selectivity was developed by incorporating CO 2-selective adsorptive silica nanoparticles in situ into the tertiary amine containing polyamide membrane formed by interfacial polymerization (IP). Various techniques were employed to characterize the polyamide and polyamide-silica composite membranes. The TGA result shows that nanocomposite membranes exhibit superior thermal stability than pure polyamide membranes. In addition, gas permeation experiments show that both nanocomposite membranes have larger CO 2 permeance than pure polyamide membranes. The enhanced CO 2/N 2 separation performance for nanocomposite membranes is mainly due to the thin film thickness, and multiple permselective mechanisms of solubility selectivity and reaction selectivity.

Synthesis and Characterization of Monofunctionalized Polyhedral Oligomeric Silsesquioxanes by Cohydrolytic and Cocondensation of Propyltrimethoxysilane and Vinyltrimethoxysilane

A monofunctional POSS [Si8O12(CH˭CH2)(C3H7)7] was synthesized by the cohydrolysis and cocondensation of propyltrimethoxysilane and vinyltrimethoxysilane in methanol solvent under acidic conditions. Then, the structure of the product was investigated using FT-IR, 1H-NMR, 29Si-NMR and XRD. Experimental results indicated that the mole rate of propyls and vinyls attached on POSS was approximately 7:1, which was controlled through altering the ratio of two monomers. Furthermore, the TGA result also showed a rapid mass loss began at temperature over 218°C due to the degradation or sublimation of POSS itself. The new method, in comparison with the conventional corner-capping method, offered us another simple and effective access to preparing this kind of monofunctional POSS.

A low band gap donor–acceptor copolymer containing fluorene and benzothiadiazole units: synthesis and photovoltaic properties

A new low band gap copolymer containing dialkylfluorene and 4,7-dithienyl-2,1,3-benzothiadiazole (TBT), poly(fluorenevinylene-alt-4,7-dithienyl-2,1,3-benzothiadiazole) (PF-TBT) was synthesized by Heck cross-coupling polymerization. The copolymer is soluble in common organic solvents such as chloroform, tetrahydrofuran and chlorobenzene. The TGA result indicated that the copolymer possesses good thermal stability. The absorption, electrochemical and photovoltaic properties of PF-TBT were investigated and compared with those of poly(fluorenevinylene-alt-4,7-diphenyl-2,1,3-benzothiadiazole) (PF-DBT) whose structure is similar to PF-TBT. The copolymer exhibited a broad absorption band with an absorption edge close to 700 nm and an optical band gap of 1.82 eV. Cyclic voltammetry studies indicated that the relatively low HOMO energy level assured a higher open circuit voltage (Voc) when PF-TBT is used as the donor material in a photovoltaic cell. The bulk heterojunction (BHJ) solar cell using PF-TBT as the donor and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) as the acceptor with the structure of ITO/PEDOT : PSS/copolymer : PCBM/LiF/Al, exhibited a Voc of 0.86 V, short-circuit current density (Jsc) of 3.97 mA cm−2, fill factor (FF) of 0.35, and a power conversion efficiency (PCE) of 1.18% under one sun of AM 1.5 solar simulator illumination (100 mW cm−2).

Study on the preparation and properties of novolac epoxy/graphite composite bipolar plate for PEMFC

In this study, the graphite/polymer composite bipolar plate was manufactured by a bulk-molding compound process. Low-cost novolac epoxy was chosen to compound with natural graphite and black carbon. The electrical properties and mechanical properties of composite bipolar plate were studied. The aging behavior was characterized according to the changes in property before and after the immersion test. The results show that the composite bipolar plates have good corrosion resistibility in the simulated solution of 0.005 mol L −1 H 2SO 4 + 2 × 10 −6 mol L −1 HF. TGA result shows that the novolac epoxy/NG composite has excellent thermal stability. The optimum processing conditions for preparing composite bipolar plate are: resin content about 15 wt.%; molding pressure 200 MPa; curing temperature 180 °C; graphite particle size −200 mesh. Under the optimum conditions, the composite bipolar plates have been produced, the electrical conductivity can attain to 120 S/cm and flexural strength is higher than 38 MPa.

Organic Chromophore with Enhanced Optical Nonlinearity and Thermal Stability by Introducing Julolidine as Donor Group

We prepared a nonlinear optical chromophore (Ju-TCF) with julolidine moiety as a donor and compared it with the chromophore (St-TCF) with the dialkyl-attached aminobenzene as a donor. The MOPAC calculations showed that the figure of merit (microbeta0) of Ju-TCF was estimated 70% larger than St-TCF. Based on the TGA result, Ju-TCF displayed on-set of degradation at 261 degrees C, which was about 30 degrees C higher than St-TCF (234 degrees C). The julolidine chromophore blended in the polymer exhibited 32 pm/V of electro-optic coefficient, which was 30% larger than St-TCF at the same molar chromophore content.

New selenoproteins identified in silico from the genome of Anopheles gambiae

Selenoprotein is biosynthesized by the incorporation of selenocysteine into proteins, where the TGA codon in the open reading frame does not act as a stop signal but is translated into selenocysteine. The dual functions of TGA result in mis-annotation or lack of selenoproteins in the sequenced genomes of many species. Available computational tools fail to correctly predict selenoproteins. Thus, we developed a new method to identify selenoproteins from the genome of Anopheles gambiae computationally. Based on released genomic information, several programs were edited with PERL language to identify selenocysteine insertion sequence (SECIS) element, the coding potential of TGA codons, and cysteine-containing homologs of selenoprotein genes. Our results showed that 11365 genes were terminated with TGA codons, 918 of which contained SECIS elements. Similarity search revealed that 58 genes contained Sec/Cys pairs and similar flanking regions around in-frame TGA codons. Finally, 7 genes were found to fully meet requirements for selenoproteins, although they have not been annotated as selenoproteins in NCBI databases. Deduced from their basic properties, the newly found selenoproteins in the genome of Anopheles gambiae are possibly related to in vivo oxidation tolerance and protein regulation in order to interfere with anopheles' vectorial capacity of Plasmodium. This study may also provide theoretical bases for the prevention of malaria from anopheles transmission.

Synthesis and characterization of metal ion imprinted nano-porous polymer for the selective recognition of copper

Selective recognition of metal ions utilizing metal ion-imprinted polymers (MIIPs) received much importance in diverse fields owing to their high selectivity for the target metal ions. In the present study, a copper ion imprinted polymer was synthesized without an additional complexing ligand or complex with a broad aim to avoid the conventional extra metal ion complexing ligand during the synthesis of MIIP. The complete removal of the copper metal ion from the MIIP was confirmed by AAS and SEM–EDX. SEM image of the MIIP exhibited nano-patterns and it was also found to be entirely different from that of non-imprinted polymer and polymer with copper metal ions. BET surface area analysis revealed more surface area (47.96m2/g) for the Cu(II)-MIIP than non-imprinted control polymer (41.43m2/g). TGA result of polymer with copper metal ion indicated more char yield (18.41%) when compared to non-imprinted control polymer (8.3%) and Cu(II)-MIIP (less than 1%). FTIR study confirmed the complexation between Cu(II)-MIIP and Cu(II) metal ion through carbonyl oxygen of acryl amide. The Cu(II)-MIIP exhibited an imprinting efficiency of 2.0 and it was showing 8% interference from a mixture of Zn, Ni and Co ions. A potentiometric ion selective electrode devised with Cu(II)-MIIP showed more potential response for Cu(II) ion than that was fabricated from non-imprinted polymer.

Thermooxidative degradation of natural rubber/clay composite

AbstractThe clay is treated with a reducing agent and an acid so as to obtain a clay containing various metal components with a variable‐valence state. Then, the clay is coprecipitated with natural rubber (NR) latex to prepare a vulcanized NR/clay composite. The degradation process of the NR/clay composite under hot air condition was studied dynamically by using a Fourier transform infrared spectrometer attaching an in situ sample cell and was also investigated using the TGA method. The test result obtained from the infrared spectrometry indicated that under low decomposition temperature, the decomposition products of the test samples mainly are ethylene, low molecular olefinic hydrocarbon, and carbonyl compounds. As the decomposition temperature rises, the low molecular olefinic hydrocarbon content decreases, the olefine with longer chain is formed, and a lot of alkane decomposition products are formed at the same time. When the content of the metal components with a variable‐valence state in clay such as Cu, Mn, Co, and Fe increases, the oxidation products containing the carbonyl group, the olefinic hydrocarbon, and CO2 in the decomposition product of the test sample also increase. The TGA result clearly shows a shoulder peak that appears by the side of the main peak on the DTG curve of NR/clay composite. With the increase in the content of metal components with variable‐valence state in clay, the initial degradation temperature of the test sample (T0), the degradation peak temperature (Tp1), and the final degradation temperature (Tf1) in first‐stage reaction, as well as the degradation peak temperature (Tp2) and the last final degradation temperature (Tf) in second‐stage reaction of all the test samples more or less shift to the direction of low temperature; besides, the activation energy (E) of the reaction of the test samples more or less decreases. This means that the metal components with variable‐valence state promote the oxidative degradation of the clay–rubber masterbatch. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3809–3815, 2006

Trapping characteristics of volatile ruthenium oxides by Y2O3 filter

Yttria filter has been suggested as a trapping agent for gaseous oxides of ruthenium volatilized during DUPIC fuel fabrication process. Experiments were performed to evaluate the trapping characteristics of gaseous ruthenium oxides by yttria ceramic foam filters in the two-zone furnace under air condition. Yttria filter is expected to offer stable material in which the volatility of the ruthenium can be effectively trapped because of its incorporation into a lattice of high stability over 900 ‡C under air condition. The XRF result of ruthenium trapped on an yttria filter under air condition showed that concentrations of ruthenium on the back and the front faces of the filter decreased linearly with increasing superficial air velocity, and the back face concentration of filter was lower than the front face concentration by about 30-45%. The TGA result of ruthenium trapped on an yttria filter indicates that there is weight loss of 5.8 wt% up to 1,400 ‡C, which is believed to be due to the fact that the thermally stable Y2Ru2O7 phase was formed on an yttria filter.

The chemical and physical properties of electrochemically prepared polyaniline perchlorate (PAP)

AbstractPolyaniline perchlorate (PAP) was synthesized by electrochemical oxidation from 0.2 M aniline in acetonitrile solution containing 0.1 M tetraethylammonium perchlorate as supporting electrolyte. From polarographic and cyclic voltammetry results, the values of the half‐wave potential (E1/2), transfer coefficient (α), and number of electrons related to the electrode reaction (n) were calculated to be 825 mV, 0.894, and 1, respectively. The morphology of the PAP film was observed by using an SEM analyzer. From thermal analysis of the PAP sample, the reaction rate (R) for its thermal decomposition was obtained from the TGA result and a exothermic peak at 330°C was also observed in the DSC curve. The electrical conductivity of the PAP pellet was measured at temperatures from −170 to 25°C. From a plot of conductivity vs. 1/T, the activation energy (Ea) was obtained to be 0.14 eV. The conduction mechanism in a pressed pellet of PAP is suggested to be electronic hopping conduction. The values of the ESR parameters were calculated from an ESR curve for PAP at room temperature.