Thermal Gravimetric Analysis Curves Research Articles

Structural and optical properties of new yellow emitting iridium(iii) complexes and their application as an active layer component in white organic light-emitting diodes

Iridium(III) complexes containing two 2-(3-fluorophenyl)-4-methylpyridine and one branched alkyl side group on the 2,2′-bipyridine ligand were synthesized and characterized by UV-Visible, fluorescence, FTIR, NMR spectroscopies, thermal gravimetric analysis (TGA) and cyclic voltammetry. The complexes containing 4-dihexylmetyl-4′-heptyl-2,2′-bipyridine, 4,4′-bis(3-ethylheptyl)-2,2′-bipyridine and 4-(3-ethylheptyl)-4′-methyl 2,2′-bipyridine are named as CS137, CS138 and CS139, respectively, and exhibit a yellow emission band at around 590 nm. The photoluminescence quantum yields are in the range of 0.63–0.72 in chlorobenzene. The TGA curves of the complexes present high decomposition temperatures above 280 °C. The HOMO and LUMO energy levels are in the range of −5.36–(−5.43) eV and −3.21–(−3.27) eV, respectively. Solution processed organic light-emitting diodes are fabricated by the use of these complexes as dopants at various concentrations in the poly(N-vinyl carbazole: 1,3-bis[(4-tert-butylphenyl)-1,3,4-oxadiazolyl]phenylene host. Almost no electroluminescence could be obtained from the blend containing CS139 whereas those of CS137 and CS138 resulted in white light. Commission Internationale de L'Eclairage (CIE) chromaticity coordinates shifted to the yellow region with the increase in complex ratio in the blend. The obtained device characteristics are attributed to the positive effects of higher steric hindrance in CS137 and CS138.

Synthesis and characterisation of (La,Pr) monazite solid solution series

Monazite type ceramics are considered as potential ceramic storage materials for high level nuclear waste. Natural monazite is a host for radioactive elements like U and Th without becoming metamict due to radiation damage. Monazites are also known for their chemical flexibility and thermal stability. In this context, a solid solution series of (La,Pr)PO4 was synthesised as powders and single crystals and characterised by PXRD (Powder X-Ray Diffraction analysis), EMPA (Electron Microprobe Analysis), TGA (Thermal Gravimetric Analysis) and DSC (Differential Scanning Calorimetry). La and Pr were used as inactive surrogates for the minor actinides Am, Cm and Np, which represent major challenges in nuclear waste management due to their long half-life and high radiotoxicity. The powder samples were prepared following the protocol of [1]. Ln2O3 were mixed with NH4H2PO4 in excess. Powders were ground, pressed, and heated for one day at 12500C in air. X-Ray laboratory and synchrotron data showed that all samples were single phase. A decrease in the lattice parameters and volume with increasing Pr content was observed as expected due to the smaller radius of Pr3+ with respect to La3+ in nine fold coordination. The monoclinic angle β showed a linear increase. Using EMPA, the composition of all samples was determined. The average deviation from the nominal composition was calculated to be about 4 mol% which covers both, sample inhomogeneity and, more importantly, experimental challenges due to grain shape and porosity. In TGA and DSC curves, similar behaviour for all samples was observed, except for the Pr end member. This unsolved issue is currently under investigation. Complementary IR and Raman spectroscopic data showed the expected linear trends [2]. This behaviour was also reported for LnPO4 (Ln = La-Gd) [3]. The author gratefully thanks the BMBF (02 NUK 021E) for financial funding.

A novel material of cross-linked styrylpyridinium salt intercalated montmorillonite for drug delivery.

A facile synthesis of a styrylpyridinium salt (SbQ)/montmorillonite (MMT) via cationic exchange interactions between styrylpyridinium species (specifically SbQ) and MMT platelets is reported in this work. The SbQ-MMT solutions were irradiated under ultraviolet (UV) light for a specific time to obtain the cross-linked SbQ-MMT materials. Scanning electron microscopy and atomic force microscopy analyses revealed the structures and morphologies of MMT and modified MMT. X-ray diffraction and transmission electron microscope analyses indicated that the basal spacing increased from 1.24 to 1.53 nm compared with the pristine MMT, which proved that SbQ had interacted with MMT. Thermal gravimetric analysis curves showed that the amount of SbQ in the MMT interlayers was 35.71 meq/100 g. Fourier transform infrared spectroscopy also confirmed the intercalation of SbQ species into MMT interlayers, and UV spectroscopy was used to follow up the cross-linking of SbQ-MMT. This novel material has potential applications in drug delivery, and it can also be used as an additive to improve the mechanical properties of polymers.

Synthesis and characterisation of polymethylmethacrylate/nanosilica and nanosilica/polymethylmethacrylate core–shell structure composite microspheres

The nanosilica/polymethylmethacrylate (SiO2/PMMA) and polymethylmethacrylate/nanosilica (PMMA/SiO2) core–shell structure composite microspheres were fabricated by dispersion polymerisation under similar reaction conditions. These two kinds of microspheres are different to each other by their opposite core–shell structure. The composite mircospheres were characterised by infrared spectra, transmission electron microscopy and thermal gravimetric analysis (TGA). The diameter of SiO2/PMMA particles is about 50 nm. The average diameters of PMMA/SiO2 particles are in the range of 60–70 nm as KH570 was added after methyl methacrylate polymerisation reaction for 2 h. The TGA curves show that the thermal stability of SiO2/PMMA is better than PMMA/SiO2.

Synthesis and Characterization of Polyaniline Conductive Composite Films

Conductive polyaniline(PANI) was synthesized by chemical oxidative copolymerization , using dodecylbenzene sulfonic acid (DBSA)as doping agent. PANI-DBSA/ABS conductive films were obtained by solution blending method, using chloroform as organic solvents. The products were characterized by means of digital four-point probe meter, FT-IR spectroscopy, thermal gravimetric analysis (TGA) and inverted metallurgical microscope. The results indicate that PANI-DBSA has good solubility because dodecylbenzene sulfonic acid (DBSA) plays a good doping role in polyaniline. Composite films’ electric conductivity improves with the increasing content of PANI and the percolation threshold is about 10wt% when conducting network formed. TGA curves demonstrate that product’s glass transition temperature is much higher than acrylonitrile-butadiene-styrene resin, furthermore, the thermal stability of composite films also improves compared with polyaniline or resin.

Palygorskite-cerium oxide filled rubber nanocomposites

Palygorskite (PA)-cerium oxide (CeO2) was modified with cetyl-trimethylammonium bromide (CTAB) to be used as filler of high-performance natural rubber (NR)/styrene butadiene rubber (SBR) nanocomposites. The microstructure of the filler and the rubber nanocomposites were characterized by transmission electron microscope (TEM), X-ray diffraction (XRD), high-resolution TEM (HRTEM), selected area electron diffraction (SAED), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and thermal gravimetric analysis (TGA). The TEM/HRTEM images and XRD/SAED patterns revealed that face-centered cubic CeO2 nanoparticles with an average diameter of 5nm were homogeneously distributed on the surfaces of the PA fibers. The influences of CTAB modified PA-CeO2 (CTAB-PA-CeO2) on the curing, morphological, mechanical and thermal properties of the rubber nanocomposites were investigated. The curing measurements indicated that the addition of CTAB-PA-CeO2 increased the crosslink density and shortened the curing process of the rubber nanocomposites. The SEM and TEM images demonstrated that the CTAB-PA-CeO2 fibers were homogeneously distributed within the NR/SBR matrix. The nanoscale dispersion of CTAB-PA-CeO2 and adequate rubber/filler interactions as well as the special rubber/filler network resulted in an obvious reinforcement. The TGA curves illustrated that the thermal stability of the rubber nanocomposites was also improved due to the addition of CTAB-PA-CeO2.

Delignification of sugarcane bagasse with alkali and peracetic acid and characterization of the pulp

Sugarcane bagasse was delignified with alkali and peracetic acid in a two-stage process to obtain pulps with high yield and low kappa number. The experimental results indicated that alkali pretreatment prior to peracetic acid (PAA) delignification could significantly reduce PAA loading by partially removing lignin and swelling the fibers. An optimum condition for the two-stage delignification was obtained for pulping of sugarcane bagasse. The pulps were further characterized by chemical composition analysis, strength property tests, Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD), and Thermal Gravimetric Analysis (TGA). It was found that the alkali-PAA process could be conducted under milder conditions with resulting higher pulping selectivity, higher degree of polymerization (DP), and superior mechanical properties of pulps, compared to the kraft pulping process. Both kraft pulps and alkali-PAA pulp had similar FTIR spectra, XRD spectra, and TGA (DTG) curves. However, further analysis indicated that the alkali-PAA pulp had higher infrared crystallization index and cellulose crystallinity.

Synthesis and characterization of 3C and 2H-SiC nanocrystals starting from SiO 2, C 2H 5OH and metallic Mg

Silicon carbide (3C-SiC) nanocrystals were prepared starting from SiO 2, C 2H 5OH, and metallic Mg in an autoclave at 200 °C. X-ray diffraction patterns of the sample can be indexed as the cubic phase of SiC with the lattice constant a = 4.357 Å, in good agreement with the reported value (JCPDS card no. 29-1129; a = 4.359 Å). Transmission electron microscopy images show that the product mainly composed of nanowires with diameters in the range of 10–30 nm and lengths up to tens of micrometers; High-resolution transmission electron microscopy images reveal that these 3C-SiC nanowires grow along [1 1 1] direction; As polyvinylpyrrolidine was added into the above reactant system, the final products obtained at 180 °C were mixed 3C and 2H-SiC flakes. Thermal gravimetric analysis curves reveal that these two samples have thermal stability below 800 °C, and room-temperature photoluminescence spectrum of the 3C-SiC sample show a strong emission peak centered at 403 nm.

The Effect of Oxygen on the Kinetics of the Thermal Degradation for Rice Straw

The effect of oxygen on the thermal degradation of rice straw was investigated with a thermal gravimetric analysis (TGA) reaction system. The TGA curves indicated two sharp mass changes during the process and the reaction could be simplified as occurring in two stages. Oxygen speeds up the thermal degradation of intermediates. A kinetic model was proposed and its corresponding parameters such as activation energies, pre-exponential factors, and reaction orders were determined through experiments conducted in nitrogen gas (N2), 10% oxygen gas (O2), and air at the heating rates of 2, 5, and 10 K/min. The experimental data agreed well with those predicted by the proposed model, which validated the applicability of this model to the design of agricultural waste processing systems.

Lattice Vibrations and Thermal Properties of Stoichiometric KYb(WO4)2 Crystal

Single crystal KYb(WO4)2 (KYbW) has been grown by the top-seeded solution growth (TSSG) method. Polarized Raman and infrared spectra have been recorded at room temperature. The lattice vibration modes were calculated, and the strongest peaks appear at 760 and 908 cm−1 with a line-width ΔωR of 14.2 and 10 cm−1, corresponding to relaxation times of 0.747 and 1.061 ps, respectively. This makes KYbW attractive for stimulated Raman scattering (SRS) applications and for use in the picosecond regime. Differential thermal analysis and thermal gravimetric analysis curves, high-temperature X-ray diffraction patterns, specific heat, thermal expansion and thermal conductivity have been studied. The thermal expansion anisotropy of KYbW is weaker than that of KGd(WO4)2 (KGW), but stronger than that of KLu(WO4)2 (KLuW). The thermal diffusivity along the c-axis is large (λc > λa > λb). The results are consistent with the anisotropic structure of crystalline KYbW.

Pyrolysis Kinetics of Rice Husk in Different Oxygen Concentrations

The effects of oxygen on the pyrolysis of rice husk were investigated with a thermal gravimetric analysis (TGA) reaction system. Pyrolysis experiments of rice husk were carried out in N2, 10% O2, and air at the heating rates of 2, 5, and 10K∕min. The TGA curves indicated two principal reactions, distinguished by significant and distinct mass changes over the experimental range. Oxygen enhanced the pyrolysis reactions of intermediates, which was produced from the first stage reaction of rice husk. A simple kinetic model was proposed for the pyrolysis of rice husk in different oxygen concentrations. The corresponding activation energies, preexponential factors, and reaction orders were determined. The experimental results were satisfactorily fitted by the proposed kinetic model.

High compact melamine-formaldehyde microPCMs containing n-octadecane fabricated by a two-step coacervation method

Microcapsules containing n-octadecane were successfully fabricated by an in-situ polymerization process with melamine-formaldehyde (MF) prepolymer and a hydrolyzed copolymer of styrene and maleic anhydride (SMA) as shell materials. To achieve a long service time of microcapsules containing phase change materials (microPCMs), the compactness of shells was improved by adding the MF prepolymer twice. The mechanism of this method was a two-step coacervation (TSC) under the help of hydrolyzed SMA compared to a one-step coacervation (OSC). To understand the influence of both coacervations, properties of shells were investigated in terms of morphologies, density, thickness, and stability by means of scanning electron microscopy (SEM), transmission electron microscopy, and thermal gravimetric analysis (TGA). The data of shells thickness were achieved from the cross-section SEM images. It shows that the average thickness of shells from two kinds of process are 0.1 μm. The density and stability in water of shells fabricated by TSC are both higher than that of shells by OSC. TGA curves show the expected microPCMs of TSC losing weight from 200 to 400 °C. The release curves, relationship between time and logarithmic residual weight of core, show there are two decrease-linear steps after curve regression. It can be concluded from all these results that the TSC method may be a promising method leading to a compact shell structure for various application.

Polymeric thermal analysis of C + H and C + H + Ar ion implanted UHMWPE samples

Chemical surface characterization of C+H hybrid ion implanted UHMWPE samples were carried out using DSC (differential scanning calorimeter) and TGA (thermal gravimetric analysis) techniques. Samples were implanted with a fluence of 1017ion/cm2 and an extraction voltage of 30kV. The study of TGA and DSC curves showed that: (1) Polymeric decomposition temperature increased, (2) Tm, ΔCp and ΔHm values changed while ΔCp and ΔHm increased. Tg value could not be measured, because of some experimental limitations. However, the increase in ΔHm values showed that Tg values increased, (3) the branch density which indicated the increase in number of cross-link (Mc) decreased in ion implanted samples and (4) increase in ΔHm values indicated increase in crystallinity of implanted surface of UHMWPE samples.

Direct synthesis of new soluble and thermally stable poly(urethane‐imide)s from an imide ring‐containing dicarboxylic acid using diphenylphosphoryl azide

AbstractThe direct preparation of various aromatic poly(urethane‐imide)s from 4‐p‐biphenyl‐2,6‐bis(4‐trimellitimidophenyl)pyridine (1) using diphenylphosphoryl azide (DPPA) was investigated. The polymers were mainly obtained by the conversion of imide ring‐containing diacid 1 to corresponding di(carbonyl azide) 2 with DPPA and then to diisocyanate 3 through the Curtius rearrangement of compound 2 followed by polyaddition of 3 in different amounts with aromatic dihydroxy compounds. The molecular weights of the resulting poly(urethane‐imide)s were evaluated viscometrically. All of the resulted polymers were thoroughly characterized by spectroscopic methods and elemental analyses. The poly(urethane‐imide)s exhibited an excellent solubility in a variety of polar solvents. Crystallinity nature of the polymers was estimated by means of WXRD. The glass‐transition temperatures of the polymers determined by DSC method were in the range of 191–202°C. The 10% weight loss temperatures of the poly(urethane‐imide)s from their thermal gravimetric analysis curves were found to be in the range of 392–416°C in nitrogen. The films of the resulting polymers were also prepared by casting the solution. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 869–877, 2006

Synthesis and properties of poly(methyl methacrylate)/clay nanocomposites using natural montmorillonite and synthetic Fe‐montmorillonite by emulsion polymerization

AbstractIn this article, Fe‐montmorillonite (Fe‐MMT) was synthesized by hydrothermal method. For the first time, Fe‐MMT was modified by cetyltrimethyl ammonium bromide (CTAB), and poly(methyl methacrylate)(PMMA)/Fe‐MMT nanocomposites were synthesized by emulsion polymerization. Then poly(methyl methacrylate)(PMMA)/natural montmorillonite (Na‐MMT) and PMMA/Fe‐MMT nanocomposites were compared by Fourier transform infrared (FTIR) spectra, X‐ray diffraction (XRD) patterns, transmission electron microscopy (TEM), and thermal gravimetric analysis (TGA). By XRD and TEM, it was found out that the morphology of PMMA/Fe‐MMT nanocomposites was different from that of the PMMA/Fe‐MMT nanocomposites when the content of two types of clay was same in the PMMA matrix. It was possible that the presence of iron may lead to some radical trapping, which enhances intragallery polymerization to be developed to improve layer dispersion in PMMA/Fe‐MMT systems. In TGA curves, the thermal stability and residue at 600°C of PMMA/Fe‐MMT nanocomposites were higher than those of PMMA/Na‐MMT nanocomposites. Those dissimilarities were probably caused by structural Fe ion in the lattice of Fe‐MMT. POLYM. COMPOS., 27:49–54, 2006. © 2005 Society of Plastics Engineers

Thermal degradation and flame retardancy of ethylene-vinyl alcohol copolymer blended with ammonium polyphosphate

The thermal degradation and flame retardancy of ethylene-vinyl alcohol copolymer (EVOH) blended with ammonium polyphosphate (APP) have been studied. EVOH blended with 5 wt.% or more of APP showed excellent flame retardancy. The burn time in UL-94 test and the total released heat measured by cone calorimeter decreased with increasing APP content. In particular, blended-EVOH with 15 and 20 wt.% of APP did not ignite under UL-94 test. The thermal degradation properties were observed by TGA (thermal gravimetric analysis), Py/GC/MS (pyrolysis/gas chromatography/mass spectrometry) and EA (elemental analysis). TGA curves of blended-EVOH showed three points of inflection which were considered to be due to the reaction with APP. Although 20% of the degradation temperature fell with the blending of APP, 70% of the degradation temperature rose. The results of elemental analysis showed multiple degradation reactions, one of which was the reaction of APP with OH radicals on the polymer chain to form a crosslinked structure. The effect of APP on the flame retardancy of EVOH was considered to be caused by the crosslinking as well as the dehydrogenation.

Preparation and characterizations of SiO2/TiO2/γ-glycidoxypropyltrimethoxysilane composite materials for optical waveguides

SiO2/TiO2/γ-glycidoxypropyltrimethoxysilane composite materials processed by the sol-gel technique were studied for optical waveguide applications. Waveguide films with thickness more than 1.7 μm were prepared on a silicon substrate by a single-coating process and low-temperature heat treatment from these high-titanium-content composite materials. Scanning electron microscopy (SEM), atomic force microscopy (AFM), thermal gravimetric analysis (TGA), UV-visible spectroscopy (UV-VIS), Fourier-transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS) have been used to characterize the waveguide films. TGA curves showed that organic compounds in the composite materials would decompose in the temperature range from 200 °C to 480 °C. SEM, AFM and UV-VIS results showed that a dense, porous-free, and high transparency in the visible range waveguide film could be obtained at a low heat-treatment temperature. It was also noted that the carbon content in the film with higher titanium content heated at high temperature was evidenced by XPS. The waveguide propagation loss properties of the composite material films were also investigated and showed a dependence on the titanium molar fraction.

The influence of light on the thermal decomposition of polypropylene fibers

The influence of exposure to artificial light (ultraviolet and visible spectrum) on the thermal degradation process of polypropylene fiber has been investigated. The activation energy E as a kinetic parameter of the fiber thermal decomposition has been defined by means of the Flynn–Wall and Freeman–Carroll methods. The fiber melting temperature range was also defined. The investigations have been made on the basis the of thermal gravimetric analysis and differential thermal gravimetric analysis curves determined at various heating speeds, in the temperature range from 100°–600°C. It was found that thermal stability of polypropylene fiber is reduced by light treatment (i.e., fiber softens and melts at a lower temperature). Activation energy values determined for thermal decomposition of the fiber samples exposed to the influence of light are considerably higher than the values determined on unexposed samples. The decomposition process of aged fiber is more complex and occurs in a larger temperature range. Both the methods used show almost similar results. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 2237–2244, 1999

Pyrolysis Kinetics of Paper Mixtures in Municipal Solid Waste

The pyrolysis kinetics of a mixture of the four principal papers (uncoated and coated printing/writing papers, newsprint, and tissue paper) in municipal solid waste (MSW) was investigated with a thermal gravimetric analysis (TGA) reaction system. The experiments were carried out in a nitrogen environment over the temperature range of 450 to 900 K at various constant heating rates of 1, 2, and 5 K min−1. The results indicated that there were two principal reactions in the TGA curves as distinguished by the two significant and distinct mass changes over the experimental conditions. The pyrolysis of a paper mixture can be adequately described by a two reaction model. The effect of interaction between the components of a paper mixture on the pyrolysis rate was insignificant. The results for the pyrolysis rates of paper mixtures with slow heating rates can be represented by the weighting sum of the corresponding pyrolysis rates of the components of papers in MSW. The experimental results were satisfactorily fitted by the proposed chemical reaction kinetic equations and able to provide useful data for the design of a pyrolytic processing system for the waste papers in MSW. © 1997 SCI.

Pyrolysis Kinetics of Uncoated Printing and Writing Paper of MSW

The pyrolysis kinetics of cellulosic uncoated printing and writing paper, which is one of the principal materials contributing to the municipal solid waste (MSW) of Taiwan, was investigated with a thermal gravimetric analysis (TGA) reaction system. The experiments were carried out in a nitrogen environment in the 450–850 K temperature range at various constant heating rates of 1, 2, and 5 K/min. The results indicated that there were two principal reactions in TGA curves as distinguished by the two significant and distinct mass changes over the experimental conditions. The pyrolysis of uncoated printing and writing paper can be adequately described by a two-reaction model. The corresponding activation energies, preexponential factors, and reaction orders were determined. The experimental results were satisfactorily fitted by the proposed chemical reaction model.