Thermo-infrared-spectroscopy analysis of dimethylsulfoxide-kaolinite intercalation complexes

Dimethylsulfoxide (DMSO) kaolinite complexes of low-and high-defect kaolinites were studied by thermo-IR-spectroscopy analysis. Samples were gradually heated up to 170°C, three hours at each temperature. After cooling to room temperature, they were pressed into KBr disks and their spectra were recorded. From the spectra two types of complexes were identified. In the spectrum of type I complex two bands were attributed to asymmetric and symmetric H-O-H stretching vibrations of intercalated water, bridging between DMSO and the clay-O-planes. As a result of H-bonds between intercalated water molecules and the O-planes, Si-O vibrations of the clay framework were perturbed, in the low-defect kaolinite more than in the high-defect. Type II complex was obtained by the thermal escape of the intercalated water. Consequently, the H-O-H bands were absent from the spectrum of type II complex and the Si-O bands were not perturbed. Type I complex was present up to 120°C whereas type II between 130 and 150°C. The presence of intercalated DMSO was proved from the appearance of methyl bands. These bands decreased with temperature due to the thermal evolution of DMSO but disappeared only in spectra of samples heated at 160°C. Intercalated DMSO was H-bonded to the inner-surface hydroxyls and vibrations associated with this group were perturbed. Due to the thermal evolution of DMSO the intensities of the perturbed bands decreased with the temperature. They disappeared at 160°C together with the methyl bands.     

Thermo-X-ray-diffraction analysis of dimethylsulfoxide-kaolinite intercalation complexes

DMSO-kaolinite complexes of low- and high-defect Georgia kaolinite (KGa-1 and KGa-2, respectively) were investigated by thermo-XRD-analysis. X-ray patterns showed that DMSO was intercalated in both kaolinites with a d(001)-value of 1.11 nm (type I complex). The samples were gradually heated up to 170°C and diffracted by X-ray at room-temperature. With the rise in temperature, due to the thermal evolution of the guest molecules, the relative intensity of the 1.11 nm peak decreased and that of the 0.72 nm peak (neat kaolinite) increased indicating that the fraction of the non-intercalated tactoids increased. The 1.11 peak disappeared at 130–140°C. During the thermal treatment of both complexes two additional peaks appeared at 110 and 120°C, respectively, with d-values of 0.79–0.94 and 0.61–0.67 nm in DMSO-KGa-1 and 0.81–0.86 and 0.62–0.66 nm in DMSO-KGa-2, indicating the formation of a new phase (type II complex). The new complex was obtained by the dehydration of type I complex and was composed of intercalated DMSO molecules which did not escape. The new peaks disappeared at 150–160°C indicating the complete escape of DMSO.     

Thermal decomposition and kinetics studies on poly(BDFAO/THF), poly(DFAMO/THF), and poly(BDFAO/DFAMO/THF)

The thermal behavior of kaolinite–urea intercalation complex was investigated by thermogravimetry–differential scanning calorimetry (TG–DSC), X-ray diffraction (XRD), and fourier transform infrared spectroscopy (FTIR). In addition, the interaction mode of urea molecules intercalated into the kaolinite gallery was studied by means of molecular dynamics simulation. Three main mass losses were observed at 136 °C, in the range of 210–270 °C, and at 500 °C in the TG–DSC curves, which were, respectively, attributed to (1) melting of the surface-adsorbed urea, (2) removal of the intercalated urea, and (3) dehydroxylation of the deintercalated kaolinite. The three DSC endothermic peaks at 218, 250, and 261 °C were related to the successive removals of intercalated urea with three different distribution structures. Based on the angle between the dipole moment vector of urea and the basal surface of kaolinite, the three urea models could be described as follows: (1) Type A, the dipole moment vector is nearly parallel to the basal surface of kaolinite; (2) Type B, the dipole moment vector points to the silica tetrahedron with the angle between it and the basal surface of kaolinite ranging from 20°to 40°; and (3) Type C, the dipole moment vector is nearly perpendicular to the basal surface of kaolinite. The three distribution structures of urea molecules were validated by the results of the molecular dynamics simulation. Furthermore, the thermal behavior of the kaolinite–urea intercalation complex investigated by TG–DSC was also supported by FTIR and XRD analyses.     

A comparative study of the dehydroxylation process in untreated and hydrazine-deintercalated dickite

A dickite from Tarifa (Spain) was used to study the influence of the intercalation and the later deintercalation of hydrazine on the dehydroxylation process. The dehydroxylation of the untreated dickite occurs through three overlapping endothermic stages whose DTA peaks are centred at 586, 657 and 676°C. These endothermic effects correspond, respectively, to the loss of the inner-surface, the inner hydroxyl groups, and the loss of the water molecules, product of dehydroxylation process, which has been trapped in the framework of the dehydroxylated dickite. The intercalation of hydrazine in the interlayer space of dickite and the later deintercalation affect the dehydroxylation process. It occurs through only two endothermic stages which DTA peaks are centred at 575 and 650°C. The first corresponds to the simultaneous loss of both the inner and the inner-surface hydroxyl groups, whereas the second one is analogous to that at 676°C observed in the DTA curve of untreated dickite. These effects appear shifted to lower temperatures compared to those observed in the untreated dickite.     

Thermal analysis of synthetic reevesite and cobalt substituted reevesite (Ni,Co)<Subscript>6</Subscript>Fe<Subscript>2</Subscript>(OH)<Subscript>16</Subscript>(CO<Subscript>3</Subscript>) · 4H<Subscript>2</Subscript>O

The mineral reevesite and the cobalt substituted reevesite have been synthesised and studied by thermal analysis and X-ray diffraction. The d(003) spacings of the minerals ranged from 7.54 to 7.95 Å. The maximum d(003) value occurred at around Ni:Co 0.4:0.6. This maximum in interlayer distance is proposed to be due to a greater number of carbonate anions and water molecules intercalated into the structure. This increase in carbonate anion content is attributed to an increase in surface charge on the brucite like layers. The maximum temperature of the reevesite decomposition occurs for the unsubstituted reevesite at around 220 °C. The effect of cobalt substitution results in a decrease in thermal stability of the reevesites. Four thermal decomposition steps are observed and are attributed to dehydration, dehydroxylation and decarbonation, decomposition of the formed carbonate and oxygen loss at ~807 °C. A mechanism for the thermal decomposition of the reevesite and the cobalt substituted reevesite is proposed.     

Features of light scattering in aqueous solutions of dimethyl sulfoxide

The water-dimethyl sulfoxide (DMSO) system was studied by means of static light scattering in the concentration range of 0 to 60 mol % DMSO at 20 and 50°C. In the concentration range of 10 mol % DMSO, an abnormal maximum of scattered light was detected, the intensity of which decreases with an increase of temperature. The formation of this maximum is related to hydrophobic effects in the system under study and the existence of an unattainable critical point of delayering. Temperature inversion of light scattering intensity was detected at ∼14 mol % DMSO; at higher concentrations of DMSO, the intensity at 50°C is notably higher than at 20°C (due to the increase in the concentration’s degree of fluctuation upon an increase in temperature); at 60 mol % DMSO, intensities of scattered light at 20 and 50°C almost coincide. The apparent molar volumes of DMSO in solutions were calculated from the published data on density in the temperature range of 5 to 50°C. The minima of these values from 10 to 15 mol % DMSO (i.e., in the range of the abnormal maximum of scattered light) were obtained. The manifestation of hydrophobic effects in aqueous solutions of amphiphilic molecules is explained using the example of the DMSO-H₂O system.     

Thermal behavior analysis of kaolinite–dimethylsulfoxide intercalation complex

The thermal behavior of kaolinite?Cdimethylsulfoxide intercalation complex was investigated by thermogravimetry (TG) and differential scanning calorimetry (DSC) analysis, X-ray diffraction (XRD) analysis, and Fourier-transform infrared (FT-IR) spectroscopic analysis. The samples gradually heated up to different temperatures were studied by XRD and FT-IR. The kaolinite?Cdimethylsulfoxide intercalation complex is stable below 130?°C. With the rise in the temperature, the relative intensity of the 1.124-nm peak gradually decreased and disappeared at 200?°C, however, the intensity of the 0.714?nm peak increased in the XRD patterns. In the infrared spectra, the appearance of methyl bands at 3018, 2934, 1428, and 1318?cm^?1 indicates the presence of intercalated dimethylsulfoxide, the intensities of these bands decreased with the temperature rising and remained until around 175?°C, which agree with the XRD and TG?CDSC data.     

Structure and molecular conformation of tussah silk fibroin films treated with water–methanol solutions: Dynamic mechanical and thermomechanical behavior

The thermal response of tussah (Antheraea pernyi) silk fibroin films treated with different water–methanol solutions at 20°C was studied by means of dynamic mechanical (DMA) and thermomechanical (TMA) analyses as a function of methanol concentration and treatment time. The DMA curves of α-helix films (treated with ≥80% v/v methanol for 2 min and 100% methanol for 30 min) showed the sharp fall of storage modulus at about 190°C, and the loss peak in the range 207–213°C. The TMA curves were characterized by a thermal shrinkage at 209–211°C, immediately followed by an abrupt extension leading to film failure. Both storage and loss modulus curves significantly shifted upwards for β-sheet films, obtained by treatment with ≤60% methanol for 30 min. The loss peak exhibited a maximum at 236°C. Accordingly, the TMA shrinkage at above 200°C disappeared. The films broke beyond 330°C, failure being preceded by a broad contraction step. Intermediate DMA and TMA patterns were observed for the other solvent-treated films. The loss peak shifted to higher temperature (219–220°C), and a minor loss modulus component appeared at about 230°C. This coincided with the onset of a plateau region in the storage modulus curve. The TMA extension–contraction events in the range 200–300°C weakened, and the samples displayed a final broad contraction (peak temperature 326–338°C) before breaking. The DMA and TMA response of these films was attributed to partial annealing by solvent treatment, which resulted in the formation of nuclei of β-sheet crystallization within the film matrix. The increased thermal stability was probably due to the small β-sheet crystals formed, which acted as high-strength junctions between adjacent random coil and α-helix domains. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2717–2724, 1998     

Insight into the thermal decomposition of kaolinite intercalated with potassium acetate: an evolved gas analysis

The thermal decomposition process of kaolinite–potassium acetate intercalation complex has been studied using simultaneous thermogravimetry coupled with Fourier-transform infrared spectroscopy and mass spectrometry (TG-FTIR-MS). The results showed that the thermal decomposition of the complex took place in four temperature ranges, namely 50–100, 260–320, 320–550, and 650–780 °C. The maximal mass losses rate for the thermal decomposition of the kaolinite–potassium acetate intercalation complex was observed at 81, 296, 378, 411, 486, and 733 °C, which was attributed to (a) loss of the adsorbed water, (b) thermal decomposition of surface-adsorbed potassium acetate (KAc), (c) the loss of the water coordinated to potassium acetate in the intercalated kaolinite, (d) the thermal decomposition of intercalated KAc in the interlayer of kaolinite and the removal of inner surface hydroxyls, (e) the loss of the inner hydroxyls, and (f) the thermal decomposition of carbonate derived from the decomposition of KAc. The thermal decomposition of intercalated potassium acetate started in the range 320–550 °C accompanied by the release of water, acetone, carbon dioxide, and acetic acid. The identification of pyrolysis fragment ions provided insight into the thermal decomposition mechanism. The results showed that the main decomposition fragment ions of the kaolinite–KAc intercalation complex were water, acetone, carbon dioxide, and acetic acid. TG-FTIR-MS was demonstrated to be a powerful tool for the investigation of kaolinite intercalation complexes. It delivers a detailed insight into the thermal decomposition processes of the kaolinite intercalation complexes characterized by mass loss and the evolved gases.     

Phase Diagram of the Ethylene Glycol–Dimethylsulfoxide System

The phase diagram of ethylene glycol (EG)–dimethylsulfoxide (DMSO) system is studied in the temperature range of +25 to ?140°C via differential scanning calorimetry. It is established that the EG–DMSO system is characterized by strong overcooling of the liquid phase, a glass transition at ?125°C, and the formation of a compound with the composition of DMSO · 2EG. This composition has a melting temperature of ?60°C, which is close to those of neighboring eutectics (?75 and ?70°C). A drop in the baseline was observed in the temperature range of 8 to ?5°C at DMSO concentrations of 5–50 mol %, indicating the existence of a phase separation area in the investigated system. The obtained data is compared to the literature data on the H₂O–DMSO phase diagram.     

Effect of synthesis parameters on characteristics of expanded graphite

Effect of synthesis parameters on the characteristics of expanded graphite were studied. The starting sample, intercalated graphite, was treated by several methods: thermal shock (400, 1000°C) and programmed heating (400–700°C). The samples were examined by scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction analysis, and low-temperature nitrogen adsorption. The programmed-heating method yields better texture characteristics as compared with the thermal shock. The programmed-heating method was used to obtain high-quality expanded graphite with high specific surface area (299 m² g^–1) at a comparatively moderate temperature of 400°C.     

Thermal, spectral, and diffraction properties of Co-exchanged montmorillonite with 2-, 3-, and 4-hydroxyphenol

The influence of the 2-, 3-, and 4-OH phenols on the type of interaction with Co-exchanged montmorillonite and thermal properties of these materials were studied. The results of XRD, IR, and thermal (TG, DTG) analysis show that organic species are intercalated into the interlayer space of montmorillonite. Thermal decomposition in the temperature interval 20?C700?°C of studied samples with 2- and 3-hydroxyphenol proceeds in three steps (the release of adsorbed H₂O molecules, combustion/desorption of protonated hydroxy phenols and dehydroxylation), while the sample with 4-hydroxyphenol decompose in four steps (the new peak at ~222?°C corresponds to directly coordinated organic species). The effect of different position of the hydroxyl groups on the phenol ring on the thermal decomposition is evident.     

Thermal Properties of the Aquadimethylsulfoxide Complexes [Ln(DMSO)n(H2O)m][Mo3S7Br7] where Ln=Pr,Nd, Eu,Tm

Synthesis, X-ray structural investigation, and study of the thermal properties of new aquadimethylsulfoxide complexes [Ln(DMSO)n(H2O)m][Mo3S7 Br7] containing the rare earth metals (Ln=Pr, Nd, Eu, Tm) were performed. In all complexes DMSO is co-ordinated through the O atoms. Thermal transformations of these salts were studied by quasi-equilibrium thermogravimetry a variant of CRTA (Controlled Rate Thermal Analysis) with constant rate of mass loss (0.3 mg min-1); helium flow keeps the partial pressure of self-generated DMSO/H2O atmosphere ~0.01 atm. [Pr(DMSO)6H2O]X where X=[Mo3S7Br7] decomposes with the formation of the intermediate phases Pr(DMSO)5X at 100-190°C and Pr(DMSO)3X at 250-270°C. Thermal decomposition of [Nd(DMSO)6(H2O)X·CH3CN leads to the intermediate phase Nd(DMSO)5X at 200-210°C. [Eu(DMSO)7(H2O)]X forms the intermediate phases Eu(DMSO)6X at 50-150°C and Eu(DMSO)5X at 190-210°C. Thermal decomposition of [Tm(DMSO)6(H2O)]X gives the intermediate phases Tm(DMSO)5X at 170-200°C and Tm(DMSO)4X at 240-250°C. The further decomposition takes place continuously for all phases. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis and Characterizations of Hydroxy-aluminum Cross-Linked Montmorillonite

Cross-linked montmorillonite was prepared by reacting homoionic sodium form of bentonite (Na-M) from Istenmezeje (Hungary) with high molecular weight polyhydroxy-aluminum complex. The complex was prepared by controlled hydrolysis of alumina macrocation. The intercalated clay (Na-Al-M) was thermally treated to convert the hydroxy cations to oxide pillars. The pillared products were characterized by X-ray powder diffraction (XRD), Fourie transform infrared spectroscopy (FTIR), (thermogravimetry (TG), differential thermal analysis (DTA) and thermal analysis-mass spectrometry (TA-MS) methods. The specific surface area as well as pore size and pore structure distribution of samples were measured by nitrogen, water and carbon tetrachloride adsorption, and the heat of immersion was also determined. The pillared products were characterized by d(001) reflections of 19 Å, which is stable even at 500°C. The interaction of polymer alumina caused several changes in the obtained FTIR spectra due to the formation of different new bonds. The rate of dehydroxylation of the pillared product is very moderate, the water release occurred in different temperature ranges according to TA-MS results. Dehydration starts at interfaces and at the wall of pores, occurring nearly with uniform rate at 250-500°C. DTA curve indicates the formation of a new phase at 950°C. The obtained surface area of the pillared product by nitrogen adsorption becomes larger (208 m2 g-1) with respect to the non pillared clay, which decreases less than 10% upto 700°C. The pillared sample has a definite pore structure, the quantity of micropores (0-40 Å) decreased with increasing of macropores (>1000 Å). The obtained domestic pillared montmorillonite possesses a high degree of thermal stability and may be used as adsorbent.     

Synthesis of nylon 6–clay hybrid by montmorillonite intercalated with ϵ-caprolactam

It was found that montmorillonite was intercalated with ?-caprolactam. X-ray diffraction revealed that the chain axes of the ?-caprolactam were parallel to the montmorillonite plates. The intercalated montmorillonite was swollen by molten ?-caprolactam at 200°C. ?-Caprolactam and 6-aminocaproic acid (accelerator) were polymerized with the intercalated montmorillonite at 260°C for 6 h, yielding a nylon 6-clay hybrid. X-ray diffraction and transmission electron micrography revealed that the silicate layers of the hybrid were uniformly dispersed in the nylon 6 matrix. Mechanical properties of the hybrid were improved. The strength and the modulus of the hybrid increased compared with the previously reported nylon 6 clay-hybrid (NCH) synthesized by montmorillonite intercalated with 12-aminolauric acid. The heat distortion temperature (HDT) of the hybrid was 164°C, which was 12°C higher than that of NCH. © 1993 John Wiley & Sons, Inc.     

The effect of annealing on slow crack growth in an ethylene-hexene copolymer

A quenched ethylene-hexene copolymer was annealed in the temperature range of 86 to 127°C. The morphological changes were monitored by differential scanning calorimetry (DSC) and density. The slow crack growth resistance tested at 80°C was a maximum at an annealing temperature of 113°C and a minimum of 123°C. The lifetimes can be varied by more than a factor of 20 depending on the thermal treatment. The increase in slow crack growth resistance between 86 and 113°C is attributed to an increase in the strength of the crystals by becoming more perfect and to the conversion of loose tie molecules into taut tie molecules. The decrease in strength between 113 and 123°C is attributed to the decrease in tie molecules when a large fraction of the as-quenched crystals begin to melt.     

Influence of calcite in a ceramic body on its thermophysical properties

We study thermal expansion, mass changes, heat capacity, and thermal diffusivity and conductivity for a ceramic body with (10 and 20 mass%) and without waste calcite content, using the TDA, TG, DTA, DSC, and flash method. The measurements were performed (a) for green samples either isothermally or by a linear heating up to a temperature 600, 1,050, or 1,100 °C, depending on the measurement method; (b) at the room temperature for samples preheated at 100, 200,…, 1,100 °C. In case (a) we show that a high calcite content may double the energy consumption during the anorthite creation at 950 °C. On the other hand, calcite has a slight positive effect on the final contraction and quite substantial effect on the thermal conductivity in the range 150–550 °C, decreasing it even by 50 %. In case (b) a positive impact of calcite on the final contraction is about 10 times higher than in case (a). A clear effect of calcite on the thermal diffusivity occurs in case (b) only above 600 °C, resulting in a rather different behavior for the 10 and 20 mass% calcite content.     

Stereoregular P(MMA)‐clay nanocomposites by metallocene catalysts: In situ synthesis and stereocomplex formation

This contribution reports the synthesis and characterization of stereochemically controlled, as well as crystalline stereocomplex, P(MMA)‐clay nanocomposites using metallocene complexes and alane‐intercalated clay activators. The ligand elimination and exchange reactions involving Lewis acids E(C₆F₅)₃ (E = Al, B) and an organically modified montmorillonite clay were employed to synthesize the alane‐intercalated clay activators. When combined with dimethyl metallocenes of various symmetries, these clay activators brought about efficient MMA polymerizations leading to in situ polymerized, stereochemically controlled P(MMA)‐intercalated clay nanocomposites. The most noticeable thermal property enhancement observed for the clay nanocomposite P(MMA), when compared with the pristine P(MMA) having similar molecular weight and stereomicrostructure, has a considerable increase in T_g (≥10 °C). Mixing of dilute THF solutions of two diastereomeric nanocomposites in a 1:2 isotactic to syndiotactic ratio, followed by reprecipitation or crystallization procedures, yielded unique double‐stranded helical stereocomplex P(MMA)‐clay nanocomposites with a predominantly exfoliated clay morphology. Remarkably, the resulting crystalline stereocomplex P(MMA) matrix is resistant to the boiling‐THF extraction and its clay nanocomposites exhibit high T_m of 201 to 210 °C. Furthermore, the stereocomplex P(MMA)‐clay nanocomposite shows a one‐step, narrow decomposition temperature window and a single, high maximum rate decomposition temperature of 377 °C. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2581–2592, 2007     

Thermal stability of flexible polyurethane foams containing modified layered double hydroxides and zinc borate

Abstract

Flexible polyurethane foams (FPUFs) have been modified to contain layered double hydroxides (LDHs) by dihydrogen phosphate (H₂PO₄ ^?). The thermal stability of the prepared foams has been characterized using thermogravimetric analysis (TGA) at 5, 10, 20, 30, and 40?°C/min heating rates. The experimental data indicate that the temperature range for the two pyrolysis stages of FPUF is about 212–350?°C and 350–565?°C, respectively. Integral programmed decomposition temperature (IPDT) has been calculated according to the measured data, which was found that the IPDT of the modified FPUF was increased to 526?°C. Additionally, the thermal stability of FPUF composite has been also evaluated by the activation energy (E) on the basis of the pyrolysis kinetics of FPUF composites during thermal decomposition using Coats–Redfern integral method. These results manifest that the presence of intercalated LDHs enhances the thermal stability of FPUF.     

Thermal decomposition of SO4 2?-intercalated Mg–Al layered double hydroxide

The thermal properties of SO₄ ^2?-intercalated Mg?CAl layered double hydroxide (SO₄·Mg?CAl LDH) were investigated using simultaneous thermogravimetry?Cmass spectrometry (TG?CMS), and the elimination behavior of sulfur oxides from this double hydroxide was examined. The TG?CMS results showed that SO₄·Mg?CAl LDH decomposed in five stages. The first stage involved evaporation of surface-adsorbed water and interlayer water in SO₄·Mg?CAl LDH. In the second, third, and fourth stages, dehydroxylation of the brucite-like octahedral layers in SO₄·Mg?CAl LDH occurred. The fifth stage corresponded to the elimination of SO₄ ^2? intercalated in the interlayer of Mg?CAl LDH, producing SO₂ and SO₃. The thermal decomposition of SO₄·Mg?CAl LDH resulted in the formation of SO₂ and SO₃ at 900?C1000?°C, which then reacted with H₂O to form H₂SO₃ and H₂SO₄. The elimination of sulfur oxides increased with the decomposition time and temperature. Almost all of the intercalated SO₄ ^2? was desulfurized from SO₄·Mg?CAl LDH at 1000?°C; however, Mg?CAl oxide was not formed due to the production of MgO and MgAl₂O₄.