Thermal, spectral and AFM studies of calcium silicate hydrate-polymer nanocomposite material

A non-ionic polymer (poly(vinyl alcohol) (PVA)) has been incorporated into the inorganic layers of calcium silicate hydrate (C–S–H) during precipitation of quasicrystalline C–S–H from aqueous solution. C–S–H and a C–S–H-polymer nanocomposite (C–S–HPN) material were synthesized and characterized by X-ray fluorescence (XRF), energy dispersive spectroscopy (EDS), ²⁹Si magic angle spinning nuclear magnetic resonance (²⁹Si MAS NMR) and ¹³C cross-polarization nuclear magnetic resonance (¹³C CP NMR) spectroscopy, atomic force microscopy (AFM), thermal conductivity, thermogravimetric analysis (TG) and differential thermal analysis (DTA). Thermal conductivity of PVA, C–S–H and C–S–HPN material was studied in the temperature range 25–50°C. C–S–HPN materials exhibited the highest thermal conductivity at 25 and 50°C. The thermal conductivity increases from 25 to 50°C are 7.03, 17.46 and 14.85% for PVA, C–S–H and C–S–HPN material, respectively. Three significant decomposition temperature ranges were observed on the TG curve of C–S–HPN material.     

Thermal degradation behaviour of resins in aluminium composite under isothermal condition

As a member of the aluminium composite, GLARE (GLAss fibre/epoxy REinforced aluminium laminates) was used in the upper fuselage of Airbus A380 because of its superior mechanical properties over monolithic aluminium alloys. Thermal processing is a potential method for materials recycling and reuse from GLARE scrap with the aim of environmental protection and economic benefits. Thermal delamination is a crucial pre-treatment step for GLARE recycling. Differential scanning calorimetry (DSC) and Thermogravimetric analysis (TGA) tests have been used to identify the decomposition temperature range of epoxy resins under non-isothermal condition in our previous work [1]. To obtain an appropriate solution for GLARE thermal delamination, the thermal degradation behaviour of epoxy resins in GLARE under isothermal conditions were investigated and isothermal decomposition kinetic models were built up based on DSC and thermogravimetric analysis TGA. The thermal delamination process of GLARE is determined based on thermal analysis results and experimental optimization.     

Polymerization and photoinitiation behavior in the light-cured dental composite resins

The polymerization behavior and photoinitiation process in the visible light-cured dental composite resins were studied using ESR and IR spectroscopies. The concentration of methacryl propagating radical corresponded to the transmittance of irradiated light. While the radical was stable and long-lived in the cured resin, its concentration quickly decreased in the oral cavity due to the ventilation of atmospheric oxygen accompanied by respiration. Camphorquinone radical in the presence of tertiary amine easily initiated the radical polymerization. A decrease in monomer consumption was explained by the inhibition effect of oxygen in the photoinitiation process. Post-curing by the residual radical proceeded effectively in the deeper part of the resin.     

Thermal behaviour of advanced composite materials based on SiC fibres

Emanation thermal analysis (ETA) was used for characterization of thermal behaviour of SiC_f/SiC composites on heating in argon and air, respectively. Effect of gas environment (argon, air) and helium ions implantation on the microstructure development of the SiC_f/SiC composite prepared by chemical vapour infiltration (CVI) from Nicalon CG fibres was investigated under in situ conditions of heating. The annealing of near surface structure irregularities was observed in the range 280-700°C and evaluated by means of the mathematical model, assuming that the structure irregularities served as diffusion paths for radon. The ETA reflected the formation of amorphous silica and its subsequent crystallization to crystoballite. Morphology of the SiC_f/SiC samples before and after the heat treatments was characterized by means of SEM. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal degradation and isoconversional kinetic analysis of light-cured dimethacrylate copolymers

Thermal degradation kinetics of copolymers based on bis-phenol A ethoxylated dimethacrylate (Bis-EMA) with triethylene glycol dimethacrylate (TEGDMA), and urethane dimethacrylate (UDMA) with TEGDMA in wt/wt ratios 30/70, 50/50, or 70/30 were investigated using thermogravimetric analysis as a means to provide specific information regarding the internal structures of these resins. Thermogravimetric scans were taken at four different heating rates to perform an isoconversional analysis to determine the change of the effective activation energy as a function of conversion. A two-step degradation mechanism was found to occur in almost all copolymer compositions attributed to the existence of inhomogeneities in the macromolecular structure and the formation of weak links inside the polymeric network.     

Thermal analysis and gelation property of multifunctional epoxy resins used for pultruded composite ropes

Non-isothermal curing reactions of three different multifunctional epoxy resin systems were investigated by differential scanning calorimetry. The Kissinger equation was applied to calculate the apparent activation energy, and the Levenberg–Marquardt algorithm was used to fit the curing kinetic data. It was observed that the two-parameter model was in good match with the curing kinetics. In addition, dynamic mechanical thermal analysis was used to obtain the glass transition temperature (T _g). Furthermore, the thermal stabilities of the systems were studied by thermogravimetric (TG) analysis, the integral procedure decomposition temperature and temperature index T _s were used to characterize the thermal stability. Finally, the gelation time was measured by plate–knife method of a home-made device, and the relationship between gelation time and temperature was established, according to which the pultrusion process parameters were predicted.     

Thermal characterizations of multifunctional epoxy/anhydride systems used for pultruded composite ropes

The viscoelastic characterization and thermal stability property of some multifunctional epoxy/anhydride systems cured at different schedules were investigated by dynamic mechanical thermal analysis (DMTA) in single cantilever mode at fixed frequency, and by non-isothermal thermogravimetric (TG) analysis, respectively. According to the DMTA results, three obviously different glass transition temperatures (T _g), were observed, among which TGDDM/MHHPA system exhibits the largest T _g. While from the TG curves, the results of the mass loss and thermal stability showed that, after cured for a prolonged duration, the TGDDM/MHHPA system possessed the most excellent performance in heat resistance.     

Thermal behaviour of a modified encapsulation agent

Thermal behaviour of heptakis-6-iodo-6-deoxy-beta-cyclodextrin (HIDBCD) under inert and oxidative conditions was investigated by TG/DTG/DTA, FTIR, and using the hyphenate technique TG–FTIR. Due to the fact that thermal behaviour of HIDBCD was not studied before, we set our goal in the investigation of thermal degradation process in a dynamic air atmosphere vs. nitrogen atmosphere at a heating rate of 10 °C min^?1, up to 500 °C, respectively, 600 °C. It was found that the degradation process in air occurs in a single step, with a total mass loss of 99.9 %. The results of TG/DTG/DTA–FTIR indicated that the thermal behaviour of this cyclodextrin can be divided into three stages and more information was provided about the reaction sequences and the relevant products of reaction.     

Thermal,spectral and magnetic behaviour of 4-chloro-2-methoxybenzoates of light lanthanides(III)

4-Chloro-2-methoxybenzoates of light lanthanides(III) were obtained as mono-, di-or trihydrates with metal to ligand ratio of 1:3 and general formula Ln(C₈H₆ClO₃)₃·nH₂O, where n=1 for Ln=Ce, Pr, n=2 for Ln=Nd, Sm, Eu, Gd and n=3 for Ln=La. The complexes were characterized by elemental analysis, IR spectra, thermogravimetric studies, X-ray diffraction and magnetic measurements. The carboxylate group appears to be a symmetrical bidentate, chelating ligand. All complexes seem polycrystalline compounds. Their thermal stabilities were determined in air. When heated they dehydrate to form anhydrous salts which next are decomposed to the oxides of the respective metals. The solubilities of light lanthanide(III) 4-chloro-2-methoxybenzoates in water at 293 K are of the order of 10⁻⁵ mol dm⁻³. The magnetic moments were determined over the range of 77–300 K. They obey the Curie-Weiss law. The values of μ_eff calculated for all compounds are close to those obtained for Ln³⁺ by Hund and Van Vleck. The results indicate that there is no influence of the ligand field of 4f electrons on lanthanide ions and the metal ligand bonding is mainly electrostatic in nature.     

Thermal energy storage properties and thermal reliability of PEG/bone char composite as a form-stable phase change material

Journal of Thermal Analysis and Calorimetry - Bone char (BC) is a promising porous material that can be used for preparing a form-stable composite phase change material (PCM). In this paper,...     

X-ray spectral study of a material containing BN nanostructures

The multicomponent substance obtained by laser evaporation of the BN target under nitrogen was studied by X-ray fluorescence and X-ray absorption spectroscopy. The BK _α spectra of the substance and boroncontaining compounds rh-BN, B₂O₃, and α-B were measured on a laboratory instrument using an ethyleneglycol distearate crystal as an analytical element; X-ray absorption spectra near the boron and nitrogen K edge were recorded on a BESSY synchrotron radiation station. The contents of the components in the synthesized substance were evaluated by decomposing the BK _α spectrum into the spectra of the test boron-containing compounds. A comparison of the X-ray absorption spectra near the NK edge of the substance and rh-BN revealed that BN nanostructures obtained by laser evaporation were defective.     

Thermal behaviour of melamine

Melamine undergoes condensation on heating with elimination of ammonia and formation of insoluble products. Thermogravimetry and infrared characterisation show that two products of successive condensation can be reproducibly obtained upon heating atT}<500 °C and then at 600 °C. Above 620 °C, the melamine condensate undergoes thermal degradation with quantitative formation of volatile products.

---

Zusammenfassung Melanin geht beim Erhitzen eine Kondensation unter Abgabe von Ammoniak und Bildung unlöslicher Produkte ein. Durch Thermogravimetrie und Infrarotspektroskopie wird gezeigt, daß beim Erhitzen zwei Produkte von aufeinanderfolgenden Kondensationsreaktionen beiT}<500 °C undT= 600 °C reproduzierbar erhalten werden. Oberhalb 620 °C wird das Melaminkondensat vollständig unter Bildung flüchtiger Produkte thermisch zersetzt.

---

. , . , 500°, — 600°. 620° .

---

---

The authors wish to thank Dr. N. Del Fanti of Mantefluos, Italy for most helpful discussion.

---

This work has been supported by the Consiglio Nazionale delle Ricerche through the Progetto Finalizzato Chimica Fine e Secondaria.     

Thermal behaviour of riboflavin

From the thermal decomposition curves of riboflavin at various heating rates in static air atmosphere, the stages of thermal decomposition of this compound were established. The following kinetic parameters were calculated for the first decomposition stage of this process: activation energy (E _a ), reaction order (n), preexponential factor (A) and reaction rate constant (k). A mechanism of the changes is proposed.

---

Zusammenfassung Die Stadien der thermischen Zersetzung von Riboflavin wurden aus den Kurven der thermischen Zersetzung in Luftatmosphäre bei verschiedenen Aufheizgeschwindigkeiten ermittelt. Für den ersten Zersetzungsschritt dieses Prozesses werden die Werte für die Aktivierungsenergie (E _a ), die Reaktionsordnung (n), den präexponentiellen Faktor (A) und die Reaktionsgeschwindigkeitskonstante (k) berechnet. Für die Umwandlungen wird ein Mechanismus vorgeschlagen.

---

, , . , (E _a ), (n), (A) (k). .

     

Thermal and infrared spectral analyses of sabugalite

The thermal decomposition and infrared spectrum of sabugalite were studied. The infrared spectrum was interpreted on the basis of site and factor symmetry analysis and correlated with the X-ray powder diffraction data. The dehydration of sabugalite is characterized by three endotherms. The anhydrous phase decomposes at 440–680 °C. On the basis of the infrared spectrum in Nujol, oxonium ions are postulated in the structure of sabugalite. The infrared spectrum in a KBr disk is probably influenced by the sample preparation mode. Sabugalite does not form a meta I hydrate. Its first new partly dehydrated phase is isostructural with metaautunite II.

---

Zusammenfassung Die thermische Zersetzung und das IR-Spektrum von Sabugalit wurden untersucht. Das IR-Sektrum wird auf der Grundlage von Site- und Faktor-Symmetrie-Analysen interpretiert und mit Pulver-Röntgenbeugungsdaten korreliert. Die Entwässerung von Sabugalit ergibt 3 endotherme Effekte. Die wasserfreie Phase zersetzt sich bei 440 bis 680 °C. Auf Grund des IR-Spektrums in Nujol werden Oxonium-Ionen in der Struktur des Sabugalit vermutet. Das IR-Spektrum in KBr-Tabletten wird wahrscheinlich durch die Probenpräparation beeinflusst. Sabugalit bildet kein Metal-Hydrat. Seine erste teilweise entwässerte Phase ist isostrukturell mit Metaautunit II.

---

. ** - . . 40–80°. , . . I . II.

     

Polymerization contraction of light-cured composite resins containing silica/polymethylmethacrylate bonded microstructured networks

The adsorption of methylmethacrylate polymer at silica/methylmethacrylate interfaces was determined to provide microstructured networks whose structural characteristics were determined to be controlled by the amount of polymer initially supplied to the system. First, the microstructure was investigated by determining as a function of the amount of polymer (i) the shrinking rate due to evaporation of the methylmethacrylate monomer, (ii) the rate of sedimentation of the silica/polymer complexes in the methylmethacrylate monomer, and (iii) the height of the sediment in the long term. These different characteristics were found to be strongly correlated. Second, the sedimentation characteristics were determined as a function of the amount of polymer initially supplied to the dispersion of the same silica/polymer system in the ethylene glycol dimethacrylate monomer. Then the rate of the polymerization contraction during light-curing of the resin was determined for the sediment recovered after centrifugation. The slowest polymerization contraction and the smallest contraction were obtained with the filler/polymer/resin system composed of aggregates of medium porosity and size.     

Thermal,structural and optical properties of Al2CoO4-Crocoite composite nanoparticles used as pigments

Novel zinc(II) complex compounds of general formula Zn(C₆H₅COO)₂·L₂ (where L=caffeine (caf) and urea (u)) were synthesized and characterized by elemental analysis and IR spectroscopy. The thermal behaviour of the complexes was studied during heating in air by thermogravimetry. It was found that the thermal decomposition of the anhydrous Zn(II) benzoate compounds with bioactive ligands was initiated by the release of organic ligands at various temperatures. On further heating of the compounds up to 400°C the thermal degradation of the benzoate anions took place. Zinc oxide was found as the final product of the thermal decomposition of all zinc(II) benzoate complex compounds heated to 600°C. Results of elemental analysis, infrared spectroscopy, mass spectroscopy and thermogravimetry are presented.     

Radiation-induced modification of montmorillonite used as a filler in PP composite

In order to improve compatibility between inorganic fillers and polymeric matrix, montmorillonite (MMT) particles were modified with maleic anhydride (MA), then irradiated with electron beam, and finally were dispersed in polypropylene (PP). It was found that absorption of MA on the surface of layered clay results in the formation of salt-type bonding. Radiation treatment generates in the organic modifier stable carbon-centered radicals which, upon dispersion of activated particles in PP, induce filler-matrix linkages. Thus, such a process is another approach which has been shown to be an effective way in overcoming organophobic character of inorganic fillers in polymeric composites.     

Niflumic acid-collagen delivery systems used as anti-inflammatory drugs and analgesics in dentistry

Collagen sponges are known to be safe and well-characterized supports for drug delivery systems. The aim of this study was to prepare, characterize and test drug delivery systems that contain collagen as support and niflumic acid as a drug. Type-I collagen and niflumic acid gels were cross-linked with different concentrations of glutaraldehyde and then freeze-dried in order to obtain collagen matrices (spongious form). The physical-chemical properties were assessed by infrared spectroscopy (FTIR) and morphological properties were evaluated by water absorption. Niflumic acid release from cross-linked collagen spongious forms was also investigated and the kinetic mechanism was discussed.     

Thermal behaviour of some minerals

Thermal behaviour of some minerals (kaolinite, halloysite, two montmorillonites, quartz and calcite) for different sample amounts and heating rates has been investigated using differential thermal analysis. On the basis of the DTA analysis carried out, the PA curves of each mineral have been obtained for different heating rates. These diagrams can be employed in the semiquantitative evaluation of identical substances contained in uncharacterized polymineral samples.