Polydicyclopentadiene based aerogel: a new insulation material

Lightweight polydicyclopentadiene (pDCPD) based aerogels were developed via a simple sol-gel processing and supercritical drying method. The uniform pDCPD wet gels were first prepared at room temperature and atmospheric pressure through ring opening metathesis polymerization (ROMP) incorporating homogeneous ruthenium catalyst complexes (Grubbs catalyst). Gelation kinetics were significantly affected by both catalyst content and target density (i.e., solid content), while gel solvents also played important role in determining the appearance and uniformity of wet gel and aerogel products. A supercritical carbon dioxide (CO₂) drying method was used to extract solvent from wet pDCPD gels to afford nanoporous aerogel solid. A variety of pDCPD based aerogels were synthesized by varying target density, catalyst content, and solvent and were compared with their xerogel analogs (obtained by ambient pressure solvent removal) for linear shrinkage and thermal conductivity value (1 atm air, 38 °C mean temperature). Target density played a key role in determining porosity and thermal conductivity of the resultant pDCPD aerogel. Differential scanning calorimetery (DSC) demonstrated that the materials as produced were not fully-crosslinked. The pDCPD based aerogel monoliths demonstrated high porosities, low thermal conductivity values, and inherent hydrophobicity. These aerogel materials are very promising candidates for many thermal and acoustic insulation applications including cryogenic insulation.

Calculation method based on DTG curve for evaluation of activation energy

Authors have pointed out three calculation methods based on the weight loss rate of the sample to discuss and to compare them by means of describing kinetically the thermal decomposition of malonic acid. Values ofE _A calculated by different methods are well comparable. The method based on the calibrated DTG curve measured by the Derivatograph leads to reliable results and it seems to be convenient for the calculation ofE _A of transformations involving weight changes.     

Polyurea based aerogel for a high performance thermal insulation material

Less fragile lightweight nanostructured polyurea based organic aerogels were prepared via a simple sol–gel processing and supercritical drying method. The uniform polyurea wet gels were first prepared at room temperature and atmospheric pressure by reacting different isocyanates with polyamines using a tertiary amine (triethylamine) catalyst. Gelation kinetics, uniformity of wet gel, and properties of aerogel products were significantly affected by both target density (i.e., solid content) and equivalent weight (EW) ratio of the isocyanate resin and polyamine hardener. A supercritical carbon dioxide (CO₂) drying method was used to extract solvent from wet polyurea gels to afford nanoporous aerogels. The thermal conductivity values of polyurea based aerogel were measured at pressures from ambient to 0.075 torr and at temperatures from room temperature to −120 °C under a pressure of 8 torr. The polyurea based aerogel samples demonstrated high porosities, low thermal conductivity values, hydrophobicity properties, relatively high thermal decomposition temperature (~270 °C) and low degassing property and were less dusty than silica aerogels. We found that the low thermal conductivities of polyurea based aerogels were associated with their small pore sizes. These polyurea based aerogels are very promising candidates for cryogenic insulation applications and as a thermal insulation component of spacesuits.     

Water intake of cellulose materials monitored by positron annihilation lifetime spectroscopy

Cellulose - In this study, for the first time, the experimental technique of positron annihilation lifetime spectroscopy (PALS) has been applied to monitor in situ the microstructural changes of...     

Cupel assay of gold by an activation method

The difficulties of determining gold in rocks and ores are due to two causes: low gold concentrations in rocks (Clark 1 to 4·10⁻⁷%), and non-uniform distribution of gold in ores. A method is proposed which is based on neutron activation of the lead alloy obtained by cupel melting in the procedure of determining gold by cupel assay. Samples of 50 to 100 g are used for cupel melting. Such large samples guarantee their representativeness. Discs of 2 to 3 g are cut from the lead alloy block and activated in a neutron flux of 10¹¹ to 10¹³ n·cm⁻² sec⁻¹. The gold content is determined from the photopeak of¹⁹⁸Au using a standard for comparison. The sensitivity of the method is 0.02 g/metric ton, its accuracy at a gold content in the order of 1.0 g/metric ton is 10% relative. The method is distinguished by the fact that it is fast and requires little labour.     

Thermal decomposition of cellulose

Journal of Thermal Analysis and Calorimetry - Cellulose has been pyrolysed in nitrogen at two heating rates, and the rates of formation of total gases, and the oxides of carbon, have been measured....     

A simple method of determining the activation energy of an isothermal solid-state decomposition reaction

A simple approach to determine the activation energy (E) of solid-state decomposition reactions is described. The activation energy is calculated from the slope of the logarithm of the maximum peak height of the isothermal DTA trace versus the reciprocal of the absolute temperature. The proposed method is applied in the study of the kinetics of thermal decomposition of cadmium carbonate. The activation energy calculated from this method (90.8±2.2 kJ mole^–1) is in very good agreement with the value (87.5±2.5 kJ mole^–1) obtained by the conventional method.

---

Zusammenfassung Eine einfache Annäherung zur Bestimmung der Aktivierungsenergie (E) von Festphasenzersetzungsreaktionen wird beschrieben. Die Aktivierungsenergie wird aus dem Anstieg des Logarithmus der maximalen Peakhöhe der isothermen DTA-Kurve als Funktion der reziproken absoluten Temperatur errechnet. Die vorgeschlagene Methode wird zur Untersuchung der Zersetzungskinetik von Cadmiumcarbonat eingesetzt. Die hiernach berechnete Aktivierungsenergie (90.8±2.2 kJ mol^–1) ist in guter Übereinstimmung mit dem durch die konventionelle Methode erhaltenen Wert (87.5±2.5 kJ mol^–1).

---

Résumé On décrit une méthode simple d'approximation pour déterminer l'énergie d'activation (E) des réactions de décomposition en phase solide. Le calcul de l'énergie d'activation s'effectue à partir de la pente du logarithme de la hauteur maximale du pic de la courbe d'ATD isotherme en fonction de l'inverse de la température absolue. On a appliqué la méthode proposée lors de l'étude de la cinétique de la décomposition thermique du carbonate de cadmium. L'énergie d'activation calculée à partir de cette méthode (90.8±2.2 kJ mole^–1) est en bon accord avec la valeur (87.5±2.5 kJ mole^–1) obtenue par la méthode conventionnelle.

---

. . . (90.8+2.2 .^–1) 87.5± 2.5 .^–1, .

---

---

The authors express their thanks to Dr. V. V. Deshpande and to Shri M. S. Kumbhar for their help in the DTA studies.     

Thermogravimetric analysis of cellulose insulation and determination of activation energy of its thermo‐oxidation using non‐isothermal,model‐free methods

The aim of the work was to determine the effect of heating rate on initial decomposition temperature and phases of thermal decomposition of cellulose insulation. The activation energy of thermo‐oxidation of insulation was also determined. Individual samples were heated in the air flow in the thermal range of 100°C to 500°C at rates from 1.9°C min^?1 to 20.1°C min^?1. The initial temperatures of thermal decomposition ranged from 220°C to 320°C, depending on the heating rate. Three regions of thermal decomposition were observed. The maximum rates of mass loss were measured at the temperatures between 288°C and 362°C. The activation energies, which achieved average values between 75 and 80.7 kJ mol^?1, were calculated from the obtained results by non‐isothermal, model‐free methods. Copyright © 2014 John Wiley & Sons, Ltd.     

Mineral composition of fruit by-products evaluated by neutron activation analysis

Brazil is one of the largest producers of fruits cropping 40 million tons per year. In agro-food processing, approximately 50 % of raw material is discarded generating large amounts of by-products. The lack of information on the nutritional quality of agroindustrial by-products precludes their potential use in the manufacture of food products accessible to all. In this context, the objective of this work was to investigate the nutritional quality of by-products of the industrial processing of fruits. Samples of bagasse, peel and seeds of several fruits (banana, camu camu, coconut, cupuaçu, guava, jackfruit, mango, orange, papaya, pineapple, and soursop) were analysed by neutron activation analysis for the determination of Br, Ca, Co, Cr, Cs, Fe, K, La, Na, Rb, Sc and Zn. In general, higher levels of minerals were found in the by-products rather than in the pulps of fruits. This indicates that the use of the by-products should be encouraged, thereby reducing the economic and environmental impact of waste generated by agroindustrial processing.     

Excluded volume effect for solutions of cellulose derivatives evaluated by wormlike chain model

Third-power law type equations of the linear expansion factor α_s and of the excluded volume effect $\text{z}$h($\text{z}$), expressed by a conventional notation, are derived for a wormlike chain as an extension of the Yamakawa and Stockmayer theory [J. chem. Phys.57, 2843(1972)], in which the corresponding fifth-power law type equations were obtained. The literature data on 11 systems of solutions of cellulose and its derivatives are analysed, by using a penetration function method based on the derived equations, to evaluate an excluded volume effect for a wormlike chain model. The results are compared with those deduced for a pearl necklace model.     

A numerical analysis of heat transfer in an evacuated flexible multilayer insulation material

In this article, the theoretical heat transfer of flexible multilayer insulation material which can be used in high (<433 K) and low temperature (>123 K) environments has been analyzed. A mathematical model has been developed to describe the heat flux through flexible multilayer insulation material, where the heat transfer consists of thermal radiation, solid spacers and gas heat transfer. The equations for heat transfer model have been solved by iterative method combining with dichotomy method using Matlab. Comparison between the experimental results and the calculated values which are obtained from the model shows that the model is feasible to be applied in practical estimation. The investigation on the flexible multilayer thermal insulation material will present active instruction to improve the performance and accomplish optimum design of the material.     

Thermal properties of cellulose carbamate

The thermal properties of cellulose carbamate with various nitrogen content are discussed. Thermal analysis was performed in air and under nitrogen atmosphere. The increase in the nitrogen content in cellulose carbamate brings about only a shift of the maximum decomposition rate towards lower temperatures. It can be concluded that cellulose carbamate heated to 320 °C is readily dehydrated and cross-linked, which results in the formation of aromatic structure.     

Thermal properties of oxidized cellulose

Three series of oxidized celluloses – 2,3-dialdehyde celluloses (DACs), 2,3-dicarboxycelluloses (DCCs) and sodium 2,3-dicarboxycelluloses (NaDCCs) — were prepared, having incremental changes in their degrees of oxidation. Their thermogravimetric analysis (TG) and differential thermal analysis (DTA) were studied. It was found that oxidation generally destabilized cellulose at lower temperatures (below 250 °C), but at higher temperatures the oxidized products were found to be more stable. Cellulose, DACs, and DCCs all showed final weight losses in the region of 80–85%. However, 80% NaDCC and 98% NaDCC showed weight losses of only 30 and 37%, respectively.NCL Communication No. 6051.     

Thermal stabilization of TEMPO-oxidized cellulose

A partially C6-carboxylated cellulose with carboxylate content of 1.68 mmol/g was prepared by 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation of a softwood bleached kraft pulp. Thermogravimetric analyses of the TEMPO-oxidized cellulose (TOC) and its related materials were studied to improve thermal stability of the TOC. Thermal decomposition (T_d) points of the TOC with sodium carboxylate groups, alkali-treated TOC with free carboxyl groups of 0.23 mmol/g and the original cellulose were 222 °C, 264 °C and 275 °C, respectively. Thus, the anhydroglucuronic acid units formed by TEMPO-mediated oxidation of the native wood cellulose and present in the TOC cause the decrease in T_d point by decarbonation during heating process. When carboxyl groups in the TOC were methylated with trimethylsilyl diazomethane (TMSCHN₂), the T_d point increased from 222 °C to 249 °C, and the peak temperature in its derivative thermogravimetric (DTG) curve increased from 273 °C to 313 °C, which was almost equal to that of the original cellulose. Thus, the methyl esterification of carboxyl groups in the TOC is effective in improving thermal stability. When sodium ions present in the TOC as counter ions of carboxylate groups were exchanged to some other metal ions, thermal stability was improved to some extent. Especially, when CaCl₂, Ca(OAc)₂, Ca(NO₃)₂ and CaI₂ solutions were used in the ion-exchange treatments, the peak temperatures in the DTG curves increased to approximately 300 °C. MgCl₂, NiCl₂, SrCl₂ and Sr(OAc)₂ solutions were also effective to some extent in increasing the peak temperatures of DTG curves. Thus, thermal stability of the fibrous TOC can be improved to some extent by methyl esterification of the sodium carboxylate groups present in the original TOC with TMSCHN₂ or ion-exchange treatments with some metal salt solutions.     

A carbon-silica composite material based on powdered cellulose: Synthesis and properties

A procedure was developed for preparing a carbon-silica composite by thermolysis of powdered cellulose in the presence of tetraethoxysilane. The resulting composite was studied in model processes of trimethylhydroquinone oxidation and hydrogen peroxide decomposition.     

Vibrational lifetime measurements of matrix isolated molecules by an optical “double resonance” method

An optical-optical “double-resonance” experiment has been developed and successfully applied to the study of vibrational lifetimes. This pulsed dual laser technique should be applicable to all species possessing resolvable allowed vibronic transitions and it permits the direct measurement of vibrational lifetimes which, at present, may be as short as 20 μs. Application of this technique to the υ″ = 1 and υ″ = 2 states of matrix isolated C₂^? yields half lifes of 0.2 and 1.2 ms, respectively, in an argon matrix at 16K, and 0.3 and 1.3 ms in an N₂ matrix at 14K. No significant temperature variation of these rate constants has been found in the range 14 to 24 K. This is the first direct measurement of the vibrational lifetime of a homonuclear diatomic molecule isolated in a matrix environment.     

Dialdehyde cellulose as a niche material for versatile applications: an overview

Cellulose - Dialdehyde cellulose (DAC) has garnered substantial scientific interest, thanks to broad spectrum of possible chemical reactions offered by the aldehyde moieties in its backbone. In the...     

Thermal degradation of cellulose in nitrogen

The thermal degradation of four different forms of cellulose in nitrogen has been studied by using a thermobalance. In TG experiments a total weight loss at 900°C was 80% in the cases of film and pulp samples and 83% for two powder forms. The results for the isothermal degradation of the four samples at 270°C are plotted as degree of degradation α against reduced time t/t_0.5 and compared with the master plots of Sharp, Brindley, and Achar. The experimental data fit most closely the plot for the Avrami-Erofeev equation in the form kt = {–ln (1–α)}^1/n where n = 2. An activation energy of 144 kJ/mole has been found for the degradation of one of the celluloses from the results of isothermal runs at six different temperatures. It is postulated here that the thermal degradation occurs by random nucleation and nucleus growth in the cellulose fibrils so as to yield a carbon whose microporous structure is a replica of the pore system in the parent cellulose.