Thermal oxidation of cellulose investigated by chemiluminescence. The effect of magnesium and calcium carbonates and of different pHs

Whatman cellulose impregnated with calcium and magnesium carbonates was oxidized and chemiluminescence accompanying this oxidation has been measured. It was shown that magnesium ions in deacidified cellulose pulp promote the light emission significantly. On the other hand, acid papers give the more pronounced light signals at temperatures close to ambient. The relation between chemiluminescence runs and paper degradation has been implicated, with an attempt to extrapolate half-lives of paper samples to conditions close to ambient. To cite this article: J. Rychlý et al., C. R. Chimie 9 (2006).     

Neural stem cells express melatonin receptors and neurotrophic factors: colocalization of the MT<Subscript>1</Subscript>receptor with neuronal and glial markers

Background  

In order to optimize the potential benefits of neural stem cell (NSC) transplantation for the treatment of neurodegenerative disorders, it is necessary to understand their biological characteristics. Although neurotrophin transduction strategies are promising, alternative approaches such as the modulation of intrinsic neurotrophin expression by NSCs, could also be beneficial. Therefore, utilizing the C17.2 neural stem cell line, we have examined the expression of selected neurotrophic factors under different in vitro conditions. In view of recent evidence suggesting a role for the pineal hormone melatonin in vertebrate development, it was also of interest to determine whether its G protein-coupled MT₁ and MT₂ receptors are expressed in NSCs.     

Burning of thermally thin polyethylene mixtures

The burning of polyethylene in the mixture with aluminium hydroxide, aluminium oxide, cellulose and Irganox 1010 has been examined by cone calorimeter under non-standard sizes of the sample. The time to ignition of pure polyethylene decreases with decreasing initial amount of polyethylene powder. The subtraction of the mass of water released from the total mass lost for polyethylene with aluminium hydroxide give the same values of effective heats of combustion as for pure polyethylene up to the load about 50 mass% of aluminium hydroxide. The mean heats of combustion determined from the cone calorimeter software are higher than those determined from the total oxygen consumed and mass lost multiplied by the factor 13.1. The additivity rule was found for effective heat of combustion and total smoke released for polyethylene with cellulose. The free radical scavenger Irganox 1010 does not show a significant effect on the flammability of polyethylene except for the increase of the total smoke released. The equation describing the heat release rate evolution in time has been proposed showing a good fit to the experimental runs.     

Comparison of isothermal and non-isothermal chemiluminescence and differential scanning calorimetry experiments with benzoyl peroxide

Difference in the kinetics of chemiluminescence (CL) and differential scanning calorimetry records for decomposition of originally solid benzoyl peroxide continuing as a melt reaction was outlined. While the main portion of heat measured by DSC is released in the spontaneous decomposition of benzoyl peroxide starting as a homolytic scission of peroxidic bonds, the CL light emission in oxygen comes presumably from the subsequent disproportionation reaction of polyphenyl peroxyl radicals and monitors the induced decomposition of peroxide. Thermogravimetry revealed that oxygen remains partially bound to the products of benzoyl peroxide decomposition.     

The effects of annealing in inert atmospheres and of oxygen concentration on chemiluminescence from polypropylene

It has been shown that heating polypropylene powder under a nitrogen atmosphere leads to the significant prolongation of the oxidation induction time measured by chemiluminescence in oxygen at 130 and 140 °C. While heating in nitrogen from 0 to 4 h at 140 °C leads to the linear increase of oxidation induction time, the maximum chemiluminescence intensity I_stat increases with the time of sample annealing until 2 h; then it starts to decay. The different and sometime unknown thermal history of the sample may thus explain the scatter of induction times of oxidation observed with different PPs whether they be pure or stabilised. Maximum chemiluminescence intensity plotted vs. concentration of oxygen in the surrounding atmosphere at 130 and 140 °C also increases linearly; however, this does not correspond with very small reduction of oxidation induction time. The four-parametric “master equations” used in our earlier papers were applied to fit the chemiluminescence runs both in oxygen and in nitrogen. The equation operates with the rate constants of hydroperoxide decomposition and oxidation spreading but at the same time, it takes into account the possible effect of oxidation products on decomposition of hydroperoxides.     

Role of the interphase dynamics in the induction time of the thermo-oxidation of isotactic polypropylene

This work completes an earlier study on the influence of molar mass and microstructure on the thermal stability of low molar mass isotactic polypropylenes (iPP). The relative dependence of induction time (t_i) on both parameters has been assessed for new metallocene iPP samples (M-PP) with molar masses from 65,000 to 182,000. The new M-PP series includes one metallocene ethylene-propylene copolymer (M-EP) with an ethylene content of 2.6 mol%.When the new t_i data are considered together with those previously reported, neither the molar mass nor the microstructure, taken as sole parameters, is able to explain the global t_i evolution of the M-PP samples.On the basis of the results corresponding to the M-EP copolymer, it is proposed that local chain dynamics occurring at high free volume regions, associated to propylene segment interruptions, play a main role in the ability of the interphase to initiate the oxidation. The correlation of the characteristic interphase chain dynamics, as measured by DMTA, with t_i data supports this suggestion. This hypothesis provides a more unified insight about the actual origin of the iPP thermo-oxidation, as it integrates the influence of parameters which have been found to drive partially the thermal stability of iPP, in particular, molar mass and microstructure.     

Chemiluminescence accompanying the oxidation of hemicelluloses

On the series of hemicelluloses such as xyloglucans and xylans the effect of O-CH₃ substitution and initial molar mass on chemiluminescence intensity measured under non-isothermal conditions in oxygen and nitrogen from 40 to 220 °C was examined. It was ascertained that the rate constants of oxidation determined from non-isothermal chemiluminescence experiments describe quite well the relative stability of the respective hemicellulose. Similarly as in the case of cellulose and pullulan increasing molar mass has an adverse effect on the intensity of the light emission.     

Solid-state electrochemical analysis of Inka pottery from Qotakalli archeological site in the Cusco (Perú) area

Journal of Solid State Electrochemistry - A series of sherds from the archeological site of Qotakalli in the area of Cusco (Perú), corresponding to four different Inka periods, were studied by...