Main Weight Loss Research Articles

Modelling the thermal decompositions of wood and leaves under a nitrogen atmosphere

The thermal decomposition of six di⁄erent samples of wood and leaves in nitrogen has been studied by using dynamic thermogravimetry. In the experiments two main weight loss processes took place and the total weight loss at 500iC was over 95% in all six cases. By means of the Doyle method, the two processes were found to fit most closely the plot for the second-order equation in the form da/dt 5 k(1!a) 2 , and each of the weight loss processes was found to be controlled, respectively, by two dominant reactions as the temperature increases. It was inferred that competing reactions occur during the overall temperature interval for all the six samples. By comparing the activation energies using this model with those by the method of Moll et al., and by comparing the experimental and theoretical thermogravimetric curves, the ‘second-order’ model was tested to be able to predict the weight loss processes of the samples with very good accuracy. It can be concluded that the ‘second-order’ kinetic model acts much better than the conventionally adopted first-order model. ( 1998 John Wiley & Sons, Ltd.

Lower Fat Intake as a Predictor of Initial and Sustained Weight Loss in Obese Subjects Consuming an Otherwise ad Libitum Diet

Objective To determine what predicts initial and sustained weight loss in subjects consuming a reduced-fat diet ad libitum and the relationship between achieved level of fat intake and weight loss. Design Placebo arm of a randomized, controlled trial of a weight-loss drug (dexfenfluramine) in the context of an ad libitum, reduced-fat, diet. Subjects Thirty-nine subjects (initial mean body mass index±standard deviation=34.9±3.4; body mass index is calculated as kg/m 2) from the placebo group who completed the 9-month study. Intervention Dietary assessment and education (month 0) followed by monthly meetings during the single intervention of reducing fat intake (months 1 through 6); one follow-up at 9 months. Main outcome measures Initial weight loss (first 3 months) and sustained weight loss (over 9-month period). Statistics Dietary intake, body size, exercise levels, age, and gender were included in multiple regression linear models of initial and sustained weight loss if they were significant independent predictors. Results Greater initial weight loss was associated with a greater decrease in fat intake and a lower achieved fat intake at 3 months. Greater sustained weight loss was associated with a lower achieved fat intake, a higher baseline waist circumference, and higher moderate-intensity exercise levels (months 3 and 6). Weight loss occurred in all subjects who reported a fat intake of 40 g/day or less. Applications The obese persons most likely to achieve and sustain weight loss on an ad libitum, reduced-fat diet are those who can substantially reduce fat intake, those with high initial levels of abdominal fat, and those who undertake regular moderate-intensity exercise. A target of less than 40 g fat per day might be an appropriate goal to ensure weight loss, but dietary underreporting and the difficulty of sustaining very-low-fat intakes need to be considered. J Am Diet Assoc. 1998;98:35-39.

Mineralogical characterization of paulingite from Vinarická Hora, Czech Republic

AbstractA sample of the zeolite paulingite from the locality Vinarická Hora was investigated by means of chemical, thermal, powder and single crystal X-ray methods. The fully transparent, colourless to pale yellow crystals exhibit the form {110} and occur together with phillipsite. The chemical composition is (Ca2.57K2.28Ba1.39Na0.38)(Al11.55Si30.59O84)·27H2O, Z = 16 with minor amounts of Mg (<0.05), Sr (<0.13), Mn (<0.01), and Fe (<0.04). The chemical differences from previously described paulingites are a high Ba-content, a lower Si/(Al+Fe) ratio of 2.64, and a reduced water-content. The calculated density is 2.098 g cm−3, and the observed refractive index is 1.482(2). The dehydration behaviour is characterized by a main weight loss from 24–190°C (−11.2 wt.%, ≅ 21H2O) and a minor weight loss from 190–390°C (−3.1 wt.%, ≅ 6H2O). The rehydration capability was proven up to 150°C. The dehydration process during the main weight loss is accompanied by a reduction of the cell volume of 11%. The refined lattice parameters of the X-ray powder data are a a = 35.1231 (5) Å and a = 33.7485(8) Å of an untreated and a dehydrated sample, respectively. A breakdown of the paulingite structure can be observed while the remaining water content decomposes. The single crystal X-ray refinement of this chemically different sample material derived three main cation positions, which are inside a so called paulingite or π-cage (Ca), between 8-rings of neighbouring π-cages (Ba), and in the centre of the non-planar 8-rings of the γ-cage (K). Further partially occupied cation positions (Ca,Na) were located in the planar 8-rings of the α- and γ-cages. No positions within the double 8-membered rings were detected. The water is localized around the main cation positions and in three clusters of partially occupied sites.

Thermal analysis of cellulose treated with boric acid or ammonium phosphate in varied oxygen atmospheres

Thermal analyses (TG, DTG, and DSC) of cellulose treated with diammonium phosphate or boric acid were conducted in atmospheres of differing oxygen concentration (N2, and 2.5, 10, 21% O2 in He). The weight loss process from both untreated and treated cellulose consists of a first, slow stage, a second, rapid stage, and a third, prolonged, char oxidation stage. The first two stages appear to be first-order reactions; their Arrhenius parameters were obtained. Both of the additives accelerate the beginning of the weight loss, increase the char yield, and inhibit the char oxidation. Boric acid inhibits the first stage and ammonium phosphate promotes it. The effects of oxygen are smaller than those of the additives. Oxygen produces three effects: acceleration of the beginning of the weight loss, an increase in the char yield, and oxidative gasification of the char. However, the dominant of these three effects changes depending on the oxygen concentration. The main weight loss and the char yield for untreated and treated cellulose may be explained by a chain reaction consisting of random-scission initiation, depropagation producing levoglucosan, and grafting termination, all describable by Arrhenius kinetics.

Thermal degradation of metal-complexed humic substances

A series of humic acid (HA) metal (Fe, Al) complexes were prepared and subjected to thermogravimetric and spectroscopic studies. The activation energies of decarboxylation were found to be 6–9 kcal/mole. H 2 O and CO 2 accounted for the main weight loss of HA and its complexes. No distinction could be made between organic and inorganic sources of water. Interaction of Fe 3+ with HA at a low pH probably causes reactions, such as oxidation of phenols to quinoids, transamination, decarboxylation etc. This is supported by i.r. spectroscopy and elemental analysis. It is assumed that humic acids fixed on clays might possess thermal properties similar to those of the HA oxidized by Fe 3+ at low pH.