Anthony P. Simonelli

Thermal analysis of reactions and transformations in the solid state. II. Theoretical analysis of different reaction and transformation systems using thermogravimetry

Abstract A new mathematical approach has been developed to follow the kinetics of reactions and transformations in the solid state using thermogravimetry. The technique requires a thermogravimetric trace containing both an integral and first derivative recorded at a single heating rate. The approach permits one to extract kinetic parameters from a wide range of systems as it can be readily adapted to most complications generally encountered, including the presence of inert material and changing atmosphere conditions. The approach can utilize one or more process models and in this way is able to account for the overlapping stages which can occur due to a change in the mechanism. The equations lend themselves well to graphical analysis, yielding linear plots from which kinetic parameters of desolvation, chemical degradation, and phase transformation of organic, inorganic, and polymeric compounds can be successfully extracted. The method provides a means to obtain kinetic parameters that must otherwise be obtained from more tedious, time consuming isothermal techniques.

Thermal analysis of reactions and transformations in the solid state. III. Kinetic studies of desolvation, chemical degradation and phase transformation using thermogravimetry

Abstract The experimental applications of the previously introduced theoretical models were used to calculate the kinetic parameters of desolvation, chemical degradation and phase transformation of five compounds of different chemical structures. These compounds are calcium oxalate monohydrate, anhydrous theophylline, urea, 50% filled ethylene/propylene rubber and unfilled cross-linked polyethylene. The approach produces kinetic parameters which are consistent, reproducible and independent of the experimental conditions. In addition, the new method allows the study of complex and overlapping reactions in both urea and polymer degradations. Enthalpy of calcium oxalate monohydrate dehydration was found to be 32.7 kcal/mole; however, its decomposition occurs in two separate steps and the heats of activation were found to be 71.7 and 65.8 kcal/mole, respectively. The kinetic parameters for the phase transformation of theophylline are 35.4 kcal/mole for the first step and 30.7 kcal/mole for the second step. The application of the new method on cross-linked polyethylene showed that the polymer decomposes in at least three overlapping stages. Each stage has an activation energy characteristic of the process. On the other hand urea decomposition is complex and occurs in overlapping steps; each step with its characteristic heat of activation.

Examination of the moving boundaries associated with non-fickian water swelling of glassy gelatin beads: Effect of solution pH

Abstract The moving boundaries associated with non-Fickian water swelling in glassy gelatin beads were studied. Using optical microscopy, dynamic profiles for both the swelling gelatin front and the inwardly moving water front were established. Interestingly, the water front profile exhibited three distinct regions of movement, and they were defined as: an initial square root of time region (Fickian), a steady-state velocity region (apparent Case II transport), and a final region where the front accelerated near the beads center (apparent Super Case II transport). Solution pH of the swelling medium was shown to have no measurable effect on the steady-state velocity of the water front, even though separate water sorption studies demonstrated substantial pH effects on total water uptake by the ionizable gelatin matrix.

Thermal analysis of reactions and transformations in the solid state. I. Experimental evaluation of published kinetic methods using thermogravimetry

Abstract A review of the non-isothermal mathematical models used to study the kinetics of reactions and transformations in the solid state is presented and their deficiencies discussed. An experimental evaluation of the new tabular method introduced by Gyulai and Greenhow is presented. Thermograms of several compounds of different sample size were obtained at different heating rates and analyzed by the Gyulai—Greenhow technique. The analysis showed a wide variation for the enthalpy calculated by this technique, as a function of the sample size and the heating rate ratios. For example, the calculated enthalpy of desolvation for the tertiary butanol solvate of methyl prednisolone obtained from different runs using the same heating rate but different sample sizes, yielded values between 16 and 95 kcal/mole. Variation in the heating rate ratios also affected the results. The enthalpy of theophylline varied between 17 and 39.6 kcal/mole with different heating rate ratios. Similar differences were found with calcium oxalate samples.

The investigation of dual-wavelength spectroscopy for the analysis of dissolved drug in microcapsule suspensions

Abstract The rationale for using the method of dual-wavelength spectroscopy to study suspensions and other highly turbid systems was theoretically developed. In order to demonstrate the usefulness of this technique, dual-wavelength spectroscopy was used to accurately determine the release of hydrocortisone 21-acetate from microcapsules in aqueous suspension. In contrast to other analytical procedures, experimental artifacts introduced by filtering and the tableting of microcapsules were eliminated. In addition dual-wavelength spectroscopy enabled extremely low concentrations i.e. 0.6 μg/ml hydrocortisone 21-acetate, to be reproducibly determined i.e. ± 2% (n = 3).

A non-isothermal technique using thermal optical analysis to follow the kinetics of polymer crystallization and solid state phase transformation and the determination of the length of the crystalline segment☆

Abstract A non-isothermal technique was developed to study the kinetics of solid transformations using thermal optical analysis (TOA). Similar to the methods using TGA and TXA were previously reported, an expression was derived that utilizes integral and differential curves. TOA involves the measurement of transmitted light intensities of a material examined between cross polars and does not require a weight change or an extractable crystalline peak. For quantitative data, it is necessary to have instrumentation in which the photometer optics and temperature state are integrated to optimize the light intensities and to record them quantitatively. In addition, circular polarized light was used to eliminate sample orientation. In order to confirm its applicability and for comparison, the technique was applied to the low density crosslinked polyethylene polymer previously studied using TGA and TXA. The enthalpy for the transformation was found to be 13.2 kcal/equiv. which was in agreement with TXA results. TOA also showed, however, a second transformation at higher temperatures and low % crystallinities, with a 67.2 kcal/equiv. enthalpy.

Rates and Mechanisms of Dissolution of Renal Calculi. I. Rates and Mechanism of Dissolution of Pure Calcium Oxalate Monohydrate in Acid and Edta Solution

In the past there has been varying degrees of clinical interest in dissolving renal calculi by some type of in situ irrigation technique. The physical-chemical rationale for the selection of the best irrigation solutions has been based on the equilibrium solubility of calcium oxalate or other stone minerals in the particular medium without regard to other possible factors which may govern the dissolution process.

A non-isothermal technique using thermal x-ray diffraction to follow the kinetics of polymer crystallization, solid state phase transformations and the determination of the length of the crystalline segment

Abstract We previously introduced a non-isothermal technique using TGA to study the kinetics of solid—solid transformations. TGA can only be applied to systems undergoing weight change. For this reason, a technique using Thermal X-ray Analysis (TXA) was developed. The technique involves the determination of the % crystallinity vs. temperature curve and its first derivative. The following equation was derived and found to be applicable. The Klug and Alexander technique for the quantitation of a crystalline compound in a powder mixture using an internal standard was used to determine the crystallinity of each sample studied. The technique was applied to the phase transformation for a semicrystalline, low density, chemically cross-linked polyethylene polymer. The enthalpy for the crystalline-amorphous transformation was found to be 13.2 kcal/equiv. For a high density, non-crosslinked polyethylene, the enthalpy was 20.8 kcal/equiv. A technique to calculate the length of the crystalline segment from the kinetic data was also developed and showed that the crystalline lengths were 65 and 30 A, respectively.

Rates and Mechanisms of Dissolution of Renal Calculi. III. Mechanisms and Rates of Dissolution of Simulated Oxalate Calculi in Acid and Edta Solutions

A previous communication1 showed that dissolution or urinary calculi sections did not exhibit zero-order (i. e., constant) rates under sink conditions. Since pure calcium oxalate discs did exhibit a constant dissolution rate, it was concluded that controlling processes other than the intrinsic solution properties of calcium oxalate must be operative in the dissolution behavior of real calculi. In this paper we intend to compare models described previously2 with the dissolution behavior of artificial calculi in various media.

A Method to Analyze the Surface of Microcapsules Using Diffuse Reflectance

AbstractThe diffuse reflectance of infra-red energy from microcapsules was shown to be a useful analytical technique to study the structural properties of microcapsules. The technique of diffuse reflectance is unique in that the anisotropic nature of reflected light enables spectral differences to be explained on the basis of molecular orientation. As a result of the collection and analysis of diffuse spectra, spectral differences that may correspond to structural differences in the capsule wall structure were found to be dependent on the core material. More specifically, in microcapsules of kaolin and talc, produced with a block copolymer of d-tartaric acid and 1,8-octanediol, the relative orientation of hydroxyl functional groups for the respective core materials differed by forty-nine degrees while carbonyl groups differed by 15 degrees.