Authors:S. Romero, P. Bustamante, B. Escalera, M. Cirri, and P. Mura
Differential scanning calorimetry (DSC), supported by hot stage microscopy, IR spectroscopy and X-ray powder diffractometry,
was used to investigate the characteristics of the solid phases of mefenamic, niflumic, and flufenamic acids and of paracetamol,
before and after equilibration with saturated solutions in different solvents. Mixtures of Lewis base (dioxane and ethyl acetate)
and amphiprotic solvents (ethanol and water) were prepared for evaluating the influence of both nature and polarity of the
solvents. Solid-state analysis performed on the original samples (commercial products) made it possible to establish that
paracetamol, mefenamic acid and flufenamic acid were in their respective Form I. No polymorphic modifications are known for
niflumic acid. Paracetamol, niflumic and mefenamic acids did not show any change after equilibration with the various solvents
or solvent mixtures, regardless of their different chemical nature. In contrast, DSC, IR and X-ray analyses revealed the partial
recrystallization of flufenamic acid into its polymorphic Form III in solid phases at equilibrium with ethanol, ethyl acetate
and their blends, as well as in dioxane-water mixtures containing 30 to 100% dioxane and in ethanol-water mixtures with a
water content less than 50%.
Authors:M. Cirri, F. Maestrelli, S. Furlanetto, and P. Mura
Natural crystalline (α-, β-, γ-) and amorphous derivative (hydroxypropyl-β- and methyl-β) cyclodextrins were selected as potential
carriers for obtaining, through a co-grinding technique, a stable activated amorphous form of glyburide with improved dissolution
properties. Differential scanning calorimetry (DSC) was used to investigate solid-state modifications of the drug induced
by co-grinding with the selected carriers in a high energy vibrational micro-mill. X-ray powder diffraction and FTIR spectroscopy
were employed as additional techniques to support DSC data. Equimolar drug : cyclodextrin physical mixtures were co-ground
for different times (up to 60 min) at constant vibration frequency (24 Hz). A progressive drug amorphization with increasing
grinding time was observed in all binary systems, but, interestingly, different degrees of sensitivity to the mechanical-chemical
activation were evident. In fact, blends with natural cyclodextrins, despite the initial higher crystallinity than those with
the amorphous derivatives, required the same or shorter co-grinding times (60 min) to achieve complete drug amorphization.
Stability studies indicated no appreciable drug recrystallization in co-ground products after 4 months storage in sealed containers
at 25°C or 1 month at 25°C and 75% RH. No stability differences were detected between products with natural or derivative
cyclodextrins. The results accounted for the suitability of cyclodextrin co-grinding technique to obtain and stabilize glyburide
in the activated amorphous form.
Authors:A. Yaghmur, A. Aserin, I. Tiunova, and N. Garti
The five-component system is quite unique since it allows formation of reverse micelles with hydrophilic ethoxylated alcohol in the presence of ethanol and it facilitates dilution by water/propylene glycol (1,2-propanediol, PG) aqueous phase, all the way from a water-in-oil (W/O) microemulsion via a bicontinuous phase to an oil-in-water (O/W) microemulsion.The surfactant/alcohol/PG can strongly bound water in the inner phase so that it freezes below –10°C and acts in part as bound water and in part as non-freezable water. Upon dilution to >30 mass% aqueous phase (water/PG at constant mass ratio of 1/1) the system becomes bicontinuous and the aqueous layers are composed again from bound water. Even after complete inversion to O/W microemulsions the water in the continuous phase is strongly interacting with the PG/surfactant and remains bound or non-freezable. Water/PG/ethanol have a strong effect on the head groups (freezing below -10°C) and also on the hydrophobic tails (recrystallizing and melting) at lower temperature when dilution exceeds 45 mass% water/PG (1/1).No free water was detected neither in the W/O microemulsion's inner droplet domains nor when the microemulsion was either bicontinuous or when it was inversed to O/W. Continuous phase of resulting O/W microemulsion apparently is based on water/PG at a mass ratio of 1/1.
Isotactic polypropylene (iPP) was crystallized using temperature modulation in a differential scanning calorimeter (DSC) to thicken the crystals formed on cooling from the melt. A cool-heat modulation method was adopted for the preparation of the samples under a series of conditions. The effect of modulation parameters, such as temperature amplitude and period was monitored with the heating rate that followed. Thickening of the lamellae as a result of the crystallization treatment enabled by the cool-heat method lead to an increase in the peak melting temperature and the final traces of melting. For instance, iPP melting peak shifted by up to 3.5°C with temperature amplitude of 1.0°C while the crystallinity was increased from 0.45 (linearly cooled) to 0.53. Multiple melting endotherms were also observed in some cases, but this was sensitive to the temperature changes experienced on cooling. Even with a slower underlying cooling rate and small temperature amplitudes, some recrystallization and reorganization occurred during the subsequent heating scan. The crystallinity was increased significantly and this was attributed to the crystal perfection that occurred at the crystal growth surface. In addition, temperature modulated differential scanning calorimetry (TMDSC) has been used to study the melting of iPP for various crystallization treatments. The reversing and non-reversing contribution under the experimental time scale was modified by the relative crystal stability formed during crystallization. Much of the melting of iPP was found to be irreversible.
Inorganíc polymers such as silicates, borates and phosphates can be transformed into amorphous solids by heating to an appropriate
temperature. Thermal amorphization can be obtained by: 1. thermal dissociation of a crystalline compound, 2. distortion of
the crystal structure of a solid during prolonged heat treatment, without change of its chemical composition. The specificity
of the materials received, the crystallochemical conditions necessary for the amorphization which takes place, and the high-temperature
processes of internal structure reconstitution and recrystallization in the amorphous products are considered.
Authors:F. Rey, O. Chamorro, F. Martín Gil, and J. Martín Gil
The thermal stability of selected straight-chain (C6-C14) esters of fatty acids has been studied by TG-DTG and DTA analysis. In DTG, a peak is detected between 84° and 125° C followed
by a main effect in the range 105°–215°C, whereas in DTA only an exothermic peak appears in the range of 126.5° to 187°C (onset
temperatures). The temperatures of these effects have been related with ignition points, molecular weights and boiling points.
The characteristics of melting and recrystallization of the above fatty acid methyl esters and those with carbon numbers between
C14 and C24 have been established by DSC along the melting range between −83° and 50°C. Polymorphism appears in caproic, heptanoic, palmitic
and stearic acid methyl esters.
We studied thermal transitions and physical stability
of oil-in-water emulsions containing different milk fat compositions, arising
from anhydrous milk fat alone (AMF) or in mixture (2:1 mass ratio) with a
high melting temperature (AMF–HMT) or a low melting temperature (AMF–LMT)
fraction. Changes in thermal transitions in bulk fat and emulsion samples
were monitored by differential scanning calorimetry (DSC) under controlled
cooling and reheating cycles performed between 50 and –45C (5C
min–1). Comparison between bulk fat samples
and emulsions indicated similar values of melting completion temperature,
whereas initial temperature of fat crystallization (Tonset)
seemed to be differently affected by storage temperature depending on triacylglycerols
(TAG) composition. After storage at 4C, Tonset
values were very similar for emulsified and non-emulsified AMF–HMT blend,
whereas they were lower (by approx. 6C) for emulsions containing AMF
or mixture of AMF–LMT fraction. After storage at –30C, Tonset values of re-crystallization
were higher in emulsion samples than in bulk fat blends, whatever the TAG
fat composition. Light scattering measurements and fluorescence microscopic
observations indicated differences in fat droplet aggregation-coalescence
under freeze-thaw procedure, depending on emulsion fat composition. It appeared
that under quiescent freezing, emulsion containing AMF–LMT fraction
was much less resistant to fat droplet aggregation-coalescence than emulsions
containing AMF or AMF–HMT fraction. Our results indicated the role of
fat droplet liquid-solid content on emulsion stability.
Authors:Nathaniel B. Zuckerman, Maxim Shusteff, Philip F. Pagoria, and Alexander E. Gash
The secondary high explosive 2,6-diamino-3,5-dinitropyrazine-1-oxide, or LLM-105, has been synthesized using a commercially available flow microreactor system. Investigations focused on optimizing flow nitration conditions of the cost effective 2,6-diaminopyrazine-1-oxide (DAPO) in order to test the feasibility and viability of flow nitration as a means for the continuous synthesis of LLM-105. The typical benefits of microreactor flow synthesis including safety, tight temperature control, decreased reaction time, and improved product purity all appear to be highly relevant in the synthesis of LLM-105. However, the process does not provide any gains in yield, as the typical 50—60% yields are equivalent to the batch process. A key factor in producing pure LLM-105 lies in the ability to eliminate any acid inclusions in the final crystalline material through both a controlled quench and recrystallization. The optimized flow nitration conditions, multigram scale-up results, analyses of sample purity, and quenching conditions for purity and crystal morphology are reported.
In mineralogical research differential thermal analysis can be applied as either a single or a combined method for three purposes:1.for the qualitative identification of minerals and the (semi-)quantitative determination of the components of rocks and soils,2.for the characterization of crystal-physical and crystal-chemical properties, including the study of kinetics and the determination of thermodynamic data, phase and reaction equilibria,3.for special petrogenetic investigations concerning the interrelation of mineralogical properties with the formation, decomposition or recrystallization of minerals.
Authors:M. Z. El Sabee, W. G. Perkins, R. S. Porter, V. G. Baranov, and S. Ya. Frenkel
The thermal and mechanical behaviour was measured in the U. S.for a polyethylene that had been prepared and highly drawn in the U. S. S. R. The melting point and percent crystallinity were evaluated in this studies as a function of heating rate and recrystallization. The Young's modulus and tensile stress to break in the orientation direction were 4.1 and 0.15 GPa, respectively.The tensile strain to break was about 8%.