Appearance Of Endothermic Peak Research Articles

Biomimetic hydroxyapatite and strontium-doped derivatives from crab shells and their ingenious scaffold fabrication for bone tissue engineering

The success of the most commonly used bio-ceramics in current medicine, hydroxyapatite (HAp), is due to its similar chemical and structural properties with the human bone tissue. The current research aims to calcine crab shells, a bio-waste source, to synthesize HAp, and dope it with strontium (Sr) to use it as a sustainable and economical source for bone tissue engineering. Different temperatures (900°, 1000°, and 1100 °C) were used for the calcination process. FE-SEM analysis showed the importance of temperature for morphology. The variance in the Ca/P ratio was revealed by EDX analysis. The higher the calcination temperature, the more pronounced were the peaks of HAp and (β-Tricalcium Phosphate) β-TCP were revealed by X-Ray Diffraction (XRD) analysis. Moreover, as the concentration of Sr2+ increased, both the crystallite size and crystallinity index (CI) of HAp decreased, as confirmed by XRD analysis. ATR-FTIR analysis showed the best-defined bond types (O-H, P-O, etc.). TGA and DSC analysis revealed the loss of adsorbed water and the appearance of endothermic peaks, respectively. To create a possible bone transplant substitute, scaffolds from HAp and strontium-doped HAp (Sr-HAp) were prepared utilising the foam replica method. At a Sr2+ doping of 1% (w/w) and a calcination temperature of 1100 °C, the highest percent cell viability was obtained, as determined by the MTT test. These results indicate that the concentration of the dopant (Sr2+) have a significant influence on the properties of the final material suitable for bone regeneration in situ.

Study of ZnO-CNT Nanocomposites in High-Pressure Conditions.

Recently, carbon nanotubes (CNTs) have been used extensively to develop new materials and devices due to their specific morphology and properties. The reinforcement of different metal oxides such as zinc oxide (ZnO) with CNT develops advanced multifunctional materials with improved properties. Our aim is to obtain ZnO-CNT nanocomposites by in situ hydrothermal method in high-pressure conditions. Various compositions were tested. The structure and morphology of ZnO-CNT nanocomposites were analyzed by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry—thermogravimetry (DSC-TG), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and transmission electron microscopy (TEM). These analyses showed the formation of complex ZnO-CNT structures. FT-IR spectra suggest possible interactions between CNT and ZnO. DSC-TG analysis also reveals the formation of some physical bonds between ZnO and CNT, through the appearance of endothermic peaks which could be assigned to the decomposition of functional groups of the CNT chain and breaking of the ZnO-CNT bonds. XRD characterization demonstrated the existence of ZnO nanocrystallites with size around 60 nm. The best ZnO:CNT composition was further selected for preliminary investigations of the potential of these nanocomposite powders to be processed as pastes for extrusion-based 3D printing.

THE STUDY OF THERMAL DENATURATION OF BEEF, PORK, CHICKEN AND TURKEY MUSCLE PROTEINS USING DIFFERENTIAL SCANNING CALORIMETRY

In the temperature range from 45 °C to 90 °C the process of thermal denaturation of a whole complex of muscle proteins in meat takes place. An effective mode to register the thermal denaturation process is the method of differential scanning calorimetry (DSC). As a result of studies the differences during the process of thermal denaturation of muscle proteins of pork, beef, chicken and turkey were defined by the appearance of endothermic peaks in DSC thermograms. The main variances are associated with the process of denaturation of myosin and sacroplasmic proteins and indicate indirectly their quantitative ratio in meat. The values of effective specific heat capacity in the temperature range from 20 °C to 90 °C are obtained as well as those of heat spent on the denaturation process.At reheating, the values of specific heat capacity increased by 0.1 J/(g*K) on the average, and peaks of thermal denaturation were not detected, that certifies the irreversibility of the denaturation process and the decrease in the bound moisture proportion in meat after thermal processing. Knowledge of the nature of protein thermal denaturation of each kind of meat product is one of the necessary tools for developing the technology of meat product thermal processing.

Seedless Synthesis and Thermal Decomposition of Single Crystalline Zinc Hydroxystannate Cubes

Single crystalline zinc hydroxystannate [ZnSn(OH)6] micro- and nanocubes have been successfully grown on pure tin substrates via a seedless hydrothermal synthesis method. Each ZnSn(OH)6 cube is enclosed by six equivalent {001} crystal planes. Cube size and aerial density were adjusted by controlling the reaction time and addition of diaminopropane (DAP) reagent. The hexamethylenetetramine- and DAP-assisted etching of the oxidized tin metal surface is found to play an important role in the nucleation and growth of the zinc hydroxystanate cubes. Synthesis at higher zinc nitrate concentrations as well as secondary growth resulted in the formation of ZnO nanorods in addition to the cubes. In situ scanning electron microscopy and transmission electron microscopy, thermal gravimetric analysis, and differential scanning calorimetry have been utilized to investigate the ZnSn(OH)6 thermal decomposition process. The appearance of endothermic peak near ∼540 K, attributed to the ZnSn(OH)6 decomposition, was correlated with morphology changes induced via resistive thermal annealing and localized electron beam heating.

Investigation of the Impact of Annealing on Global Molecular Mobility in Glasses: Optimization for Stabilization of Amorphous Pharmaceuticals

The purpose of this research was to investigate the effect of annealing on the molecular mobility in lyophilized glasses using differential scanning calorimetry (DSC) and isothermal microcalorimetry (IMC) techniques. A second objective that emerged was a systematic study of the unusual pre-T(g) thermal events that were observed during DSC warming scans after annealing. Aspartame lyophilized with three different excipients; sucrose, trehalose and poly vinyl pyrrolidone (PVP) was studied. The aim of this work was to quantify the decrease in mobility in amorphous lyophilized aspartame formulations upon systematic postlyophilization annealing. DSC scans of aspartame:sucrose formulation (T(g) = 73 degrees C) showed the presence of a pre-T(g) endotherm which disappeared upon annealing. Aspartame:trehalose (T(g) = 112 degrees C) and aspartame:PVP (T(g) = 100 degrees C) showed a broad exotherm before T(g) and annealing caused appearance of endothermic peaks before T(g). This work also employed IMC to measure the global molecular mobility represented by structural relaxation time (tau(beta)) in both un-annealed and annealed formulations. The effect of annealing on the enthalpy relaxation of lyophilized glasses, as measured by DSC and IMC, was consistent with the behavior predicted using the Tool-Narayanaswamy-Moynihan (TNM) phenomenology (Luthra et al., 2007, in press). The results show that the systems annealed at T(g) -15 degrees C to T(g) -20 degrees C have the lowest molecular mobility.

Cold crystallization effects in free charge relaxation in PET and PEN

A comparative study of free charge relaxation in amorphous and partially crystallized poly(ethylene-2,6-naphthalene dicarboxylate) (PEN) and poly(ethylene terephthalate) (PET) has been carried out by thermally stimulated depolarization currents (TSDC), differential scanning calorimetry (DSC), and X-ray diffraction. Amorphous films have been crystallized thermally at temperatures between 170 and 200°C (PEN); 100 and 150°C (PET) by the thermal stimulation by steps method. The windowing polarization (WP) technique has been applied to form PET and PEN thermoelectrets. TSDC of these electrets polarized at 86°C (PET) and 130°C (PEN) show only one peak which is attributed to space charge relaxation ( ρ peak). The evolution of this peak has been fitted to the general kinetic order model. DSC measurements of these samples show the appearance of a small endothermic prefusion peak once the crystallization of the sample is completed. This peak increases and shifts towards higher temperatures as the sample is further thermally treated. Associated with the appearance of this endothermic peak, the ρ relaxation passes through a maximum with a sharp decrease with further heat temperature. The X-ray diffraction measurements of these samples show that the decrease in the ρ peak is associated with the improvement of the amorphous–crystal interphases.