Effect of dehydration and urea on stability of homosulfamine in solid states

In the presence of urea in solid states, the stability of unpulverized homosulfamine hydrate (phase I; UHH) is significantly decreased whereas that of unpulverized homosulfamine anhydrate (UHA) is not. The stability of UHH is decreased slightly more by pulverization (PHH). The major objective of this study was to investigate the effects of urea, dehydration, and pulverization on the stability of homosulfamine in solid states. Binary mixtures of UHH and urea, PHH and urea, and UHA and urea in a ratio of 1:1 (wt/wt) were prepared as physical mixtures and were analyzed by scanning electron microscopy (SEM), powder X-ray diffraction (PXRD), and Fourier transform infrared (FTIR) spectroscopy to study their appearance and structural changes before and after storage. PXRD analysis revealed that physical mixtures comprising UHH and urea and PHH and urea have the same diffraction pattern as that of the mixture of UHA and urea after preparation. The dehydration rate of the crystal water of UHH was accelerated by the presence of urea in addition to pulverization. Moreover, the PXRD patterns of the physical mixtures of UHH/urea and PHH/urea were significantly altered during storage, whereas that of UHA/urea was not, which was consistent with the SEM and FTIR results. The particle shape and appearance of UHH varied significantly as a result of pulverization. The stability of homosulfamine was influenced not only by the presence of urea and dehydration but also by the surface state and particle size of the crystalline form.     

Preparation of budesonide-poly (ethylene oxide) solid dispersions using supercritical fluid technology

The purpose of this study was to investigate the possibility of preparing solid dispersions of the poorly soluble budesonide by supercritical fluid (SCF) technique, using poly (ethylene oxide) (PEO) as a hydrophilic carrier. The budesonide-PEO solid dispersions were prepared, using supercritical carbon dioxide (SC CO₂) as the processing medium, and characterized by scanning electron microscopy (SEM), powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC), solubility test and dissolution test in order to understand the influence of the SCF process on the physical status of the drug. The endothermic peak of budesonide in the SCF-treated mixtures was significantly reduced, indicating that budesonide was in amorphous form inside the carrier system. This was further confirmed by SEM and PXRD studies. The enhanced dissolution rates of budesonide were observed from SCF-treated budesonide-PEO mixtures. The amorphous characteristic of the budesonide, the better mixing of drug and PEO powders in the presence of SC CO₂, together with the improved wettability of the drug in PEO, produced a remarkable enhancement of the in vitro drug dissolution rate. Thus, budesonide-PEO solid dispersions with enhanced dissolution rate can be prepared using organic solvent-free SCF process.     

Preparation of Budesonide-Poly (Ethylene Oxide) Solid Dispersions Using Supercritical Fluid Technology

The purpose of this study was to investigate the possibility of preparing solid dispersions of the poorly soluble budesonide by supercritical fluid (SCF) technique, using poly (ethylene oxide) (PEO) as a hydrophilic carrier. The budesonide-PEO solid dispersions were prepared, using supercritical carbon dioxide (SC CO₂) as the processing medium, and characterized by scanning electron microscopy (SEM), powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC), solubility test and dissolution test in order to understand the influence of the SCF process on the physical status of the drug. The endothermic peak of budesonide in the SCF-treated mixtures was significantly reduced, indicating that budesonide was in amorphous form inside the carrier system. This was further confirmed by SEM and PXRD studies. The enhanced dissolution rates of budesonide were observed from SCF-treated budesonide-PEO mixtures. The amorphous characteristic of the budesonide, the better mixing of drug and PEO powders in the presence of SC CO₂, together with the improved wettability of the drug in PEO, produced a remarkable enhancement of the in vitro drug dissolution rate. Thus, budesonide-PEO solid dispersions with enhanced dissolution rate can be prepared using organic solvent-free SCF process.     

Effects of spray drying process parameters on the solubility behavior and physical stability of solid dispersions prepared using a laboratory-scale spray dryer

Purpose: The purpose of this study is to determine the process parameters of the laboratory-scale spray dryer affecting the solubility behavior and physical stability of solid dispersions.

Methods: Solid dispersions of the model drug (nilvadipine or nifedipine) and hypromellose (HPMC) (w/w: 1/1) were prepared using the laboratory-scale spray dryer. As process parameters, nitrogen flow rate, sample concentration and pump speed were investigated. The samples were characterized by dissolution tests, powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC), scanning electron microscope (SEM), and nanoscale thermal analysis (Nano-TA). The physical stability was monitored after 7 months storage at 25°C.

Results: Solubility behavior and physical stability were improved by setting the low nitrogen flow rate and high sample concentration. DSC showed that the physical state depends on the spray drying conditions, whereas, every sample showed the similar morphology from SEM results. The difference of solubility behavior and physical stability were found to come from the microstructural phase separation of the spray dried particles using a novel analytical technique (Nano-TA).

Conclusions: This study demonstrated that nitrogen flow rate and sample concentration should be the critical parameters for the enhancements of the solubility and physical stability of solid dispersions.     

Synthesis,characterisation and sustained release properties of layered zinc hydroxide intercalated with amoxicillin trihydrate

The intercalation of amoxicillin trihydrate (AMOX) into layered zinc hydroxide (LZH) has been achieved via ion-exchange method. The resulted nanocomposite (AMOX-LZH) has been thoroughly characterised by a number of techniques including powder X-ray diffraction (PXRD), FT-IR spectroscopy, TGA/DTG analysis and scanning electron microscopy (SEM). The PXRD results showed that the gallery height of LZH was expanded from 9.57 to 11.97 Å, indicating that the AMOX anions were successfully intercalated into the interlayer space of LZHs. The increased thermal stability of nanocomposite was confirmed by TGA/DTG analyses. Improved antibacterial activity and minimum inhibitory concentration of AMOX-LZH nanocomposite was evaluated against Gram-positive bacteria Staphylococcus aureus, Klebsiella pneumonia and Gram- negative Escherichia coli using the disk diffusion technique. The sustained release of amoxicillin drug from the AMOX-LZH nanocomposite was also verified.     

Cryomilling-induced solid dispersion of poor glass forming/poorly water-soluble mefenamic acid with polyvinylpyrrolidone K12

The effect of mechanical impact on the polymorphic transformation of mefenamic acid (MFA) and the formation of a solid dispersion of mefenamic acid, a poor glass forming/poorly-water soluble compound, with polyvinylpyrrolidone (PVP) K12 was investigated. The implication of solid dispersion formation on solubility enhancement of MFA, prepared by cryomilling, was investigated. Solid state characterization was conducted using powder X-ray diffraction (PXRD) and Fourier-transform infrared (FTIR) spectroscopy combined with crystal structure analysis. Apparent solubility of the mixtures in pH 7.4 buffer was measured. A calculation to compare the powder patterns and FTIR spectra of solid dispersions with the corresponding physical mixtures was conducted. Solid state characterization showed that (1) MFA I transformed to MFA II when pure MFA I was cryogenically milled (CM); and (2) MFA forms a solid dispersion when MFA was cryogenically milled with PVP K12. FTIR spectral analysis showed that hydrogen bonding facilitated by mechanical impact played a major role in forming solid dispersions. The apparent solubility of MFA was significantly improved by making a solid dispersion with PVP K12 via cryomilling. This study highlights the importance of cryomilling with a good hydrogen bond forming excipient as a technique to prepare solid dispersion, especially when a compound shows a poor glass forming ability and therefore, is not easy to form amorphous forms by conventional method.     

Enhanced performance of 4,4′-bipyridine-doped PVDF/KI/I<Subscript>2</Subscript> based solid state polymer electrolyte for dye-sensitized solar cell applications

Pure (PVDF/KI/I₂) and 4,4′-bipyridine-doped PVDF/KI/I₂ solid state polymer electrolytes were prepared by solution casting method using N,N-dimethylformamide (DMF) as solvent. The solid state polymer electrolytes were characterized by the powder X-ray diffraction (PXRD), Fourier transform infrared (FTIR), AC-impedance, dielectric measurements and scanning electron microscopy (SEM) analysis. The crystallinity of the solid state polymer electrolytes was analyzed by PXRD measurement. The functional groups of the solid state polymer electrolytes were confirmed by FTIR analysis. The AC-impedance analysis was carried out to calculate the ionic conductivity of the solid state polymer electrolytes. The ionic conductivity value of pure (PVDF/KI/I₂) and 4,4′-bipyridine-doped PVDF/KI/I₂ solid state polymer electrolytes are 2.00?×?10^?6 S cm^?1 and 4.60?×?10^?5 S cm^?1, respectively. The dielectric properties of solid state polymer electrolytes were calculated by using the dielectric measurements. From the SEM analysis, the surface morphology of the solid state polymer electrolytes was analyzed. The power conversion efficiencies of pure (PVDF/KI/I₂) and 4,4′-bipyridine-doped PVDF/KI/I₂ solid state polymer electrolytes are 1.8% and 4.4%, respectively. 4,4′-bipyridine-doped PVDF/KI/I₂ solid state polymer electrolyte has higher power conversion efficiency due to its increased amorphous nature and ionic mobility.     

Solid-State Stability of Theophylline Anhydrous in Theophylline Anhydrous-Polyvinylpyrrolidone Physical Mixtures

There are contradictory evidences in the literature concerning the role of excipients with a high affinity for water in the formulation when the formulation is exposed to moisture. A few reports indicate the stabilization of a drug in the presence of hygroscopic excipients. Other reports indicate the rapid moisture-induced changes of the drug in the presence of an excipient with high affinity for water. The objective of this study was to understand the effect of PVP and the relative humidity of storage on the solid-state stability of anhydrous theophylline. In this study, physical mixtures of theophylline anhydrous and polyvinylpyrrolidone were prepared in varying proportions. These mixtures were then stored in a range of humidities at room temperature. X-ray powder diffraction, moisture uptake, HPLC, and FTIR spectroscopy were used to monitor the physical and chemical changes occurring in the mixtures. A hypothesis is presented on the role of amorphous polymeric excipients in the formulation. The hypothesis agrees with the recent knowledge on the mobility of water associated with amorphous polymeric materials. The mechanism of protection by the PVP against the hydration of theophylline could be described as desiccant action. The efficiency of this desiccant action of PVP will then be dependent on the amount of water molecules in the system and the kinetics of reaching the equilibrium moisture content.     

About thaumasite formation in Portland-limestone cement pastes and mortars––effect of heat treatment at 95 °C and storage at 5 °C

Owing to the presence of finely divided calcite, mortars and concretes made with Portland-limestone cements are particularly susceptible to damaging thaumasite formation during sulfate attack at lower temperatures. This work reports the results of investigations on mortars made according to DIN/EN 196 and pastes (w/c ratio of 0.5) with CEM I 42,5 R, as well as with mixtures of cement with limestone filler. Some of the samples were heat-treated at 95 °C. The length changes and resonant frequencies of the samples were measured during long-term water-storage at 20 and 5 °C. There was no evidence from X-ray diffraction data of thaumasite formation in the samples. Only for pastes containing 30 wt.% limestone filler were small areas found by SEM and X-ray microanalysis whose chemical analysis matched thaumasite or a thaumasite–ettringite solid solution.     

Thermal Behavior of Ursodeoxycholic Acid in Urea: Identification of Anomalous Peak in the Thermal Analysis

The objective of this study was to clarify the thermal behavior of ursodeoxycholic acid (UDCA) in mixtures with urea. Physical mixtures of UDCA and urea in various ratios were prepared, and the thermal analysis of these sample mixtures was investigated using conventional differential scanning calorimetry (DSC) and variable-temperature powder X-ray diffractometry (VTXRD). The hot-stage microscopy (HSM) and powder X-ray diffractometry (PXRD) were used as complementary techniques. From the DSC results of all sample mixtures, it was found that there was no endothermic peak at the melting temperature of intact UDCA crystals. The DSC thermograms of each ratio showed only the endothermic peak at about 136°C due to the melt of urea and the anomalous endothermic peak at about 155°C-157°C. The VTXRD study revealed that the crystals of urea completely disappeared at a temperature of 140°C. At this temperature, it was identified that the VTXRD pattern obtained was of UDCA crystals. The crystalline peaks gradually decreased in intensity at a temperature of 150°C. When the temperature was up to 160°C, the identical crystalline peaks of UDCA crystals completely disappeared. It was concluded that the anomalous endothermic peak at 155°C-157°C was the peak due to the dissolution of UDCA crystals in the surrounding melted urea.     

<Emphasis Type="Italic">In vitro</Emphasis> bioactivity studies of larnite and larnite/chitin composites prepared from biowaste for biomedical applications

Larnite (Ca₂SiO₄) was synthesized by the sol–gel combustion process by using raw eggshell powder as a calcium source and urea as a fuel. The main focus of this work is to convert biowaste into a biomedical material at a low-processing temperature. X-ray diffraction (XRD) pattern confirms the phase purity of the larnite and Fourier transform infrared (FTIR) spectra confirms the presence of characteristic functional groups of larnite. Scanning electron microscopy (SEM) image shows agglomerated particles with cauliflower-like morphology and energy dispersive X-ray spectroscopy (EDX) confirms the presence of the stoichiometric ratio of required elements. Atomic force microscope (AFM) images reveal the presence of pores on the surface of spherical particles. Larnite/chitin composites were fabricated into scaffold with different ratios of bioceramic to biopolymer (70:30, 80:20) to investigate the influence of the polymer content on the apatite formation ability in simulated body fluid (SBF) medium. XRD pattern and FTIR spectra of the scaffold immersed in SBF shows apatite deposition within 5 days. The deposition of hydroxyapatite (HAP) on the scaffold surface increases with the increase in polymer content of the composite.     

Characterization and mechanical properties of polyacrylonitrile/silica composite fibers prepared via dry-jet wet spinning process

Polyacrylonitrile (PAN)/silica composite fibers were fabricated by dry-jet wet spinning process. PAN/silica composite fibers were characterized with SEM and FTIR. The former revealed that beads were formed and aggregated when silica content was more than 1 wt.%, while the latter confirmed the presence and increment of silica content. The tensile test was performed to obtain the mechanical properties of PAN/silica composite fibers, which showed an optimum Young's modulus at 5.94 GPa and tensile strength at 1.07 MPa at 1 wt.% silica. Therefore, the addition of silica particle at 1 wt.% has enhanced the mechanical properties of PAN/silica composite fibers.     

Synthesis of polyaniline/ZrO<Subscript>2</Subscript> nanocomposites and their performance in AC conductivity and electrochemical supercapacitance

Polyaniline/zirconium oxide (PANI/ZrO₂) nanocomposites have been synthesized by incorporating ZrO₂ nanoparticles into the PANI matrix via liquid–liquid interfacial polymerization method. The composite formation and structural changes in PANI/ZrO₂ nanocomposites were investigated by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). PXRD pattern of PANI/ZrO₂ nanocomposites exhibited sharp and well-defined peaks of monoclinic phase of ZrO₂ in PANI matrix. SEM images of the composites showed that ZrO₂ nanoparticles were dispersed in the PANI matrix. The FT-IR analysis revealed that there was strong interaction between PANI and ZrO₂. AC conductivity and dielectric properties of the nanocomposites were studied in the frequency range, 50–10⁶ Hz. AC conductivity of the nanocomposites obeyed the power law indicating the universal behaviour of disordered media. The nanocomposites showed high dielectric constant in the order of 10⁴, which could be related to dielectric relaxation phenomenon. Further, the materials were checked for their supercapacitance performance by using cyclic voltammetry (CV), chronopotentiometry (CP) and electrochemical impedance spectroscopy (EIS). Among the synthesized nanocomposites, PANI/ZrO₂-25 wt.% showed a higher specific capacitance of 341 F g^?1 at 2 m Vs^?1 and good cyclic stability with capacitance retention of about 88% even after 500 charge–discharge cycles.     

Effect of acrylic copolymer and terpolymer composition on the properties of in-situ polymer/silica hybrid nanocomposites

Acrylic copolymer- and 5% acrylic acid (AA) modified terpolymer-silica hybrid nanocomposites were synthesized by free radical bulk polymerization of ethyl acrylate (EA), butyl acrylate (BA) and acrylic acid (AA) with simultaneous generation of silica from tetraethoxysilane by sol-gel reaction. The pure polymers were analyzed by using Fourier Transform infrared (FTIR) spectroscopy and solid state nuclear magnetic resonance (NMR) spectroscopy. The hybrid samples were characterized by scanning electron microscopy (SEM), FTIR spectroscopy, NMR spectroscopy, dynamic mechanical, mechanical and thermal properties. SEM images confirmed the presence of nanosilica particles within the polymer matrices, whose dispersion and particle size distribution and visual appearance were dependent on the relative polarity (hydrophilicity) of the polymer matrices and the concentration of the filler. There was no evidence of strong chemical interaction between the polymers and the dispersed silica phase, as confirmed from the FTIR results. Terpolymer-silica hybrids demonstrated superior mechanical properties compared to the copolymer-silica hybrids. They also showed higher dynamic storage modulus and positive shift in the loss tangent peaks. The thermal stability of the nanocomposites was marginally higher which was possibly due to the dipolar interaction at the organic-inorganic interface.     

Application of cryomilling to enhance material properties of carbon nanotube reinforced chitosan nanocomposites

Cryomilled multiwall carbon nanotube (MWCNT) reinforced chitosan nanocomposites having improved conductivity have been prepared by solution casting method. The MWCNTs were crushed to smaller particles via cryomilling, which was effective in cleaving the nanotubes regularly as well as in reducing the entanglements and agglomeration. The cryomilled CNTs were chemically oxidized by acid and base methods, where basic oxidation generated high graphitic structure. The cryomilled and oxidized CNTs were characterized by XRD, Raman spectroscopy, FTIR and SEM. The conductivity of the nanocomposites was improved by cryomilling and it was further improved by chemical oxidation. Base oxidized cryomilled CNT/chitosan nanocomposites showed large improvement in conductivity compared to all other nanocomposites having 1 wt.% CNT content. Thermal stability and tensile properties of the CNT/chitosan nanocomposites also have been improved significantly by the incorporation of acid and base oxidized cryomilled CNTs. SEM picture of the fractured surface and FTIR showed nano-level dispersion of the functionalized CNTs and good chemical interaction between chitosan and CNTs respectively.     

Structure reinforcement of porous hydroxyapatite pellets using sodium carbonate as sintering aid: Microstructure,secondary phases and mechanical properties

Porous HAP pellets suitable for loading therapeutic agents were prepared using microcrystalline cellulose (MCC) as pore former and sodium carbonate as sintering aid (SAID). The effect of sintering temperature on the microstructure, mechanical properties and disintegration of pellets prepared at different SAID content was studied. Pellets were characterized by SEM, image analysis, porosimetry and surface area. Secondary phases were identified by PXRD, ATR-FTIR and Raman spectroscopy. Increasing the sintering temperature decreased the diameter, porosity, surface area and friability of the pellets but increased the pore size, tensile strength and disintegration time. The effect of SAID was dependent on sintering temperature. With 5% SAID, a secondary β-tricalcium phosphate (β-TCP) phase was formed, indicated by FTIR peak at 980 cm^?1 and characteristic PXRD reflections, whereas with 10%, a secondary B-type carbonated hydroxyapatite phase (CHA) formed, indicated by FTIR peaks at 878 and 1450 cm^?1, a broad Raman peak in the region 1020 to 1050 cm^?1 and PXRD reflections. Pellets prepared with SAID showed high strength and also porosity. The biphasic HAP/β-TCP pellets exhibited remarkably great strength (4.39 MPa) at the high sintering temperature, while still retaining 43.9% porosity. Relationships were established between the mechanical properties or disintegration time of the porous pellets and the microstructural parameters.     

Effect of PVP loading on pervaporation performance of poly(vinyl alcohol) membranes for THF/water mixtures

This work reports an experimental study on the pervaporative dehydration of an industrial solvent tetrahydrofuran (THF) using a blend membrane of PVA/PVP crosslinked with maleic acid. The influence of feed composition and permeate pressure on the pervaporation flux and selectivity has been investigated. The membrane was found to exhibit a water flux of 0.007 kg/m² h with a water selectivity of infinity for dehydration of 97% THF at 30 °C. FTIR of the blend was carried out to interpret its behavior on the basis of interactions between carbonyl groups of the cationic PVP and hydroxyl groups of the neutral PVA polymer. X-ray diffraction and sorption studies were carried out to study the degree of crystallinity and polymer–liquid interactions. The variation in film morphology was examined by scanning electron microscopy (SEM). Pervaporation experiments showed that high selectivity and promising permeability were obtained with a 9:1 blending ratio of PVA/PVP membrane crosslinked with 5 wt% maleic acid.     

Preparation of zeolite T membranes by microwave-assisted in situ nucleation and secondary growth

Zeolite T membranes were firstly prepared on the α-Al₂O₃ tubes by microwave-assisted in situ nucleation and secondary growth. The obtained membranes were characterized by XRD, SEM, single gas permeation, and pervaporation (PV). In the PV dehydration of ethanol and 2-propanol, the as-synthesized membranes displayed high separation performance. For the 90 wt.% alcohol/water mixtures at 338 K, the water flux reached 1.23 kg m^− 2 h^− 1 for the dehydration of ethanol and 1.52 kg m^− 2 h^− 1 for the dehydration of 2-propanol; both separation factors were higher than 10, 000.     

Preparation,characterization and thermal stability of bentonite modified with bis-imidazolium salts

Sodium bentonite was modified with several organic bis-imidazolium salts. Organoclays with water soluble surfactants were prepared by the traditional cation exchange reaction. The bis-imidazolium-bentonites were characterized by Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction analysis (PXRD) and thermogravimetric analysis (TGA). The effect of chemical composition and molecular weight of the salts on the thermal stability and basal spacing were evaluated. The bis-imidazolium-bentonites showed enhanced thermal stability (300–400 °C) and may be potentially useful materials for melt processing of polymer/layered silicates nanocomposites.     

Synthesizing tertiary silver/silica/kaolinite nanocomposite using photo-reduction method: Characterization of morphology and electromagnetic properties

Silver was loaded on silica/kaolinite by photo-reduction technique. The present study investigated the effects of the UV irradiation on different characteristics of the particles employing X-ray diffraction (XRD), Fourier-transform infrared spectra (FTIR), UV–vis spectrophotometer (UVS), Brunauer–Emmett–Teller specific surface area method (BETM), zeta potential measurement (ZPM), thermal gravimetric analysis (TGA), scanning electron microscope (SEM), electron dispersive X-ray spectrometer (EDX) and electromagnetic transition instrument (ETI). XRD, FTIR as well as UV absorption methods evidenced that synthesizing procedure was successful under UV irradiation. TGA results demonstrated that the Ag nanoparticles (AgNPs) generated on the silica/kaolinite surface can decrease thermal stability of particles due to proton delocalization of hydroxyl groups and Hofmann–Klemen effect. EDX results showed the presence of chemical elements namely Fe, Al, Si, Mg, K, Ti, Ag, Ca and Fe on the surface of tertiary nanocomposite. The synthesized silver/silica/kaolinite particles were found to have a higher electromagnetic absorption activity compared with silica/kaolinite. As a result, they can be used in polymer-based composites for preparing high performance electromagnetic interference shielding materials.