Viscoelastic, thermal, and morphological properties of nanocomposites based on modified PVA using a twin-screw melt extrusion process

Melt polymer nanocomposites were prepared using polyvinyl alcohol (PVA) with the different weight percentage of calcined clays (CCs) in a twin-screw extruder at 210°C and 70 r min−1 for 8 min. Bentonite was surface functionalized with benzidine using dilute hydrochloric acid at 60°C and calcined at 600°C for 6 h. The CCs were incorporated into the PVA matrix to study their morphology and rheological properties. The melt viscosities of the composites were measured by the cone-plate rheometer, the rheogram show non-Newtonian and thixotropic flow behavior. Scanning electron microscope confirmed the degree of exfoliated nanocomposites. The polymer and functionalized nanoclay interactions were reflected in the enhancement of thermal stability and mechanical properties. The melting endotherm temperature ( T m) and glass transition temperature ( T g) of the nanocomposites tend to increase with increase in weight percentage of the calcined nanoclays. Thermal properties show that addition of calcined nanoclays would improve the thermal decomposition temperatures from 295°C to 307°C when CC content was 2 wt% in covalent or ionic bonding system.

Analytical Investigation of the Possible Chemical Interaction of Methyldopa with Some Reducing Carbohydrates Used as Pharmaceutical Excipients

Purpose: Assessment of drug substance and excipients compatibility is an important issue during pre-formulation studies as well as the quality control of pharmaceutical dosage forms. In this study, potential incompatibility between methyldopa and reducing excipients was evaluated using physicochemical methods. Methods: Dextrose and lactose (anhydrous & monohydrate) were selected as reducing carbohydrates. The initial incompatibility was studied with DSC and FTIR on binary mixtures with 1:1 mass ratio. Results were confirmed using HPLC studies coupled with mass spectrometry. Results: The DSC curves indicated the elimination of the melting endotherm of methyldopa in the binary mixtures. A new peak at 1719 cm-1 was observed in the FTIR spectra that can be attributed to the loss of type one amine functionality. The m/z of the proposed compound was observed in the mass spectra. Conclusion: The potential incompatibility of Methyldopa with reducing carbohydrates was established using physicochemical methods.

Studies of Interactions of Valsartan, Glimepiride and Ciprofloxacin HCl by DSC and HPLC

This article deals with the results of in vitro interactions among glimepiride, ciprofloxacin HCl and valsartan at the molar ratio of 1:1:1 by DSC and HPLC method. The DSC thermogram of the mixture (glimepiride, ciprofloxacin HCl and valsartan) showed different melting endotherm than the melting endotherm for standard valsartan, ciprofloxacin HCl and glimepiride. Since the melting endotherms of mixture and individual drugs were not identical, it demonstrated the presence of interactions among the drugs. This result was further verified by HPLC to observe their recovery range. The % recovery ranges were found as 25.33, 23.49 and 135.82% for glimepiride, ciprofloxacin HCl and valsartan, respectively. The abnormal percentage recovery range and peak areas fluctuation further indicated the interactions among glimepiride, ciprofloxacin HCl and valsartan.Bangladesh Pharmaceutical Journal 20(2): 194-199, 2017

Synthesis of High cis-Polybutadiene in Styrene Solution with Neodymium-Based Catalysts: Towards the Preparation of HIPS and ABS via In Situ Bulk Polymerization

In a first step, 1,3-butadiene was selectively polymerized at 60°C in styrene as solvent using NdV3/DIBAH/EASC as the catalyst system. The catalyst system activation process, the addition order of monomers and catalyst components, and the molar ratios [Al]/[Nd] and [Cl]/[Nd] were studied. The catalyst system allowed the selective 1,3-butadiene polymerization, reaching conversions between 57.5 and 88.1% with low polystyrene contents in the order of 6.3 to 15.4%. Molecular weights ranging from 39,000 to 150,000 g/mol were obtained, while cis-1,4 content was found in the interval of 94.4 to 96.4%. On the other hand, the glass transition temperatures of synthesized materials were established in the range of −101.9 to −107.4°C, explained by the presence of polystyrene segments in the polybutadiene chains; in the same sense, the polybutadienes did not show the typical melting endotherm of high cis-polybutadienes. In a second step, the resulting styrene/high cis-1,4 polybutadiene solutions were used to synthesize ABS (adding a fraction of acrylonitrile monomer) and HIPS via in situ bulk polymerizations and the results were discussed in terms of morphological development, molecular parameters, dynamical mechanical behavior, and mechanical properties.

Polymorphic Forms of Lamivudine: Characterization, Estimation of Transition Temperature, and Stability Studies by Thermodynamic and Spectroscopic Studies

The present study is focused on estimation of transition temperature and stability of various forms of lamivudine. The forms were recrystallized from variety of solvents and preliminarily identification on the basis of SEM revealed existence of three forms (Forms I, II, III). DSC scans of Forms I and III show that these are metastable and undergo heat mediated transformation to Form IH and Form IIIH, respectively. Form II is phase pure with single sharp melting endotherm at 178.6°C. The thermal events are visually observed by hot stage microscopy. Enthalpy of solution of the forms is endothermic and magnitude varies in the order Form II > Form IL > Form IIIL suggesting Form IIIL to be least crystalline which is well correlated with XRPD data. The transition temperature of the polymorphic pairs IL/IH and IIIL/IIIH derived from enthalpy of solution and solubility data revealed monotropy whereas enantiotropy exists in IIIH/II. The slurry experiments showed Form II to be thermodynamically most stable. Forms IL and IIIL though stable in water are converted to Form II in ethanol, acetonitrile, and propanol after 1 day. Form IIIL is converted to Form IL in water after 7 days and the observation is of importance as this instability can effect the pharmaceutical preparations whereas Form IL shows a balance between stability and solubility.

A Study of Mechanisms of Poly (PhenyleneSulfide) Thermal Degradation in Air

Because of its special properties and commercial significance, Poly(phenylene sulfide) (PPS) has been the subject of many research efforts since its commercial introduction in 1967. Intensive work has been done on its crystalline structure and morphology and its thermal behaviour. But fewer investigations have been carried out to understand long term behaviour in high temperature environments. Always anticipating industrial needs linked to power integration, we have launched an extensive study on thermal aging in air of PPS at 250°C. This study has shown that PPS thermal degradation in air happens by intermolecular branching reaction, similar to crosslinking. This phenomenon was already known for temperature above 300°C. This crosslinking is evidenced by rheometry where the relative position of G’ and G’’ above melting temperature changes with aging. IR spectroscopy confirms that para substituted benzene in PPS molecule is transformed in 1,2,4 trisubstituted benzene. DSC measurements evidence both an elevation of melting temperature and a change in melting endotherm showing significant changes in crystalline morphology along aging, which tends to indicate that crosslinking occurs in crystalline phase. Then degradation implies drastic loss of mechanical properties leading to destruction of the sample.

Vitrification and devitrification of the rigid amorphous fraction in poly(ethylene terephthalate)

Vitrification and devitrification of the rigid amorphous fraction (RAF) of poly(ethylene terephthalate) (PET), analyzed during development and disappearance of the three phase structure, are detailed in this contribution. Upon cooling from the melt at a constant rate, the rigid amorphous fraction starts to vitrify when the crystallization process is almost finished, and continues on further cooling. The rigid amorphous fraction is formed in the same temperature range of the secondary crystal growth. Analysis of the low melting endotherm that is observed in isothermally crystallized PET a few degrees above the crystallization temperature reveals a joint contribution of melting and devitrification of the rigid amorphous fraction. The results confirm a link between secondary crystallization and vitrification of the rigid amorphous fraction in semicrystalline polymers. Secondary crystallization takes place in geometrically restricted areas, in which the polymer chains undergo large constraints, so that the mobility of the amorphous chain portions coupled with the crystal phase is reduced. Similarly, the gain in mobility upon partial melting of thinner and/or more defective crystals allows an increase in mobility of the coupled amorphous regions, which results in concurrent mobilization of the rigid amorphous fraction.