Celina Maria Damian

Functionalized single-walled carbon nanotubes/polypyrrole composites for amperometric glucose biosensors.

This article reports an amperometric glucose biosensor based on a new type of nanocomposite of polypyrrole (PPY) with p-phenyl sulfonate-functionalized single-walled carbon nanotubes (SWCNTs-PhSO3−). An environmentally friendly functionalization procedure of the SWCNTs in the presence of substituted aniline and an oxidative species was adopted. The nanocomposite-modified electrode exhibited excellent electrocatalytic activities towards the reduction or oxidation of H2O2. This feature allowed us to use it as bioplatform on which glucose oxidase (GOx) was immobilized by entrapment in an electropolymerized PPY/SWCNTs-PhSO3− film for the construction of the glucose biosensor. The amperometric detection of glucose was assayed by applying a constant electrode potential value necessary to oxidize or reduce the enzymatically produced H2O2 with minimal interference from the possible coexisting electroactive compounds. With the introduction of a thin film of Prussian blue (PB) at the substrate electrode surface, the PPY/GOx/SWCNTs-PhSO3−/PB system shows synergy between the PB and functionalized SWCNTs which amplifies greatly the electrode sensitivity when operated at low potentials. The biosensor showed good analytical performances in terms of low detection (0.01 mM), high sensitivity (approximately 6 μA mM−1 cm−2), and wide linear range (0.02 to 6 mM). In addition, the effects of applied potential, the electroactive interference, and the stability of the biosensor were discussed. The facile procedure of immobilizing GOx used in the present work can promote the development of other oxidase-based biosensors which could have a practical application in clinical, food, and environmental analysis.

Box-Behnken experimental design for chromium(VI) ions removal by bacterial cellulose-magnetite composites

In this study bacterial cellulose-magnetite composites were synthesised for the removal of chromium(VI) from aqueous solutions. Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis and X-ray Photoelectron Spectroscopy (XPS) were used to characterize the bacterial cellulose-magnetite composites and to reveal the uniform dispersion of nanomagnetite in the BC matrix. Magnetic properties were also measured to confirm the magnetite immobilization on bacterial cellulose membrane. The effects of initial Cr(VI) concentration, solution pH and solid/liquid ratio upon chromium removal were examined using the statistical Box-Behnken Design. Because of the possibility of magnetite dissolution during chromium(VI) adsorption, the degree of iron leaching was also analysed in the same conditions as Cr(VI) adsorption. From the factors affecting chromium(VI) adsorption the most important was solution pH. The highest Cr(VI) removal efficiency was observed at pH 4, accompanied by the lowest iron leaching in the solution. The adsorption experiments also indicated that the adsorption process of chromium(VI) is well described by Freundlich adsorption model. Our results proved that the BC-magnetite composites could be used for an efficient removal of chromium(VI) from diluted solutions with a minimum magnetite dissolution during operation.

Porous Gelatin-Alginate-Polyacrylamide Scaffolds with Interpenetrating Network Structure: Synthesis and Characterization

We report for the first time a simple method for the synthesis of porous gelatin-alginate-polyacrylamide scaffolds with interpenetrating networks structure. The materials are obtained through a step-by-step procedure, starting with the polymerization of acrylamide and followed by the cross-linking of the natural components. Porosity was induced through freeze-drying. The composition of the resulting porous matrices is responsible for elastic properties, high water affinity, and mechanical behavior appropriate for drug delivery and soft tissue engineering use. All these properties can be modulated by slightly modifying the initial polymer mixtures. The in vitro degradation behavior can be also controlled via compositional approach.

Effect of POSS-NH2 functionalization of MWNTs on reinforcing properties in epoxy nanocomposites

The research focuses on multiwalled carbon nanotubes (MWNTs) functionalization with aminoethyl aminopropyl polyhedral oligomeric silsesquioxane to increase their compatibility with epoxy polymers and enhancement of interface adhesion. Functionalization of MWNTs consisted of a three-stage reaction by oxidation and further amidation through acylation with thionyl chloride. The new nanomaterials were dispersed as reinforcing agent in a weight ratio of 0.3% related to the epoxy matrix, which was further cured with an aromatic polyamine. Characterization of functionalized MWNTs by infrared spectroscopy revealed the presence of POSS cages bonded to the MWNTs through the formation of amide groups, these findings were also proved by transmission electron microscopic images. Although catalytic influence of the reinforcing agent on the curing reaction was not significant at this level of reinforcement, scanning electron microscopic images of the nanocomposites fracture surface revealed strong interfacial adhesion and crack retardant effect of POSS-functionalized MWNTs.

Characterization of New Inorganic-Organic Composites Based on Mesoporous Silica and Vinyl Acetate

New polymer composites were synthesized by a new approach: radical polymerization in an ultrasonic field of the vinyl acetate inside the silica pores. The systems were extensively characterized by different techniques: X-ray photoelectron spectroscopy (XPS), gel permeation chromatography (GPC), thermogravimetric analysis (TGA), derivative thermogravimetry (DTG), dynamic mechanical analysis (DMA), and scanning electron microscopy (SEM). The formation of hybrid materials was proved by XPS. The molecular weight of the entrapped polymer in the cavities of the inorganic structure was assessed by GPC. The thermal properties of the composites were determined by TGA/DTG and DMA.

Electrochemical Deposition of Zinc Oxide on the Surface of Composite Membrane Polysulfone-Graphene-Polystyrene in the Presence of Water Soluble Polymers

The aim of this study consisted in the development of an alternative synthesis procedure for hybrid ultrafiltration membranes for water purification. The membranes were obtained by wet-phase inversion method based on aliquots of polysulfone (PSF) and graphene nanoplatelets modified with poly(styrene) (G-PST). The hybrid materials were modified by electrochemical deposition of zinc oxide (ZnO) on one side of the membranes in the presence of water soluble polymers. Raman, XPS, and TGA analyses were used to characterize the chemical and thermal characteristics of the PST-G. SEM analysis showed the formation of asymmetric porous configuration in all cases and the generation of ZnO with different shapes/structures on the bottom surface of the membrane or inside the porous channels. EDS analysis confirmed the formation of ZnO.

New Evidences on the Process Sensitivity of Some Renewable Blends Based on Starch considering Their Melt Rheological Properties

The degradability and processability of new renewable materials based on starch and PVOH were studied using the melt flow index (MFI) method by measuring the melt rheological properties which depend not only on the extrusion conditions and material formulation but also on the macromolecule characteristics which can be modified by chemical degradation. These results were correlated with other material properties like color and cross-linking degree. The obtained results show that flowing in the melted state of the studied materials is accompanied by a second process of chains chemical degradation. It was observed that, at the same level of additivation, under identical extrusion conditions, the melted blends with corn starch as main component are highly mechanically sensitive and degrade mostly by chains scission and those with PVOH as major component are highly temperature sensitive and degrade mainly by cross-linking. The obtained results show also that each PVOH-starch blend requires particular formulation and individual windows of melt processing conditions. These results are a good proof that the MFI method is a good path to study the degradability and moldability of process sensitive polymeric materials like those based on starch and PVOH.

Effect of polyhedral oligomeric silsesquioxane nanoreinforcement on the properties of epoxy resin/monoglycidylether-terminated poly(dimethylsiloxane) nanocomposites

This article reports the synthesis and characterization of several types of organic–inorganic nanocomposites based on epoxy resin/monoglycidylether-terminated poly(dimethylsiloxane) reinforced with 2, 5, or 10 wt% polyhedral oligomeric silsesquioxanes (POSS) bearing one glycidyl (1GE-POSS) or eight glycidyl(8GE-POSS) groups. The morphological features of the studied samples were established through atomic force microscopy, contact angle measurements, X-ray photoelectron spectroscopy, and scanning electron microscopy/energy-dispersive X-ray spectroscopy, and it was demonstrated that 8GE-POSS is well dispersed within the polymer matrix, while 1GE-POSS exhibits a high tendency to form aggregates. Differential scanning calorimetry (DSC) and Fourier transform infrared resonance (FTIR) measurements are used to follow the curing behavior and to study the polymerization kinetics of epoxy groups. As evidenced by DSC and FTIR results, the inclusion of 8GE-POSS within the polymer matrix leads to a lower epoxy polymerization rate of the resulted nanocomposites than those reinforced with 1GE-POSS. The dynamic mechanical analysis results revealed that the thermomechanical properties are gradually improved with increasing of 8GE-POSS content due to the higher cross-linking density.

Advanced studies on synthesis and cure reaction of fluorinated epoxy resin

Fluorinated epoxy resins (FERs) were extensively studied for applications in electronic packaging, optical waveguides, and antifouling coatings. This research focuses on the synthesis and characterization of FER following a polycondensation reaction between fluorinated bisphenol and epichlorohydrin. Cure reaction was monitored using dispersive Raman spectroscopy and by calculation of the oxirane groups conversion. After one short postcuring stage, the decomposition temperatures of fluoroepoxy showed increased values with 28–35°C for the samples cured at 50°C. The resultant materials showed excellent fracture morphology, while the presence of fluorine was revealed by energy-dispersive X-ray and X-ray photoelectron spectroscopic techniques. Hydrophobic surface was evidenced through the surface energy resulted from contact angle measurements.

Controlling the Melt Resistance to Flow as a Possibility of Improving the Miscibility and the Time Behavior of Some Blends Based on Starch

The paper proves that the miscibility of some blends based on starch can be improved by finding for each of them the melt resistance to flow at which the nonstationary flow and the melt degradation are avoided and the developed shear rate homogenizes optimally the material composition. The obtained results show that, for process sensitive materials like starches, the border between good and less miscibility is so narrow that the window of melt processing conditions and the best formulation must be found for each of them. The improving of miscibility by controlling the melt resistance to flow proves to be a good method to prevent retrogradation and plasticizer leaching and so to handle the new compounds behavior during usage.