Horia Iovu

Sodium alginate/graphene oxide composite films with enhanced thermal and mechanical properties

Sodium alginate/graphene oxide (Al/GO) nanocomposite films with different loading levels of graphene oxide were prepared by casting from a suspension of the two components. The structure, morphologies and properties of Al/GO films were characterized by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), scanning (SEM) and transmission electron microscopy (TEM), thermal gravimetric (TG) analysis, and tensile tests. The results revealed that hydrogen bonding and high interfacial adhesion between GO filler and Al matrix significantly changed thermal stability and mechanical properties of the nanocomposite films. The tensile strength (σ) and Youngs modulus (E) of Al films containing 6 wt% GO increased from 71 MPa and 0.85 GPa to 113 MPa and 4.18 GPa, respectively. In addition, TG analysis showed that the thermal stability of Al/GO composite films was better than that of neat Al film.

Synthesis, characterization, and in vitro studies of graphene oxide/chitosan-polyvinyl alcohol films.

Nanocomposites based on chitosan-polyvinyl alcohol (CS-PVA) and graphene oxide (GO) were prepared by casting the stable aqueous mixture of the components. SEM, TEM and X-ray diffraction showed that graphene oxide is largely dispersed on molecular scale within CS-PVA matrix. FTIR investigation indicated the occurrence of some interaction between graphene oxide nanosheets and CS-PVA. The obtained composites are mechanically strong and exhibit improved thermal stability. By addition of 6 wt.% GO within CS-PVA blend, the elastic modulus increased over 200%. The cell viability and proliferation results showed that MC3T3-E1 mouse osteoblastic cells can adhere and developed on the CS-PVA/GO composite films. A significant proliferation potential was displayed by the cells in contact with CS-PVA/GO 6 wt.%. Graphene oxide reinforced CS-PVA with high mechanical and bioactive properties are potential candidates for tissue engineering.

New polymer-halloysite hybrid materials--potential controlled drug release system.

New hybrid materials based on a natural host (halloysite), biodegradable polymer (poly(vinyl alcohol)) and diphenhydramine hydrochloride as drug were synthesized and tested as a potential controlled drug delivery system. The formation of these hybrid materials was proved using different characterization methods like Spectroscopic techniques (FTIR, XPS and UV-vis), thermogravimetrical analysis and scanning electron microscopy (SEM). The hybrid materials exhibit different features regarding the drug release. In vitro drug release tests showed that there are several factors which exhibit a strong influence on the drug release rate. Thus the initial drug concentration used at the hybrid materials synthesis, the presence of a polymer in the hybrid composition and the pH value of the release medium are the most important factors.

In vitro cytocompatibility evaluation of chitosan/graphene oxide 3D scaffold composites designed for bone tissue engineering

Extensively studied nowadays, graphene oxide (GO) has a benefic effect on cell proliferation and differentiation, thus holding promise for bone tissue engineering (BTE) approaches. The aim of this study was not only to design a chitosan 3D scaffold improved with GO for optimal BTE, but also to analyze its physicochemical properties and to evaluate its cytocompatibility and ability to support cell metabolic activity and proliferation. Overall results show that the addition of GO in the scaffolds composition improved mechanical properties and pore formation and enhanced the bioactivity of the scaffold material for tissue engineering. The new developed CHT/GO 3 wt% scaffold could be a potential candidate for further in vitro and in vivo osteogenesis studies and BTE approaches.

Modelling of the butadiene and isoprene polymerization processes with a binary neodymium-based catalyst

Abstract In the present work we study the mechanism of the polymerization processes of isoprene and butadiene with the NdCl3·3TBP–TIBA catalyst system (TBP=tributylphosphate, TIBA=triisobutylaluminium) using two mathematical models: one which takes into account a monomolecular termination and the other which considers that no termination reactions occur during the polymerization process. Both for isoprene and butadiene, by comparing with the experimental data, the best results were achieved from the equations derived in the frame of the polymerization model considering the absence of the termination reactions. The product between the rate constant of the propagation reaction and the active centres concentration depends mainly on the [Al]/[Nd] molar ratio used which is an argument for the participation of TIBA in the formation of the active centres.

Epoxy-Based Nanocomposites Reinforced with New Amino Functionalized Multi-Walled Carbon Nanotubes

The aim of the work was to synthesize epoxy-based nanocomposites reinforced with multi-walled carbon nanotubes (MWNT). MWNTs were first functionalized in order to increase the dispersion degree within the polymer matrix and thus to ensure good adhesion between the two components. The functionalization process consists of two steps: first, MWNT were oxidized, and then an amidation reaction occurred with various amines using carbondiimide and succinimide as activators. Thus, new modified MWNT with benzylamine (BA) and nonylphenoxy polypropyleneoxyamine (B100) were synthesized. The nanocomposites obtained were based on diglycidyl ether of bisphenol A (DGEBA) and modified MWNT and were fully characterized by TGA, DMA, XPS, SEM, TEM, and FTIR.

Characterization of Novel Epoxy Composites Based on Hybrid Inorganic/Organic Polyhedral Oligomeric Silsesquioxane

New nanocomposites were synthesized by the reaction between a polyhedral oligomeric silsesquioxane (POSS) with eight epoxy groups (epoxy-POSS) and diglycidyl ether of bisphenol A (DGEBA) using Jeffamine D230 as curing agent. The reactivity of the systems was extensively studied by Raman spectroscopy. The hybrid materials were characterized by different techniques like thermogravimetric analysis, dynamical mechanical analysis, X-ray photoelectron spectroscopy, differential scanning calorimetry, and scanning electron microscopy. The “Si‒O‒Si” cages of the POSS component form aggregates, which was shown by the conversion data obtained from the Raman spectra and confirmed by the DSC curves, XPS spectra, and SEM images.

Synthesis of Polyvinylacetate‐Sodium Montmorillonite Hybrids by Emulsion Polymerization in the Presence of Anionic Surfactants

The emulsion polymerisation of vinyl acetate (VAc) in presence of sodium dodecylsulphate (SDS) and sodium montmorillonite (NaMMT) is used in order to achieve polymer‐clay hybrids. The influence of the polyvinylacetate (PVAc), SDS, and PVAc‐SDS complex on the NaMMT structure also was investigated. The VAc emulsion polymerization rate exhibits a maximum as the NaMMT concentration increases. The XRD patterns correspond to hybrids with intercalated structure. If a water soluble comonomer, ammonium sulphato ethylmethacrylate (ASEMA) is used for copolymerization with VAc, a exfoliated hybrid structure (from XRD spectra) is obtained. The solid materials were analysed by TGA, FTIR, XRD, SEM, and TEM.

Butadiene polymerisation using binary neodymium-based catalyst systems. The effect of catalyst preparation

Abstract The influence of preparation conditions on the activity of NdCl3.3TBP-TIBA catalysts for the polmerisation of butadiene have been investigated. The highest catalysts activities and resulting polymer molecular masses have been found where the catalyst is “preformed” in the presence of precise and small amounts of butadiene (molar ratio [Butadiene] [Nd] = 2 ) and is aged for 1 hr at 20 °C. Polybutadienes with a 1,4-cis content of 98–99% are readily achieved irrespective of the method of catalyst preparation. The enhanced reactivity of the “preformed” catalyst is explained in terms of a stable π-allylic complex involving the butadiene unit.

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.