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Oprea S.,Petru Poni Institute of Macromolecular Chemistry
Journal of Materials Science | Year: 2011

Polyurethane (PU) elastomers were elaborated from polyethylene glycol of high molecular weight (MW = 4,000), 1,6-hexamethylene diisocyanate and polyethylene glycol (PEG1500) (MW = 1,500) as a long linear chain extender and/or castor oil as a cross-linker and were obtained in the form of transparent films. These poly(ether urethanes) elastomers are obtained by replacing the short-chain diol monomers with high molecular weight polyethylene glycols (PEG1500). High molecular weight polyethylene glycol (MW = 4,000 and 1,500, respectively) have greater chain length thus producing networks with lower cross-linking densities and higher average molecular weight between two consecutive cross-links. The PU properties were investigated using Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry, mechanical analysis and thermogravimetry. The results showed that the prepared polyurethanes (PUs) had very good tensile properties. The stress-strain data show that the PU elastomers obtained using a 60/40% OHPEG1500/OH castor oil ratio have the best mechanical properties. The thermal degradation of the castor oil cross-linked PU elastomers starts at 280-300 °C, compared to the thermal degradation of linear PUs which begins at 220 °C. During storage at 25 °C, the morphology and mechanical properties of the elastomer films have been observed to change in time. © 2010 Springer Science+Business Media, LLC. Source


Oprea S.,Petru Poni Institute of Macromolecular Chemistry
Composites Part B: Engineering | Year: 2013

Films from multi-crosslinked polyurethane with different contents of guar gum (1-10 wt%) were prepared through a solution-casting method, followed by a thermal treatment or natural light exposure crosslinking procedure. Acrylic terminated prepolymers were prepared by capping the NCO groups of polyurethane prepolymers with pentaerythritol triacrylate. The effect of the guar gum content on the miscibility, morphology and physical properties of the blend films was investigated by Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, surface properties and tensile tests. The results reveal that small guar gum content is well embedded in the crosslinked polyurethane network and forms films with good mechanical properties, thermal behavior and hydrophilic properties. These results prove guar gum to be eco-friendly filler for multi-crosslinked polyurethane network. In the case of polyether urethanes, incorporating up to 3 wt% guar gum leads to a slight enhancement of the elongation at break, while for polyester urethanes incorporation up to 3 wt% guar gum slight increases stress at break values. Incorporating guar gum into the polyurethane networks leads to an increase in the hydrophilic nature of the polymer blends and improved surface structure. The properties of guar gum - which can be abundantly found in nature - make it desirable for polymer blends for biomedical applications. © 2012 Published by Elsevier Ltd. Source


Manea A.,Petru Poni Institute of Macromolecular Chemistry
Frontiers in bioscience (Scholar edition) | Year: 2012

Oxidative stress is a major contributor to the etiology of all severe vascular pathologies, such as atherosclerosis. NADPH oxidases (Nox) are a class of multicomponent enzymes whose unique function is the generation of reactive oxygen species (ROS) in the vascular cells and in circulating immune cells interacting with blood vessels. Physiological production of Nox-derived ROS contributes to the maintenance of vascular homeostasis. In pathological states, hyperactivity of Nox induces oxidative stress. Nox-derived ROS interact and stimulate other enzymatic sources of oxygen/nitrogen reactive intermediates, and amplify the initial response to insults. In atherosclerosis, Nox-induced lipid peroxidation is highly deleterious and expands the free radical reactions initially produced by activated Nox. Therefore, understanding the molecular mechanisms of Nox regulation, vascular and subcellular compartmentalization of ROS production and its subsequent biological significance, may lead to a focused and effective anti-oxidative stress therapy. We present here, recent advances in Nox regulation in the vasculature and discuss novel potential intrinsic feedback mechanisms and current and pharmacological perspectives to target Nox, which may have an impact in vascular health and disease. Source


Oprea S.,Petru Poni Institute of Macromolecular Chemistry
JAOCS, Journal of the American Oil Chemists' Society | Year: 2010

Castor oil-polyurethane elastomers were prepared by reacting poly (1,4-butane diol) (Terathane 1400) with aliphatic 1,6-hexamethylene diisocyanate. The pre- polymers were chain-extended with bifunctional precursor chains and/or with castor oil as a trifunctional crosslinker at stoichiometric ratios. These resulted in a series of cross-linked polyurethane elastomers with different structures of the hard segment. The properties of the material were measured by differential scanning calorimetry, thermo- gravimetric analysis, atomic force microscopy, as well as tensile properties measurements. The effect of stoichiom- etric balance (i.e., OH/NCO molar ratio) on the final properties was evaluated. The formation of hydrogen bonds was observed by Fourier transform infrared.spectroscopy The measured properties were found to be strongly influenced by the molar ratio of chain extenders to the diiso-cyanate component. The glass transition temperatures (Tg) for the polyurethanes with OHpolyol/NCO/OHchain extender having molar ratios of 1: 2: 1 and 1: 4: 3 were found to be -70 and -57 °C, respectively. The polyurethanes networks with a OH/NCO molar ratio of 1: 2: 1 had excellent mechanical properties, indicating that this is the optimum ratio to be used in castor oil polyurethane elastomer formulations. The objective of this work was to study the effect of the castor oil crosslinker on the morphology of the resulting crosslinked polyurethanes and to correlate the morphology with the properties of these bio-based crosslinked polyurethanes. © 2009 AOCS. Source


Dragan E.S.,Petru Poni Institute of Macromolecular Chemistry
Chemical Engineering Journal | Year: 2014

Interpenetrating polymer networks (IPN) hydrogels have gained great attention in the last decades, mainly due to their biomedical applications. This review aims to give an overview of the recent design concepts of IPN hydrogels and their applications in controlled drug delivery, and separation processes. In the first part, the main strategies for the synthesis of semi-IPN and full-IPN hydrogels, their relevant properties, and biomedical applications are presented based on the nature of the networks, the main categories selected being: IPN hydrogels based on polysaccharides (chitosan, alginate, starch, and other polysaccharides), protein based IPN hydrogels, and IPN hydrogels based only on synthetic polymers. The influence of the second network on the stimuli responsiveness of the "smart" IPN hydrogels is discussed based on the most recent publications in the field. In the second part, an overview of the most specific applications of IPN hydrogels in separation processes is critically presented. Factors which control the separations of dyes and heavy metal ions by semi-IPN and full-IPN as novel sorbents are discussed based on the recently published articles and own results. A special concern is given to the macroporous IPN composite cryogels, which are very attractive materials for separation processes being endowed also with a high reusability. © 2014 Elsevier B.V. Source

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