Browse Articles

The birefringence of some polymeric esters of alkoxy benzoic acid (PEABA) in tetra chloromethane (TCM) was determined by previously proposed interferometric methods in polarized light. An increase in PEABA birefringence when an external electric field acts on the liquid crystal layer was evidenced in this paper. The decrease of PEABA birefringence with the increase in the alternate electric field frequency was also evidenced. The dipolar nature of the collective interactions between the side-chains of PEABA in liquid crystalline phase and also the viscosity of the lyotropic liquid crystal obtained by mixing PEABA with TCM in concentrations of about 10-2 g / cm3, at room temperature are sustained by the results obtained in this paper. Keywords: PEABA birefringence, tetra chloromethane (TCM), polarized light

Extracellular matrix biocomposites based on poly(ester urethane), and hydrolyzed collagen, elastin, chondroitin sulfate and hyaluronic acid have been prepared. Different surface morphologies for each of the test matrices were revealed by Environmental Scanning Electron Microscope (ESEM). The biological material used is a very wide spread aggressive fungal species in all media for life, Mucor mucedo. Evaluation of the biologically active potential of these biocomposites against Mucor mucedo has been done through inoculation onto Sabouraud –agar nutrient medium. Fungal growth was monitored over 60 days.Visual observations of the fungal growth show that Mucor mucedo was aggressive and caused rapid grow after 72 h of inoculation onto Sabouraud-agar nutrient medium, but the biopolyurethane composites samples relatively to the fungal attack particularly showed a different relationship. Keywords: biomaterials; composites; polyurethanes; Mucor mucedo; extracellular matrix

In the context of developing new phosphazene/silica hybrids for preparation of thermally resistant membranes for gas separation processes, two cyclophosphazenes/organosiloxane monomers (1 and 2, scheme 1) were synthesized via aminolysis of hexachlorocyclotriphosphazene (N3P3Cl6) with the monoamine functional trialkoxysilanes: 3-(triethoxysilyl)-propylamine (H2N-(CH2)3-Si(OC2H5)3) or 3-(trimethoxysilyl)-propylamine (H2N-(CH3)3–Si(OCH3)3), respectively, as new starting compounds for cyclophosphazene/SiO2 composites prepared by the sol-gel process. The siloxane monomers, N3P3Cl3[N(CH2)3Si(OCH3)3]3 (1) and N3P3Cl4[N(CH2)3Si(OCH2CH3)3]2 (2), as well as the corresponding composites {N3P3Cl3[N(CH2)3]3}y-(SiO2)41y (1’) and {N3P3Cl4[N(CH2)3]3}y-(SiO2)80y (2’) issues from the sol-gel process, have been characterized by infrared spectroscopy and elemental analysis, TG-DTA-DSC coupled thermal analyses, as well as by XPS, XRD, and SEM-EDAX investigations. Keywords: cyclophosphazene, sol-gel process, organic-inorganic hybrid materials

This paper presents the synthesis and characterization of a new class of biodegradable copolymers based on carbohydrates. A new oligomer was synthesized by the polycondensation of 1-benzyl-5,6-(bis(maleyloxy))-2,3-isopropylidene-D-mannofuranose with propane-1,3-diol in the presence of p-toluenesulfonic acid and then it was copolymerized with 2-hydroxypropyl (meth)acrylate, using benzoyl peroxide as initiator. The mannose based oligomer was characterized by FTIR and NMR spectroscopy and HPLC-MS, and the copolymers were analyzed using FTIR and thermogravimetry. Keywords: D-mannose, glycopolymers, maleic anhydride

The effects of UV exposure on physico-chemical properties of polymer membranes were studied in this paper. The membranes having different surface energy, resilience and initial modulus of elasticity were obtained from a series of blends of poly (hydroxy-urethane) and poly (vinyl alcohol). UV treatments in air, at room temperature, decrease the water contact angles as a result of higher surface energies of the polymer membranes. Some important modifications appear in ATR-FTIR spectra. The mechanical properties of the untreated polymer films are better than of the UV treated samples. Short-term UV irradiations lead to a photo stabilization effect of polymer surface. Bulk chemical changes are induced through photo oxidation and photo degradation processes for long-term UV irradiation. Keywords: UV treatment, photo oxidation, photo degradation, photo stabilization resilience

In this work, different types of neural networks and modeling methodologies are used and compared: feedforward and recurrent networks, stack neural networks and a hybrid model composed from a simplified phenomenological model and a neural network. For each situation, the performance of the networks was evaluated through mean squared error and correlation between training data and neural network predictions. Accurate results were obtained with different types of neural models, but our approach recommends feedforward neural networks which are simple to train and use. The well known free radical polymerization of methyl methacrylate, accompanied of gel and glass effects and achieved in a batch bulk process is considered as example. In a hybrid methodology, the kinetic model used until the onset of the gel effect is associated with a neural model which replaces the diffusional effects representing the difficult part to model in the process. Keywords: neural networks, free radical polymerization modeling, polymethyl methacrylate, hybrid model

Since discovered, rubbers were tested, among other possible utilizations, for their military use. In the present study, NBC protection properties of a new bromobutyl rubber-based composite (BrBR) are presented: protection time against liquid droplets of mustard gas (also known as yperite, 1,5-dichloro-3-thiapentane or HD), flame resistance and flame propagation properties. The tests performed demonstrated the improvement brought by BrBR in comparison with the materials in use in the Romanian army, this material offering the same protection level as the materials used nowadays in developed countries. Keywords: NBC protection, composites, mustard gas, burning time

Photoluminescent composite of poly-ethyleneterephtalate-SrAl2O4: EU2+, Dy3+ was prepared by of a new procedure based on mixing the constituents in specific solvents for PET. In a first step it was studied the possibility of preparing europium and dysprosium doped strontium aluminate using a method that allows obtaining crystals in nanometric range compatible with polymer matrix. Also, the dependence of transparency in UV-VIS range of the polymer matrix density and experimental paths for obtaining a low crystallinity of PET at co-precipitation from solution were investigated. Characteristics of absorption / photonic emissions, phosphorescent decay time were investigated for europium/dysprosium doped strontium aluminate, and respectively for the composite prepared. The prepared photoluminescent composite presents a series of applications in optoelectronics, highway/ railway and utilitarian signaletics. Keywords: long persistence phosphorescent compounds, phosphorescent composites, polymer matrix, polyethyleneterphtalate

The three-dimensional printing is a rapid prototyping technology, used to create complex three-dimensional parts directly from a computer model of the part, with no need for tooling. This paper investigates the use of a modern RP technology known as 3-D printing. Using the Rapid Prototyping 3D Zcorp 310 Printer system, we manufactured the prototypes for orthopedic adaptive modular plates based on intelligent materials, human bones and an artificial hand necessary for ‘in vitro’ simulations, experimental tests, experimental measurements. The material used is a High performance composite powder Zp131. After printing, we used Z-Max Resin - High Strength Epoxy Infiltrant System to provide strength and impart specific properties. Using Rapid Prototyping as a fabrication method one can finally obtain functional assemblies. Experimental studies of the staple made of the shape memory alloy named Nitinol are presented. The complexity of the shapes and dimensions of the fabricated parts recommends Rapid Prototyping method as a future fabrication method in different applications and scientific fields of research. Keywords: CAD-CAM, rapid prototyping, 3D-printing, Nitinol, composite powder, epoxy resin, orthopedic applications

This paper presents the research performed in the laboratory of Renewable Energy Sources within the Petroleum-Gas University of Ploieºti regarding the use of heat pumps for surface geothermal energy extraction. The paper also examines the decrease of thermal power extracted via heat exchangers mounted in the soil, due to the cooling of the surrounding soil. The results obtained for a simple U-shaped loop mounted in a vertical shaft are presented as well. Keywords: thermal decline, Geoexchange, polyethylene, heat pump, numerical models