Browse Articles

Propolis is a natural apicultural product derived from plant resins with impressive health benefits. Its major biologically active substances are barely soluble in water, but this could be increased by proper formulations.The aim of the present study was to obtain a transmembrane delivery system based on polyurethane microstructures for eight propolis samples collected from different regions of Western Romania and to characterize them by differential scanning calorimetry (DSC); the assessed parameters were the particle size, the polydispersity index and their clustering tendency. Polyurethane polymers based on isophorone-diisocyanate and polyethylene glycol 200/ethylene glycol were chosen as carriers for the propolis extract. A perfect inclusion of propolis inside the structures was observed for half of the samples. Particle size ranged between 504 and 621 nm and was confirmed by the low stability against aggregation (Zeta potential: 16.3-19.8 mV). The polydispersity index was between 0.4 and 0.7.

The new generation of newly developed materials, namely the high-crystallinity and high temperature polypropylene random copolymer, called PP-RCT, increases the crystalline capability of polypropylene, which allows pipes produced from this material to operate at higher pressures at elevated temperatures. Pressure tests on pipes made of PP-RCT materials show a resistance over a period of 50 years at 7000C (1580 F) 5 MPa (725 psi) compared with 3.2 MPa (464 psi) for standard materials PPR. By reinforcing PP-RCT with aluminum, glass and basalt composite results in a more resistant structure. As a result of the traction tests, it was found that in all three samples the tensile strength exceeds the manufacturer s limit (10 - 12.7 MPa), the values obtained being: st1 = 8 MPa - sample no. 1; st2 = 13 MPa - sample no. 2; st1 = 11 MPa - sample no. 3. The fiber glass insert is less resistant, the best variant being the basal insect sample (st2 = 13 MPa). Elongation at break for specimen no. 3 was recorded at 0.027 mm / mm. Tests on these material combinations were performed for stretching and flexing requests and compared to 3D created virtual models. Simulations of internal pressure behavior were also performed for different material configurations and the results were compared with the experimental data and the data supplied by the manufacturers.

This paper shows the ageing study of some coatings and / or impregnation lacquers due to microbiological stress through fungal attack. Dielectric spectroscopy has shown that the dielectric losses of the investigated materials increase as result of microbiological ageing. The mean recorded increases are about 4 times for the alkyl-epoxy-melamine copolymer, 2 times for epoxy polymer and 1.5 times for urethane polymer in agreement with the mould coverage degree of about 20 %, 10 %, and 3 %, respectively. The fungal attack of the investigated polymers led to a decrease in volume resistivity of about 65 % for the alkyl-epoxy-melamine copolymer, 45 % for the epoxy polymer, and 14 % for polyurethane, in agreement with the increase of dielectric losses and degree of mold coverage of the samples. FTIR determinations have shown that fungal attack significantly increased the number of aliphatic -OH and C-H bonds and decreased the number of C–O bonds, respectively of C–O–C oxiran groups and C-C aromatic bonds. DSC thermograms recorded at different temperature ranges and the activation energies calculation for first major oxidation process indicate that after the fungal attack the thermooxidative reactivity of the investigated polymers increases.

PLGA (Poli-lactic-co-glycolic acid) nanoparticles (NPs) are curently used as drug delivery systems for many types of drugs including antioxidants such as vitamin E. The main aim of our study was to test the antioxidant effects of PLGA-vitamin E on Wistar male rats. Two groups of Wistar rats received a hypercaloric diet for 21 days: the first group received besides the hypercaloric diet a daily dose of PLGA loaded with vitamin E and the control group received only the hypercaloric diet. Spleen cellular lysate has been used to detect biomarkers of oxidative stress such as malondialdehyde, glutathione, advanced human oxidative protein and vitamin E. After 3 weeks of treatment, statistical significant changes have been detected between the two groups.

The aim of this study was to evaluate the efficiency in using intermaxillary elastics to stimulate mandibular growth and advancement in orthodontic patients diagnosed with skeletal Class II malocclusion as well as to compare the use of these Class II elastics in two different therapeutic approaches. The sample consisted of 60 orthodontic patients aged 10-15 years, 34 girls and 26 boys. The sample was divided into two equal groups (each consisting of 30 patients). Patients belonging to the first group (Group 1) were subjected to 1/4¹¹ - 6.0 oz elastics and were advised to change the elastic every 24 hours. Patients belonging to the second group (Group 2) were subjected to 1/4”- 4.5 oz elastics but with a recommendation to change the elastics every 12 hours. In order to evaluate the effectiveness of these two types of Class II elastics on mandibular growth and advancement, the value of the SNB angle at the beginning of the treatment (T1) was compared with the value of the SNB angle after 5 months of wearing intermaxillary elastics (T2). All patients showed statistically significant increased values of the SNB angle during the orthodontic treatment (p[0.001). Patients in Group 2 showed a significantly higher statistical increase (p[0.05) than patients in Group 1.

The enterprise has an intricate and elaborate system of relationships between the departments, functioning closely as a cell within an organism, with its defined role within the market. In the complex context of actual economic system, resources are limited and enterprises seek for efficiency in order to reduce costs. In this paper we present the development of a solution for the optimization of an agricultural enterprise related to the plastic-based materials usage in the agricultural processes. In this matter, the experimental part consists in the creation of a model of a plastic management system using methodologies from the literature (e. g., System Dynamics or SD etc.) and its simulation with specific tools used traditionally. Besides the experimental part, we will make a short analysis regarding the structural and economic issues regarding plastics used in agriculture and some considerations regarding the bioplastic material that can be obtained from different types of agricultural waste.

It was found that the obtaining of quality 3D printing filaments, without defects and natural color, from corn starch physical modified with PVOH, depends also on the melting behavior at compounding, both of starch and of PVOH, and on the controlling of the process sensitivity of the new compounds. A comparable melting behavior was possible by compounding the two polymers as powders with similar small sized particle. The controlling of the process sensitivity was achievable, mainly, by diminishing the melt resistance to flow, via formulation with a flow agent. The selected compounds which had controlled miscibility, few defects and natural color were shaped, with good results, as filaments with silky and smooth surface. These filaments were compatible with 3D printing because proved to have the ovality and the diameter tolerance in the accepted limits in the fields.

The aim of this study was the development and formulating of an eye contour serum containing hyaluronic acid (HA) and the assessment of stability tests performed for the cosmetic product, transfered into a glass cosmetic bottle with polipropylene (PP) pump and cap. Sample of cosmetic serum were stored using 20 mL glass bottles with PP (Polypropylene) pump and cap. The developed cosmetic formulation was monitored under accelerated stability studies, performed over a period of 30 days while maintaining the product at 4, 20 and 40°C. Quality control initial, and after initiating the accelerated stability test was performed for the developed cosmetic formulation.

Although Romania has a consistent hydro energetic potential, till now is valuated just approximate 30 percent of it. On the big rivers there are already installed high power hydro plants, but a lot of small and medium rivers are not valuated energetically. Installing a new high power hydro plant tends to affect the zone, being necessary a lot of changes in the environment. The Cross-Flow hydraulic turbines don’t need very complex hydro settlements, being very suitable for small and medium power hydro plants. Also a quite big potential in the use this type of hydraulic machines is the energy recovery in the water treatment and sewage plants. The turbine’s blades surfaces enters in contact with the pressurized water jet. The water jet creates a hydrodynamic force that tends to stress the blade. Mainly the Cross-flow turbine blades are made from steel. This article presents the hydrodynamic design and the possibility of using new polymeric material Delrin ®AF for the Cross-Flow turbine runner blades, together with the stress analysis.

The present paper is concerning to an empirical analysis of tensile properties of plies and laminates formed with an epoxy matrix and with various carbon fiber fabrics. The analysis was started with the aim of finding some correlations between the elastic parameters of plies and elastic parameters of laminates when fabrics are used as reinforcements. Six different carbon fiber fabrics were used to analyze the plies and laminates mechanical parameters. The epoxy system Epiphen RE-4020-DE4020 was used in both cases as matrix. The mechanical response to tensile test was analyzed for above mentioned materials and the results had been compared with values obtained by application of various purposed models.