Browse Articles

Direct photoreduction and photosensitization are powerful approaches for the in-situ synthesis in a polymer matrix. A silver–acrylate nanocomposite was prepared using a novel one-pot strategy involving simultaneous photoinduced reduction and free radical polymerization processes. The fabrication of metal nanocomposite was performed using an acrylate functionalized oligomer (polyethylene glycol 600 diacrylate) and a silver salt (AgNO3). The formation of Ag-nanoparticles was followed by UV–Vis spectroscopy which shows a surface plasmon band at a wavelength range between 410 and 440 nm. Transmission electron microscopy revealed that the synthesized nanoparticles were spherical in shape with a diameter between 5 to 20 nm. The polymerization process was followed quantitatively by infrared spectroscopy, monitoring the disappearance of the characteristic bands for the acrylate double bonds (1410 cm-1). The optimum conditions for obtaining the silver-polymer nanocomposites have been determined (silver precursor concentration, molar ratio silver precursor/photoinitiator, irradiation time and intensity). A reaction mechanism was proposed to explain the polymerization rate dependence on the silver cations content. Keywords: Silver nanoparticles, photo polymerization, acrylate, nanocomposites

In this paper, data on Melana-type polyacrylonitrile fibres dyeing with Crystal violet (CV) - triphenylmethane dye- in the presence of maleic acid copolymers with vinyl acetate (NaM-VA) or styrene (NaM-S) are presented. Mathematical models of the studied dyeing processes have been developed and the necessary information on their significant factors is produced by means of experiment planning methods, known as Design of Experiment (DoE) or Experimental design. Optimal correlations between the application conditions and the colour differences obtained on Melana-type fibre have also been studied. Keywords: Melana fiber, Maleic copolymers, Crystal violet dye, Color differences, Statistic modeling, Optimization process

Difficulty to objectively determine the moment of bone fracture consolidation by classical imaging methods makes necessary the development of a method that will allow establishing, by objective criteria, the moment in which biomechanical loading of the injured bone segment may be permitted. We propose a method based on the approximation between bone diaphysis and a beam, analysing its behaviour under frequency excitation at one end and measuring the vibrations at the other end. Variation of parameters measured in the structurally sound structures compared to the fractured ones, as well as the possibility to analyse their evolution in the presence of osteosynthesis materials used for the surgical treatment of fractures is ascertained. The existence of composite plastic materials of which the used anatomical bone mould for this experiment is made simulates the real pathological situation, which allows extending the determinations to clinical cases. Key words: bone, fracture, mould, polyurethane, osteosynthesis material, composite material

The paper presents a comparative analysis between the performances of pressure sensitive adhesives based on polychloroprene rubber and hybrid acrylic adhesive. The analysis was based on peel, shear and tensile tests for the assemblies on various substrates. Adhesion work was also determined from the contact angles and superficial tensions. The values of the adhesion work confirm the results obtained with the above mentioned tests. Keywords: pressure sensitive adhesives, polychloroprene-based rubber, hybrid acrylic adhesives

This paper has had as purpose rendering of some researches related to extrusion velocities while obtaining multilayer films with five layers of polymer. An installation comprising five extruders has been used for trials and conditions and optimal areas for every single extruder had been set. The results thus obtained made possible to settle the optimum parameters for the extrusion process so that to ensure a stable flow of the molten polymer, which resulted in a uniform multilayer, faultless structural film. Keywords: polyethylene, extrusion, co-extrusion, multilayer film

This article deals with weld quality in reference to strength and seal using in experiment quasi-simultaneous laser thermoplastic welding, method for PA 6.6 GF 35, base material. In laser welding of thermoplastics, sometimes referred to as „laser transmission welding” or „through transmission IR welding (TTIr)”, transparent and absorbing parts are bonded together. The laser beam penetrates the transparent plastic and is converted to heat in the absorbing plastic. Since both parts are pressed together during the welding process, heat is conducted from the absorbing to the transparent plastic, allowing both materials to melt and create a bond. Internal joining pressure is also generated through the local warming and thermal expansion. Almost all thermoplastic materials and elastomeres can be welded with the LASER beam – including ABS, PA, PC, PP, PMMA, PS, PBT, as well as glass fibre reinforced plastics. The strength of the welding seam is comparable with the base material strength. Keywords: laser thermoplastic welding, transparent plastic, internal joining

Using environmentally friendly products in the roads construction like friendlier warm mix asphalts, involves reducing the temperature of asphalt mixtures manufacturing. For this purpose it is recommended to identify synthetic additives that reduce the temperature of asphalt mixture preparation and therefore energy costs of asphalting process. The waxes presence in conventional bitumen road was considered along time inopportune. Three types of amide waxes were synthesized by treating ethylene diamine with a fatty acid and a dicarboxylic acid. Prepared additives characterization was performed by determining the melting points and thermogravimetric behaviour. Keywords: bitumen, wax additive, catalyst

The aim of the present paper was to obtain epoxy nanocomposites reinforced with layered clays type nanofiller. Nanocomposites materials have been obtained through mechanical mixing of resins based on diglycidyl ether of bisphenol A (DGEBA) chemically modified with low molecular glycols filled with Cloisit type layered clays and crosslinked using 4,4 ‘diaminodiphenyl metane ( DDM)as curing agent. Epoxy nanocomposites have been obtained and characterized as compared to standard epoxy nanocomposites not only by conventional methods-physical-mechanical properties, but also by DMA tests in order to establish the degree of dispersion of the nanocaly in the epoxy matrix. Flexural strength and impact tests have shown that the reinforcement of composite materials with laminated clays leads to an improvement in their properties as compared to unmodified epoxy systems. Keywords: epoxy nanocomposite, glass transition, dynamical properties, mechanical properties

Orthodontic appliances are intraoral devices used to induce changes in relations between the teeth and the underlying bone structures. Removable orthodontic appliances, which contribute to the alignment of misaligned teeth and to the development of maxillaries, are not fixed to teeth and can be inserted/removed easily on/off the teeth of the dental arches. The aim of this study was to evaluate some characteristics of removable orthodontic appliances achieved by two different technologies (heat-curing and vacuum-forming), realised by using two dental materials (Superacryl Plus-SpofaDental thermo-cured acrylic resin and Biocryl® C and Biocryl® M -Scheu thermoplastic materials). The study included 123 adolescent patients, to which were manufactured one or two removable orthodontic appliances, on one or both of the dental arches. A total of 141 removable orthodontic appliances were manufactured for the selected adolescent patients. The manufacturing of all types of removable orthodontic appliances followed the same technological procedures, specific to each type of used material. The results of the study demonstrate that the aesthetic effect of the two dental materials presented different results, and the best results were observed at the orthodontic appliances achieved by the vacuum-forming technology, using Biocryl® C and Biocryl® M–Scheu thermoplastic materials. Keywords: removable orthodontic appliances, materials, technologies, aesthetics

Relaxation time reflects dynamic phenomena in the early stages of electrospinning after an abrupt application of an external electric field. Experimental counterpart of relaxation times, i.e., characteristic hydrodynamic times, have been measured using a laboratory device designed especially for this kind of experiments. The experiments supporting the hypothesis are carried out with aqueous solutions of poly (vinyl alcohol) of various concentrations. Experimental data are compared with theoretical predictions of relaxation times aiming to a deeper analysis of dynamic phenomena during the earliest stages of electrospinning. Qualitative and quantitative comparison of theoretical and experimental relaxation times determined that characteristic hydrodynamic times are encouraging. Moreover, the experimental apparatus for characteristic hydrodynamic time investigation revealed regular discharges in a spinning zone of the electro-spinner that imminently precede electrospinning jet appearance. Results of the work contribute to a deeper understanding of a spin-ability of polymeric solutions using electrospinning and are an inspiration for new electrospinning variants. Keywords: nanofibers, needleless electrospinning on the rod, polyvinyl alcohol aqueous solutions, rod, relaxation time