Browse Articles

Mathematical modeling of resin flow into the cavity of the mold is a very complex problem due to the porous medium realized by reinforced material. The paper is presented the start evolution and the velocity of the flow for the polyester resin thermosetting in the molding process of the composite plate through „Resin Transfer Molding” (R.T.M.) procedure. Considering an elementary volume dV, the following were determined: friction forces in porous medium, elementary mechanical work dL, and power P in injection process. At the end, the equation of the fluid flow rate u(x,y,z) was established and graphical represented using MATHCAD program. Resin flow modeling and simulation allows the optimum choice of the injection point in the case of complex parts. The validation of a theoretical model was established by the experimental tests. Keywords: resin, composite, friction, flow, fluid

The secondary rheodynamic quantities in case of strain(e)-controlled relaxation processes, including the storage, loss, and absolute compliances as well as the corresponding loss factor, are considered from the standpoint of frequency dependence. The exact relationships providing different e - characteristic frequencies related to maximum and inflection points are obtained for the (1,1) standard linear viscoelastic model, the results being illustrated in natural, semi-logarithmic, logarithmic and double-logarithmic coordinate representations. Keywords: exact relationships, rheodynamic relaxation, linear viscoelasticity, polymer systems

The paper presented aspects relats to the thermoforming simulation with T-SIM and the crash simulation with LS-DYNA, of a polymeric energy absorber called SafetyPlastic®. SafetyPlastic® is an energy absorbing technology that offers a performance, cost, and mass competitive energy management solution. It is characterized by a connected plurality of structural recesses of various shape that repeatedly give resistance, and then buckle when impacted. By considering the strain rate dependence of the polymer, a good correlation of the associated finite element analysis with the experiment was obtained enabling the model to be used in automotive industry for the simulation in both head and side impact, FMVSS 201u and FMVSS 214 respectively, tests. Keywords: polymeric energy absorber, finite element model, buckling, strain rate sensitive

Polyurethane elastomers (PEs) based on polyether diols and polyester diols can be used as passive isolation bearings in building applications. In the present study polyetherdiol, polyesterdiol, aromatic diisocyanate have been used in polyurethanes, using glycerine, ethylene glycol as chain extenders. The optimization of the synthesis of polyurethanes was studied based upon a design matrix with 9 experiments and a forward stepwise regression procedure was employed to achieve a statistically significant regression equation. These empirical equations were used to construct contour plots, facilitating comparisons of synergistic/antagonistic effects among the mixed polymers. The contour plots show that the maximum of the force and elongation at break appears at a maximum of the polyester in the reaction compound. The interaction between the experimental evaluation of algorithm behavior and the theoretical analysis of algorithm performance plays an important role in our research. The satisfactory performance of polyurethanes indicates the feasibility of applying the results found in this study for the fabrication of polyurethanes. Keywords: polyurethane elastomers; optimization; mechanical properties; passive isolation

The paper is a study regarding the obtaining of TiO2 nanostructured by the sol-gel reaction of tetraisopropoxytitanate in the presence of two templants, CTAB and DA. We are also interested in the effect of PTC on the capacity of nanostructuring. In the presence of CTAB nanostructured hibrids with interlamellar distance of 25,6Å were obtained, only in the absence of PTC. Nanostructured hibrids have been obtained in the case of DA addition, only in the presence of PTC with interlamellar distance of 32,7Å. For the nanostructured samples, the temperature with maximum decomposition speed of CATB and DA is the higest due to strong interaction between templants - TiO2. The SEM images put in evidence that the hibrids obtained in the presence of the templants are formed of submicronic units obtained during the sol-gel process. TiO2 prepared in the presence of CTAB catalizes the photo degradation of rodamine B (RB) in water. The samples obtained without CTAB followed by nanostructured hibrids present the most intense activity. The IR spectres evidenced that during irradiation, CTAB diffuses in water and stabilizes by micelles formed and RB becomes more stable at photodegradation. Keywords: templants, CTAB, TiO2, PTC, RB

The paper presents, some experimental results obtained with different types and amounts of reinforcement in composite materials based on polypropylene matrix for automotive applications. There where characterized fourteen experimental samples. The reinforcing agents utilized were: particulate reinforcement (organic and biodegradable – powder wood and inorganic and non-biodegradable – talc powder) and fibrous reinforcement (organic biodegradable-short flax fibers). Keywords: composite, polypropylene, flax fibers

The development of new polymeric materials –either synthetic or biologic- for the surgical repair of abdominal wall primary or incisional defects (one of the most frequent surgical procedures performed in a clinic of general surgery) dates back from the 1950s; inspiration for developing new materials came from several sources, such as the evolution of the surgical techniques, the emergence of laparoscopy and the technologic revolution of the past years. The history of the meshes began with Usher’s polypropylene mesh; curently used meshes basically contain polypropylene, polyester and ePTFE, used per se or in different combinations (composite meshes) with various additional materials (omega 3, titan, monocryl, PVDF, hyaluronate). The most important features of the meshes used in the surgical process are: the type of material used, its porosity and its resistance, elements which determine its weight and ability to integrate into the recipient body. The use of meshes allows the repair of many types of abdominal wall defects of various dimensions and the substitution of the areas with lack of substance, as the prostheses stimulate the collagen synthesis. The present article envisages the review of the meshes which have been used more often in our clinic during the past year, and also their features and indications. Keywords: substitution materials, abdominal wall defects, types of prostheses

Poly(ethylene terephtalate) (PET), recycled from post-consumer bottles was depolymerized by glycolysis process using diethylene glycol (DEG) in the presence of zinc acetate catalyst. The glycolized products were mainly represented by monomer and dimer units. After a relatively long reaction time (over 2 h), an equilibrium was achieved between the two species. Considering the importance of the next steps, in attaining unsaturated polyesters with excellent mechanical properties, this study was concentrated on the identification and characterization of glycolysis reaction equilibrium phase. The evolution of the depolymerization reaction was investigated by the viscosity procedure, which was compared and found to be in good agreement with the functional analysis method. Keywords: PET waste, glycolysis, oligomers, viscosity, equilibrium phase

The aim of the present paper was to highlight the interaction between two composite resins available for dental restorations with artificial saliva in connection with the material properties. The study was focused on specific tribological aspects concerning wear, microhardness of composite material surfaces, friction and lubricant film. The two types of tested materials were composite resins: CERAM-X and FILTEK SUPREME. The experimental researches were based on important laboratory equipment such as microhardness device, metallographic microscope and spectrophotometer. Keywords: composite resins, tribology, wear, microhardness, dental medicine

Plastination as a means of preserving human biological tissues indefinitely, involves the use of reagents and polymers (S10, E12 and P40 ), with physical methods as vacuum, cold temperatures and photo polymerization. Invented over 30 years ago by the German pathologist Gunther von Hagens, plastination methods can be used successfully in over six areas of medicine and other specialties such as archeology or anthropology. The used of plastination of the oral tissues is directed towards the teaching and scientific research that implies microscopy and optical coherence tomography. Keywords: plastination, polymers, oral tissue, biotechnology, preservation