Volume 45, Issue 1

Abstract: Cross-linked polyurethane/filler composites based on polyester, diphenylmethane diisocyante, glycols, and glycerin were synthesized and characterized. The mechanical and thermal properties of PU/filler composites were investigated through tensile, thermogravimetry experiments. Therefore, to understand the behaviour of fillers, such as graphite, talc, CaCO3, and polyamide fiber added to cross-linked polyurethane resins, several thermal and mechanical tests were conducted on samples, using these new materials. It is shown that cross-linked polyurethane composites have decreased tensile strength, improved hardness and thermal stability, relative to bulk polyurethane. The results show that the polyurethane component ratios in cross-linked polymers, the types of filler, and the amount of powder added all affect the damping behaviours and degree of phase separation of unfilled and filled cross-linked polyurethanes. The addition of filler into polyurethane composites yields an increase in the Young´s modulus and a decrease in the elongation at break. Keywords: composite, cross-linked polyurethane, mechanical properties, filler

Abstract: This paper presents the influence of the processing temperatures on the physico – mechanical properties of PC used in injection molding of high performance sport products. The samples (test-pieces) were obtained by processing PC at the following temperatures: 280°C, 295°C, 310°C, 325°C and 340°C. It was established that the pressure in the mold decreases as the processing temperature rises. Further, thermal analyses were performed (TG, DSC, and DMA) and it was noticed that the processing temperature had an influence on the thermal stability of the polymer and on the activation energy (Ea) of the glass transition phase, but the glass transition temperatures Tg were slightly influenced by the processing temperature. Keywords: polycarbonate, injection molding, TG, DSC, DMA

Abstract: Guardrails are systems designed to keep vehicles in certain places, by preventing access in dangerous areas. They can be a source of injuries because their rigid structure, designed to face high level of strength. Depending on their speed and mass, vehicles can load guardrails in various forms. The authors propose the use of adaptive guardrails, involving polymers, which react different by different load levels. The behaviour is studied using modeling and simulation with the FEM; different types of guardrails and external loads displacement and stress are presented, as support to choose the most convenient type of guardrail for each application. Keywords: adaptive guardrails, traffic security, polymers, FEM simulation

Abstract: Inexpensive plastic covered greenhouse structures of the type used by the horticulture industry for plant production are frequently used. We have developed “selective film” with the following properties: transmit the visible light portion of the solar radiation spectrum, the only portion utilized by plants for photosynthesis; absorb the small amount of ultraviolet radiation in the spectrum and cause some of it to fluoresce into visible light, useful to plants, absorb infrared radiation , which plants cannot use and which cause greenhouse interiors to overheat. Plant growth inside the experimental greenhouses covered with photoselective films were compared with plants grown inside growth chambers covered with clear conventional greenhouse films. The results are summarized in the paper. Keywords : greenhouses, photoselective film, plasticulture, solar radiation

Abstract: The kinetics of the equilibrium anionic polymerization of some cyclic siloxanes is modelled by using neural networks. Feedforward neural networks with one or two hidden layers have been used to appreciate the rates of disappearance of octamethylcyclotetrasiloxane and aminopropyl disiloxane at different catalyst concentrations (direct modelling). Alternatively, another neural model has been developed to estimate the amount of catalyst, which leads to an imposed final concentration of siloxane (inverse modelling). Experimental data for the polymerization of octamethylcyclotetrasiloxane in the presence of KOH as a catalyst and 1,3-bis(aminopropyl)tetramethyldisiloxane as a functional endblocker were used as training data sets for neural models. Satisfactory agreement between experimental data and network predictions obtained in validation phases proved that the projected models have good generalization capacities and, consequently, they describe well the process. Keywords: neural networks, direct and inverse neural modelling, polysiloxane, cyclic siloxanes, anionic ring opening polymerization

Abstract: This paper presents a monitoring methodology of the processing temperature for the polymeric composite materials. An experimental stand was realized consisting of a computer with an acquisition card and the LabVIEW software that allows the real time monitoring of the composite materials temperature during the processing through the aid of a new heat sensor LM 335Z. This digital sensor had proved to be more efficient than the classical thermo-couplings. Using the LabVIEW software, a virtual instrument called “Virtual Thermometer” was created. This virtual instrument has the same functions as a real instrument, but with a much more complexity as well as the possibility of real time measuring, save, analysis and presentation of the collected data. Keywords: monitoring, polymeric composites, virtual instrument

Abstract: In this paper the linear polymers transport through a nanopore is simulated. The major effects of superimposed electric field and the monomers number on the polymer translocation have been proved. The polymer escape time is inversely proportional with the electric field’s intensity and directly proportional with the polymer’s length. Keywords: transport phenomena, Langevin equation, nanometer pore, translocation time

Abstract: In this paper the calculation methods of the demolding force in case of thin-wall injected plastic parts with linear, curvilinear or combined profile are presented. The magnitude of this force directly influences the constructive solution of the ejector system. Key words: injected part, demolding force, ejector system

Abstract: This paper proposes the insertion of correction coefficients for the volumes of natural gas measured with mechanical gas meters. These coefficients are based on the annual average values of the atmospheric pressure and temperature, also taking into account the altitude of the measuring point, as they were experimentally established in the laboratories of the Petrol – Gaze University in Ploiesti. Keywords: mechanical meters, correction coefficients, natural gas

Abstract: The incorporation of functionalized carbon nanotubes in a polymer matrix is expected to greatly enhance the physical and mechanical properties of the polymer due to inherent superior properties of carbon nanotubes (CNTs): high modulus and strength, high thermal stability and enhanced electrical conductivity. Nanocomposite materials based on epoxy polymer matrix and different types of functionalized carbon nanotubes were synthesized. The effect of CNTs on dynamic mechanical properties by DMA, on curing process by DSC and themostability by TGA and DTG were studied. The system based on diglycidylether of bisphenol A (DGEBA) cured with a polyetheramine (D230) and reinforced with amino-functionalized double-wall carbon nanotubes (DWNT-NH2) showed lower Tg values. SEM images reveal an enhance of dispersion if amino-functionalized CNTs are used. Keywords: epoxy, nanotubes, nanocomposites, thermostability, glass transition temperature

Abstract: Literature relates the membrane modification as a way to obtain affinity membranes having new mechanical and physical-chemical properties, specific to each application. One of the most used technique for the modification of the membrane characteristics consists of grafting the different reactive functions on polymeric chain: -COOH, NH2, -SO3H, -X, -OH etc. This paper offers an original variant for preparation of modified polysulphone by Friedel-Crafts acylation and the obtaining of brominated polyphenileneoxide. Keywords: polysulphone, polyphenileneoxide, reactive functions, acylation, bromination

Abstract: The paper presents the synthesis and characterisation of a new Mannich polyether polyol with high nitrogen content and thermostable isocyanuric structure. The synthesis was performed by the alkoxylation in the absence of any catalyst of a Mannich base obtained by the reaction of cyanuric acid with a Mannich precursor reagent 1,3-oxazolidine. The Mannich polyol was characterised by 1H NMR and 13C NMR, infrared spectroscopy and by the determination of some usual characteristics such as hydroxyl number, viscosity, amine echivalent, water content. The main application of this polyol is the production of “spray” rigid polyurethane foams with higher thermostability and inherent flame retardancy properties. Keyword: 1,3-oxazolidine; isocyanuric Mannich polyether polyol; rigid polyurethanic foams

Abstract: Analysing the Maddock and Egan dispersive zones, their thermal homogeneisation effect and their role in dispersing agglomerated particles within the melt, resulted a correlation between the barrier zone slit height, h3 and the length of the barrier zone, L02 assuring the dispersing of the agglomerated particles within the melt. Given the role the Maddock and Egan zones have, based on the obtained relations, their dimensions (h3, B3, L02,j) can be calculated. Keywords: Maddock and Egan, thermal homogeneisation, in dispersing, barrier zone

Abstract: This paper describes the kinetic evolution, in solution, of N-phenylmaleimide - vinyl acetate alternating copolymerization. The rate of consumption for the equimolar composition of the two monomers is described by the empirical equation: Valt=k . [M]1.70[I]0,49. There were formulated hypotheses to explain those dependences. The copolymers obtained were analysed by SEC. It was proved the structure of the alternate copolymer and the fact that high molecular products results . Keywords: N-phenylmaleimide, vinyl acetate, alternate copolymerization, alternate copolymer

Abstract: Thermoplastics are widely used for engineering application and customer goods. One of the application area is automotive industry. The passengers’ compartment is an example of using high quality materials and advanced design solution in order to achieve aesthetic interiors and performance when safety is the issue. The impact of the passenger’s head with the cockpit module is studied by experimental and numerical simulation. Material models are studied in order to obtain good results and to validate the numerical model for further investigation. Keywords: thermoplastics, material characterization, impact, experiment, numerical simulation

Abstract: In this paper, a methodology to evaluate the dynamic fracture toughness of polymethyl methacrylate (PMMA) is presented. The proposed methodology is based on a hybrid-numerical formulation and requires the evaluation of the dynamic stress intensity factor along the experimentally measured dynamic crack fronts, and the three-parameter Weibull stress model for brittle fracture. The apparent fracture toughness master curves are determined for Double Cantilever Beam (DCB) specimens of PMMA with different thickness. Keywords: dynamic fracture toughness, polymethyl methacrylate, Weibull master curve

Abstract: The behaviour of some microstructured polymers obtained in dynamic conditions using a mixture (1:1) of EPDM (ethylene-propylene-dien monomer) rubber and high-density polyethylene (in the presence of sulphur as reticulating agent) was studied. The experiments consisted in determination of swelling by maintaining the polymeric composite materials in three organic solvents (benzene, p-xylene, carbon tetrachloride) and also in recording their IR spectra. The results are useful for selection of operating conditions during preparation and for choosing the appropriate utilization of polymeric products. Keywords: microstructural polymer, EPDM (ethylene-propylene-dien monomer) rubber, polyethylene, swelling, IR spectroscopy

Abstract: The paper deals with the shrinkage and warpage phenomenon briefly presenting the most important influence factors and their interaction involved in dimensional changes of injected plastic parts. The predictable tolerances, design strategy and the main required action are debated for one final purpose: maximum and yet realistic accuracy of dimensional precision, in a cheapest, easy manufacturability and easy operating injection tool. Finally, there are presented some useful considerations for minimizing the effect of shrinkage and warpage in dimensional variance of injected plastic parts. Keywords: injection moulding, tolerance, shrinkage, warpage

Abstract: In this work we have applied a Hays –Kendall mathematical model to the Vickers microhardness values to eliminate the troublesome indentation size effect (load dependence of hardness) and obtain a unique value representing the true hardness for each coating. Examination of the unique hardness values has been possible in conditions of heat treatment at 190 0C and 420 0C. Key words: Hays –Kendall model, Ni-P/SiC coatings, hardness, ISE effect, heat treatment

Abstract: Degenerative disc disease in the lumbar spine is marked by a dehydration of the intervertebral disc and loss of biomechanical function of the spinal unit. Since the current surgical procedures are ineffective in restoring natural biomechanical function back to the diseased disc, researchers have looked to replace the intervertebral disc. These designs are flawed in that they either don’t restore natural movement back to the spinal unit, require surgeries that are highly invasive, or they further promote disc degeneration of adjacent spinal levels. Recently, researchers have sought to only replace the central portion of the disc called the nucleus pulpous. A potential nucleus replacement could mimic a healthy nucleus pulpous in restoring healthy biomechanical function to the spinal unit. A hydrogel, poly (vinyl alcohol) (PVA), has been investigated to serve as a nucleus replacement. However, semi crystalline PVA suffers dissolution under physiological conditions and for this reasons are tested others hydrogels (HEMA) which are biocompatible, maintain the liquid transport function, the shape and the size of intervertebral disc and are very good shock-absorbent. Keywords: prosthesis, hydrogel, HEMA, intervertebral disc

Abstract: Poly-(vinyl alcohol) (PVA) films, colored with pyridinium ylids and dried by water evaporation, become stretched under the heating influence. The visible electronic spectra of the stretched films were measured for linearly polarized visible radiations having their electric field intensity parallel and perpendicular on the stretching direction. The dichroism of the colored PVA films depends on the stretching degree. The birefringence of each film was estimated by using a polarizing microscope with compensatory wedge. Keywords: stretched PVA films, pyridinium ylids, dichroism, birefringence

Abstract: A mathematical model of the heat transport in nanofluids using the fractal theories (the scale relativity theory in the topological dimension DT = 2) is established. Through a scale covariance form of the Newton’s equation, a Navier-Stokes type equation with an imaginary viscosity coefficient and particularly a Schrödinger’s type equation are obtained. Some applications of the model are given like the heat transport through an effective thermal conductivity, by Brownian motion or by liquid layering at liquid-nanoparticle interface. It results that the heat transport in nanofluids is performed through an unique mechanism, the above standard sequences mentioned being imposed by the interaction scales. Moreover, the quantum thermal conductance of electrons in an one-dimensional wire is obtained. Keywords: nanofluid, heat transfer, fractal, thermal conductance

Abstract: The paper proposes an analysis on the influence of the elastic rubber elements as component parts of the elastic tram wheels, as well of the railroad, on the stress state, on the wear and the loss in time of the mechanical properties under dynamic conditions. It is noticed the importance of the proping of the rubber elastic element (all degrees of freedom or vulcanized on a metallic support) going to a „brick” element shape proposal, which is absolutely „covered” for practical applications. This approximation leads to new correction coefficients, as well as to the validation of the simplified „brick” shape of specimens for a future experimental test standartization. Keywords: elastic wheel, stress, mechanical testing, finite element analysis

Abstract: A degradation mathematical model based on the dependence of the carbonyl index by the degradation time to measure the polyolefins degradability was proposed. The mathematical model was verified with good results with own and literature degradation data. It was demonstrated that the three aging parameters of the mathematical model that can be calculated by fitted method, reflect the degradation behaviour of primary and secondary polyolefins and can be used for quantitative estimation of the polyolefins degradability. The possibility of using the mathematical model for estimation the opportunity of using the mechanical recycling as recycling method is the practical importance of the obtained results. There is also, a mathematical demonstration of the reason for which the polymers can not be infinitely recycled as other materials like metals, glass e.g. Keywords: mechanical recycling, ageing parameters, contamination