Volume 49, Issue 4

Abstract: The main objective of this paper is to develop a complex experimental investigation and, by this way, to describe and analyze the influence of pulsed Nd: YAG laser cutting main parameters on the process energy consumption. The tested material was a Glass fiber/epoxy composite. The experimental program was performed by two approaches, factorial and classic. The design of experiments allowed the research results presentation as regression polynomial equation, Pareto effects diagram, response surfaces diagrams and single-factorial classic diagrams. A pertinent final discussion gave a global image and proved the validity of developed research. Keywords: design of experiments, pulsed Nd: YAG laser cutting, Glass fiber/epoxy composite, energy consumption ratio

Abstract: Silk fibroin, from Bombyx mori solutions were electrospun into nanofibers with circular and ribbon like morphology. Diameters of the electrospun fibers were ranged from 60 to 7000 nm. The effects of electrospinning temperature, solution concentration and electric field on the formation of nanofibers and their morphology were studied. Optical and scanning electron microscope were used to study the morphology and diameter of electrospun nanofibers. It was observed that the nanofibers morphology depends on the electrospinning parameters and became flattened with ribbon like shape with increasing the electrospinning temperature. The nanofiber diameter increased with the increase in the concentration of silk solution at all electrospinning temperature. Electric field showed different effects on the nanofiber morphology at 25oC. Referring to the literature the probable mechanism responsible for the change of morphology was pointed out. Response surface methodology (RSM) was used to obtain a quantitative relationship between selected electrospinning parameters and average fiber diameter and its distribution. It was shown that concentration of silk fibroin solution and electrospinning temperature had a significant effect on the fiber diameter. Keywords: biopolymers, scanning electron microscope, morphology, proteins, nanofibers, statistical analysis

Abstract: This article presents the study of the opportunities and limits of employing nano-ZnO as additive to Paraloid B72 solutions used for consolidation of degraded, frail wood. The experiments were carried out on degraded spruce samples (Picea abies) in different conservation levels that were extracted from a frail wooden element of a massive gateway from the historic centre of Brasov (Romania) during its restoration. In this respect the samples were dimensioned at (20x20x30) mm and divided into three batches according to their initial conservation state: level I, very degraded samples with obvious loss of resistance and cohesion; level II, samples highly degraded but with structural cohesion and level III, samples with little degradation. Two consolidant formulations based on Paraloid B72 were used: a solution of 10% in ethanol and acetone mixture 1/1 (coded C4) and a similar solution modified with nano-ZnO additive in proportion of 2.5 % (coded C4-ZnO-2.5). All the samples were treated by total immersion for 1 hour in the prepared consolidants. The application treatment efficiency was evaluated by determining the consolidant uptake Csp [Kg/m3] and retention WPG [%], while the actual effects of the consolidation procedure were evaluated by determining the compression strength parallel to the grain tc// [MPa] and the water absorption in a total immersion test, WA [%]. Keywords: wood consolidation, Paraloid B72, nano-ZnO, compressive strength, FTIR spectroscopy

Abstract: This paper analyses the influence of processing temperatures of acrylonitrile butadiene styrene (ABS), polyamide 6.6 (PA 6.6) and polyoxymethylene (POM) on some mechanical properties when injecting items used in the automotive industry. The ABS specimens were made at the following injection temperatures: 220, 230, 240 and 250°C. The PA 6.6 specimens were made at the following injection temperatures: 280, 290, 300, 310 and 320°C. The POM specimens were made at the following injection temperatures: 180, 190, 200, and 210°C. The mechanical properties were measured using tensile tests, the Izod impact test and the Shore Durometer hardness test. It was observed that for these three polymers, the increase in processing temperature leads to insignificant changes in hardness. The Izod impact strengths of PA 6.6 and POM decrease to a minimum with an increase in processing temperature, while the further increase in processing temperatures leads to an increase in impact strength. Where ABS is concerned, the increase in processing temperature results in an increase in Izod impact strength. The tensile strength at break is influenced by the processing temperature. The highest tensile strength at break for ABS was recorded at 220°C, for PA 6.6 at 310°C and for POM at 200°C. The lowest values were recorded at the lowest and highest processing temperatures. Keywords: acrylonitrile butadiene styrene (ABS), polyamide 6.6 (PA 6.6), polyoxymethylene (POM), tensile tests, Izod impact test, Shore Durometer hardness test

Abstract: This work presents a study on the possibility of hydroxyapatite thin layers deposition on porous polyurethane support using biomimetic method, and pyridoxine (vitamin B6) incorporation in this layer. To achieve the formation of hydroxyapatite deposition on the surface of polyurethane and to incorporate the pyridoxine in the apatite layer, two types of biomimetic solutions, i.e. a supersaturated calcification solution (denoted SCS) and a modified SCS solution (denoted M-SCS) were used. The M-SCS solution was prepared by adding in the original SCS solution appropriate quantities of pyridoxine. The hydroxyapatite deposits are investigated by scanning electron microscopy (SEM) and Fourier-transform infrared transmission spectroscopy (FT-IR). The results obtained from SEM images and FT-IR spectra have shown that porous polyurethane/hydroxyapatite scaffolds with an interconnected network were produced, and pyridoxine is incorporated in the apatite layer. Keywords: Hydroxyapatite, polyurethane, pyridoxine, scaffold

Abstract: The use of polymeric materials to replace metal or wood has become increasingly popular lately in most fields of activity. Specific amounts of reinforcement materials have been included in the structure of these polymeric materials in order to improve their mechanical properties. The increasing popularity of these types of materials was accompanied by the development of different machinery and technologies designed to process them, so as to make them as productive as possible and to achieve inexpensive high performance parts. Natural polyamide 6.6 is a polymeric material noted for its high rigidity, hardness, impact resistance, etc. The reinforcement materials added improve the mechanical properties of this type of material. Our research consisted of a comparative study of the behavior of polyamide reinforced with glass fibers and glass microspheres when subject to different mechanical stresses. The test specimens were processed by injection and relied on an experimental Taguchi plan with six input parameters each of them with two levels. The materials employed to carry out the comparisons designed to determine the mechanical and tribological properties were natural polyamide 6.6 reinforced with 30% glass fibers and 1% furnace black, and natural polyamide 6.6 reinforced with 30% glass microspheres and 1% furnace black used to prevent microsphere agglomerations. Considering all these issues, the actual research was focused on tensile stress vs. tensile strain comparisons at 23oC and 60oC, and on determining the friction coefficient using disc rotation and oscillation, XRD analysis, Scanning Electron Microscopy (SEM) and EDAX analysis. As concerns tensile stresses, high values were recorded both on the 23°C and 60°C tests when polyamide was reinforced with glass fiber. This is also supported by the SEM structure for the two composite materials under survey. The mean value of the disc rotation friction coefficient was lower when glass fiber was used as reinforcement material. This was also the case with the disc oscillation friction coefficient. The diffraction study conducted on the two materials revealed that polyamide 6.6 reinforced with 30% glass fiber did not have an amorphous structure, given the high number of peaks resulted further to diffraction, whereas polyamide 6.6 reinforced with glass microspheres exhibited an amorphous structure and a structure-specific diffraction. The chemical elements spectrum (EDAX analysis) reveals high mass and atomic percentages of C, O, Ca for both composite materials under survey. Keywords: fibers, microspheres, glass, mechanical properties, tribology, spectrum

Abstract: Waste rubber cause both health and environmental problems and this has forced governments to develop laws for recycling. Using particles of recycled rubber in the domain of soundproofing materials is of major importance from a technical, economical and ecological point of view. In this paper we determine the ability of sound absorption of each obtained material by measuring the sound absorption coefficient depending on frequency, using the impedance tubes. Materials, as composite materials prototype, were made from particles of recycled rubber and a polyurethane binder, in combination with other materials existent on the market (cork of fabric). Keywords: recycled rubber particles, acoustical materials, sound absorption coefficient

Abstract: This work reports on a study concerning the behaviour of an elastic system subject to a periodic external excitation. Oscillatory movement is the most common type of mechanical movement found in nature and, of course, in technique. A system executing simple harmonic motion is called harmonic oscillator system. If the harmonic oscillator motion describes a path as the straight line, the harmonic oscillator is called linear harmonic oscillator. Such linear harmonic oscillator is considered an elastic system when the force acts upon it is an elastic one. If in the elastic system dissipative forces are involved then they have the effect of energy losses during oscillation, so that, after a while, the oscillator energy is lost in various forms. To compensate the energy losses of dissipative forces, the oscillator must be driven by a periodic external disturbing force that produces forced oscillations in the elastic systems. If external disturbing force is periodical, the oscillator will run a new type of oscillations called forced oscillations. In this case the period and frequency of forced oscillations of the elastic system will be the same as the period and frequency of disturbing force. In this situation there is a transfer of energy between the two systems. Studying forced vibrations, in terms of energy intake, through excitation forces, are overrun highlight the importance of phase shift between force and oscillator movement. Keywords: harmonic oscillator system, periodic external excitation, phase shift, energy, resonance phenomenon

Abstract: The chitosan based nanofibers web is a biocompatible, biodegradable, antimicrobial and non-toxic structure which has both physical and chemical properties to effectively capture and neutralize toxic pollutants from air and liquid media. Despite such potentials, the mechanical properties of nanofibers web is very poor to use in filtration applications. To remedy this defect, nanofibers web could laminate into a strength structure. The purpose of this study is to consider the influence of laminating temperature on nanofibers web/multilayer structure properties. The nanofibers web morphology and multilayer cross-section was observed under an optical microscope and scanning electron microscope, respectively. Also, air permeability experiments were performed to examine the effect of laminating temperature on air transport properties of multilayer structures. Optical microscope images showed that the nanofiber web began to damage when laminating temperature was selected above melting point of adhesive layer. Air permeability decreased with increasing laminating temperature. It is also observed that the adhesive force between layers was increased by increasing laminating temperature. Keywords: chitosan, nanofibers web, filtration, lamination

Abstract: The present study pursues the influence of polyelectrolytes based on maleic co-polymers with styrene (NaM-S) and vinyl acetate (NaM-VA) under the form of natrium salt, on the colour parameters CIE L*, a*, b* of the Melana-type polyacrylonitrile fibres dyed with Crystal Violet. The colour differences are ascribed to the modifications appeared in the colour components, in terms of concentration, polyelectrolyte character and tinctorial parameters: dyeing duration and temperature. Keywords: maleic anionic polyelectrolytes, Crystal Violet, Melana - type polyacrylonitrile fibres, colour parameters CIE L*a*b*

Abstract: Acrylic adhesives show high stability towards atmospheric agents and degradation resistance. On the other hand they have low adhesion for low energy surfaces (non-polar thermoplastics: polyethylene, polypropylene etc.). Pressure sensitive adhesives based on hybrid acrylic polymers could eliminate these drawbacks by combining the performances of classical acrylic adhesive with those of elastomeric adhesives. This work is focused on the study regarding the performances of pressure sensitive adhesives based on hybrid acrylic polymers. Peel strength, shear strength and tensile strength are also determined. Keywords: acrylic adhesives, pressure sensitive adhesives, acrylic saturated rubber, hybrid pressure sensitive adhesives

Abstract: Epoxy resin / carbon nanotubes (CNTs) nanocomposites are nowadays intensively studied in order to produce high performance materials with enhanced properties for specific applications in all activity fields, from electronics to automotive and aeronautics. In order to improve the interactions of CNTs with the polymer matrix, a functionalization of CNTs surface is often required. In this work, functionalized CNTs/epoxy nanocomposites were obtained and investigated by thermogravimetric analysis. Non-covalent functionalized CNTs with three types of surfactants were used. Activation energies of the degradation processes were calculated using Kissinger-Akahira-Sunose isoconversional method. The influence of surfactant type, functionalization mode (covalent or non-covalent) and functionalized CNTs content in composite on the activation energy as a function of the degradation conversion degree was studied. Keywords: thermal degradation, isoconversional method, carbon nanotubes

Abstract: Base isolation systems are nowadays largely used to protect the build environment and to avoid loss of life. While the behaviour of natural rubber bearings NRB and lead rubber bearings LRB is well-known, hybrid devices incorporating a NRB and a LRB, due to their complex behaviour, are difficult to be modeled. The authors have developed a theoretical model able to describe with high accuracy the performance during earthquakes of hybrid isolation systems, meantime permitting to determine the equivalent stiffness for all levels of horizontal loads. At the end of the paper numerical simulations give an overview about the possibilities to control the structure response by fitting some parameters of the device. Finally comparison with the behaviour of “classical” devices is performed. Keywords: rubber, neoprene, composites, base isolation, earthquake

Abstract: The study investigates the effect of several injection moulding parameters, such as the melt and mould temperature, on the adhesion obtained at the moulding of bi-component tensile test specimens. Mono- and bi-component specimens were subject to uniaxial tensile tests. The aim is to obtain a model analysis for the study of the mechanical behaviour of bi-component parts submitted to uniaxial tensile tests. The localised information on the state of stresses and strains at the interface between the two polymeric components is obtained through this analysis.The use of the G’Sell-Jonas model offers a good prediction regarding the mechanical behaviour of the two component tensile test specimens on both the elastic and the plastic regions. The simulation of the mono-component tensile test showed a good agreement between the experimental and the predicted results, with a correlation coefficient ranging between 0.9973 and 0.9998. High levels of confidence were obtained for the mono-component tensile test specimen results, further applied for FEA analysis of the two-component specimen (HDPE/LDPE). The necking effect observed in the experiments, at a 255°C melt temperature for the LDPE, was similar to the one revealed by the finite element analysis. Keywords: polymers, adhesion, tensile test, FEA