Volume 46, Issue 3

Abstract: This paper contains the results of an experimental study regarding the thermal stability of the urethane and alophanate groups from model compounds obtained in chemical reactions between phenylisocyanate and mono- or bifunctional stabilizers. The results can be used to estimate the thermal stability of the polyurethanes which were thermal and photo-oxidative (additive and reactive) stabilized. Keywords: urethane, alophanate, phenylisocyanate, antioxidant compound, photo-stabilizer compound

Abstract: The aim of this study was to optimize microwave post-polymerization treatment parameters, power and irradiation time, in order to achieve the maximum applicable flexural and impact strength of autopolimerizing poly(methyl-methacrylate) denture reline resins. Specimens were produced from two types of commercial materials. Control group was left untreated, while the other twelve were post-irradiated in a microwave oven with different power and time settings: 500, 550, 600 and 650 W; and 3, 4 and 5 minutes. The amount of residual monomer was determined using DSC and FTIR. Furthermore, visual control has been conducted, in order to check if there any surface changes have appeared. Microwave post-irradiation resulted in increase of all tested mechanical properties, for all specimens. The highest mechanical properties were obtained with maximum irradiation power, which was confirmed by the results of ANOVA statistical analysis. It has been found that residual monomer content strongly influences the benefits in all tested mechanical properties, increasing biocompatibility. The fracture mode of all specimens in untreated and treated conditions was found to be mostly brittle. However, the highest power (650 W) and the longest irradiation time (5 min) resulted in unacceptable surface color and roughness modifications. Keywords: biopolymers, microwave post – polymerization, mechancal properties, residual monomer

Abstract: Orthopedic research in hip endoprosthesis is advancing rapidly. The new techniques that are being used in the domain of Rapid Prototyping (RP) have given the possibility to build scaffold structures from metallic and plastic materials. This paper presents the designing process and a FEM simulation of a tailored hip endoprosthesis with a scaffold structure which is placed all over the stem and also brings into discussion the fixation place, which is influenced by the in-growth process of the bone tissue. The hip endoprosthesis simulation use as material Ti6Al4V because it is biocompatible and can be used to manufacture the endoprosthesis using RP technology like Electron Beam Melting (EBM). Keywords: scaffold structures, orthopedic implants, electron beam melting, modeling

Abstract: The paper presents the use of FEM (Finite Element Method) for calculus performing at the injection moulding of a high accuracy part made of plastic material type Polyacetal, referring at: pumping of the mould cavity, thermal resistance and mechanical strength. There are presented: diagrams of variation for the pumping full degree function of time at four temperatures of the mould, thermal representation of the part for the temperature of the mould at 80oC, the results obtained after the part’s testing at drop-test, the results of static stress for the part made of injected plastic material. Keywords: injection moulding, pumping, thermal resistance, mechanical strength

Abstract: Water soluble cadmium selenide (CdSe) nanoparticles were chemically obtained by polymer assisted synthesis at 70 Celsius degree from aqueous solution, using Cd(CH3COO)2·2H2O or Cd(NO3)2·4H2O as cadmium source and H2SeO3 as selenium source. The clustering of CdSe nanoparticles synthesized in poly(amidehydroxyurethane) matrix was clearly revealed by X-ray diffraction and Atomic Force Microscopy films studies. The obtained CdSe nanocrystallites have hexagonal symmetry with an average dimension of 25 nm. The Fourier Transform Infrared spectra show the interaction between the nanoparticles and urethane carbonyl and C – O – C etheric groups of polymer. The dimension of CdSe – polymer entities in water solution was explored by Laser Diffraction method and confirmed the capping of CdSe nanoparticles by the polymer. Keywords: CdSe, nanoparticles, polymer assisted synthesis, structural characterization

Abstract: The flow rate coefficient was calculated both theoretically, based on calculus relationships, and experimentally, based on data obtained on two extruders with screw diameters of 45 mm and 90 mm, respectively. The concordance of the theoretical results with those obtained experimentally in two situations were verified, namely: free discharge, no backpressure, and discharge with backpressure. Keywords: flow rate coefficient; feeding zone; single screw extruder; flow rate

Abstract: Due to their lightweight, exceptionally high strength and modulus, high stiffness, good fatigue life, and excellent corrosion resistance, polymer matrix composites are increasingly being used in the aircraft and spacecraft industry. Nowadays, a significant amount of advanced polymer composites is used for military and commercial aircraft and satellite components. Due of their low density, higher physical and mechanical properties and low manufacturing cost, these materials have replaced metals, such as aluminum alloys, in many applications. This paper deals with the class of polymer composites, new material recipes and testing results. This approach refers to the possible use of ferrite additive to improve mechanical and magnetic properties of polymer composites. Keywords: lightweight, polymer, composite, ferrite

Abstract: Construction of passive insulation elements in neoprene single microstructure mixture has demonstrated that the isolators can have the necessary elastic characteristics but low internal damping. The reduced scale models have in the structure viscoelastic materials basing on natural rubber symmetrically distributed in respect to the geometrical reference system chosen for the isolator. The materials consisting of natural or synthetic rubber are used as filling elements symmetrically located so that, globally, the isolator can be properly characterized both at compression and shear. For the present paper there were used two material types modelled as Voigt-Kelvin and Hooke-Maxwell elements. Key words: rheological modelling, antivibrating isolator, composite neoprene

Abstract: Pralidoxime chloride (PAM) was encapsulated in biopolymeric membranes in order to evaluate the kinetics of release in aqueous solution. PAM is an efficient cholinesterase reactivator with a pronounced hydrophilic character. The biopolymeric membranes were prepared by crosslinking, directly in aqueous solution and the monodisperse spherical microcapsules made by this method had diameters between 1 and 3 mm. PAM was embedded “in situ” in microcapsules prepared from natural polymers as sodium alginate, chitosan and gelatin. The release data were fitted by first order kinetic equation, Weibull, Peppas and Higuchi semiempirical equations to obtain the kinetic parameters of controlled PAM release. The embedding of PAM in biopolymeric membranes was achieved in order to prepare a sustained release pharmaceutical formulation for oral administration. Keywords: biopolymeric microcapsules, Pralidoxime chloride, drug release

Abstract: The most modern restorative interventions in dental practice are mainly based on a new generation of composite materials specialy designed for this kind of applications. Their complex structures offer a quasi-plastic behavior concerning the special tribological phenomenon developed in the intraoral environment. Starting from this, the paper intends to present the experimental data obtained as research results for two composite materials - InLine (IVOCLAR) and HeraCeram (HERAEUS Kulzer). The study is focused on the influence of the most important mechanical factors from occlusion areas such as loads, lubricants, speeds, composite materials hardness concerning the wear processses and their influence onto the mastication areas. Keywords: composite materials, tribology, wear, dental medicine

Abstract: Lyocell fibers are ecological cellulose regenerated fibers and represent the most important discovery in the field of “artificial fiber engineering”. These fibers can be situated at the border between natural fibers (in terms of comfort, biodegradability) and chemical fibers (by high resistance in dry and wet environment, low contraction). In order to characterize the structural Lyocell fiber properties, electronic microscopy analyses, birefringence and X-ray diffraction have been accomplished. The present analysis on the structural properties of Lyocell fibers allowed to conclude that the microscopic images depict that Lyocell fibers present uniform longitudinal aspect and regular cross-section; the Lyocell fiber birefringence is 1.6 times higher than similar feature of viscose fiber (0.04263 as compared to 0.0265) and the diffraction analysis reveals that the distortion degree of the crystal lattice of Lyocell and viscose fibers is in accordance with the crystalline factor. The average tenacity – deformation diagrams for Lyocell and viscose fibres, in conditioned and in wet medium, allowed to determine the rheological parameters of the fibers. Keywords: Lyocell fiber properties, electronic microscopy, birefringence, diffraction analyses

Abstract: Lactic ester of maleoabietic acid (RAMALA) was obtained by chemical reaction between Diels-Alder adduct of resin acids with maleic anhydride (RAMA) and lactic acid (LA). The obtained product was characterized by elemental analysis and by spectroscopic methods (IR and NMR). Curing reaction of three epoxy resins (diglycidylether of bisphenol A (DGEBA), diglycidyl ether of hydroquinone (DGEHQ) and diglycidylaniline (DGAN), with (RAMALA) in the presence of triethylbenzylammonium chloride (TEBAC) as catalyst was examined by differential scanning calorimetry (DSC) at different heating rates. Using the literature methods the kinetic parameters of crosslinking reactions were obtained. The activation energies of the curing reactions varied in the range of 48 to 85 kJmol-1 depending on epoxy systems. The thermal behaviour of cured products was also investigated using dynamic thermogravimetric analysis (TGA) technique. The cured products present good thermal stability and the activation energies of the degradation process exhibit values between 82 to 155 kJ×mol-1. Keywords: Diels-Alder adduct of resin acids, lactic ester of Diels-Alder adduct of resin acids with maleic anhydride ,epoxy resin, crosslinking reactions, thermal properties

Abstract: The qualitative and quantitative information concerning the dependence between the kinematic viscosity and the activation energy of the viscous flow by the polyvinyl chloride – thermoplastic polyurethane blends composition were obtained. The results reveal that the blend composition and the melt temperature are the most important parameters that control the PVC – TPU blends melt processing. A high injection speed increases both the tensile strength and the breaking elongation. The shorter time for the mould loading increases the tensile strength and decreases the breaking elongation. The measurement of the rheological properties based on the MFI methods is a good instrument for the estimation of the rheological properties of the polymeric blends in practical conditions Keywords: polyvinyl chloride -thermoplastic polyurethane blends, rheological properties, kinematic viscosity, melt viscous flow, activation energy of the viscous flow

Abstract: The optimization of the ultrasound welding of composed materials means finding an objective function that comprises all acoustic, mechanical and technological parameters and determining the minimum cost of the process or the maximum productivity in obtaining a superior quality of the welded join.In the paper there are presented the dependency of the quality of composed materials welded joins on acoustic parameters and mechanical and technological parameters. Key words: ultrasounds, welding, plastic material, technology

Abstract: Experimental investigations of a diblock copolymer (polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) film doped selectively with tetrakis(4-carboxyphenyl)porphine (TCPP) into the nanoscale spherical domains of P4VP) used as target in a Nd: YAG laser (l = 532 nm) ablation process, were performed. The ionic current oscillations and the velocity of diblock copolymer plasma plume were experimentally obtained . Keywords: polymer, laser ablation

Abstract: Polymer plasma laser ablation has been investigated theoretically. An elegant mathematical tool using the fractal structure of space-time was developed. The model was verified with good accuracy on the existing experimental results. Keywords: polymer, laser ablation, fractal space-time theory

Abstract: The group of circular knitting machines with large diameter includes machines with one or two needle-beds with diameters higher than 178 mm and that use knitting process with final loop for stitch forming. The fabrics produced by circular knitting machines with large diameter are designed both for underwear products, clothing products and other destinations items (items for interior decorations, bed linen, technical articles, toys). Manufacturers of circular knitting machines have improved these machines in particular for: increasing productivity and polyvalence of these machines, reducing production costs, increasing quality of knitted fabrics. Appearance and uniformity of knitted fabrics are quality characteristics that directly depend on technological parameters of knitting. The paper presents ways for adjustment of fabric density at knitted fabrics produced by circular knitting machine with large diameter, type interlock, belonging to Mayer & Cie company. Keywords: circular knitting machine, knitted fabrics, fabric density

Abstract: The paper presents the results of the research work on the evaluation of the mechanical properties (bending strength, MOE, shearing strength of the adhesive bond) of the laminated wood-textiles composite materials made of wood veneer (beech and poplar wood) and textiles: natural fabric made of jute (sackcloth) and woven fabric with synthetic fiber insertions (MTR-polyester, cotton, staple rayon). The layers of veneer and textiles were glued together by two types of adhesives, successively: a natural one (bone glue) and a polyvinyl adhesive (Jowacoll 107.10). Four types of wood-textile composite samples have resulted, as follows: beech veneer – sackcloth glued with bone glue, beech veneer – sackcloth glued with polyvinyl adhesive, poplar veneer – sackcloth glued with bone glue and beech veneer – woven fabric with MTR glued with bone glue. The samples resulted were loaded to the bending strain and the bending strength and MOE were calculated with the value of breaking force obtained for each tested sample. The shearing strength of adhesive bond has been also experimentally determined in order to establish which adhesive is more appropriate to be used both with wood and textile materials into the composites. The influence of the flexibility of the synthetic fibers on the elastic properties of the resulted composites has been also investigated by determining MOE of the corresponding composites. Based on the results obtained, it is concluded that the synthetic fibers (67%) contained by woven fabric with MTR does not increase MOE of the composites, whilst the natural jute fabric behaviour into the wood-textile composites gives unexpected results in strength and elasticity of the new product. Keywords: synthetic fibers, MOE, bending strength, shearing strength, composite, elasticity

Abstract: Mixing and processing characteristics, mechanical properties and thermal characteristics of dimethyl vinyl silicone/poly(tetrafluoroethylene)(MVQ/PTFE) blends were investigated. With the rise Poly(tetrafluoroethylene) (PTFE) portion in blends, the values of both torque and total torque of blend materials decrease. In MVQ/PTFE blends, PTFE act as inactive filler and some mechanical properties decreases in blends compared to component polymers with the increases portion of plastic in blend compositions. The heterogenity of MVQ/PTFE blends was determined by thermomechanical analysis-dilatometry. Silicone (MVQ) and PTFE show separate Tgs, which indicate that they are not compatible. Thermogravimetric analysis of these blends, show that with increased portion of PTFE in blends, the TGA characteristics Tbeg and T5% is moved at higher temperature, which mean increased of thermal blend stability. Keywords: blends, dilatometry, TGA

Abstract: Cellulose composites with maleic anhydride – dicyclopentadiene copolymer matrix were obtained by “in situ” free-radical polymerization. The syntheses were carried out in two different solvents: toluene and dioxane, aiming at determining their influence upon both the polymerization process and properties of the resulting materials. The composite materials obtained were characterized both structurally by FT-IR, XRD and SEM, and from the thermal behavior point of view by TGA-DSC-MS analyses. Keywords: cellulose composites, maleic anhydride – dicyclopentadiene copolymer, in situ polymerization

Abstract: Among the methods used nowadays for studying the microscopic properties of polymers, proteins, membranes and other bio-materials is the molecular dynamics. One of the widely used software in molecular dynamics is Gromacs developed at the University of Groningen. From a computational perspective, molecular dynamics requires large computational power and an increased storage capacity. Different physical models were recently defined for trying to reduce the complexity and to make more efficient the computational it molecular models. In this paper we present the Gromacs implementation of a new multiscaling MD model with a space dependent multiscaling parameter and we discuss efficiency measurements. Keywords: polymers, molecular dynamics, Gromacs, multiscaling modeling

Abstract: A rheological study was performed in order to appreciate the compatibility of the expanded polystyrene beads with the concrete matrix. In order to prepare homogeneous dispersions of the expanded polystyrene (EPS) in the cement paste, the EPS beads were first surface pre-treated with carboxymethylcellulose (CMC), intending to achieve the compatibility between the hydrophilic concrete matrix and the hydrophobic polystyrene beads. In this study, the mass fractions of aggregates, cement and water were maintained constantly for all the probes and it was checked the influence of two parameters: the EPS mass fraction and the CMC concentration. The study was performed with EPS mass fractions between 0.0028 – 0.0041 and with CMC – water solutions having concentrations between 0.5% - 2% (mass). The results showed that CMC can achieve the compatibility between concrete and EPS and that within a 2% CMC solution an important amount of EPS beads can be incorporated. Keywords: lightweight concrete, expanded polystyrene, concrete rheology

Abstract: Functionalized organogelators derived from 1,3;2,4-bis-O-benzylidene-D-sorbitol with methoxy and carbonylaminoethyl methacrylate moieties were prepared, characterized and their gelation ability was evaluated in order to be utilized as additives for dental materials obtained by photopolymerization of several dimethacrylate (DMA) monomers. Keywords: 1,3:2,4-bis-O-(p-methoxybenzylidene)-D-sorbitol, 1,3:2,4-bis-O-benzylidene-5,6-bis-carbonylamino -ethyl methacrylate-D-sorbitol, isocyanatoethyl methacrylate

Abstract: Development of CAx for numerical simulation of injection molding and mold design have opened new possibilities of product analysis during the design process of plastic production. This development contributes to higher quality performance as well as to lower cost of production. The paper deals with the design of plastic products with state-of-the-art integrated CAD/CAE software for mold design. The possibility of solving problems in mold construction appeared by integrated CAx universal system with unique applications (CAE/II module) for mold parameters verification, mold calculation and selection and final mold modeling (CAD/II module). Thus, the specializated CAD/CAE system for automated mold design is successfully created. Keywords: plastic injection molding, mold design, CAD, CAE