Volume 50, Issue 2

Abstract: 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

Abstract: 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

Abstract: 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

Abstract: Our objective was to compare 2 friction couples: ceramic/ceramic and metal/polyethylene in total hip prosthesis. Between 2005-2007, 64 patients with primary osteoarthritis of the hip were enrolled in a prospective study: 32 cases underwent arthroplasty with uncemented total hip prosthesis with a friction couple ceramic/ceramic (Group1), while the other 32 cases underwent arthroplasty with uncemented total hip prostheses with a friction couple of metal on Ultra-High Molecular Weight Polyethylene (UHMWPE) (Group 2). Group 1 was considered the test group and group 2 was designed so that the two groups to be similar in terms of gender and age distribution. We followed: the emergence of osteolysis areas, component loosening to a degree requiring revision, clinical outcome quantified by Harris score. The radiological aspect was determined by several radiological check-ups: immediately after operation, at 6 weeks, at 3 months postoperatively and then annually. Mean follow-up time was 5.2 years (ranging from 3 years and 2 months to 7 years and 8 months). The presence of osteolysis areas was observed in a single case in the ceramic/ceramic group (3.12%) and in 4 cases in the metal/polyethylene group (12.5%), the difference not being statistically significant (p > 0.05). In Group 1 we performed one revision which required replacement of both components (3.12%), while in Group 2 there were 2 such kind of interventions (6.24%) - the difference being not statistically significant (p > 0.05). Harris Score evolved in Group 1 from 52.34 ±6.36 preoperatively to 94.32 ±8.82 at the end of the follow-up period (p < 0.01), and in Group 2 from 51.52 ±7.21 to 92.44 ±9.24, respectively (p < 0.01). Keywords: ceramic, friction couple, hip prosthesis

Abstract: Two curing protocols were used to polymerize a difunctional benzoxazine monomer based on 4,4`-diamino diphenyl methane. The thermal degradation behaviour of both resulted materials (named PBZ_190 and PBZ_250) was investigated by thermogravimetric analysis coupled with mass spectrometry (TGA/MS), Fourier transform infrared spectroscopy (FT-IR) and X-Ray photoelectron spectroscopy (XPS). The dependence of activation energy on conversion was established using Kissinger-Akahira-Sunose isocoversional method. Degradation of PBZ_250 starts at lower temperatures compared with PBZ_190 but its residual char is higher than for PBZ_190. The degradation of PBZ_250 exhibits a lower activation energy at conversion a < 0.3, and higher values than PBZ_190 for a > 0.3. Keywords: polybenzoxazine, degradation kinetics, thermogravimetric analysis (TGA)

Abstract: This paper refers to the electromechanical strain response of PDMS/TiO2/SiO2 composites as an electroactive polymer actuator. Lightweight electro-active polymers (EAPs) are ideal for control surface since they offer high strain rate, fast response, high elastic energy density and ease of manufacture [1,2]. We investigate the frequency response and vibrational modes of rectangular films with aluminum electrodes using Scanning Laser Doppler Vibrometry (SLDV) technique described elsewhere [3,4]. The results showed a similar behaviour with those of acrylic and silicone films coated with carbon-based compliant electrodes from literature. Field-induced vibrational strains decrease with frequency due to the increase in stiffness of sample and change of dielectric permittivity. These materials are possible candidates in polymer actuators for micro-pump and micro-valve applications in MEMS. Keywords: electroactive polymers, dielectric elastomers, non-destructive technique, frequency response, vibrational modes

Abstract: This paper presents the maleinization study of linear styrene-butadiene block-copolymers carried out in solution by radical mechanism. The vinyl microstructure effect of the polybutadiene block on the kinetics reaction was established and the physical and mechanical properties were correlated with the maleinization degree of the elastomers. Keywords: styrene-butadiene block-copolymers, maleic anhydride, functionalized block-copolymers

Abstract: An aromatic photosensitive polyimide is prepared from 3,3`,4,4`-benzophenone tetracarboxylic dianhydride and 4,4`-diaminodiphenyl methane and its structuring ability upon UV-laser exposure is investigated. Surface modification is performed at two laser fluences, i.e. 89 and 244 mJ/cm2, and different number of pulses. The changes of the surface morphology, induced by the employed patterning technique, are examined. According to atomic force microscopy data cone-like structures are formed and their appearance mechanism is analyzed taking into account the laser irradiation conditions. Surface wettability tests reveal an intensification of hydrophobic character, which may be ascribed to the formation of a thin carbon-enriched layer at the polyimide surface. Keywords: polyimide, laser, morphology, wettability

Abstract: By skilful combination between polythiophene backbones and poly(ethylene glycol) (PEG) side chains of different lengths, amphiphilic, fluorescent copolymers having branched architecture of “hairy rods” type were obtained by Suzuki polycondensation. Their structural characterization was performed by 1H-NMR, 13C-NMR and FT-IR spectroscopies and thermal behaviour was followed by differential scanning calorimetry (DSC) and thermogravimetrical analysis (TGA). Photophysical properties in aqueous solutions were evaluated using UV-Vis and fluorescence measurements. The amphiphilic nature of the synthesized polythiophenes and the presence of PEG side chains induced the self - dispersability in water, as well as the formation of fluorescent nanoparticles through self-assembling. The size of the nanoparticles in water was assessed by dynamic light scattering (DLS) and atomic force microscopy (AFM) investigations and the effect of incubation time on three cell lines viability was evaluated, as well. Keywords: polythiophenes, nanoparticles, Suzuki polycondensation, “hairy-rods”, self-assembling

Abstract: Necuron is a polyurethane material (PUR) that is used for various applications of industry. The use of these materials in industry increased in recent years because of their good mechanical and machinability properties. Good knowledge of the mechanical behaviour of these materials is highly important therefore this work presents the results of tensile tests carried out on four different types of Necuron. The twenty-eight specimens used were divided in two categories: one without defects and one with defects of two types. Results show that Necuron 1020 is the stiffest material, whereas Necuron 1300 is the strongest. Keywords: tensile testing, necuron, tensile strength, Young’s modulus

Abstract: The development of resins represented a great step forward in dental technique, the first thermopolymerisable acrylic resins being developed in 1936. Due to their disadvantages, several new materials and their processing technologies, which promise better quality, were introduced on the market, among them diacrylic composite resins. Initially composites were elaborated as esthetic restorative materials, subsequently they developed very much, so nowadays are being used in many various fields of dentistry. Indications for diacrylic composite resins. (DCR) in dental technique include: esthetic veneering for mixed metal-polymeric fixed prosthetic restorations (FPR), unidental or temporary FPR, inlays, onlays, epitheses, repairing damaged porcelain veneers, artificial teeth, manufacturing the base of mobile and removable dentures, repairing and/or re-optimization of the mobile and removable dentures. The aim of this study is to bring into discussion the superior qualities of the the new generation, VITA VM LC (VITA) composite veneering resins. The laboratory steps to be followed in order to obtain a VITA VM LC veneered FPR are the usual ones. After completing the metallic frame, the following step is veneering with VITA VM LC. The VITA VM LC layering concept is oriented after the natural model and is clearly distinguishable from all the other stratification concepts. The natural fluorescence and opalescence reproduction possibility leads to individual results with an aesthetically impressive appearance. A layered restoration performed with VITA VM LC behaves like a natural tooth in different lighting conditions. The excellence in dentistry is often achieved by combining scientific principles with artistic creativity, while choosing the material and technique has a major importance. Keywords: diacrylic composite resin for veneering, VITA VM LC, layering concept, aesthetic results

Abstract: Dielectric relaxation studies were carried out on unfilled and silica particle filled highly crosslinked PDMS samples, at temperatures above the calorimetric glass transition temperature. Our experiments suggest that the main a relaxation peak is preceded by a pre - a relaxation one, whose characteristics are not dependent in their nature on the presence of the reinforcing silica particles. This suggests that its presence may be characteristic of the high crosslink density PDMS. Keywords: highly crosslinked siloxane elastomers, silica filler, dielectric relaxation in the glass transition region, a-relaxation

Abstract: Starting from the dynamic response of a sandwich beam with damping (which is in free vibration), is established a method used to determine the damping factor. We experimentally calculated the stiffness and damping factor per unit length and unit mass for beams with middle layer made of polystyrene and polypropylene honeycomb respectively; the external layers were made of epoxy resin reinforced with fiber-glass fabric and carbon-fiber fabric respectively. Keywords: sandwich beam, damping factor, polystyrene, polypropylene honeycomb, free vibrations

Abstract: The dynamic behaviour of an orthotropic shaft leads to a nonlinear differential equation, Mathieu type, whose solving is quite difficult. Certain problems in theoretical physics lead to Mathieu equation, particularly the problem of the propagation of electromagnetic waves in a medium with a periodic structure, the problem of the electrons’ motion in a crystal lattice in the quantum theory of metals. The parametric equation was solved numerically for time history and was time integrated using Runge-Kutta method with initial boundary values. The results show a totally different dynamic behaviour of the shaft made of an orthotropic material compared with the one made of an isotropic material. Key-words: orthotropic material, shaft, orbit precession motion

Abstract: It is a well-known fact that either pellets or granules used in sandblasting operations for cleaning/finishing metal surfaces of any kind, are subject over time to processes of either splitting or wear of the surface, thus diminishing their operational features, such as, for instance: the angularity and dimension. When being used in sandblasting operations, the granule size fractions that have lost their capacity of finishing surfaces are being sorted by sifting and eliminated. In industrial conditions, where very large surfaces are being sandblasted, the grit turns into a major problem, since it often requires large warehouse surface areas for storage. In that sense, this paperwork presents experimental data regarding the worn grit fractions management by using it in asphalt mixtures, conferring, beside an economic benefit, also that of environment protection, since those lightweight fractions oftentimes form very polluting air floating powder. By eliminating those fractions that are reusable in the process of sandblasting, on the remaining sort resulted from sifting through the 1.0 mm strainer granulation and bitumen behaviour studies were carried out. The analysis of proposed asphalt mixtures, holding a certain percentage of grit, highlighted the fact that the latter, by both the 0.4- 0.1 mm granule size and by the floatable particles of less than 0.2 mm granule size, allow for the replacement of natural quartz sand. The physical-mechanical features of studied mixtures were established on cylindrical probes made of bitumen, in which smashed silicone stone chippings were mixed, within standard required range of granule size, crushing sand and worn grit, in very well controlled mixing proportions. the results were compared to those derived from standard samples made of solely quartz crushing sand, alongside the other components that make up type BA8 asphalt mixtures, of a mere 6.5% bitumen of a 50/70 proportion, according to local standards. By comparing the two asphalt mixture type features (standard and experimental), it allowed for highlighting that worn grit may be very successfully used instead of crushed sand. Keywords: grit, asphalt mixture, recycling, exploitation, environmental protection

Abstract: This article presents a new material obtained from a mix of waste of carbon fibre, sand and an epoxy resin. The obtained material values the reinforcement material waste that is accumulated in the process of production, of the companies that produce fibre-reinforced composite material. This new material obtained from the integral value of the carbon fibre waste is used as a material for the consolidation of the moulds made of composite material or in the domain of construction materials. The authors realize a study regarding the physico-mechanical characteristics of the morphology of the breaking surfaces and a chemical analysis of the EDAX constituents. The mechanical characteristics of this new material at compression, show us values doubled from the ones of a classic concrete and a density decreased with approximately 20 percent. Keywords: composite materials, carbon fibre, epoxy resin