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The paper presents a comparative study on the structure of some polyvinyl alcohols used in PVC-S technology. The obtained data clearly showed that the degree of hydrolysis can be determined, with the same high precision through chemical method, IR and 13C-NMR spectra. The carbonyl content determined from the IR spectra also correlates with the carbonyl content determined from 13C-NMR spectra. A fast and reliable IR method for checking the degree of hydrolysis as technological support can be provided, the normalized carbonyl content determined from IR spectrum being linearly correlated with the degree of hydrolysis. Keywords: Polyvinyl alcohols, vinyl alcohol-vinyl acetate copolymers, IR spectra, 1H-NMR spectra, 13C-NMR spectra

Hydrogels are networks consisting of crosslinked hydrophilic polymers that absorb and retain water or biological fluids. Poly(vinyl alcohol) (PVA) based hydrogels are non-toxic, non-carcinogenic, easily processed and therefore have been examined for tissue replacements, artificial skin, hemodialysis membrane and oral drug release systems. The research focuses on the synthesis of PVA–acrylamide based hydrogels, using glutaraldehyde, sodium tetraborate and N,N’-methylenebisacrylamide/sodium tetraborate mixture as crosslinking agents. The crosslinking copolymers were characterized by infrared spectroscopy (IR), thermal analysis (TG, DSC), and swelling behaviour in distilled water at 37.5 0C temperature. Keywords: crosslinked copolymers, poly(vinyl alcohol)-acrylamide, glutaraldehyde, sodium tetraborate, N,N’-methylenebisacrylamide

The new materials have physical and mechanical properties that allow their processing by using classical methods, specific for synthetic polymers. In vitro biocompatibility studies were performed on a primary culture of human dermal fibroblasts by the MTT test. The biocompatibility of the materials was tested in vitro by determining cell viability in a culture of human dermal fibroblasts by using the MTT method. The physical and mechanical properties and also the biocompatibility properties of the new materials recommend them to be used in the manufacture of medical devices. Key words: synthetic polymers, natural polymers, blends, polyvinyl chloride, collagen, elastin, biocompatibility, cell viability

Complete dentures technology uses especial heat curing acryllic resins, which are included in DIN EN ISO classification at number 1567, group 1. Polimetacrilates are fragile materials, which fracture easily and often need prosthetic pieces repairs. Evaluation of acryllic resins structural qualities allows choosing of the material with maximum mechanical resistance. Present paper intends to determine some comparative structural studies of three heat curing acryllic resins, concerning behaviour after mechanical testing . There were realized 8 samples from each heat curing resins (Meliodent, Superacryl, and Vertex), using the complete denture technology recommended by the producer. Their mechanical characteristics were determined with help of Zwick Roel equipment. Transversal and longitudinal sections of the fractured zones were evaluated by stereomicroscopy and scanning electron microscopy. Following the mechanical tests, there were obtained the following results: ultimate tensile strength 64 MPa / Meliodent, 66 MPa/ Superacryl, Vertex/ 70MPa; total elongation was 11% for Meliodent, 9% for Superacryl and 5% for Vertex; Young’s elasticity modulus was 4570MPa for Meliodent, 5125 MPa for Supercryl and 6243 MPa for Vertex. By stereomicroscopy there was noticed fragmentation, number of fibres from the transversal cross section, or the aspect, shape, colour of fibre from the matrix. At the scanning electron microscopy, microscopic features may be put in evidence: the aspect of the broken matrix (which is brittle for all the samples), the manner of fracture, the nature of the interface, which is incoherent. Finally the correlation between mechanical behaviour and fracture mechanism was made for dental heat curing resins. Keywords: heat curing acryllic resins, stereomicroscopy, scanning electron microscope

This paper presents the influence of the processing temperatures on the physical–mechanical properties of polyoxymethylenes (POM) used in injection molding of high performance sport products. The test-pieces were obtained by processing POM at the following temperatures: 180°C, 190°C, 200°C, 210°C, 220°C, 230°C and 240°C. It was established that the pressure in the mold decreases as the processing temperature increases. Further, thermal analyses (TG, DSC and DMA) were performed and it was noticed that the processing temperature had an influence on the thermal stability of the polymer, but the vitrification temperatures (Tv) and the melt temperatures (Tt) were poorly influenced by the processing temperature. Keywords: polyoxymethylene (POM), injection molding, Thermogravimetry (TG), Differential Scanning Calorimetry (DSC), Dynamic-Mechanical Analysis (DMA)

This paper presents the synthesis and study of some Mn(II) coordination polymers hybrid with the following acids as ligands: dibuthilphosphinic, dibuthiltiophosphinic, dibutildithiophosphinic, dioctilphosphinic, dioctiltiophosphinic, dioctilditiophosphinic. The study was performed by means of chemical analysis, gel chromatography, IR spectroscopy, ESR, X-ray diffraction, thermogravimetry. The experimental results were used to propose the structural formulae of these compounds and to calculate the kinetic parameters of the thermal decomposition reactions.

Atomic force microscopy (AFM) has become established as a significant and versatile tool for investigating local mechanical properties of various materials. In addition, through the AFM tip-sample interaction, it has become possible to study the effects of perturbations and modifications to the surface of samples such as composite materials based on polymers that can ensure a transfer selective in the process of friction, trough formed an antifriction selective layer. The selective layer can get by friction between a surface of steel with a sample of composite material (polytetrafluorethylene (PTFE) with added cooper oxide (Cu2O) in various greased media) and formed of very thin layer, tribological performed on surface of steel in which predominated Cu. The accurate knowledge of their response to the continuous AFM scanning could help to design new materials with desirable mechanical properties. In this paper, we present results obtained applying a new method to investigate friction and wear properties on the composite material PTFE/Cu2O. This material is used with high tribological performance at tightening the cylinders of motor vehicles and compressors of petroleum installations. Keywords: atomic force microscopy, selective transfer, substrate, friction and wear, ripple, topography

The copolymerization reaction between bisphenol A glycerolate dimethacrylate (BisGMA) and urethane dimethacrylate (UDMA) monomers was studied and the monomer reactivity ratios were determined on the base of the FTIR data obtained at different times of reaction. Both Fineman-Ross and copolymer composition equations were used. Also ProCop computation program was used in order to establish the values for the reactivity ratios. Keywords: Dimethacrylates; Copolymerization; Monomer Reactivity Ratios; FTIR; ProCop

Nowadays more and more people have or get sick of venous diseases such as venous insufficiency, low foot blood pressure or even the phenomenon of swelling for diabetic people or for the post-birth period. Medical stockings provide a method to fight against these problems since ancient times but the results after every use was in compliance with the level of technology used to produce the stocking. This situation creates a challenge for the stocking manufacturers with developing new technologies and technical materials that give the best results and maximize the effects of compression stockings on the people that wear them. This paper is integrating the total design of a product, regarding the cycle of the product, profitability and satisfaction of the client problems, proposing new ideas of client approach using new technologies like mass customization through computer integrated manufacturing systems including 3 - dimensional body scanning and individual approaches to the client; and using this knowledge develops a kind of compression stockings that are fit-to-wear and satisfy the requirements of the clients concerning the efficiency of the product, comfort properties and durability. Keywords: compression stocking, yarns, total product design, mass customization, apparel for technical applications, 3-D body scanning, computer integrated manufacturing

The paper directs the attention to the detrimental influences exerted by longitudinal notches on the polyethylene pipe surface when subjected under high pressure to long time service. It was shown that the detrimental degree is influenced by the notch depth, working pressure and service duration. Depending on these parameters, researches evinced two types of fracture behaviour: ductile and brittle. The conditions they produce and the transition limits of the ductile – brittle behaviour were demonstrated in two different environments: water and air, at the temperature of 80°C. Keywords: mechanical behaviour, testing duration, environment, PE 80 polyethylene, pressure, longitudinal notches, temperature, pipes