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Mechanical properties of epoxy resin ROPOXID-501 additivated with polyethylene glycol-400 and chlorendic anhydride were studied. The behaviour of those mixtures exposed different times at UV radiation was also investigated. The added chlorendic anhydride enhances the strain at the break, the hardness and elastic energy and improves the stability at UV radiation. Keywords: epoxy resin, mechanical properties, UV radiation, additives

The vertically acting load of soil causes a deflection of the pipe, which in turn results in a horizontal supporting soil pressure to show up. The pipe wall will be then subjected to both compression stresses and bending stresses. As consequence, the design of flexible PE pipe buried in the ground follows quite different rules from those classically accepted for rigid pipes. The article presents the soil burial loads of flexible pipes. The short-term, the long-term maximum vertical defelction and the resistance to buckling were determined. Keywards: polyethilene pipe, buried plastic pipes, strength, buckling

The paper describes the aspects concerning moisture absorption on the behaviour at bending in case of composite materials made of E-glass fibres reinforced polymeric resins. These fibres were used to randomly reinforce the following resins: two polyester resins (Heliopol 8431 ATX, Polylite 440-M880), epoxy resin (LY 554) and vinyl-ester resin (Atlac 582). The first of all, experimental data concerning moisture absorption was analysed during ten months. Three different environments were considered: water, water / detergent mix and natural seawater (Black Sea). Then, the composite material specimens were subjected to the flexural test (three point’s method). The results obtained in case of the submerged specimens (9200 hours) were compared with the results obtained in case of the dry specimens. Finally, the conclusion was that the moisture absorption in composite materials tested leads to the decreasing of the flexural mechanical characteristics (elastic flexural stress se, flexural modulus E and failure energy). The paper briefly describes the laboratory tests and shows graphically the final results. Keywords: composites; moisture; flexural modulus; flexural stress; failure energy

The present paper continues a previous article [1] where multiobjective optimization of a polymerization process was approached with a classical method – sequential quadratic programming. In this article, an optimization method based on genetic algorithms is used for the free radical polymerization of methyl methacrylate. The influence on the optimization results of the main parameters (the size of the initial population, the number of generations, recombination rate, mutation rate), as well as that of different variants of genetic algorithms (different ways of recombination, mutation and selection) is studied. The main conclusion of the article is that these values and methods depend on the studied process, but also inter-condition each other, such that the optimization results are rather more correlated with the overall set of values considered. Thus, we try to establish some directions to guide the search for optimal values. Keywords: genetic algorithms, optimization, free radical polymerization

The studies were concerned on the releasing of nystatin from polyurethane urea (PUU) microporous membrane at different pH values at room temperature. The whole ATR-FTIR spectrum of PUU-nystatin is shifted to smaller wave numbers compared to control PUU which indicates the increasing of structurated degree of PUU-nystatin. The stress-strain curves are sustained by the ATR-FTIR results demonstrating the structurating effects of a polar bioactive nystatin materialized through an increasing of the initial modulus. The nystatin delivery in watery solution has a strong reaction to pH. At pH 3, in the first 170 minutes, the nystatin is released in proportion of 38% whereafter drug release is approximately constant in time. Key words: polyurethane urea, nystatin, release

Aromatic polyimides containing side azobenzene groups has been synthesized by low-temperature solution polycondensation of certain aromatic dianhydrides with aromatic diamines containing preformed side azobenzene groups followed by chemical imidization at 100 °C în the presence of pyridine and acetic anhydride. The glass transition temperature of these polyimides is in the range of 185-230°C and the average weight molecular weight is in the range of 16000-129000. Keywords: polyimides, side azobenzene groups, glass transition

The paper presents the modalities employed in the achievement of peptide chains and our contributions regarding the introduction of peptide moieties in the macromolecular structure. Keywords: organic synthesis, peptide, biomacromolecules

Developed in last decade, the shape memory polymers have been gaining widespread attention for new product innovation. They are lightweight, have high strain/shape recovery ability, easy to process and required properties can be tailored for variety of different applications. Polyurethane elastomers (PUs) based on polyether diols and aliphatic diisocyanates can be used as passive isolation bearings in railway applications. In the present study poly(1,4-butane) diols (Terathane) and 1,6-hexamethylene diisocyanate (HDI) have been used in polyurethanes, using glycerin, 1,4-butane diol or 1,6 hexane diol as chain extenders. Effect of varying the concentrations of diisocyanates and structure and amount of chain extenders on polyurethane elastomers has been discussed with reference to mechanical properties. IR and thermal analysis techniques (TGA) were used for characterization. Keywords: polyurethane elastomers, chain extenders, mechanical properties, railway isolation

This paper discusses the reaction mechanism and kinetic study of linear unsaturated polyesters, based on polycondensation reaction of maleic anhydride with different glycols (ethylene glycol, diethylene glycol and neopentyl glycol) utilized for the fabrication of polyurethanes. This polyester-diols with relatively high molecular weight (1000-1500) were characterized by IR, H-NMR, GPC, end groups analysis, as well as by the double bond content determination. Keywords: unsaturated polyester, reaction mechanism, kinetic study

For more than 30 years, ultra-high-molecular-weight polyethylene (UHMWPE) has been used as a bearing material in total-joint-replacement prostheses. Such orthopaedic implants usually comprise a metal (typically a cobalt-chromium alloy) or ceramic component that articulates against a UHMWPE component in vivo use. It has been well established that the longevity of such implants depends on the wear performance of the UHMWPE components [1, 2]. The presence of particulate wear debris of UHMWPE that is generated due to the sliding of UHMWPE components against the metal or ceramic counter-face has been linked to complications such as tissue inflammation, bone loss (or osteolysis), and implant loosening. Osteolysis resulting from wear of UHMWPE is recognized as the leading problem in orthopaedic surgery today. Because de wear volume influence the mechanical performances of a prosthetic device in this paper is studied the variation of the wear volume depending on the number of cycle motion and the time. Keywords: polyethylene, prosthesis, cross-linked, wear