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Polypropylene or polypropene (PP) is a thermoplastic polymer, made by the chemical industry and used in a wide variety of applications, including food packaging, ropes textiles, plastic parts and reusable containers of various types, laboratory equipment, loudspeakers, polymer banknotes and vehicle components. The authors had tested the behaviour of polypropylene used in the fabrication of some vehicle components (internal part of doors, instrument panels, seat elements aso.) under axial stress in various conditions (different speed levels for the applied force, simulated damages like holes and initial application of stress cycles). Some mechanical properties of polypropylene, which permit to fix the conditions in which it can be used successfully in vehicle components manufacture have been estimated. A comparative analysis between the polypropylene versus LDPE and HDPE has been performed. Keywords: polymer, polypropylene, mechanical properties, vehicle elements

Analytical computation of ultrasonic transducers is a very complicated task. Its framework is the theory of elastic waves propagation in magnetostrictive, electrostrictive and piezostrictive medium and a series of constraints that need to be satisfied so that the optimum vibration modes can be found out for efficient use. The use of Finite Element Methods (FEM) allows the determination and optimization of design and functional parameters of ultra-acoustic systems for ultrasonic welding of intelligent composite materials with polymeric matrix. The modeling was done individually for each component of the ultra-acoustic system. A diagram of the particle speed amplitude variation both at the top of the ultrasonic transducer and along the length of the ultra-acoustic system was obtained. Keywords: finite element method, smart composite materials, ultrasonic method

The cooling time of the plastic materials obtained through injection represents a very important component of the total duration of the injection cycle. Due to this fact, the specialized literature mentions a large number of theoretical and experimental researches which make reference to the importance of the cooling speed for the economy of the injection process. This paper presents a comparative study regarding the application of more mathematical models that may permit the determination of the cooling time for a complex material obtained through injection within a mono cavity mould. Keywords: cooling time, injection moulding, plastic materials

This paper presents the synthesis of some new inulin mixed esters were obtained using methacryloil and palmitoyl chloride. These esters were then copolymerized with n-butyl acrylate in order to obtain plastics for everyday use with biodegradable properties. The obtained compounds were characterized using FT-IR spectroscopy, thermogravimetric analysis; also density, tensile and torsion stress were evaluated. Keywords: inulin mixed esters, FT-IR spectrometry, thermogravimetric analysis, tensile and torsion stress

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