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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

The paper presents the methodology of determining the plasticity of some composites specimen through bending test. The equipment is presented both for room temperature testing and under cryogenic conditions. Particularities of the measurements under cryogenic conditions are specified. The influence of talc concentration in the composite material is presented. Key words: composite materials, deflection, cryogenics.

The study presents rheological behaviour of some solution mixtures from poly(vinyl alcohol) (PVA) and starch in water, with addition of glycerol as plasticizer and urea (nitrogen source for microorganisms). These solutions were used to obtained biodegradable films. The effect of temperature and concentration on the rheological behaviour of poly(vinyl alcohol) and starch solutions in water, was studied in the temperature range of 20-60 0C and concentration 10-20 % at different gravimetrical ratio PVA/starch (3.00, 1.66, 1.00, 0.60, 0.33). The rheological behaviour was studied to gradient of shear rate which varied between 3 and 1310 s-1. From experimental data it was established that concentrated solutions of PVA/starch blends exhibit a non-newtonian rheological behaviour of pseudoplastic type. The flow activation energies versus temperature are situated in range of 11.86-49.92 kJ/mol, while against the concentration between 1.61-4.54 kJ/mol. The consistency index increased with decrease of temperature and recording great values in the concentrated solutions case. The solutions with PVA/starch subunitar gravimetrical ratio have great values of consistency index, to compare those with supraunitar ratio. This fact shows that the starch is the polymer which confers solutions a great viscosity, but low temperatures determines even their jellification. Keywords: biodegradable materials, rheological behaviour, poly(vinyl alcohol), starch

Cross-linked polyurethane/filler composites based on polyester, diphenylmethane diisocyante, glycols, and glycerin were synthesized and characterized. The mechanical and thermal properties of PU/filler composites were investigated through tensile, thermogravimetry experiments. Therefore, to understand the behaviour of fillers, such as graphite, talc, CaCO3, and polyamide fiber added to cross-linked polyurethane resins, several thermal and mechanical tests were conducted on samples, using these new materials. It is shown that cross-linked polyurethane composites have decreased tensile strength, improved hardness and thermal stability, relative to bulk polyurethane. The results show that the polyurethane component ratios in cross-linked polymers, the types of filler, and the amount of powder added all affect the damping behaviours and degree of phase separation of unfilled and filled cross-linked polyurethanes. The addition of filler into polyurethane composites yields an increase in the Young´s modulus and a decrease in the elongation at break. Keywords: composite, cross-linked polyurethane, mechanical properties, filler