Browse Articles

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

A series of phosphorous-containing copolyesters was prepared by polycondensation of 2-(6-oxido-6H-dibenzo[c,e][1,2]oxaphosphorin-6-yl)1,4-benzenediol, 1, or of an equimolecular amount of 1 and different aliphatic diols 2, such as: ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol and 1,12-dodecanediol with an aromatic diacid chloride containing two preformed ester groups 3, namely terephthaloyl-bis-(4-oxybenzoyl-chloride). The copolyesters exhibited good thermal stability having the decomposition temperature above 360°C and char yield at 700°C in the range of 8.4-41%. The glass transition temperature was in the range of 83-160°C. The polymers exhibited thermotropic liquid crystalline behaviour. Keywords: polyesters, phosphorus-containing polymers, solution polycondensation, thermal properties

Some methods for the preparation of cellulose microfibrils and polymer composites with such microfibrils are presented in this paper. Morphological aspects of microfibrils and their dispersion in the polymer matrix are characterized using SEM and optical microscopy. Cellulose microfibrils show a clear reinforcing effect of the polymer matrix as pointed out by mechanical characterization. Keywords: polymer composites, cellulose microfibrils, mechanical properties

The paper presents the kinetic characteristics in non-isothermal conditions obtained by degradation in argon of some aromatics copolyethers with semi rigid and flexible spacer and by comparing the results obtained for the homopolyethers corresponding to the bisphenols and spacer used. Copolyethers were synthesised by phase transfer catalysis method in liquid/liquid system. Oxetanic, diethyl etheric or hexamethilenic spacers have been used. 4,4’-dihidroxy azobenzene and 4,4’ dihidroxy biphenyl were used as bisphenol. Thermogravimetric analysis and derivative thermogravimetric analysis were applied. The kinetic characteristics suggest the complexity of the thermal degradation mechanism up to 1000°C. The degradation rate is depending on the chemical structure of the main chain. Compensation equations are proposed. Keywords: kinetic characteristics, aromatic copolyethers, thermal degradation