Volume 45, Issue 4

Abstract: The compression properties of a novel family of hydrogels prepared from diepoxy-terminated poly(ethylene glycol)s of approximate molecular weights 600, 1000, 2000 and 4000 Daltons and various aliphatic polyamines of different chain length and functionality (ethylenediamine, 1,4-diaminobutane, hexamethylenediamine, 1,8-octanediamine, diethylenetriamine, triethylenetetramine, tris(2-aminoethyl)amine) were determined by uniaxial compression. It was shown that both elastic and compression moduli, and compression strength of the fully swelled hydrogels depended on the molecular weight of the PEG oligomer, structure and functionality of the aliphatic amine employed as crosslinker, and mole ratio between the reacting groups, as a consequence of the different crosslinking degree of the resulting networks. Keywords: hydrogels; poly(ethylene glycol), epoxy groups, aliphatic polyamines, uniaxial compression

Abstract: A simple, efficient and general one-pot method has been developed for the synthesis of aminophosphonates grafted on styrene-divinylbenzene copolymers from benzaldehyde grafted on styrene-divinylbenzene copolymer with amines and diethyl phosphite in tetrahydrofuran. The aminophosphonates grafted on insoluble macromolecular supports were characterized by infrared spectroscopy, thermogravimetric analysis and scanning electron microscopy. Keywords: aminophosphonate groups, stirene-divinylbenzene copolymers

Abstract: Surface characterization of PTFE composites in the case of water lubrication is discussed. Methods for analysis of surface quality are shortly presented. The study of the effect of wear is based on Abbott-Firestone curves which provide many advantages. Roughness studies were performed by the help of digital profilometer applied on PTFE samples. The surface quality study points out the statistical character of the information concerning the profile of composites with polymeric matrix. Keywords: PTFE, surface quality, Abbott-Firestone curves, water lubrication

Abstract: The effect of organofunctional silane coupling agents on the morpho-structural (XRD) and thermal (TGA) characteristics of the organically modified montmorillonite was examined. The modification of the organosilicates was carried out using organofunctional silane coupling agents in ethanol. The obtained results demonstrate the interaction of the silane-coupling agents with the organosilicate layers. The thermal stability and the basal spacing of the organosilicates increases with silane coupling agent’s concentrations. Using organosilicate modified with functionalized coupling agent PP based nanocomposites with enhanced thermal stability and a more disordered lamellar structure were obtained. Keywords: organically modified montmorillonite, silane coupling agents, polymer nanocomposites

Abstract: Epoxy-based composites with modified carbon nanotubes (CNTs) were synthesized using different types of CNTs. These were first modified by amidation of the carboxylic groups from the CNT’s surface and then embedded into the epoxy matrix. The modified CNTs and the corresponding composites were analyzed by FTIR, TGA, DMA and Raman Spectroscopy. The influences of CNT type and the nature of the organic modifier were pointed out in connection with the composites structure. Keywords: functionalization, carbon nanotubes, polymer nanocomposites, thermostability, Raman Spectroscopy

Abstract: 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

Abstract: Epoxy resins are used in many applications because of their strength, stiffness, good thermal stability, and excellent adhesion properties. Liquid crystalline epoxy (LCE) networks are an important area of research due to their potential use in a number of applications, such as electronics, advanced composites, non-linear optics etc. The synthesis of LC epoxy resins can be carried out either by using LC epoxy prepolymers, which preserve their ordered morphology in the curing process, or by curing of some functionalized mesogenic rigid molecules using a suitable curing agent In recent years growing interest has been focused on LC thermosets (LCTs), because of their opportunities found in ordered, anisotropic network structures. This paper is a review on our proper results regarding the synthesis and characterization of some LCTs based on monomers with both naphthalene and azomethine mesogenic rigid structures in the main chain. Keywords: epoxy, mesophase, thermoset, liquid crystal, curing

Abstract: Polyurethane-elastomer material was synthesized with an aim to determine the influence of the polyurethane chemical structure as well as of the length of the linear chains between cross-linking points on properties in such systems. Polyurethane elastomers were obtained from polyurethane prepolymers with a mixture of the diol or/and glycerin. The polyurethane prepolymers were synthesized from 4,4’-diphenyl methane diisocyanate and polyesters with molecular weight of about 2000. These polymers had improved properties and have formed flexible films with well stress-strain properties. This effect was explained by the formation of hydrogen bonds between urethane groups, independent of the polyurethane linear chain length, physical networks, which control the molecular mobility. By contrast, the chemical nature of the cross-linker precursors strongly influences the mechanical properties and glass transition. We report the synthesis of the cross-liked polyurethane elastomers and study its properties, the influence of the nature and length of the hydrocarbonate chain of the various micro glycols on the thermal and mechanical characteristics. The chemical cross-linking process decreases the soft segment crystallinity and increases stress properties. Investigation of these properties showed that the elastomers could be tailor made in order to fulfill industrial needs. Keywords: polyurethanes, cross-link, chain extenders, mechanical properties, thermal behavior

Abstract: In this paper we introduce a formula for the calculus of resistance to fracture for the composite plates with a random reinforcement’s distribution. Also, we give a formula for the calculus of upper limit of resistance to fracture for the composite plates, described as depending on the volumetric proportion of reinforcement. As applications, we give the variation of resistance to fracture depending on the volumetric proportion for two types of composite materials and, in addition, we determine the characteristic curves and the resistance to fracture for a traction test considering the two composite materials. Keywords: composite materials, strength to rupture, traction

Abstract: Fluorinated block copolymers containing imide and 1,3,4-oxadiazole rings were prepared in two steps. In the first step a bis(amino)aryl-ether-1,3,4-oxadiazole oligomer was prepared via a nucleophilic substitution reaction. The molecular weight of the oligomer was 7000 g/mol, as determined by 1H NMR spectroscopy. In the second step the oligomer was co-reacted with an aromatic diamine, namely 2,2-bis[4-(4-aminophenoxy)phenyl]propane, and a fluorinated diacid chloride containing preformed imide rings. The resulted block copolymers were easily soluble in organic solvents such as N-methylpyrrolidone and some of them could be cast from solution into thin flexible films having good mechanical properties. They showed high thermal stability with decomposition temperature being above 440°C. Multiphase morphologies were observed irrespective of the concentration of the oligomer in the block copolymer. Electrical insulating properties of a copolymer were evaluated on the basis of dielectric constant and dielectric loss and their variation with frequency and temperature. Keywords: fluorinated block copolymers, thermal stability, thin films, dielectric constant

Abstract: Mechanical behaviour of removable partial dentures is a priority among experimental papers, in order to define the fracture mechanism of acrylic resins. Present paper presents experimental results concerning mechanical behaviour of two different dental acrylic resins, respectively Meliodent and Royaldent. There are determined mechanical characteristics on Zwick Roell Equipment with testXpert system. The fracture samples were examined on stereomicroscope Olympus. The difference in mechanical behaviour is explained in terms of stereomicorscopic analysis. Keywords: dental resins, removable partial denture, stereomicroscopy, fiber, composite material

Abstract: The paper presents a theoretical-experimental approach of a particular class of composite materials known as multiphase composites in order to retrieve its effective elastic coefficients and identify the major influencing factors on these variations. Moreover, in the paper is being presented a particular homogenization concept based on the well known theoretical predictions from the micromechanics of composite materials approaches, the Mori-Tanaka that applies to the particle reinforced composites and Halpin-Tsai that applies to the random fibre composites. The theoretical values were used against the experimental data, the later being retrieved during a simple tensile, compression and three point bending tests at room temperature on samples made using a self-developed manufacturing technology. The samples were ceramics and metal reinforced particles of various volume fraction embedded along with random E-glass fibres into a polyester matrix. Keywords: composite, multi-phase, elastic coefficient, micromechanics, testing

Abstract: Thermal stability of alendronate sodium in a mixture with cross-linked acrylic acid polimers and chitosan, formulated and preparated as oral matrix systems, was qualitatively evaluated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and infrared spectroscopy (FT-IR). The results of the study have shown alendronate stability in association with carbopol and chitosan. DTG curves and FT-IR results suggest certain interactions between carbopol and chitosan, most probably ionic and hydrogen bonds. We consider that the nature and intensity of these bonds could be a positive factor decreasing pH dependence of Carbopol in releasing drug substance. Keywords: alendronate, carbopol, chitosan, thermal analysis

Abstract: The work presents the main results obtained at the application of the ultrasonic energy in the separating process of the rubber on the metallic insertions in the case of the transporting belts. Results refer mainly at the influence ultrasounds’ application has over the specific resistance at extraction of the metallic insertion from the rubber matrix, and these are quantified through an efficiency coefficient at extraction. The importance of the results presented in the work derives from the fact that the separating processes of the rubber on the metallic insertions are complex enough and big energy consumers, and the results presented in the work can be applied in practice and they allow a substantial increase of the economic profitability for the capitalization processes of the wastes of transporting belt reinforced with metallic insertion Keywords: belts, ultrasonic energy, rubber, metallic insertions

Abstract: Production process of plastic products depends significantly on cost of quality, time to market and cost to produce appropriate molds. Basic course of improvement and rationalization of production process for plastic injection molds is directed on automation design mold and their process planning. Working area of process planning in large number of cases is the bottleneck in production systems, because of impossibility of development multipurpose program system which would be effective in planning and designing a huge number of activities that makes process planning. The model and program system for automated process planning for plastic injection molds manufacturing have been developed, in order to solve this problem. This solution presents integrated CAPP system, which is based on integration of CAD, CAPP and CAM activities. Keywords: Plastic injection mold manufacturing, CAPP, Data base, Knowledge base

Abstract: In this study were synthesized some polyurethanes based on polycaprolactone diol (PCL) with Mw=2000g/mol and 4,4’-diphenylmethane diisocyanate (MDI), using as chain-extending agents different linear diols with methylene number between 2 and 6, without adding catalysts. Effect of the diisocyanates concentration and chain extender structures on the polyurethanes has been discussed with reference to the thermal stability and mechanical properties. The physical and mechanical properties (hardness, stress-strain, resilience, abrasion resistance, etc.) of these polymers were measured according to standard methods. All the polymers were characterized by conventional methods. Thermal analysis (TGA and DSC) were used for characterization. The structures were confirmed by infra-red analysis (IR). The results showed that the thermal stability and mechanical properties of the final products can be controlled by the amount of the MDI and/or of the chain extenders nature. Keywords: polyurethanes, mechanical properties, thermal stability

Abstract: The study consists of a new know - how applied to the organic optical glass used to manufacture optical components. The study was developed on several organic optical glasses, usually used to manufacture pieces with optical properties. The innovative methods, subject of this paper, are manufacturing active optical surfaces with a high quality surfaces. That is the reason of complex control, based on different methods which can reveal changes of inner or outer structure thinking of nanometric level. Keywords: organic optical glass, nanometric structure

Abstract: Polymers with polyimide, polyamide or poly(amid-imide) structure have been obtained by polycondensation of 2,2-bis(3-amino-4-oxyhexyloxy-phenyl-4’-butoxyazobenzen) hexafluoropropane with hexafluoroisopropylidene diphthalic dianhydride or two different aromatic diacid dichlorides. These polymers have been characterized by FTIR and UV-VIS spectra, molecular mass determination, solubility and optical properties. The photochromic behaviour upon UV-Vis nopolarized and polarized light was also investigated. Keywords: pendent azobenzene groups, polyimide, polyamide, polyamid-imide, photoinduced optical properties

Abstract: Copolymers based on dicyclopentadiene and maleic anhydride have been reacted with several aromatic amines (typical polymer-analogous reaction) to obtain the corresponding amides, and subsequently imides. An appropriate procedure has been established and the conversion has been appreciated. All the products have been characterized from the structural point of view, as well as by measuring the improved thermal properties. Keywords: dicyclopentadiene; maleic anhydride; polymer-analogous reaction; thermal properties

Abstract: New reinforcing agents based on modified montmorillonite with different amines and polyhedral oligomeric silsesquioxanes were synthesized and characterized by different techniques like FTIR Spectrometry, Thermogravimetric Analysis (TGA), X-Ray Diffraction (XRD) and Differential Scanning Calorimetry (DSC). DSC analyses show that the presence of the modified montmorillonite leads to an increase of epoxy resin reactivity due to the catalytic effect of the montmorillonite modifier which included amino groups. The glass transition temperature (Tg) for the final hybrid systems which contain modified montmorillonite with amines exhibits lower value than the epoxy systems without any reinforcing agent. The thermostability of the final hybrid systems was not influenced by the introduction of these reinforcing agents. Keywords: epoxy, layered silicate, polyhedral oligomeric silsesquioxanes, glass transition temperature, nanocomposites

Abstract: This work presents a theoretical model of calculation of cylindrical assemblies joined with adhesive, based on an energy method. After the determination of the cinematically acceptable field of stresses, according to the applied load, a variational calculus on the expression of elastic potential energy leads to the complete expression of the stress field in the whole assembly. A first parametric analysis (geometrical and physical parameters) is carried out on an assembly of tubes and makes it possible to deduce the optimal length and the thickness of the adhesive. The model is validated by comparison with a finite elements model. For the assembly, the total force-displacement behavior is well defined. Thus the analytical model makes it possible to determine the rigidity of the assembly and to obtain a simple formulation very rapidly which gives the total behavior of the assembly. Keywords: adhesive joints; glass fibers; modeling; finite element analysis, stress transfer