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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

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

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

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

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

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

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

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

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

The solution properties of some cationic polyelectrolytes with ammonium quaternary centers either attached to an acrylic macromolecular chain (polycation PDMAEMQ type) or in the backbone (polycation PCA type) have been measured in order to identify how charge density, polyelectrolyte concentration, solvent polarity as well as temperature influence their behavior in solution by viscometric, conductometric and rheological methods. The viscometric data revealed that all copolymers PDMAEMQ exhibit a polyelectrolyte behaviour in water and methanol and were plotted in the terms of Rao equation. Straight lines were obtained in all cases, allowing the calculation of intrinsic viscosity, [h]. Data from the conductometric study emphasized for PDMAEMQ50 and PCA5 an increase of the equivalent conductivity values, L, with decreasing concentration over the whole concentration range in water, methanol and their mixture (1:1). The comparison between the complex viscosity values h*, at the same polymer concentration, cp = 4%, for PCA5D1 and PCA5 shows higher values in the whole interval of temperatures under study (T = 10-60 C°) and a pseudoplastic behaviour at temperatures higher than 50°C for the former system. Keywords: polyelectrolyte, viscosity, electrolytic conductivity, rheology