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The debates study the influence of the molecular structures for polymers welding and establish the conditions when is possible to obtain a welding joint of these and a transition area near welding with properties which ensure good usage. The testing of aptitude of materials for high frequency (HF) welding, were done with Polyvinyl Chloride (PVC) foils with textile insertion and Malivat materials, defining in an experimental way, the optimum process parameters which ensure a good resistance breaking for welding. Key words: polymer, structure, welding ability

Gypsum/ poly(butyl acrylate) composites have been prepared based on natural gypsum and the monomer butyl acrylate by means of gamma irradiation. The conversion of polymerization was followed up with respect to the irradiation dose using thermogravimetric analyzer (TGA). The data show that yield of polymerization increases with increasing the irradiation dose. A yield of about 98% was achieved by exposure of the samples to a dose of 5 kGy. A thermomechanical analyzer (TMA) was used to locate the range of the glass transition temperatures (Tg) using the mode with alternative variable force; the mode with constant force was used to determine the Tg of the pure polymer and the composite prepared at the same irradiation dose. Also differential scanning calorimeter (DSC) was used to ensure the location of the glass transition temperatures. Keywords: Gypsum; polymer composites; butyl acrylate; polymerization; radiation

Three types of polyhedral oligomeric silsesquioxane (POSS) compounds were used to synthesize nanocomposites based on urethane dimethacrylate (UDMA). An advanced characterization of POSS compounds was done by X-Ray Photoelectron Spectroscopy (XPS) for chemical structure, X-Ray Diffraction (XRD) for crystalline phase and Differential Scanning Calorimetry (DSC) for thermal transitions. The POSS compounds generally influence the thermostability of UDMA-based nanocomposites acting both as a comonomer and reinforcing agent. Keywords: polyhedral oligomeric silsesquioxanes, XPS, XRD, DSC, nanocomposites, TGA

The study presents experimental data regarding the curing reactions of some epoxy systems consisting of diglycidyl ethers of bisphenol A and different amine hardeners at room temperature and at microwaves. The curing reaction of the system composed of an epoxy resin (ROPOXID P 401) and 4,4’-diamino-diphenylmethane (HT 972) was studied by differential scanning calorimetry (DSC) and FT-IR spectroscopy. The degree of conversion obtained using FT-IR method is very close to that obtained using calorimetric method. Keywords: epoxy, amine, microwaves, kinetic

Two types of aromatic-aliphatic polyimides have been synthesized: polyaddition polyimides, from the Michael reaction between 4,4’-diaminodibenzylbismaleimide and ethylenediol (diethyleneglycol respectively) and solution polycondensation polyimides, from the reaction of 5-(2,5-dioxotetrahydrofurfuryl)-3-methyl-3-cyclohexenyl-1,2-dicarboxylic acid anhydride (epiclon) with 4,4’-diaminodibenzyl [1,4-bis(p-amino phenoxy)benzene respectively]. All monomers and polymers were characterized by conventional methods, and the physical properties of the polymers, including solubility, thermal, optical, electrical or mechanical properties were discussed. Keywords: bismaleimides, Michael reaction, epiclon, aliphatic polyimides

The paper presents the multidisciplinary studies dedicated to the minimization of the residual stresses in an Acrylonitrile-Butadiene-Styrene part. The first stage of the study consists of an experimental research employed to measure the physical characteristics of the polymeric material. The next stage is a simulation of the moulding process for a plate-wise specimen made of the material previously tested, being interested by the values of the residual stresses. The next stage is the experimental research of the residual stresses by the use of the hole-drilling method applied on the previously simulated plate-wise specimen. The results of the two studies are close one to the other and the conclusion regarding the material and the parameters employed for the simulation are used for the next study dedicated to the simulation of the moulding process for a complex part. Several studies were performed in order to find the best parameters of the moulding process which lead to a minimum level of the residual stresses. Other parts made of the same material may be also simulated in order to minimize the residual stresses. We conclude considering that a high degree of confidence regarding the results of the numerical model may be achieved only if the results of experimental studies are employed. Keywords: polymeric part, residual stress, experiment, numerical model, applications

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