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New formaldehyde resins were synthesized by the polymerization of a mixture of 4,4’-methylenedianiline (MDA) and p-tert-butylphenol (p-TBPH) with formaldehyde (FA) (at a molar ratio monomers/formaldehyde, 1/1), in the presence of an acid catalyst (HCl).The mixture of DMF/toluene was used as reaction medium and as carrier for the aqueous condensation. These polymers were characterized by elemental, spectral and thermal analysis and used as hardener for epoxy resins (diglycidyl ether of bisphenol A (DGEBA) and diglycidyl ether of hydroquinone (DGEHQ)). The obtained resins have low molecular weight and are soluble in medium and high polar solvents. The curing and the temperature behaviour of epoxy resin/formaldehyde resin systems were investigated using differential scanning calorimetry (DSC) and thermogravimetry (TG) techniques. The activation energies of the curing reactions are situated in the range of 52 to 66 kJ×mol-1 for DGEBA systems and at 54 to 72 kJ×mol-1 for DGEHQ systems. The cured products have good thermal properties, and the activation energies of the degradation reactions have values between 36-65 kJ×mol-1 for epoxy systems. Keywords: formaldehyde resins, epoxy resin, crosslinking reactions, thermal properties

The present study is aimed to investigate the effect of damage due to hygrothermal fatigue on the mechanical behaviour of CFRP (Carbon Fiber Reinforced Polymer) laminates as well as on the skin-core interfacial stress field in sandwich structures having CFRP laminates as core material and aluminum as skin. The above behaviour was both experimentally and analytically studied using a model recently developed by the CMG group at University of Patras. Keywords: hygrothermal fatique, polymeric composite laminates, sandwich structures, interfacial phenomena

Damping capacity is comparatively analyzed for a composite with polymer matrix (vinyl ester) and a shape memory alloy (copper-zinc-aluminium). A good damping capacity of shape memory alloy results in structural transformation domain in detriment of composite material. The theoretical model developed on the analyzed material behaviour describes qualitatively the temperature dependence of the dissipation capacity. Keywords: polymer, shape memory alloy, dissipation capacity, fractal

Thin foils of poly (vinyl alcohol) (PVA) with different thickness were prepared and dried without modifying their separation surfaces. The induced by stretching under heating birefringence of PVA films was measured under with a Babinet Compensator. An increase of birefringence versus the stretching degree of the PVA foils was evidenced for all studied samples. The dependence of the birefringence on the films thickness was evidenced in this paper. Keywords: birefringence, Babinet Compensator, stretching degree

Coefficient of thermal expansion of multiphase composite materials plays an important role in the process of engineered materials design especially while approaching thermal management issues. Tailoring and designing material combinations in order to develop a composite structure to prove stability over a wide range of temperatures, from cryogenic to high values, to withstand extreme environmental conditions is the dream and purpose of any engineering team involved in such study/research area. The paper aims to approach and present the variations of the CTE with extreme environmental conditions (e.g. cryogenic conditioning) for particular combinations of particle-fibers multiphase polymeric composite materials. Influencing factors will be underlined to accompany the experimental research. Keywords: multiphase, polymer, composite, cryogenic, coefficient of linear thermal expansion

The implants surfaces investigated in the present study were modified with the films of poly (vinyl) alcohol (PVA) which were formed in physiological serum (0.9% NaCl). Surfaces evaluation included electrochemical measurements such as linear potentiometry (LP) and electrochemical impedance spectroscopy (EIS). These suggest that PVA acts by adsorption at site on the metal surface and formed a compact, adherent and uniform layer. The composition of layer was estimated using Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM/ EDX) and X-ray Photoelectron Spectroscopy (XPS) techniques, which confirm the adsorption of PVA on the surfaces, through –OH groups, with a specific affinity to the titanium sub­strate. Keywords: titanium electrode; electrochemical measurements; poly (vinyl) alcohol; SEM/ EDX; XPS

Polymeric matrix composite materials are used when high characteristics are needed, good resistance under severe working conditions and low specific weight. Implementing polymeric matrix composite materials, specially, glass reinforced ones, resulted in the substituting of classical materials, whose quantities are more, and more, limited. Composite material products can be obtained to their final shape when manufacturing or, when necessary, can be submitted to further machining processes. Polymeric matrix composite materials can be conventionally machined (cutting, turning, drilling, milling or broaching) or / and non-conventionally machined (laser, ultrasound, etc.). Researches on milling machinability of glass fibers reinforced polymeric composites are at their very beginning, in our country, this paper pointing out some important aspects of research on cutting forces in cylindrical-face milling. There is also presented a data measuring, acquisition and processing system for the experimental model, as well as a real time control scheme designed to determine the measuring errors. Keywords: polymeric matrix, glass fibers, milling, cutting forces, automation system

Atomistic molecular modeling based on forcefield simulations, dissipative particle dynamics (DPD) mesoscale computational method and electrochemical techniques are here used to investigate the mechanical properties, structural morphology and electrochemical response of poly(pyrrole) (PPY )- poly(aniline) (PANI) conductive polymer composite. Computational bulk models of PPY-PANI were implemented at atomistic- and meso-scale and composite films were made available by electropolymerisation on platinum support. Further data concerning mechanical properties, structural morphology and electrochemical response of PPY-PANI composite films were collected by means of in silico investigations, scanning electron microscopy (SEM) and cyclic voltammetry (CV). Both approaches showed that the new formed composite material behave as new material with enhanced characteristics when compared with single component. Concerning material morphology and mechanical properties, simulated bulk systems were homogeneous and their Young’s moduli ranged from 0.04 to 0.475 GPa depending on the material composition. Based on CV measurements, it is stated that the electrochemical activity, reversibility, electrical conductivity and cycle-life stability of the PANI-PPY composite is significantly higher than the pure conducting polymer. Keywords: PPY-PANI films, atomistic- and meso-scale modeling, mechanical testing, electrochemical properties

A series of bismaleimides were used to prepare polymers in an attempt to achieve materials with improved properties. Structurally different bismaleimide compounds were synthesized by the reaction between 3(4)-maleimidobenzoylchloride with various diphenols having or not substituents to the aromatic rings. Polymers based on these compounds were prepared by the Michael addition of diamine to bismaleimides. Fourier transform infrared (FTIR), proton nuclear resonance (1H-NMR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and atomic force microscopy (AFM) were used to characterize these materials. Keywords: bismaleimide monomers and polymers, thermal characterization

The multilayer structure consisting of alternative sheets of paper and ethylene-propylene elastomers was investigated for electrical applications. The changes in the main electrical characteristics, namely volume resistivity, dielectric loss, permittivity were determined for the evaluation of material stability under accelerated degradation promoted by g irradiation. The satisfactory response of this sandwich structure is illustrated by sample resistivity placed around 1015 W.m, permittivity less 2.025 and dielectric loss not higher than 0.04. The correlation between degradation effects and electrical properties is presented. Keywords: electrical insulation, synthetic rubber, cellulose, multilayer structure