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Aromatic polyimides containing side azobenzene groups have been synthesized by low-temperature solution polycondensation of certain aromatic dianhydrides with aromatic diamines containing preformed side azobenzene units followed by chemical imidization at 100°C in the presence of pyridine and acetic anhydride. The obtained polyimides were characterized and evaluated by FT-IR, UV-Vis, DSC and TGA analyses. These polymers show a good thermal stability with starting decomposition temperature above 300oC and glass transition temperature in the range of 111-230°C. These polyimides show a good solubility in various solvents. The photochromic behaviour, determined by the trans-cis isomerization process of azo-groups, in solution and in solid state, was also evaluated. Keywords: azopolyimides, photochromic behavior, thermal stability

The present work provides new insights about the micro and nanostructure of native starch granules from potato and maize by scanning electron microscopy (SEM) and atomic force microscopy (AFM). SEM images revealed the shape and the size distribution of the granules as well as some features, such as holes and wrinkles, on the surface of granules. These data were confirmed by AFM observations which showed the presence of numerous protrusions (nodules) on the granules surface of both starches. The structure of granules surface consisted of small spherical particles of about 30 nm in diameter, identified particularly for potato starch. These nanoparticles might be related with highly branched amylopectin molecules in substantial agreement with amylopectin blocklets (of about 20 nm) model. Larger particles of about 60 nm up to 80 nm were also visualized especially on the surface of maize starch granules representing different associations of amylopectin and amylose. The largest elongated particles of about 100 nm to 200 nm found randomly on granules of both starches might be assigned to arise from the granule-surface components, such as starch carbohydrates attached to granule proteins and phospholipids, in general agreement with starch granule surface composition data. This investigation also supports the complex structural network for the starch granule surface (periphery) and its role in maintaining the integrity of starch granules and in the starch gelatinization process. Keywords: starch granules, potato starch, maize starch, granule surface, supramolecular structuring, scanning electron microscopy (SEM), atomic force microscopy (AFM)

In this paper, the behaviour of polyamide 66 with 30% short glass fibers (PA66 GF30) is investigated using instrumented indentation technique combined with the dynamic mechanical analysis (DMA). The visco-elastic-plastic behaviour of PA66 GF30 is described by a rheological model which incorporates a spring, a plastic element and Kelvin-Voigt elements. The time-temperature superposition (TTS) principle was used to investigate the effect of time and temperature on the behaviour of PA66 GF30. Keywords: indentation, polyamide 66, creep, dynamic mechanical analysis

Experimental thermal properties on carbon nanotube with polymer matrix composites are analyzed. Increasing of thermal conductivity with carbon nanotube percentages enhancing is obtained and some phenomenological considerations on the heat transfer mechanisms are presented. Keywords: carbon nanotubes, thermal conductivity, effusivity

The paper presents the experimental results obtained for the Necuron 1020 rigid polyurethane specimens with stress concentrators, at traction test. The resistances of these specimens are evaluated based on the critical distances theory, obtaining a good agreement with the experimental results. Keywords: rigid polyurethane, the critical distances theory

Physical properties, such as thermal and dielectric characteristics, of some aromatic polyimides which contain methylene units have been investigated. The results indicated that the polymers were highly thermostable with decomposition temperature over 450°C and low dielectric constants. The thermogravimetrical values processed by differential method Freeman-Caroll showed that the activation energies and reaction orders are lower in air than in nitrogen. Keywords: methylene units, polyimides, thermal characterization, activation energy, dielectric constants

Modulus I interlaminar fracture toughness of wood laminated composite materials has been evaluated using the critical strain energy release rate associated with the onset of crack growth in double cantilever beam specimens (DCB). The advantage of using the DCB test for determining the critical strain energy release rate in the case of wood laminated composites relies on the working method which is focused on failure analysis in adhesive layer through the presence of initial interlaminar crack, but also due to the energetic approach in deduction of calculus relations. Data analysis was conducted by two methods namely, the corrected compliance method which is based on the linear elastic fracture mechanics principles, and the area method which accounts the whole shape of load-displacement curve obtained through a complete loading-unloading cycle. In general there is a good agreement between the results obtained by the two methods and those reported in literature. Keywords: wood laminated composites, interlaminar fracture, critical strain energy release rate, Double Cantilever Beam (DCB) specimen

This paper presents an experimental study aiming to obtain a new polymer composition by using styrene-butadiene radial block-copolymer with styrene-butadiene diblock-copolymer blend, in order to manufacture masking solution for metal protective coating in the chemical milling process. Keywords: styrene-butadiene block-copolymers, masking solution, protective coating

This paper presents the influence of processing temperature on the physico-mechanical properties of polypropylene (PP) used at the injection molding of performance sport items. The test-pieces were molded at the following real injection temperatures: 220, 240, 260, 280 and 300°C. It was determined that the in-mould pressure decreases with the increase of processing temperature The thermal analysis performed were: TG, DSC and DMA. It was established that the processing temperature influences the thermal stability of the polymer molded at 300°C, but the vitrification temperature and the melting temperature are slightly influenced by the processing temperature. The storage modulus E’ is influenced by the processing temperature and stress frequency. Keywords: polypropylene (PP), injection molding, Thermogravimetry (TG), Differential Scanning Calorimetry (DSC), Dynamic-Mechanical Analysis (DMA)

Poly(amide-imide)/polyaniline blends containing 2% and 10% polyaniline have been prepared by casting the dispersion resulting from the mixture of polyaniline (micrometer size) with poly(amide-imide) in tetrahydrofuran as solvent onto glass plates. Polyaniline has been synthesized by chemical polymerization of aniline in the presence of (NH4)2S2O8 followed by dedoping with ammonium hydroxide. The poly(amide-imide) has been obtained by solution polycondensation of a fluorinated bis(o-aminophenol), 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, with a diacid chloride having imide rings and hexa-fluoroisopropylidene unit, namely 2,2-bis[N-(4-chloroformylphenyl)phthalimidyl]hexafluoropropane. The thermal properties and sensitivity of pure poly(imide-amide) and its blends with polyaniline to vapors of acetone, ethanol and liquefied petroleum gas were investigated. All samples showed high thermal stability, decomposition temperature being above 270°C. They exhibited sensitivity to the tested gases, those containing 10% polyaniline presented the greatest sensitivity to acetone vapors. Keywords: polymer blends, polyaniline, poly(amide-imide), thermal stability, sensors