By impedance spectroscopy, Gonzalez‐Campos et al. J Polym Sci Part B: Polym Phys 2009, 47, 932–943, reported the first evidence of a glass transition in a polysaccharide. To gain a better understanding on the molecular relaxations in polysaccharides, we study composites of chitosan (CS)/silver nanoparticles (AgnP) films by dynamic mechanical analysis (DMA) and dielectric spectroscopy in the 2–250 °C temperature range. CS/AgnP films conductivity increases in two orders of magnitude in comparison with pristine CS. Three relaxation processes ascribed to the α‐relaxation, σ‐relaxation, and degradation process have been observed for the first time. Molecular dynamics and conductivity strongly depends on moisture content; since a plasticizing effect on the glass transition temperature is observed, similarly the increase in AgnP weight percent leads to a glass transition temperature decrease and also increases CS thermal stability. Infrared spectroscopy analysis reveals the AgnPs interaction with OH, NH2, CO.NH2, and COC groups implying an evident redistribution of the vibration bands for these groups. These new bonds affects the molecular dynamics of the CS chain bearing important changes in relaxations processes when compared CS/AgnP composite with pristine CS. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 739–748, 2010

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Adsorption stand out among other standard techniques used for water treatment because of its remarkable simplicity, easy operation, and high removal capability. Expanded graphite has been selected as a promising agent for oil spill adsorption, but its production involves the generation of corrosive remnants and massive amounts of contaminated washing waters. Although the advantageous use of the H2O2–H2SO4 mixture was described in 1978, reported works using this method are scarce. This work deals with the urgent necessity for the development of alternative chemical routes decreasing their environmental impact (based on green chemistry concepts), presenting a process for expanded graphite production using only two intercalation chemicals, reducing the consumption of sulfuric acid to only 10% and avoiding the use of strong oxidant salts (both environmentally detrimental). Three process parameters were evaluated: milling effect, peroxide concentration, and microwave expansion. Some remarkable results were obtained following this route: high specific volumes elevated oil adsorption rate exhibiting a high oil–water selectivity and rapid adsorption. Furthermore, the recycling capability was checked using up to six adsorption cycles. Results showed that milling time reduces the specimen’s expansion rate and oil adsorption capacity due to poor intercalant insertion and generation of small particle sizes.

This study aimed to obtain a second-generation snack by extrusion from the by-product of rice milling enriched with amaranth. The raw material used was amaranth flour (AF), rice starch (NS) and modified rice starch (MS), which were evaluated by the analysis of substitution degree (SD), differential scanning calorimetry (DSC), viscosity (RVA), Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD). The snacks were expanded by extrusion and microwave oven, as a reference method. The samples were evaluated in hardness (D), expansion index (EI), apparent density (DAP), and protein content (P). Afterward, the optimized samples were evaluated by scanning electron microscopy (SEM) and resistant starch (RS). During the thermal characterization, a clear trend in the decrement in gelatinization temperatures was observed (78.35 to 63.90 °C in NS and MS respectively). The curves obtained in RVA analyses showed typical behavior of native (6.35 Pa.s) and extruded starches (2.88 Pa.s), with a significant decrease in viscosity peak. Through the analysis of FT-IR, the introduction of the functional acetyl group (stretching at a wavelength of 1735 cm−1) was corroborated. Snack samples results showed a maximum hardness in MS, with a value of 121 N, and the NS (100%) presented the highest EI value (1.41). The lowest DAP values were obtained for the MS (0.48 g/cm3, 100%) and AF (0.49 g/cm3, 100%) samples. P increased to a higher concentration of AF. In the optimum formulation, the SEM image showed that the expanded microwave sample increased the porosity and obtained an RS value of 8.2%. The formulation obtained in the present study presents high characteristics to be used in the development of a healthy snack.

The molecular dynamics of poly(vinyl alcohol) (PVA) were studied by dielectric spectroscopy and dynamic mechanical analysis in the 20-300 C range. The well-established plasticizing effect of water on the glass-transition temperature (T g ) of PVA was revisited. Improper water elimination analysis has led to a misinterpretation of thermal relaxations in PVA such that a depressed T g for wet PVA films (ca. 40 C) has been assigned as a secondary b relaxation in a number of previous studies in the literature. In wet PVA samples, two different Vogel-Fulcher-Tammann behaviors separated by the moisture evaporation region (from 80 to 120 C) are observed in the low-(from 20 to 80 C) and high-(>120 C) temperature ranges. Previously, these two regions were erroneously assigned to two Arrhenius-type relaxations. However, once the moisture was properly eliminated, a single non-Arrhenius a relaxation was clearly observed. X-ray diffraction analysis revealed that the crystalline volume fraction was almost constant up to 80 C. However, the crystallinity increased approximately 11% when temperature increased to 180 C. A secondary b c relaxation was observed at 140 C and was related to a change in the crystalline volume fraction, as previously reported. V C 2012 Wiley Periodicals, Inc. J Appl Polym Sci 125: [4082][4083][4084][4085][4086][4087][4088][4089][4090] 2012

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The present work deals with the study of some aluminum (Al) composites reinforced with metallized-graphite (MG) particles prepared by mechanical milling and powder metallurgy routes. Density, morphology evolution and mechanical performance of composites were investigated as a function of MG concentration and milling time. The as-milled powders were characterized by X-ray diffraction and optical/electron microscopy; meanwhile, the mechanical testing was carried out on cylindrical specimens prepared from powders by powder metallurgy. Evidence reveals that high-energy ball milling induce a homogeneous dispersion of graphite nanoparticles in the Al matrix; this is related to an enhancement of hardness and strength response of studied composites. The composite sample with 0.5% MG addition (in weight) reached an increase of 40% on hardness and 50% on strength (compared with pure Al sample); nevertheless an adverse effect was observed with longer milling and/or higher MG concentration.