A simple and inexpensive technique to measure molecular diffusion coefficients

The experiment proposed is simple and inexpensive and provides an accurate method for measurement of the molecular diffusion coefficient, D _m. It is a novel method that has the added advantage of easily providing data at temperatures and pressures that differ significantly from ambient values. The experimental results for naphthalene in air are in excellent agreement with the experimental values of the molecular diffusion coefficient measured by other authors. Experimental measurements of mass transfer in water were also carried out for a range of the relevant parameters. The soluble spheres used in the experiments were made of either benzoic acid or 2-naphthol, and the ranges of temperatures covered were 293–333 and 293–373 K, respectively. Using the mass transfer theory presented in this work, the molecular diffusion coefficient of the two solutes was determined, and good agreement with literature values was found.     

In vitro monitoring of surface mechanical properties of poly(L‐lactic acid) using microhardness

Poly(L ‐lactic acid) (PLLA) was immersed in a simulated body fluid (SBF) solution at 37.5°C for distinct times. The variation of the surface mechanical properties of PLLA samples with immersion time was followed by microhardness. These measurements showed that PLLA microhardness decreased significantly (～ 60%) after only 30 days of immersion. The results were explained in terms of hydrolytic degradation of the samples. The dependence of microhardness with the applied dwell time was also analyzed. The creep curves were successfully described by a power law. A decrease of the creep constant k as the immersion time increased was found. Differential scanning calorimetry was also used to analyze the changes in the physical properties of PLLA, namely in crystallinity degree (X_c) and glass transition temperature (T_g), as a function of the immersion time in SBF. A significant variation in the crystallinity degree of PLLA, initially nearly amorphous (X_c = 9%), was detected after only 3 days of immersion (X_c = 37%). The interpretation of this behavior was based on the hydrolysis process suffered by PLLA. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Modeling and optimization of reactive cotton dyeing using response surface methodology combined with artificial neural network and particle swarm techniques

Clean Technologies and Environmental Policy - This work explores the modeling and optimization of the conditions to obtain blue color intensities in the dyeing cotton process with Reactive Black 5...     

Thermal evaluation of PHB/PP‐g‐MA blends and PHB/PP‐g‐MA/vermiculite bionanocomposites after biodegradation test

This study aimed to evaluate the thermal behavior of polyhydroxybutyrate (PHB)/polypropylene grafted with maleic anhydride (PP‐g‐MA) blends and PHB/PP‐g‐MA/vermiculite bionanocomposites submitted to the biodegradation test according to ASTM G 160‐03. The blends and bionanocomposites were prepared by melt intercalation method using a single screw extruder, and then, compression molded. The thermal analyzes were performed by thermogravimetry (TG) and differential scanning calorimetry. It was verified the decrease of onset degradation temperature and the melting temperature mainly after 86 days of exposure to the simulated soil. This behavior was more pronounced in bionanocomposites because of interactions between the maleic anhydride groups and the clay favoring biodegradation, making the systems more amorphous and propitious to the attack of microorganisms. POLYM. ENG. SCI., 56:555–560, 2016. © 2016 Society of Plastics Engineers