On the curing kinetics of unsaturated polyesters with styrene

The curing kinetics of a general purpose unsaturated polyester (UP) with styrene was studied by differential scanning calorimetry and dielectric capacitance measurements. Benzoyl peroxide was used as initiator. Results showed that there is a complete change in the phenomenological kinetics, in different temperature ranges. At low temperatures (70–90°C), the rate went through a maximum and then showed a first-order decay. At high temperatures (100–160°C) a second-order kinetics was suitable for all the conversion range. At T > 160°C another mechanism took place when the initiator amount was less than a critical value. From the changes in the dielectric capacitance it was inferred that the conversion rate of UP unsaturations followed a first-order decay after a certain conversion, with an activation energy close to values reported for diffusion of UP radicals. Possible free radical mechanisms accounting for experimental observations are discussed.     

The effect of cooling rate on the impact performance and dynamic mechanical properties of rotationally molded metallocene catalyzed linear low density polyethylene

This article examines changes to the morphology of rotationally molded metallocene catalyzed linear low density polyethylene brought about by varying the cooling rate during processing. These changes in morphology lead to variations in the impact performance, which is reflected in the dynamic mechanical characteristics of the materials. Various analytical techniques are used in an attempt to explain the differences in impact behavior. Slow cooling is shown to result in high crystallinity, and in the formation of large spherulites, which in turn is detrimental to the impact performance of the material, particularly at low temperatures. The high crystallinity corresponds with a shift in the β transition of the material to a higher temperature, and is shown to result in a higher brittle–ductile transition. A case study was also carried out on samples from a finished part provided by an industrial molder, one section of which failed in a brittle manner when impact tested while the other failed in a ductile manner. Microscopy results showed that the brittle material had large spherulites at the inside surface, while the ductile material showed incipient degradation at this surface, which has previously been shown to be of benefit to impact strength in rotationally molded parts. Dynamic mechanical studies again showed a β transition at a higher temperature in the brittle samples. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1963–1971, 2006     

Modification of porous copolymers network based on acrylonitrile

Summary The preparation of a chelating ion-exchange network based on acrylonitrile was carried out by chemical modification with hydroxylamine. The beads of resin were synthesized by aqueous suspension copolymerization of acrylonitrile (AN), styrene (STY) and divinylbenzene (DVB). The influence of diluent used in the suspension polymerization on the structure of the resulting copolymers was evaluated. The diluents employed were heptane (HEP), toluene (TOL) and anisole (ANI). It was found that the AN incorporation into copolymer structure was dependent on the diluent used. Conversion of nitrile groups into the amidoxime was conducted by treatment with hydroxylamine under alkaline solution. The resins were characterized by apparent density, surface area, average pore diameter, elemental analysis (CHN), FTIR and optical microscopy. Based on the results obtained, it was possible to control the porosity by diluent employed in the synthesis and to modify chemically a resin containing nitrile groups by hydroxylamine reaction. Received: 6 October 2001/Revised version: 2 April 2002/ Accepted: 11 April 2002     

Comparative study of homogeneous and heterogeneous styrene polymerizations with Ni(acac)2/MAO catalytic system

Styrene polymerization was carried out with Ni(acac)₂/MAO and Ni(acac)₂/SiO₂/MAO. The influence of reaction parameters (Al/Ni mole ratio, catalyst concentration, temperature and time polymerization) on styrene polymerization was evaluated. It was observed that both catalytic systems were affected by reaction parameters and that the heterogeneous catalyst presented higher activity than the homogeneous one. Polystyrenes with different molecular weight, stereoregularity and polydispersity were obtained. These results suggest that different active catalyst species could have been present. In addition, two types of methylaluminoxane (MAO) with different molecular weights were also evaluated as cocatalyst. As a result, the catalyst activity and stereospecificity were strongly affected by the MAO type.     

The role of Lewis bases on the improvement of the stereospecificity and activity of TiCl3/AlClEt2 catalyst system

Summary The effect of di-n-butyl ether (DBE) in the synthesis of a highly active propylene polymerization catalyst was studied. Electron-donors having ester and phosphate groups (ethyl benzoate-EB, diisobutyl phthalate-DIBP and tri-n-butyl phosphate-TBP) were added as second internal bases (IB₂) to the catalysts prepared by the reduction of TiCl₄ with AlClEt₂ (DEAC) in the presence of DBE as a first internal base (IB₁). The crystalline forms were examined for all catalyst samples by X-ray method. Special attention has been paid to the -TiCl₃ samples showing the best catalytic properties. These catalysts were evaluated in propylene polymerization in the absence and presence of external bases (EB, DIBP and DBE). The effects of internal and external bases on the catalyst activity and stereo-specificity are discussed.     

A color image watermarking framework for copyright protection of stereo images based on binocular just noticeable difference and LU decomposition

Multimedia Tools and Applications - The copyright protection of three-dimensional (3D) content is a matter of interest in artistic and creative works due to the rights of the holder for the...     

Measuring and improving the quality of development processes based on usability and accessibility

Universal Access in the Information Society - Measurement of both usability and accessibility is an important concern in software development today. However, while a great amount of attention has...     

Sharing Context-Aware Road and Safety Information

We present an integrated vehicular system for the collection, management, and provision of context-aware information on traffic and driver location. This system uses an integrated vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) communication paradigm enriched with an information management system. The infrastructure manages vehicle-detected safety hazards and other relevant information, adapting them to the vehicle's context and driver's preferences. This vehicular integrated system resembles the concept of a smart road.     

Guarino Guarini and Universal Mathematics

Guarini considered the mathematical studies to be of fundamental importance for all artists and scholars. His own knowledge of mathematics was vast and profound. The aim of this present paper is to show, through an analysis of the most substantial of his mathematical works, Euclides adauctus, along with the Appendix to this printed a few months later, the role that philosophical and mathematical studies had on his cultural formation, on the new and original research that he conducted, and on his teaching activities, while looking for traces of the mathematical sources that he consulted and cited that indicate which authors and works exerted the greatest influence on him.