ABSTRACT:In this study, we investigated the synthesis of high-impact polystyrene through a series of (batch and bulk) polymerizations of styrene in the presence of 6 wt % polybutadiene. The reactions with rubber involved three stages: dissolution, prepolymerization, and finishing. The prepolymerizations were isothermal (at 70°C) and nonisothermal (with an initial heating period from 70 to 120°C). Purely thermal reactions were compared with chemically initiated polymerizations involving tert-butyl peroctoate (TBPO), 2,2Ј-azobisisobutyronitrile (AIBN), and their mixtures. Most prepolymerizations involved a stirring rate of 125 rpm. The particle morphology was mainly determined by the evolution of the grafting efficiency, stirring rate, and system viscosity during prepolymerization. In the nonisothermal prepolymerizations with pure AIBN, the grafting efficiency was lower than in equivalent prepolymerizations without an initiator, yielding unstable emulsions and a poor final morphology. In the nonisothermal prepolymerizations with pure TBPO, a large amount of graft copolymer was produced early in the prepolymerization, yielding a submicrometer core-shell morphology. The particle size and morphology could be controlled by the appropriate adjustment of the recipe and the prepolymerization conditions.

No abstract

No abstract

The aim of the present study is to investigate the synergistic effect of silicon and aluminum content on the austeniteferrite transformation temperatures on cooling (Ar3, Ar1) in non-oriented (GNO) Al-Si-low carbon electrical steel strips. Two specimens with different Al contents: A=0.22 wt% and B=0.61 wt%Al, were analyzed by "in-situ" high temperature X-ray diffraction experiments. The samples were austenitized at 1050°C for 5 minutes and sequentially cooling in a stepwise manner by steps of 10°C inside an environmental chamber installed in a Philips X'Pert multi-purpose diffractometer. X-ray diffraction patterns were recorded every 10°C during cooling from 1000 to 720°C. The austenite to ferrite transformation temperatures on cooling, Ar3 and Ar1, were estimated from changes in the intensities of the (110)-α and (111)-γ peaks as a function of temperature. The results of the experiments show that the transformation temperatures increase with increasing aluminum content from 0.22 to 0.61 wt%. In addition, the two-phase field (austenite + ferrite in the system Fe-C decreases with increasing silicon and aluminum contents for these GNO steels. X-Ray diffraction results were supported by microstructural observations of quenched samples of steel B which were subjected to similar heat treatment conditions than those applied in the X-ray diffractometer experiments. Thin ferrite films (~4-10 µm) were observed in the microstructure of specimens of steel B quenched from temperatures close to the experimental Ar3. KeywordsGNO steel; In-situ X-ray diffraction; Austenite-ferrite transformation; Electrical steel; Thin ferrite film.Efecto del contenido de aluminio sobre la temperatura de transformación austenita-ferrita en aceros de bajo carbono (Al-Si) eléctricos de grano no-orientado laminados en caliente ResumenEl objetivo del presente trabajo es investigar el efecto del contenido de aluminio y silicio sobre la temperatura critica de transformación, durante el enfriamiento, en aceros eléctricos de grano no-orientado (GNO) de bajo carbono laminados en caliente. Dos muestras, con diferentes contenidos de aluminio: A=0,22 y B=0,61 % en peso, fueron analizadas mediante la técnica in-situ de difracción de rayos X a alta temperatura. Las muestras fueron austenizadas a 1.050°C durante 5 min y, subsecuentemente, enfriadas de manera escalonada cada -10°C dentro de la cámara de alta temperatura instalada en un difractometro Philips X'pert. Los patrones de difracción fueron registrados cada -10°C durante el enfriamiento desde 1.000 hasta 720°C. La temperatura de transformación austenita -ferrita, Ar3, fue estimada a partir de los cambios en la intensidad de los picos (110)-α y (111)-γ en función de la temperatura. Los resultados de dichos experimentos mostraron que la temperatura de transformación, Ar3, aumenta con el incremento del contenido de aluminio, desde 0,22 a 0,61 % en peso. Adicionalmente, el rango bifásico (austenita + ferrita) en el sistema Fe-C disminuye con el incremento de aluminio y silicio en los aceros experi...