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Effects of Chemical Reactions on the Rheological and mechanical Properties of PC/LCP Blends
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Rheological and mechanical properties of polycarbonate-liquid-crystalline polymer blends with controlled chemical reactions
No full textChemical reactions can occur during the melt blending of polymers containing an ester group because ester groups are usually unstable at high temperatures; this instability generally deteriorates the mechanical properties of blends. Here, effects of chemical reactions on the rheological and mechanical properties of polycarbonate (PC)/liquid-crystalline polymer (LCP) blends are carefully investigated to determine a method for minimizing such undesirable impacts. For comparison, a physical blend, in which chemical reactions were minimized, was prepared at 300 degreesC in a twin-screw extruder. Both shear viscosity and complex viscosities of reactive blends were lower than those of physical blends, being almost proportional to [(M-w) over bar](3.4) as a result of depolymerization and transesterification. Because of the enhanced miscibility, the tensile modulus of reactive blends increased compared with that of physical blend, according to the increase in the degree of incorporation (DI). It was also possible to increase tensile modulus if triester was added to the reactive blends. (C) 2001 John Wiley & Sons, Inc
Effects of chemical reactions on the properties of polycarbonate liquid crystalline polymer blends
No full textEffects of chemical reactions on the properties of the polycarbonate (PC)/ liquid crystalline polymer (LCP) blends are considered here. Not only thermal and rheological behaviors, but also morphology and molecular weight change are investigated. Reactive blends were prepared in a cylindrical flask at 300 degrees C with varying processing time in the presence of a catalyst by the melt-phase reactions. For comparison, physical blends, in which chemical reactions were minimized, were also prepared at 300 degrees C in a twin-screw extruder. It seems that transesterification and repolymerization did not occur, but depolymerization reaction took place slightly in PC/LCP physical blends. In reactive blends, however, transesterification and repolymerization as well as depolymerization reaction took place simultaneously. The depolymerization reaction occurred mainly at an early stage of processing; whereas, repolymerization reaction becomes especially dominant after some time (more than 30 min) in the presence of the catalyst, which had a great impact on its molecular weight. Also, chemical reactions changed the glass transition temperature and morphology as well as rheological behavior, which resulted in the enhanced miscibility in reactive blends. (C) 1999 John Wiley & Sons, Inc
Effects of chemical reaction on the properties of reactive blends between poly(butylene terephthalate) and liquid crystalline polymer
No full textIn order to understand the effects of chemical reaction on the properties of the reactive blend prepared by the melt-phase reaction of poly(butylene terephthalate) and liquid crystalline polymer (LCP), the crystallization behavior, complex viscosity and the molecular weight of the blends were studied. Because of the hindered crystallization due to the presence of the melt phase LCP, the crystallization temperature of the PBT/LCP blend decreased with increasing LCP content. The trans esterification reaction had no effect on the crystallization behavior and complex viscosity, except for A2 sample (PBT90/LCP10 reactive blend at 260 degrees C for 1 hour) and B2 sample (PBT70/LCP30 reactive blend at 260 degrees C for 1 hour). The reactive blends showed the fast crystallization due to annealing and increased the molecular weight due to the end-to-end reaction
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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