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Type: Artigo de periódico
Title: Phase transitions and relaxation processes in ethylene-vinyl acetate copolymers probed by fluorescence spectroscopy
Author: Yamaki, SB
Prado, EA
Atvars, TDZ
Abstract: The steady-state fluorescence of pyrene and anthracene are used to investigate the relaxation processes of several random ethylene-co-vinyl acetate copolymers, EVA, with defined comonomer compositions (EVA-9, EVA-18, EVA-25, EVA-33 and EVA-40). The temperature of the relaxation processes are compared with those of low-density polyethylene (LDPE) and poly(vinyl acetate) (PVAc). The polymer relaxation processes are assigned to T-g = 300-310 K (glass transition temperature of the PVAc); T-alpha = 270-300 K (relaxation processes of the ethylene units present in LDPE and EVA); T-g = 220-250 K (glass transition of the LDPE and of the EVA); T-gamma or T-beta = 160-190 K (relaxation processes of interfacial defects of methylenic chains of LDPE and rotation of the acetate group of the PVAc and the EVA); and T-gamma = 90-130 K (relaxation processes of small sequences of methylene units of LDPE and end groups of PVAc). An Arrhenius-type function was employed as an attempt to represent the experimental data of fluorescence intensity versus temperature above the gamma-relaxation temperature. As obtained with other techniques, there is not a simple relationship between the polymer relaxation processes and the vinyl acetate content that can be explained by the morphology in these copolymers. (C) 2002 Elsevier Science Ltd. All rights reserved.
Subject: ethylene-co-vinyl acetate copolymers
phase transitions
relaxation processes
fluorescence spectroscopy
Country: Inglaterra
Editor: Pergamon-elsevier Science Ltd
Citation: European Polymer Journal. Pergamon-elsevier Science Ltd, v. 38, n. 9, n. 1811, n. 1826, 2002.
Rights: fechado
Identifier DOI: 10.1016/S0014-3057(02)00067-8
Date Issue: 2002
Appears in Collections:Unicamp - Artigos e Outros Documentos

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