Poli(oxido de etileno-co-epicloridrina) : degradação foto-oxidativa e termica, e blenda com polipropileno

AUTOR(ES)
DATA DE PUBLICAÇÃO

2003

RESUMO

Polymers derived from ethylene oxide and epichlorohydrin, like poly(epichlorohydrin-co-ethylene oxide) elastomer, are studied as polymer electrolyte for application in photo-electrochemical devices. These materiaIs present the ability to form complexes with alkali salts, presenting high ionic conductivity. In these devices the conversion of the solar energy depends of the transport of ions by the polymer electrolyte, which consist in the coordination of the cation with various oxygen atoms of the polymeric chain. These devices are submitted to different radiations, mainly UVB, UVA, and visible. Hence, during their use there is the possibility of degradation of the polymer electrolyte due to the absorption of light by the polymer itself or by inherent or inadvertent impurities containing chromophores. During the degradation process there is the formation of new functional groups and chain-scission. These events change the distance between the oxygen atoms of the polymeric chain difficulting the ionic transport, leading to a lower efficiency and stability of the photo-electrochemical devices. Thus, the objective of the present work was to study the photo-oxidative and thermal degradation mechanism of the poly(epichlorohydrin-co-ethylene oxide) elastomer. The photo-oxidative degradation was studied by infrared spectrophotometry, derivatization reactions, gel permeation chromatography and scanning electron microscopy. From these results it was possible to observe that the elastomer degradation is characterized by degradation products containing carbonyl, hydroxyl and esters groups. Its generation is mainly due to the free radicaIs resulting from the homolytic break of C-O bonds, in both co-monomer units, and C-Cl bonds, from the chloromethylene group of the epichlorohydrin co-monomer unit. The formation of hydroperoxides was also observed in the initial stage of the degradation process, they are responsible for the formation of different carbonyl containing products. Thus, in this study it was possible to propose a mechanism for the photo-oxidative degradation of the elastomer. Aiming to propose a mechanism for the thermal degradation and to evaluate the degradation reaction rate constants at different temperatures, the thennal degradation of the elastomer was also studied using the pyrolysis-GC-MS technique. Through this technique, which provides the identification of the volatile pyrolyses products of degradation by GCMS, it was observed that the thermal degradation of the elastomer occurs by homolytic chain scission localized at the C-O and C-C bonds, and by hydrogen abstraction from a carbon atom adjacent to the C-O bond. Thus, a mechanism for the thermal degradation of the elastomer was proposed. The average values found for the overall rate constants of thermal degradation reaction of the elastomer, from sequential pyrolyses, were 0.15 ± 0.03; 0.25 ± 0.03, and 0.6 ± 0.2 s at 350, 387, and 400°C, respectively. In addition, the values obtained in this study are appreciably higher than those reported in the literature for other polymeric materiaIs, like, e.g. polyvinyl chloride and polychloroprene. This confirmed the high instability of the material in comparison to similar chlorinated polymers. In this work the physico-chemical properties of the blends based on poly(epichlorohydrin-co-ethylene oxide) and polypropylene, prepared with a compatibilizer, and the effect of its dynamic vulcanization were also evaluated. The interest of this study was to obtain a material with the properties of an elastomer but processable like a thermoplastic, thus a thermoplastic elastomer, TPE. By scanning electron microscopy and stress-strain studies it was observed that the addition of a compatibilizer (polypropylene grafted with dimethylol or maleic anhydride groups) causes a reduction in the interfacial tension between polypropylene and the elastomeric phases. The studies of resistance to solvent, according to ASTM D 471-93, showed that the blends compatibilized, or dynamically vulcanized, present a high resistance to ASTM A, B, C, and D solvents. The studies of mechanical properties show that the blends, compatibilized and dynamically vulcanized, present, in general, poorer mechanical properties than the elastomer crosslinked with ethylenethioureia. Thus, from the results obtained in this work, we propose the use of these materiaIs for the construction of fuel hoses for low temperatures uses, and fabrication of different finished parts for the automotive industries by injection molding.

ASSUNTO(S)

polipropileno termoplasticos elastomeros

ACESSO AO ARTIGO

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