resumo
This work aims to verify the impossibility mentioned in the literature of saturating the crystallization kinetics of pre-sheared metallocene polyethylene melts. Similarly to results reported for other materials, and contrary to other published works, an acceleration of crystallization kinetics with the increase of shear strain and its saturation at large strain values was found. Similar strain values, with the same temperature variation, were evaluated with independent experiments using different devices, which allowed us to identify the steady state as the melt state responsible for the saturation of crystallization kinetics. Since this is a partially disentangled melt state, with viscosity lower than that of fully entangled (relaxed) melts, we assign the acceleration of crystallization kinetics by application of shear, and its saturation, mainly to the facilitated diffusion of chain segments to the lamellae growth front. This conclusion is supported additionally with the experimental results of other authors.
palavras-chave
POLYMER MELTS; ISOTACTIC POLYPROPYLENE; ISOTHERMAL CRYSTALLIZATION; MEMORY; ENTANGLEMENTS; DISENTANGLEMENT; DYNAMICS; BEHAVIOR; FLOW
categoria
Chemistry; Polymer Science
autores
Krakowiak, J; Martins, JA; Zhang, WD
nossos autores
José António da Purificação Martins
Professor CatedráticoGrupos
agradecimentos
We thank Choon K. Chai for supplying us the materials used in these experiments, Andrzej Galeski for the NMR and SEM experiments and the Portuguese Foundation of Science and Technology for funding the projects FCOMP-01-0124-FEDER-007151 (PTDC/CTM/68614/2006). This work was supported by the European Community fund FEDER and project 3599/PPCDT.