Shear-induced crystallization of polyamide 11

Autor: Regine Boldt, Maria Laura Di Lorenzo, Katalee Jariyavidyanont, Salvatore Mallardo, René Androsch, Pierfrancesco Cerruti, Alicyn M. Rhoades
Rok vydání: 2021
Předmět:
Zdroj: Rheologica acta
(2021). doi:10.1007/s00397-021-01264-6
info:cnr-pdr/source/autori:Katalee Jariyavidyanont, Salvatore Mallardo, Pierfrancesco Cerruti, Maria Laura Di Lorenzo, Regine Boldt, Alicyn M. Rhoades, René Androsch/titolo:Shear-induced crystallization of polyamide 11/doi:10.1007%2Fs00397-021-01264-6/rivista:Rheologica acta (Print)/anno:2021/pagina_da:/pagina_a:/intervallo_pagine:/volume
ISSN: 1435-1528
0035-4511
Popis: Shear-induced formation of crystal nuclei in polyamide 11 (PA 11) was studied using a conventional parallel-plate rheometer. Crystallization of PA 11 after shearing the melt at different rates for 60 s was followed by the evolution of the complex viscosity. The sheared samples showed in an optical microscope a gradient structure along the radius, due to the increasing shear rate from the center to the edge. The critical shear rate for shear-induced formation of nuclei was identified at the position where a distinct change of the semicrystalline superstructure is observed, being at around 1 to 2 s−1. Below this threshold, a space-filled spherulitic superstructure developed as in quiescent-melt crystallization. Above this value, after shearing at rates between 1 and 5 s−1, an increased number of point-like nuclei was detected, connected with formation of randomly oriented crystals. Shearing the melt at even higher rates led to a further increase of the nuclei number and growth of crystals oriented such that the chain axis is in parallel to the direction of flow. In addition, optical microscopy confirmed formation of long fibrillar structures after shearing at such condition. The critical specific work of flow of PA 11 was calculated to allow a comparison with that of polyamide 66 (PA 66). This comparison showed that in the case of PA 11 more work for shear-induced formation of nuclei is needed than in the case of PA 66, discussed in terms of the chemical structure of the repeat unit in the chains. Graphical abstract
Databáze: OpenAIRE
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