Morphology of polymer blends in the melting section of co‐rotating twin screw extruders

Abstract

The properties of polymer blends are largely determined by the morphological structure of the polymer combinations that are involved. In terms of extruder design, this means it is necessary to have models available for estimating the development of the morphology over the length of the screws. Since significant morphological changes are observed in the melting section, in particular, is it necessary to analyze not only the plasticizing process for binary material combinations but also the initial formation and further development of the morphology in this section of the extruder.In the framework of this study, experimental investigations were conducted into polypropylene/polyamide 6 (PP/PA6) blends with small components (by weight) of the disperse PA phase. Apart from varying the process conditions of screw speed and throughput, the viscosity ratio was also varied through the use of two different PP grades. The degree of melting and the development of the morphology over the length of the screws were determined for the individual tests. The study of blend morphology in the melting section reveals key findings that must be taken into account for modeling the initial formation and further development of the morphology. It is very clear that, on the second component, which melts at higher temperatures, a kind of melt film removal occurs at the surface of the granules as they melt. The drops of second component in the melting section, which are directly adjacent to components that have not yet fdly melted in some cases, have already assumed dimensions (in the km range) similar to those that are seen at the end of the extrusion process. This means that, in the melting section of the twin-screw extruder, no volumes become detached from or are worn off the already-molten granule surfaces. An evaluation of scanning electron micrographs also shows that, in the melting section of co-rotating twin-screw extruders, virtually all the degradation mechanisms that can essentially be distinguished, such as quasi-steady drop breakup, folding, end pinching and decomposition through capillary instabilities, take place in parallel.

Evolution of morphological and rheological properties along the extruder length for blends of a commercial liquid crystalline polymer and polypropylene

“…The study of the evolution of polymer blend morphology during processing receives more and more attention and different techniques have been used in order to obtain an improved knowledge on this subject (see, for example, the works of Shi and Utracki [1], Tyagi and Ghosh [2], Potente et al [3,4] and Scott and Macosko [5]). During compounding, several factors influence the final morphology, including shear, elongational and hydrodynamic forces involved during compounding and also the rheological properties of the components of the blend.…”

“…This deformation processes usually starts upon melting, where the formation of droplets and/or elongated structures is expected [2]. Nevertheless, break-up processes or coalescence processes will also start and the ratio between the interfacial forces (that tend to keep the drop spherical) and the viscous forces (that tend to elongate the droplets) will define which of these will dominate [1,4]. In the mixing zones of the extruder, the shear forces are increased relatively to the previous stages, and, therefore, the breaking processes of the elongated structures will be dominant.…”

Influência das condições de processamento na obtenção de blendas PBT/ABS

“…A razão de viscosidades diminuiu com aumento da temperatura, pelo fato da viscosidade do PC ser mais sensível à temperatura que a viscosidade do ABS. Potente H. et al [22] estudaram a morfologia de blendas de polipropileno (PP)/poliamida 6 (PA6), na região de mistura dos discos misturadores em ERDCI. Analisando o desvio padrão da amostragem não foi observado uniformidade no tamanho das partículas, porém diâmetro médio das partículas diminuiu desde o início dos discos misturadores até o final na ponta das roscas, provavelmente porque a razão de viscosidades foi próxima a unidade, conforme foi previamente constatado na curva reométrica dos materiais.…”

Evolução da morfologia de fases de blendas PA6/AES em extrusora de dupla rosca e moldagem por injeção

“…Este fenômeno pode estar relacionado a capacidade da matriz da extrusora em proporcionar a ruptura das partículas devido à tensão elongacional desenvolvida na entrada da matriz. Várias investigações têm sido feitas para monitorar a evolução da morfologia de fases durante a extrusão [8][9][10][11][12][13][14][15][16][17] e em geral têm-se observado uma redução contí-nua no tamanho das partículas ao longo da extrusora para blendas não compatibilizadas, o que é atribuído à ação de elementos de mistura [11] . Entretanto, observou-se também aumento no tamanho das partículas durante o processamento por extrusão usando perfis de rosca com a presença de elementos de mistura [8] .…”

“…); composição das blendas; compatibilização (tipo, concentração, peso molecular dos grupos funcionais); intensidade de mistura (tipo de extrusora, configuração da rosca, condições de processamento, etc.). Portanto, é de extrema importância a compreensão da evolução da morfologia de fases das blendas durante o processamento e sua correlação com as condições de processamento utilizadas [7][8][9][10][11][12][13][14][15][16][17] .…”