The possibility of controlling the final morphology, and thus the resulting mechanical and functional properties, of semicrystalline polymers based on the study of polymer crystallization stimulated by flow is highly intriguing. Recent advances in experimental techniques that allow in situ measurements of material morphology under deformation have escalated research in this subject area. However, despite of the huge efforts spent, the description of the evolution of morphology under shear conditions is still challenging and even the basic principles of the phenomenon are not well understood yet. In this work, experiments of nucleation density and growth rate of spherulites were carried out under continuous shear in a range of temperature (138-144 °C) and shear rate (0-0.30 s -1 ) which, although narrow in absolute, can be considered quite wide taking into account the experimental difficulties presented by this kind of tests. Collected data were analyzed with the aim of determining scaling rules which can describe the effect of flow on crystallization kinetics. It was found that a proportionality exists between nucleation rate and spherulitic growth rate under flow, suggesting that whatever the controlling mechanism for the enhancement of nucleation rate is, it has a similar effect also on growth rate. The effect of flow on nucleation and growth rates was attributed to the increase of the melting temperature due to flow. In turn, the melting temperature estimated for the tests conducted in the whole range of temperatures and shear rates was found to be dependent on the Weissenberg number.
The automotive industry needs to produce plastic products with high dimensional accuracy and reduced weight, and this need drives the research toward less conventional industrial processes. The material that was adopted in this work is a glass-fiber-reinforced polyamide 66 (PA66), a material of great interest for the automotive industry because of its excellent properties, although being limited in application because of its relatively high cost. In order to reduce the cost of the produced parts, still preserving the main properties of the material, the possibility of applying microcellular injection molding process was explored in this work. In particular, the influence of the main processing parameters on morphology and performance of PA66 + 30% glass-fiber foamed parts was investigated. An analysis of variance (ANOVA) was employed to identify the significant factors that influence the morphology of the molded parts. According to ANOVA results, in order to obtain homogeneous foamed parts with good mechanical properties, an injection temperature of 300 °C, a high gas injection pressure, and a large thickness of the parts should be adopted.
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