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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Foam injection molding is a processing technology applied to produce a plastic part of a well‐defined shape, containing a significant fraction of voids and thus consuming less material without sacrificing mechanical properties. This technology is particularly interesting for biodegradable polymers and in particular for poly(lactic acid), PLA, since it can be adopted to save material and to avoid thermal degradation due to its high viscosity at high shear rates, which requires high temperatures in traditional injection molding process. In this work a traditional injection molding machine, modified just in the cylinder to allow the gas injection, was adopted to obtain foam injection molding of a PLA grade. In particular, the effect of back pressure on foaming was assessed. Back pressure is the pressure imposed at the back of the screw when it is returning back to prepare a new amount of material to be injected (batching phase) and thus is particularly relevant in the formation of the polymer−gas mixture. It was shown that on increasing the back pressure the percentage of foaming agent inside the injection chamber is smaller, and thus foaming is less effective. The obtained samples were characterized as far as density and mechanical properties are concerned and it was found that it was possible to reduce the density of about 25% without a significant loss of mechanical properties. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42612.

Foam injection molding is a process by which complex, thick parts with a cellular core and a compact solid skin can be manufactured. The addition of a physical blowing agent under high pressure allows the decrease of the viscosity and the glass transition temperature of the gas/polymer melt. These features of the foam injection molding are very beneficial for biodegradable polymers, in which the processability window is very narrow. In this study, morphology, rheological, and mechanical properties of parts with a complex shape, obtained by foam injection molding, were analyzed. In particular, two commercial grades of poly(lactic acid) having different rheological behavior were adopted to obtain foamed parts by injection molding process with nitrogen as a physical blowing agent. For both resins, the effect of the mold opening on morphology and mechanical properties was assessed. POLYM. ENG. SCI., 58:475–484, 2018. © 2017 Society of Plastics Engineers

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From a technological point of view, poly(lactic acid) (PLA) is one of the most important polymers produced from renewable sources, due to its versatility, relatively acceptable processability, and low cost. However, a significant limitation exists in its slow crystallization kinetics, which results in amorphous products having low mechanical properties and thermal resistance. For this reason, quantitative knowledge of the phenomenon of crystallization kinetics is fundamental. In this work, the crystallization kinetics in quiescent conditions of a commercial grade of PLA was analyzed in terms of nucleation and growth rates by direct morphological observations at different crystallization temperatures (Tc) and by calorimetric analysis in isothermal and non‐isothermal conditions. The optical analysis showed a spherulitic morphology with radial growth of the lamellae. The analysis of the growth rate evidenced the α/α'‐crystals polymorphism with a transition temperature of ~120°C. Based on experimental observation, the crystallization kinetics of the two crystalline phases were assessed.