In this work, melt spinning experiments were tentatively used for the determination of the elongational viscosity of polymer melts at different levels of tensile strain and strain rate. The materials examined were two high-density polyethylene grades for blow moulding with similar number-average molecular mass but different polydispersity index. The data from melt spinning tests were compared with transient extensional viscosity data obtained by uniform isothermal tensile tests, performed by means of an extensional rheometer, as well as with those produced by converging flow tests (Cogswell model). The results showed that for high strain and strain rate levels, the melt spinning experiments provide elongational viscosity data quite close to the transient extensional viscosity values obtained from the tensile tests

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Micro‐injection moulding is one of the key manufacturing technologies for thermoplastic polymeric materials for the mass production of high value miniaturized components. However, this process is not just a straightforward down scaling of the conventional injection moulding technique. Indeed, during the micro‐injection the polymer melt is forced to flow at high strain rates through very small channels in nonisothermal conditions; this can lead to complex microstructures and to parts with unexpected performances. In this work, the relationships among the processing conditions, the mechanical properties and the microstructural characteristics of polyoxymethylene miniaturized specimens obtained by injection moulding were investigated. The attention was focused on the influence of the process temperatures on the mechanical behavior, examined by uniaxial tensile tests, and on the microstructural characteristics of the specimens, examined by differential scanning calorimetry, wide‐angle X‐ray diffraction, polarized light microscopy, and dynamic‐mechanical thermal analysis. The results highlighted that material ductility in the miniaturized specimens is significantly affected by the mould temperature, because of the sample microstructure. Different degrees of orientation of polymer crystallites and different morphologies of the skin/core transition region were observed in dependence on the process temperatures. POLYM. ENG. SCI., 54:512–521, 2014. © 2013 Society of Plastics Engineers

In this work, the melt fracture behavior of microfilled polymer melts based on a high‐density polyethylene (HDPE) was investigated by means of a capillary rheometer, which operated at constant piston velocity. The microfilled melts examined had the same filler content (10 vol%), but differed for the type of filler (glass beads, discontinuous glass fibers, and talc). The results demonstrated that the presence of rigid fillers influences the melt fracture behavior of the filled melts in a way that is dependent on the type of filler dispersed in the HDPE melt. Opposite effects were induced by lamellar particles of talc and by glass fillers (either beads or fibers): the former promoted flow stability, whereas the latter fostered the occurrence of instabilities of “stick‐slip” type. The effects induced by the presence of the glass fillers on the oscillating flow that takes place when “stick‐slip” instabilities occur were also analyzed and discussed. POLYM. ENG. SCI., 54:364–377, 2014. © 2013 Society of Plastics Engineers

The present paper reports and discusses the results of a 3D finite element simulation of the injection molding process of a rubber component, including the stages of the mold filling dynamics and material curing, using the "Reactive Molding" module of the Moldflow 6.2 CAE software. A differential scanning calorimeter (DSC) and a capillary rheometer are employed to characterize the rubber material in order to obtain appropriate curing reaction and viscosity models, respectively. The model parameters so obtained are used to simulate the injection molding process for an engineering rubber component with a complex geometry having a thickness distribution that ranges from 1.5 mm to 20 mm. The computations are found in good agreement with the experimental results, indicating that reliable information on material viscosity and curing kinetic play a key role for well-founded predictions.

The study of the instability phenomena of polymer melts in capillary flows is of great technical relevance since, during an industrial die forming operation, these instabilities can give origin to a transition from a defect-free to a highly-defective extrudate. In this work, the instability phenomena exhibited in capillary flow by a blow moulding grade of high-density polyethylene (HDPE) were analyzed. In particular, by means of a capillary rheometer, which mimics polymer extrusion, the effects of specific extrusion parameters (temperature and imposed flow rate) on the oscillating flow, that takes place when "stick-slip" instabilities occur, were investigated.

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