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An experimental correlation between the non‐linear behaviour of commercial polyethylene melts in LAOS flow, and the pressure fluctuations associated with melt flow instabilities developed in capillary rheometry are presented. Polyethylene melts with enhanced non‐linear behaviour under LAOS conditions present larger pressure fluctuations during capillary extrusion, and consequently, larger surface distortions on the extrudate. The combination of both methods can be a tool to predict the development of melt flow instabilities in the extrusion process of polyethylene melts, and can elucidate their correlation with material structural properties ($\overline M _{\rm w}$, MWD and topology).

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A new method for the fabrication of microstructured polymer surfaces possessing features with different 3D geometries is reported. Controlled micromolding using masters with 2D topographies and fluid elastomeric precursors with various viscosities and crosslinking kinetics yielded homogeneously structured surfaces possessing microtubes and concave and convex hemispheres with defined dimensions. This fabrication strategy does not require sophisticated 3D structuring equipment and can be extended to other materials, dimensions and geometries.

Plasticating extrusion is probably the most important single operation in polymer processing. Extruders are a fundamental part of any extrusion (e.g., for producing pipes, profiles, blown and flat film, mono and multi-filaments, coated wire) and compounding line (e.g., for the incorporation of additives in general, polymer modification and polymer blending), and are also used in blow molding and injection molding machines, although in modified form.Intermeshing twin-screw extruders have found special application niches where their characteristics are used with greater advantage. Counter-rotating machines are nowadays the standard choice for extruding PVC dry blends, given their positive pumping characteristics, narrow residence time distribution and relatively low viscous dissipation as compared to conduction heat transfer (Rauwendaal, 1990). The relatively gentle thermo-mechanical environment that is created by a proper screw design and an adequate definition of the mechanical gaps, together with the inherent low screw speeds, is well suited to the limited thermal stability and the high viscosity levels of unplasticized PVC compounds (Covas et al, 1988). The co-rotating solution is often used for compounding operations, mainly because its distributive and dispersive mixing capabilities are quite good and, like the residence time distribution, can be controlled by exploring the geometrical flexibility (modular construction) of the equipment and the range of processing conditions than can be selected (Todd, 1998). Co-rotating extruders are used in important applications such as the compounding of filled polymer systems and masterbatches, the homogenization of polymer melts, the modification of polymers and the preparation of incompatible polymer blends (Xanthos, 1992;Todd, 1998). Very often, the last two operations involve, apart from polymer processing, chemical reactions. Classical examples are the peroxide-induced degradation of polypropylene to prepare grades with controlled rheology, and the grafting of maleic anhydride onto polyolefins to improve their compatibility with other polymers, respectively. A variety of other reactions/applications could also be cited (Xanthos, 1992, Utracki, 1994.The input of thermal energy and mechanical stresses to the polymer system upon flow in the extruder, which are determined by the geometry of the equipment and by the operating conditions, will cause

ABSTRACT:The addition of small amounts of liquidcrystalline polymers to thermoplastics leads to the formation of in situ-reinforced materials, with improved processability and mechanical properties. Nevertheless, the lack of adhesion between the thermoplastic and the liquid-crystalline polymer often occurs, thus requiring the use of compatibilizers. In this case, the results of several previous works show that there is an improvement of strength, usually accompanied by a decrease of toughness and, thus, the interest of LCP/TP blends for industrial applications will certainly increase if both strength and toughness are obtained. Additionally, the emphasis of previous studies has been on the evaluation of the properties of the blend under stationary conditions and not under non-stationary ones, which are, in fact, those most relevant to processing sequences. Thus, the present work focuses on the influence of type of compatibilizer on the mechanical and rheological properties of polypropylene/LCP blends under nonstationary conditions. In terms of mechanical properties, the traditional increase of tensile strength was obtained for all compatibilizers, which was essentially due to the formation, during processing, of thinner and longer fibrils of LCP dispersed in the matrix than those observed for the noncompatibilized blends. Additionally, an improvement of the impact strength and flexural modulus was also observed for the blend in which a compatibilizer with an elastomeric nature was used. Rheologically, the experiments most sensitive to the structure were those performed in transient shear, with an increase of the transient stress (in the form of an overshoot) of different magnitudes being observed for the different compatibilizers.