In this review the models applied for the description of non-Newtonian liquids were presented. Highly filled polymer melts showing distinct yield stress are such liquids. The effects of forces of geometrical and physical interactions among the filler particles on the properties were discussed. These interactions forces depend on the type, size and shape of filler particles and in case of fibers also on their orientation. The deformations and flow of fibers assemblies in the melt under shear stress were discussed. The equations used for description of three-or two-dimensionally oriented fibers sets are presented. Key words: polymer melt, filler, modeling of rheological properties, viscosity, yield stress, shear rate.CHARAKTERYSTYKA REOLOGICZNA W ZAKRESIE MA£YCH SZYBKOOECI OECINANIA STOPÓW POLIMERÓW NAPE£NIONYCH W£ÓKNAMI. Cz. I. MODELOWANIE W£AOECIWOOECI REOLO-GICZNYCH Streszczenie -W pracy przegl¹dowej przedstawiono modele stosowane do opisu w³aoeciwooeci reologicznych cieczy nienewtonowskich, którymi s¹ stopy polimerów o wysokim stopniu nape³nienia wykazuj¹ce wyraŸn¹ granicê plastycznooeci. Omówiono wp³yw na omawiane w³aoeciwooeci si³ oddzia-³ywañ geometrycznych i fizycznych miêdzy cz¹stkami nape³niacza. Si³y tych oddzia³ywañ zale¿¹ od rodzaju, wielkooeci i kszta³tu cz¹stek nape³niacza, a w przypadku w³ókien, tak¿e od ich orientacji. Przedyskutowano tak¿e deformacje i przep³yw zespo³ów w³ókien w stopie pod wp³ywem naprê¿eñ oecinaj¹cych. Przedstawiono równanie stosowane w przypadku zespo³ów w³ókien o orientacji trójwymiarowej oraz dwuwymiarowej. S³owa kluczowe: stop polimeru, nape³niacz, modelowanie w³aoeciwooeci reologicznych, lepkooeae, granica plastycznooeci, szybkooeae oecinania.

A frequent problem in the production of metallocene linear low-density polyethylene (mLLDPE) films is the occur-rence of flow instabilities, e.g. sharkskin, or degradation of material, which limit the production rate and decrease the product quality. If such problems arise, the question is what causes these phenomena and how they can be avoided. With the aim of understanding these problems and providing some guidelines for their suppression, rheological measurements together with modelling of these melt flows are often employed. In the present study, flow behaviour of two commercially available mLLDPEs was determined and used for the process simulation. The paper shows that the capillary-rheology data together with 2D finite element method can be used for the prediction of sharkskin phenomenon as well as degradation of mLLDPE melts in film blowing dies. It also reveals that the degradation of the materials in these dies can be quantified through wall shear stress. Finally, the paper describes how these findings can help optimize the flow channel in the film blowing die to avoid the undesirable flow phenomena.

Rheological behavior of fibre-filled polymer melts at low shear rate Part II. EXPERIMENTAL INVESTIGATION **) Summary-In this study, rheological properties of carbon fibre-filled polypropylene and polyethylene melts at low shear rate were measured using a cone-plate rheometer. The melts with high fibre loading show complex shear flow depending on the fibre concentration, its length and length distribution, as well as on shear rate and matrix characteristics. The existence of yield stress and time-dependent or shear-strain-dependent properties are also discussed and compared with previous results. The shear flow in the narrow gap of cone-plate rheometer influences the fibre assembly. However, the effect of low shear rate on the structure of fibre assembly is negligible.