Badania reologiczne kompozytów poliolefinowych o wysokim stopniu nape³nienia z uwzglêdnieniem charakterystyk p-v-T * *) Streszczenie-W czêoeci wstêpnej publikacji podano obszern¹ ogóln¹ charakterystykê nape³niaczy oraz omówiono mo¿liwooeci ich modyfikacji i jej wp³yw na w³aoeciwooeci uzyskiwanych z nich kompozytów. Przedstawiono wyniki w³asnych pomiarów reologicznych wysokonape³nionych (48-64 % mas.) kompozytów poliolefinowych, w których nape³nienie stanowi³ wêglan wapnia wprowadzany w postaci koncentratu i-PP/CaCO 3 do osnowy, któr¹ by³ PE-HD (tabela 1). Zastosowano przy tym tradycyjne urz¹dzenia pomiarowe, mianowicie reometr obrotowy typu sto¿ek/p³ytka (por. tabela 3), plastometr obci¹¿nikowy o zmiennym obci¹¿eniu t³oka, oraz dwuotworowy reometr kapilarny. Przebiegi uzyskiwanych za ich pomoc¹ krzywych lepkooeci kompozytów (metody typu off-line) porównywano z odpowiednimi przebiegami krzywych lepkooeci otrzymanymi na drodze pomiarów prowadzonych bezpooerednio w linii wyt³aczarskiej (metoda typu in line, reometr wyt³aczarkowy z g³owic¹ pomiarow¹ o wymiennych dyszach, rys. 3-9). Badania dotyczy³y trzech rodzajów materia³u: mieszanin PE-HD z i-PP (tabela 2, grupa R), kompozytu zawieraj¹cego koncentrat handlowy (tabela 2, grupa H) oraz kompozytu zawieraj¹cego koncentrat w³asny wytworzony w warunkach laboratoryjnych (tabela 2, grupa M). Zaobserwowano zjawisko tzw. rozrzedzania oecinaniem, czyli zmniejszania siê lepkooeci kompozytów ze wzrastaj¹c¹ szybkooeci¹ oecinania, jak równie¿ spadek tej lepkooeci ze wzrostem zawartooeci nape³niacza. Ta druga zale¿nooeae jest zauwa¿alna zw³aszcza w obszarze niewielkich szybkooeci oecinania, a niemal zanika w warunkach du¿ych szybkooeci oecinania. Porównanie krzywych lepkooeci otrzymanych metodami off-line i in-line wykaza³o istnienie analogicznych w obydwu przypadkach zale¿nooeci, pozwoli³o jednak na wykazanie znaczenia uwzglêdnienia zmian gêstooeci badanych materia³ów w toku pomiarów, a tak¿e wskaza³o na istotne znaczenie efektu pooelizgu wywo³anego przede wszystkim przez substancje modyfikuj¹ce nape³niacz (tu kwas stearynowy i woski). Pooelizg ten bezpooerednio wp³ywa na w³aoeciwooeci reologiczne kompozytów o wysokim stopniu nape³nienia modyfikowanym wêglanem wapnia. S³owa kluczowe: poliolefiny, wêglan wapnia, kompozyty, modyfikacja nape³niacza, w³aoeciwooeci reologiczne, zjawisko pooelizgu.
The article presents results of a study of the effect of selected granulometric features of plastified poly(vinyl chloride) granule on the basic parameters of extrusion. In the study, it was determined how mass polymer flow rate, power supplied to the extruder, power transmitted by the polymer, unit energy consumption, and energy efficiency of the extrusion process were related to pellet length and bulk pellet density. The tests were carried out using an extruder with a screw diameter of 25 mm and a length-to-diameter ratio of 25, and involved processing of pellets of different lengths at variable rotational speeds of the screw. It was established that the granulometric features of plastified poly(vinyl chloride) considered in this study, i.e., pellet length and pellet bulk density, affect the effectiveness of the extrusion process. It was shown that best effectiveness of extrusion is achieved with the use of a granule characterized by a pellet length that is close to the other characteristic dimension of granule -its pellet diameter.
The influence of the feed opening axis width and position in relation to the plasticizing system axis on the effectiveness of the extrusion process of poly(vinyl) chloride has been studied. The research was conducted on the extrusion line for profiles with the extruder of the screw diameter 25 mm and L/D ratio = 25. In the extruder, the extruder head was mounted with a die of a rectangular cross-section shape for extruding a sheet of a defined width and thickness. The extruder was adapted for mounting five feed segments in the feed zone of the plasticizing unit; the segments differed from one another in terms of their feed opening width, the values of which were 0.6 D, 0.7 D, 0.8 D, 0.9 D and 1.0 D, respectively, whereas the values of the longitudinal axis shift of the opening relative to the longitudinal axis of the plasticizing unit were 0.2 D, 0.15 D, 0.10 D, 0.05 D and 0.0 D, respectively, which corresponded to 5 mm, 3.75 mm, 2.5 mm, 1.25 mm and 0 mm, respectively. The effectiveness of the polyvinyl chloride extrusion process was determined by dependences of extrudate temperature, extruder screw torque, polymer mass flow rate, power supplied to the extruder and conveyed by the polymer, unit energy consumption and energy efficiency of the extrusion process on the feed opening width and its axis position relative to the plasticizing unit axis, at different values of the screw rotational speed. It was stated that the width and position of the feed opening in relation to the plasticizing system axis can be adjusted in such a way that the extrusion process will be the most effective and other conclusions were also drawn.
Extrudate properties are largely shaped by the thermal and rheological phenomena occurring in the plasticizing systems of extruders, the channels and die of the extrusion head, the calibrator, and to a lesser extent, in other parts of extrusion lines. These phenomena are affected by barrel and screw design, the type of material being processed, its granulometry, and the technological parameters of the extrusion process. Studies were carried out on the dependency of the output and selected mechanical properties of a plasticized poly(vinyl chloride) (PVC) extrudate on rotational speed of the screw, the width of the feed opening, and the length of the pellets of input polymer. It was found that the parameters tested were affected to the largest extent by the screw-rotational speed. A fivefold increase in screw-rotational speed resulted in a few hundred percent increase in the output and a several dozen percent increase in the yield strength of the extrudate, with the highest value obtained for pellets whose length was close to their diameter. Reduction of the width of the feed opening from 1.0 to 0.6 D resulted in a slight increase in the yield strength and tensile strength. High output, yield strength, and tensile strength values of PVC are most readily achieved at high screw-rotational speed, the smallest width of the feed opening, and the length of pellets close to their diameter. C
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