Kompozyty 11: 3 (2011) 273-277 Tomasz Klepka 1 *, Jacek Nabiałek 2 1 Politechnika Lubelska, Katedra Procesów Polimerowych, ul. Nadbystrzycka 36, 20-610 Lublin 2 Politechnika Częstochowska, Instytut Przetwórstwa Polimerów i Zarządzania Produkcją, al. Armii Krajowej 19c, 42-200 Częstochowa * Corresponding author. E-mail: t.klepka@pollub.pl Otrzymano (Received) 25.03.2011 ANALYSIS OF FORMING GEOMETRICAL MACROSTRUCTURE IN WALLS OF EXTRUSION PRODUCTS MANUFACTURED FROM POLYPROPYLENE COMPOSITE FILLED WITH CaCO3 Extrusion products in the form of polymeric ducts are mainly manufactured in the process of single-screw extrusion, coextrusion and extrusion with the expansion of an extrudate wall under negative pressure in movable segments. Different methods of forming the extrusion product allow one to obtain products with solid, cellular or corrugated walls. In addition, in all the mentioned extrusion processes, it is possible to apply extra technological treatments enhancing a given quality which might be significant in terms of the function to be fulfilled by the product or conditions of its use. Products obtained in this manner from the material display special, extra properties enabling their application in the latest technological solutions. At the moment, the greatest technical progress has been observed in optical communications technologies and it is in this sector that duct-shaped extrusion products have been applied most widely. They are laid in special concrete conduit installations and subsequently, innerducts of smaller dimensions or directly teletechnical, power or optotelecommunication cables are installed inside them. Considering all this, it is required that the structures of modern extrusion products have good mechanical properties. Less resistance to motion during the introduction of cables into the interior part of the extrusion product can be obtained through the manufacture of its internal wall with a proper geometrical macrostructure in the form of special slide ribs. Until present, extrusion products in the form of such ducts have been manufactured from high density polyethylene (PE-HD), however, due to the need to obtain enhanced circumferential rigidity, other alternative polymeric materials, copolymers as well as calcium carbonate () or talc (Mg 3(OH) 2Si 4O 10) filled composites have been pursued. The article presents the patterns of changes in the rheological properties of propylene composites with different content during their flow through the channel gap in the extrusion die. Numerical analysis was conducted with the use of the finite element method (FEM) in the area between the core forming the slide ribs and a cylinder-shaped external wall. The material within the core area flows through a specific number of macro depths whose shape corresponds to the shape of the slide ribs which are manufactured in the inner surface of the extrusion product. The ratio of rib height to wall thickness was 1:8. The rheological sevenparameter Cross-WLF model was used to analyze changes in the shear rate and viscosity of the material in a given section of the extrusion die. The results for the filled polypropylene composite (PP + ) were compared to the results obtained for a PE-HD without additives or fillers in the same processing conditions. Keywords: composite of polypropylene with, geometrical macrostructure, rheological properties, computer simulation ANALIZA KSZTAŁTOWANIA MAKROSTRUKTURY GEOMETRYCZNEJ ŚCIANKI WYTŁOCZYNY WYTWORZONEJ Z KOMPOZYTU POLIPROPYLENU NAPEŁNIONEGO CaCO3 Wytłoczyny będące w efekcie kanałami z tworzywa polimerowego wytwarza się głównie w procesie wytłaczania ślimakowego, współwytłaczania oraz wytłaczania z podciśnieniowym rozciąganiem ścianki kanału w ruchomych segmentach. Różne metody kształtowania wytłoczyny pozwalają na otrzymywanie wytworów o ściance litej, porowatej lub strukturalnej. Ponadto do wszystkich wymienionych procesów można stosować dodatkowe zabiegi technologiczne, poprawiające wybraną cechę, ważną na przykład z uwagi na funkcje, jakie ma spełniać wytwór, lub warunki, w jakich będzie eksploatowany. Otrzymane w ten sposób produkty z tworzywa wykazują specjalne, dodatkowe właściwości, które pozwalają na stosowanie ich w nowoczesnych rozwiązaniach technicznych. Obecnie największy postęp techniczny można zaobserwować w technikach optotelekomunikacyjnych i właśnie tam wytłoczyny kanałowe z tworzyw znalazły największe zastosowanie. Układa się je w specjalnych betonowych instalacjach, a do nich wciąga się rurociągi o mniejszych wymiarach lub bezpośrednio kable teletechniczne, energetyczne lub optotelekomunikacyjne. Wszystko to powoduje, że nowoczesne konstrukcje wytłoczyn muszą mieć dobre właściwości mechaniczne. Uzyskanie mniejszych oporów ruchu przy zaciąganiu do wnętrza wytłoczyny kabli otrzymuje się, wykonując wewnętrzną jej ściankę z odpowiednią makrostrukturą geometryczną, w postaci żeber ślizgowych. Dotychczas wytłoczyny w postaci kanałów tego typu były wytwarzane z polietylenu dużej gęstości (PE-HD), jednak z uwagi na potrzebę uzyskania większej sztywności obwodowej poszukuje się również innych alternatywnych tworzyw polimerowych, kopolimerów, a także kompozytów napełnionych kredą () lub talkiem (Mg 3(OH) 2Si 4O 10). W artykule przedstawiono przebieg zmian właściwości reologicznych kompozytu polipropylenu z różną zawartością, podczas przepływu przez szczelinę w głowicy wytłaczarskiej. Analizę numeryczną prowadzono metodą MES, w obszarze pomiędzy rdzeniem kształtującym żebra ślizgowe a walcową ścinką zewnętrzną. Przepływ tworzywa w obszarze rdzenia przebiegał przy określonej liczbie wgłębień, odpowiadających kształtom żeber ślizgowych wytwarzanej wytłoczyny. Stosunek wysokości żebra w odniesieniu do grubości ścianki wynosił 1:8. Obliczenia prowadzono przy wykorzystaniu siedmioparametrowego modelu reologicznego
274 T. Klepka, J. Nabiałek Cross-WLF, analizując rozkład zmian wartości szybkości ścinania oraz lepkości tworzywa na interesującym odcinku głowicy. Wyniki otrzymane dla kompozytu (PP + ) porównano z wynikami uzyskanymi dla PE-HD bez dodatków i napełniaczy w tych samych warunkach przetwórstwa. Słowa kluczowe: kompozyt polipropylenu z, makrostruktura geometryczna, właściwości reologiczne, symulacja komputerowa INTRODUCTION As a result of polymeric material processing, it is possible to obtain products with precisely specified qualities, properties and top-layer structure [1, 2]. Depending on the function and conditions of use, various types of axisymmetric products in the form of ducts such as innerducts, pipes, tubes, profiles with a surface of different geometrical macrostructure (Fig. 1 play a significant role in the technology [3]. Fig. 1. Examples of polymer ducts: consisting of several layers, with group of innerducts with smaller dimensions Rys. 1. Przykłady kanałów z tworzywa: składających się z kilku warstw, z grupą kanałów o mniejszych wymiarach Those elements are connected into special duct-line systems and used for the construction of different kinds of power conduits, telecommunication or water supply, heat or gas distribution. New structures made of this kind of duct-shaped products manufactured from materials characterized by additional features such as e.g. enhanced mechanical or tribological properties on a demanded surface or a given area (Fig. 1. The obtained enhanced mechanical properties in the major duct enable the placement of a relevant system of specialized conduits of inferior resistance, such as: power, telecommunication engineering or optical communications innerducts in its interior [4, 5]. This ensures their long-term mechanical protection from being crushed or resistance to the impact of the environment. It is possible to receive specific mechanical properties and enhanced resistance to external factors during the manufacturing of modern duct structures from various types of materials; copolymers and composites. These ducts and conduits may consist of a number of layers of different materials bound by adhesion during polymer processing or of material filled with a high content of calcium carbonate ( ) or talc (Mg 3 (OH) 2 Si 4 O 10 ). PROCESSING Considering the design requirements and specific nature of processing in the extrusion line, this process should run in specific conditions [1, 2]. Depending on the given type and content of filler used in the material, the conditions and processing shall be different, which ultimately also affect the product properties [6, 7]. What is more, the required geometrical macrostructure of the internal wall of the extrusion product in the form of slide ribs, results in additional complications in the manufacturing process. Due to the fact that literature provides no data useful for tool design or any guidelines regarding the dimensions of slide ribs, products of this type should be analyzed via computer simulation. In the case of manufacturing ducts made of polymeric material with ring-shaped cross sections, as a result of melt flow, they acquire a shape determined by the geometrical macrostructure of the surface of the shaping core. Thus formed, the slide ribs obtain dimensions which are determined by the shape and dimensions of the core macro depths, adjusted by shrinkage and the Barrus coefficient [6, 8]. SIMULATION INVESTIGATION In order to predict the properties of the extrusion product, simulation investigation was conducted on the laminar flow of the polymeric material in the section between the core and the external cylindrical surface of the channel gap. The extrusion product was 40 mm in diameter; the number of formed slide ribs was 120 and their height 2 mm. The finite element method was used in the investigation. The computational model (Fig. 2) was built out of tetrahedral finite elements, with a side length of 1 mm. The following conditions of extrusion were used: plastic plasticized temperature T 1 = 220 C, temperature of the extrusion die T 2 = 190 C and volumetric flow rate equal γ = 45 cm 3 /s. The study was conducted with
Analysis of forming geometrical macrostructure in walls of extrusion products manufactured from polypropylene composite filled with 275 modeled flows of the following materials: high density polyethylene PE-HD (GeForce 7740 Hostalen F - Targor Company), polypropylene composite filled with 20% (GPP20CF57HBGY) and polypropylene composites filled with 35% (GPP35CS7678) Ferro Company. Fig. 2. Appearance and selected fragments of FEM model used in the research Rys. 2. Wygląd oraz wybrane fragmenty modelu MES zastosowanego w badaniach In calculating the rheological model, a sevenparameter Cross-WLF (Cross, Wiliiams, Landel, Ferry) was used [8-11]. The mathematical model describes the rheological relation to equation (1) while the model coefficients for the analyzed materials are shown in Table 1. Viscosity plots have been presented in Figure 3. η η 0 = ( 1 n) η0 γ 1+ τ A1( T T ) and ( ) 0 = D1exp A2 + T T η (1) where: T * = D2 + D3 p A 2 ~ = A 2 + D 3 p with: η - viscosity, γ - shear rate, ηo - zero viscosity, * T - temperature, p - pressure, n,τ, D1, D2, D3, A1, A2 - coefficients. TABLE 1. Characteristics of test materials rheological model coefficients TABELA 1. Współczynniki modelu reologicznego badanych tworzyw Model coefficients PEHD PP + 20% PP + 35% n - 0.5285 0.2974 0.3255 τ [Pa] 8585.8 30397 22082 D1 [Pa s] 5.72e+017 7.35e+014 1.86e+014 D2 [K] 153.15 263.15 263.15 D3 [K/Pa] 0 0 0 A1-35.27 33.986 31.161 A2~ [K] 51.6 51.6 51.6 Fig. 3. Viscosity plots: PEHD, PP + 20%, PP + 35% Rys. 3. Krzywe płynięcia: PEHD, PP + 20%, PP + 35% ANALYSIS OF SIMULATION INVESTIGATION RESULTS On the basis of the conducted calculations and finite element analysis (FEM), a set of data was obtained allowing us to present graphically the examined changes in the rheological properties during the melt flow through the channel gap. The curves determined in accordance with the Cross-WLF model enabled us to prepare the shear rate and viscosity distribution of the
276 T. Klepka, J. Nabiałek analyzed materials. Sample results have been presented in Figures 4 and 5. Shear rate Fig. 4. Shear rate distribution during extruded plastics flow: PE-HD, PP + 20%, PP + 35% Rys. 4. Rozkład szybkości ścinania podczas przepływu wytłaczanego tworzywa: PE-HD, PP + 20%, PP + 35% Viscosity CONCLUSIONS On the basis of the duct analysis of forming geometrical macrostructure in the walls of extrusion products manufactured from a polypropylene composite filled with, it can be concluded that in the examined conditions, changes in shear rates for all the examined materials along the channel gap are of a similar nature. It is a consequence of processing all the examined materials under exactly the same conditions. Interesting results have been obtained while comparing the changes in the viscosity of the materials at different temperatures. For high density polyethylene, considerably differentiated viscosities in the area of the slide ribs in relation to the main wall have been recorded. This state of affairs will consequently lead to differentiation of the macrostructure in both of the mentioned areas. This phenomenon may be eliminated by changing the geometrical shape of the slide ribs, which the authors of the paper shall attempt to prove in subsequent research. In the case of polypropylene composites with the calcium carbonate content, the changes in viscosity are much less rapid. Therefore, it might be expected that filled polypropylene lends itself better to the manufacture of goods of this type. It should be noted however, that extrusion products will have different properties at the tops of the slide ribs than those in the main wall (Figs. 4 and 5). Differences in the forecast properties of the extrusion products are clearly visible in plastics selected for product manufacture, whereas the filler content of 20 and 35% in filled propylene is less significant for the examined scope of changes. With regard to the required complex geometrical macrostructure, a number of simulations should be conducted in order to determine the most efficient dimensions of slide ribs. This especially refers to the rib shape, their number, dimensions (ratio of height to thickness of the supporting wall) of the extrusion product with regard to the type of material and higher filler content. Advances have taken place in simulation software, which offers increasingly wider possibilities of predicting phenomena occurring during the processing of polymeric materials and composites, and therefore they can be used with success in this type of analyses. Acknowledgements An article written under the Ministry of Science and Higher Education research project no. N N 508 486138. REFERENCES Fig. 5. Viscosity distribution during extruded plastics flow: PEHD, PP + 20%, PP + 35% Rys. 5. Rozkład lepkości podczas przepływu wytłaczanego tworzywa: PEHD, PP + 20%, PP + 35% [1] Sikora R., Tworzywa wielkocząsteczkowe - Rodzaje, właściwości i struktura, Wydawnictwo Uczelniane Politechniki Lubelskiej, Lublin 1991. [2] Rauwendall C., Polimer Extrusion, Carl Hansen Verlag, Munich 1986. [3] Sikora R., Klepka T., Przegląd konstrukcji rur optotelekomunikacyjnych z tworzyw, Projektowanie, stosowanie i eksploatacja elementów maszyn i urządzeń. Politechnika Częstochowska, Częstochowa 1996.
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