Experimental study and evaluation of mixing mechanism and performance in triple-screw extruder (original) (raw)
Related papers
Compounding of polyethylene composites using high speed twin and quad screw extruders
PROCEEDINGS OF PPS-33 : The 33rd International Conference of the Polymer Processing Society – Conference Papers
The effect of high screw speed twin and quad screw extruders on mixing was investigated using polyethylene microcomposites with 1 wt% calcium carbonate. Using screws with similar designs extruder type influenced the effects that screw speeds of 300 to 200 rpm had on extruder residence time, melt temperature, drive torque, and head pressure. Parallel plate rheology indicated significant chain scission of the polymers, but better filler dispersion at screw speeds of 900 and 1500 rpm and better dispersion in the quad screw extruder. In the quad screw extruder, the lower melt temperatures and greater shear allowed better mixing at higher screw speeds than the twin screw extruder. The dispersion was confirmed with transmission electron microscopy.
Journal of Plastic Film & Sheeting
The process dynamics of single-screw extrusion on mixtures of polypropylene (PP) and recycled PP were studied using a statistical, design of experiments (DoE) approach. For a conventional screw design, barrel temperature, screw speed and two vastly different melt viscosity PP mixtures were selected as the independent factors, whilst melt pressure, mass output, screw torque and temperature rise at the die due to shear heating, were the dependent responses. A central composite design (CCD) in the framework of response surface methodology (RSM) was constructed, and an analysis of variance (ANOVA) was carried out to determine the significance of the response surface models. The resulting statistical and response surface predictions have demonstrated that the low viscosity component concentration in the blend is a dominating factor on melt pressure and screw torque, apart from the expected effect of screw speed on output. Viscous heating is affected only by screw speed and recycled PP concentration. Furthermore, the predictions have identified a wider process operating window with increased low viscosity component concentration. The data confirms that statistical tools make quantitative predictions for the effects of experimental process variables, in accordance with the expected qualitative trends towards process optimisation, providing scope towards its application in scaled-up industrial processes.
Melting of PP/PA6 Polymer Blends in Single Screw Extruders – An Experimental Study
Materials Science Forum, 2008
A prototype modular single screw extruder fitted with a screw extracting device is used to monitor melting of an immiscible polymer blend (PP/PA6, with different weight ratios) in this popular type of processing equipment. As anticipated, the observed phenomena are much more complex than those involved in extruding PP or PA6, when the well known Maddock/Tadmor mechanism is valid. Consequently a hybrid melting mechanism, involving Maddock/Tadmor and Dispersive melting sequences, is proposed.
Polymer Engineering & Science, 1999
Blends of high-density polyethylene (HDPE) and polypropylene (PP) were prepared in different twin-screw extruders. Two additives, a peroxide initiator and a polymerizable monomer, were added to the polymeric feed components. A large influence on the physical properties, such as toughness and impact strength,. and on the morphology was observed. Reactive extrusion substantially improves mechanical properties: a threefold increase of elongation at break and doubling of the impact strength. Variation of extruder settings also had a large influence on the product; the f i n a l properties were improved when the shear rate was raised, but sufficient residence time is necessary in reactive compatibilization. Scanning electron micrographs of the fracture surfaces of blends indicate a refinement of the surface structure.
Melting of polymer blends in single-screw extrusion - An experimental study
International Journal of Material Forming, 2009
Melting is a major step in plasticating single screw extrusion, but most of the existing phenomenological know how was gathered by performing Maddock-type experiments with homopolymers. Given the current widespread industrial use of polymer blends, it is worth determining whether the same mechanisms and mathematical models apply, or whether different sequences develop. This work reports the results of Maddock-type experiments using a PA6/PP blend, both in its immiscible and compatibilized varieties. A melting mechanism combining the features of the classical Tadmor mechanism and of the dispersed melting mechanism, also previously reported in the literature, was observed.
Polypropylene Degradation on Co-Rotating Twin-Screw Extruders
Polymers
Nowadays, usable plastic materials with defined properties are created by blending additives into the base polymer. This is the main task of compounding on co-rotating twin-screw extruders. The thermal and mechanical stress occurring in the process leads to a mostly irreversible damage to the material. Consequently, the properties of the polymer melt and the subsequent product are affected. The material degradation of polypropylene (PP) on a 28 mm twin-screw extruder has already been studied and modeled at Kunststofftechnik Paderborn. In this work, the transferability of the previous results to other machine sizes and polypropylene compounds were investigated experimentally. Therefore, pure polypropylene was processed with screw diameters of 25 mm and 45 mm. Furthermore, polypropylene compounds with titanium dioxide as well as carbon fibers were considered on a 28 mm extruder. In the course of the evaluation of the pure polypropylene, the melt flow rates of the samples were measured...
The development of laminar morphology during extrusion of polymer blends
Polymer Engineering and Science, 1995
Studies of the microstructure and permeability of extruded ribbons of polypropylene (PP)/ethylene vinyl alcohol copolymer (EVOH) and polyethylene (PE)/polyamide-6 (PA-6) blends have shown that it is possible to control the flow-induced morphology to generate discontinuous overlapping platelets of EVOH or PA-6 dispersed phase in a PP or HDPE matrix phase. The effects of the following factors on morphology development and blend properties were considered: blending sequence, melt temperature, composition, compatibilizer level, die design, screw type, and cooling conditions. The impact properties and interfacial adhesion of laminar blends of PP and EVOH were improved without diminishing the barrier properties. The oxygen and toluene permeability of extruded samples with EVOH content of 25 vol% resembled values obtained with multilayer systems. Processing conditions had a major influence on the morphology of blends of high.density polyethylene and polyamide-6 (HDPE/PA-6), and, under special processing conditions, laminar morphology was obtained in this system. The toluene permeability of extruded ribbons of HDPE/PA-6 blends was in the range obtained with multilayer systems.
Advances in Science and Technology Research Journal
The objective of this study was to determine the eff ect of various design solutions for intensive mixing and shearing elements located at the end of a single-screw plasticizing system on the eff ectiveness of wood polypropylene composite extrusion. Four types of such elements were used in the study: a pineapple mixer, a Maddock mixer, a ring mixer, and a helical mixer. For the purpose of the study, four blends were prepared containing 5, 10, 15 and 20% of wood fi bre, respectively. Direct and indirect resulting factors as well as variable, constant and disturbing factors were investigated. The eff ectiveness of extrusion of wood polypropylene composites was determined based on results of parameters characterizing this process, such as extrudate temperature, unit consumption of energy supplied to the extruder, mass fl ow rate, and extrusion speed. It has been shown that the eff ectiveness of the extrusion process can be improved by using diff erent mixing and shearing elements. Such screw design solutions make it possible to aff ect rheological phenomena occurring during melt fl ow in the plasticizing system, without modifying the extrusion process parameters such as screw rotation speed and polymer temperature. The literature review shows that there exist very few and general studies investigating the eff ect of screw design geometry, especially that of mixing and shearing elements, on the effi ciency of extruding and mixing wood polypropylene materials.
The effect of melt viscosity on thermal efficiency for single screw extrusion of HDPE
Chemical Engineering Research and Design, 2013
In this work, a highly instrumented single screw extruder has been used to study the effect of polymer rheology on the thermal efficiency of the extrusion process. Three different molecular weight grades of high density polyethylene (HDPE) were extruded at a range of conditions. Three geometries of extruder screws were used at several set temperatures and screw rotation speeds. The extruder was equipped with real-time quantification of energy consumption; thermal dynamics of the process were examined using thermocouple grid sensors at the entrance to the die. Results showed that polymer rheology had a significant effect on process energy consumption and thermal homogeneity of the melt. Highest specific energy consumption and poorest homogeneity was observed for the highest viscosity grade of HDPE. Extruder screw geometry, set extrusion temperature and screw rotation speed were also found to have a direct effect on energy consumption and melt consistency. In particular, specific energy consumption was lower using a barrier flighted screw compared to single flighted screws at the same set conditions. These results highlight the complex nature of extrusion thermal dynamics and provide evidence that rheological properties of the polymer can significantly influence the thermal efficiency of the process.