Analysis of process parameters related to the single-screw extrusion of recycled polypropylene blends by using design of experiments (original) (raw)
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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.
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.
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.
Polymer Testing, 2007
The effects of repetitive extrusion cycles at different die temperatures in a single screw extruder were investigated by thermal analysis (degree of crystallinity (w c ), heat of fusion (DH m ), melting temperature (T m ) and the onset melting temperature (T onset,m )) and mechanical properties (tensile and impact strength). Also, analysis of variance (ANOVA) and response surface methodology (RSM) were employed for modeling and analysis of the mechanical property results. Thermal analysis verified an increase for w c and DH m with a continuous reduction in the T m and T onset,m values with increase of die temperature and/or cycles of extrusion. For mechanical properties, the observed degradation process only slightly affects the small strain properties (yield stress and modulus) and impact strength. Break properties (break stress, break strain and energy to break) were reduced significantly by the experimental conditions adopted. According to ANOVA and RSM, the degradation process was occasioned more by high shear rate (repetitive number of cycles) than by high processing temperatures. r
Experimental study and evaluation of mixing mechanism and performance in triple-screw extruder
Advances in Polymer Technology, 2017
The mixing capacity of triangle-arrayed triple-screw extruder (TTSE) was evaluated through the extrusion of polypropylene/ethylene-propylene-diene monomer (PP/EPDM) at varying screw speeds. The micromorphology, mean residence time, melt flow rate (MFR), and mechanical properties of blends were measured for evaluation. Moreover, same experiments were applied on a twin-screw extruder (TSE) for comparison. TTSE shows better mixing performance than TSE in comparison with micromorphology and mean residence time. But the high shear effect and temperature rising in TTSE promote the degradation of PP in blends which make the samples to have worse mechanical properties and higher MFR than those of TSE.
The Impact of Reprocessing with a Quad Screw Extruder on the Degradation of Polypropylene
Polymers
During mechanical recycling, polypropylene typically is reprocessed using a single- or twin-screw extruder. The degradation of polypropylene during this reprocessing reduces the polymer’s molecular weight and, consequently, limits the performance of the recycled resin. This work investigated the impact of a quad screw extruder (QSE), which has greater free volume, on the reprocessing of an impact copolymer polypropylene. To mimic the recycling process, the polypropylene was subjected to three processing cycles using a QSE and a comparable twin-screw extruder (TSE) operated at three screw speeds. The reprocessed materials were characterized for their rheological, morphological, and mechanical properties. For both extruders, increasing the number of reprocessing cycles and the screw speed resulted in higher melt flow indices, decreases in zero-shear viscosity, and shifting of the crossover points for the storage and loss moduli, which indicate reductions in the molecular weight and na...
Computer Modeling for Single-Screw Extrusion of Wood–Plastic Composites
Polymers, 2018
Experimental and theoretical studies have been performed on the single-screw extrusion of wood–plastics composites. Experimental research has been carried out on the flow and melting of polypropylene (PP)-based composites with different wood flour (WF) content in the single-screw extruder. Based on these experimental observations, elementary models of the process phenomena have been proposed and a global model of the process has been developed. This global computer model includes the models of solid conveying, melting dependent on the wood flour content, melt flow in the screw, and melt flow in the die. 3-D non-Newtonian finite element method (FEM) screw pumping characteristics have been applied to model the melt flow in the metering section of the screw. The model predicts the extrusion output, pressure and temperature profiles, melting profile, and power consumption. The model has been validated experimentally. An effect of material slip on the extruder operation has been discusse...
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...
2019
Extrusion is an inexpensive process in terms of production costs used to produce continuous shapes of plastic materials. The mixture design method and regression analysis have been applied to evaluate the performance of the single screw extruder. The performance values of the single-screw extruder system with a glass barrel are calculated by the residence time distribution results of the tracers. Then calculated particle distributions are compared with visual data. Ethylene vinyl acetate (EVA 210W) is used as the polymeric material. In the study, the EVA 210W is studied with various screw configurations and also process conditions. Optimization is fulfilled using the response optimizer to determine the optimum screw configuration. This method is aimed at feeding and metering zones in screw design and focuses on the search for a solution for optimum screw selection. In addition, the robustness of solutions in process conditions has been redefined.