| 1. |
- Arino Marine, Ruth, 1980, et al.
(author)
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Barrier screw compounding and mechanical properties of EAA copolymer and cellulose fiber composite
- 2013
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In: International Polymer Processing. - : Walter de Gruyter GmbH. - 0930-777X .- 2195-8602. ; 28:4, s. 421-428
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Journal article (peer-reviewed)abstract
- The difficulty of feeding cellulose fibers and thermoplastics into the extruder or injection molding machine is addressed, this being a serious problem in the production of cellulose fiber composites for industrial applications. Agglomerates consisting in cellulose fibers and ethylene-acrylic acid copolymer (EAA) with different cellulose contents and different fiber lengths were processed with two different screws in order to better understand how the dispersion of the fibers can be improved by melt extrusion. A conventional screw with a compression ratio of 4 : 1 and a screw with barrier flights were used at different screw rotation speeds. The fiber length and fiber content were measured and microscopic analyses were performed in order to estimate the number and size of the cellulose fiber aggregates in the final composites. It was concluded that the barrier screw was more effective than the conventional screw in breaking up the fiber aggregates and dispersing the fibers. More but smaller cellulose aggregates were observed when the barrier screw was used, and the reduction of length was significantly greater for long than for short fibers. In contrast to that was expected, the samples containing the shorter fibers had better mechanical properties, probably due to a better dispersion of the fibers.
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| 2. |
- Arino Marine, Ruth, 1980, et al.
(author)
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Injection molding of beverage container caps made of a composite consisting of wood cellulose fiber and an ethylene-acrylic acid copolymer
- 2014
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In: International Polymer Processing. - : Walter de Gruyter GmbH. - 0930-777X .- 2195-8602. ; 29:4, s. 507-514
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Journal article (peer-reviewed)abstract
- The influence of processing parameters on injection-molded bottle caps consisting of 20 wt% of cellulose fibers and an ethylene-acrylic acid copolymer was studied. The study included three cylinder barrel temperatures and three mold temperatures. For each combination of temperatures, the holding pressure time was varied and the mold sealing time was determined. High density polyethylene caps were also produced as reference material, and injection-molded tensile test bars were also produced in order to assess the tensile mechanical properties. The results showed no major differences in sealing time for the caps containing cellulose fibers, except for the highest melt and mold temperatures where a slightly longer time was observed. The viscosity of the composite material was higher than that of the polymeric matrix. For the highest temperature and high shear rates, the viscosity of the composite material was close to the viscosity of the matrix material. The moisture content of the injection-molded bars was less than 1%, showing that almost no water was absorbed during the compounding or after several months. The crystallinity decreased when the fibers were included but was not influenced by the mold temperature. Enhanced mechanical properties were obtained by using the fibers compared to the pure ethylene-acrylic acid copolymer, both in the tensile test bars and in the caps. The reference high density polyethylene had, however, a higher mechanical performance than the composite.
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| 3. |
- Arino Marine, Ruth, 1980, et al.
(author)
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Melt processing of wood cellulose tissue and ethylene-acrylic acid copolymer composites
- 2013
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In: International Polymer Processing. - : Walter de Gruyter GmbH. - 0930-777X .- 2195-8602. ; 28:4, s. 429-436
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Journal article (peer-reviewed)abstract
- The difficulty of feeding cellulose fibers together with the polymer into the melt processing equipment is a serious disadvantage for the production of cellulose-containing composites on a large scale. In the present work, a continuous method of feeding cellulose in the form of a tissue into a twin-screw extruder through an opening downstream of the extruder cylinder was studied. With this method, composites with different fiber contents were obtained. The tissues used were one made mainly of softwood fibers and another mainly of hardwood fibers. In order to better understand how to improve the fiber dispersion by melt mixing, a second extrusion was performed with a single screw extruder with a barrier-flighted screw and also with the twin-screw used to compound the tissue with the polymer. The compounds produced were then injection molded into test bars. The test bars containing the softwood tissue exhibited some fiber aggregates also after a second extrusion, whereas no fiber aggregates were observed in samples made with the tissue containing hardwood fibers and two passes through the twin screw. The fiber length was in general reduced by each melt processing stage and the shortest fiber length was observed after two extrusions with the twin-screw and injection molding. The tensile modulus increased with increasing fiber content. A higher stiffness was obtained with more softwood fibers in the tissue whereas more hardwood fibers gave a higher tensile strength and greater elongation at break.
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| 4. |
- Aronsson, Gunnar, 1939-
(author)
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Five Geometric Principles for Injection Molding
- 2003
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In: International polymer processing. - Munich, Germany : Carl Hanser Verlag GmbH. - 0930-777X .- 2195-8602. ; 18:1, s. 91-94
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Journal article (peer-reviewed)abstract
- A condensed presentation of some results of a geometric character, concerning the injection molding of plastics, is given here. The author has derived these results from mathematical arguments and some simplifying assumptions, besides the usual Hele-Shaw flow conditions.The presentation here is intended for readers with an interest in polymer processing, rather than mathematics, so that the mathematical derivations are omitted in some cases, and sketchy in other cases. Instead we try to explain the results using figures, intuitive arguments and a few inevitable formulas. Since the experimental verification of the results is still very incomplete, we prefer to present them as proposed principles. Comments and suggestions for improvement are very welcome.
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| 5. |
- Jaruttrakool, R., et al.
(author)
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Reactive blending of thermoplastic polyurethane and polypropylene
- 2010
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In: International polymer processing. - : Carl Hanser Verlag GmbH. - 0930-777X .- 2195-8602. ; 25:5, s. 327-333
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Journal article (peer-reviewed)abstract
- In this research, reactive blending of thermoplastic polyurethane(TPU) and polypropylene (PP) was studied. Grafting of maleic anhydride (MAH) onto TPU/PP blends was performed by a twin-screw extruder in the presence of dicumyl peroxide (DCP). Mechanical properties and morphology of the blends were investigated by tensile testing and scanning electron microscopy (SEM), respectively. Thermal properties of the blends were characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The obtained results were compared with those of the uncompatibilized blends and the blends compatibilized with a commercial maleic anhydride grafted polypropylene (PP-g-MA). The results from the uncompatibilized blends clearly indicate that the TPU and PP are immiscible resulting in undesirable properties of the blends. These properties were improved significantly when TPU and PP were reactive-blended in the presence of MAH and DCP. When comparing with the blends compatibilized with PP-g-MA, the blends prepared by the reactive blending technique possessed better mechanical properties.
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| 6. |
- Lundström, Staffan, et al.
(author)
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Modelling of residual stresses and warpage in sandwich injection moulding
- 2003
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In: International polymer processing. - : Walter de Gruyter GmbH. - 0930-777X .- 2195-8602. ; 18:1, s. 95-106
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Journal article (peer-reviewed)abstract
- Sandwich injection moulding offers the possibility of combining materials with different properties and, for instance, hide a recycled constituent within a virgin ditto. This attractive potential puts great demands on the manufacturing and therefore also on the process modelling. In particular the effect on the final stress state and the deformation of the part due to the heterogeneity of the material must be clarified. This topic is addressed in this study. To start with it is confirmed that expressions for the temperature field can be much simplified without major loss of accuracy in the solution. This enables us to take an analytical approach to the modelling and the resulting equations can be solved on a spread-sheet or with a simple code. It is also shown that the derived models compare well to experiments made with a two-layered structure, indicating that the models presented can be used to estimate changes of processing conditions or material properties for sandwich structures.
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| 7. |
- Pisciotti, F, et al.
(author)
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Evaluation of a model describing the advancing flow front in injection moulding
- 2002
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In: International polymer processing. - 0930-777X .- 2195-8602. ; 17:2, s. 133-145
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Journal article (peer-reviewed)abstract
- The simulation of the advancing flow front during mould filling in the injection moulding cycle is important as a way of anticipating manufacturing defects, particularly different types of welds, air traps, cold spots and hot spots. The purpose of the present work was to evaluate a model (the distance model) simulating the advancing flow front and predicting potential issues related to the progression of the flow front such as welds and air traps. The distance model is based on a mathematical theory of Hele-Shaw flow for strongly shear-thinning fluids, i.e. fluids with a power-law index, n, equal to 0,3 or preferably less. Two grades of general-purpose polystyrene were selected according to their abilities to shear thin (weakly or moderately strong) at the selected processing temperature and in the typical shear rate range of the injection moulding process. The two grades were injection moulded into twelve mould configurations derived from two similar single-gated moulds. The flow length from the gate to the weld was measured in the mouldings obtained at three distinct rates of filling (conventional, slower and faster) and compared to the flow lengths obtained by the distance model. Good agreement was found between the predicted flow lengths and the experimental flow lengths at the conventional and faster filling conditions. Larger deviations between simulation and experiment were found at the slower filling rate, particularly for the weakly shear-thinning polystyrene grade. Some comparisons were also made with the predictions obtained using the commercial simulation code Moldflow. A comparison between the advancing front predictions of the distance model and experimental short shots of a commercial polypropylene grade in a lure-box type of mould geometry showed that the distance model, despite its simplicity, could probably be used to detect welds and air traps in more complex and practice-related mouldings.
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| 8. |
- Stenvall, Erik, 1984, et al.
(author)
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The influence of extrusion conditions on mechanical and thermal properties of virgin and recycled PP, HIPS, ABS and their ternary blends
- 2013
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In: International Polymer Processing. - : Walter de Gruyter GmbH. - 0930-777X .- 2195-8602. ; 28:5, s. 541-549
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Journal article (peer-reviewed)abstract
- A recyclable plastics waste stream of electrical and electronic equipment has previously been found to contain acrylonitrile-butadiene-styrene copolymer (ABS, similar to 40 wt%), high impact polystyrene (HIPS, similar to 40 wt%), polypropylene (PP, similar to 10 wt%) and a rest fraction consisting mainly of other styrene-based thermoplastics. In this work, one virgin and one recycled ternary blend consisting of these three components were melt-blended in an extruder to study the influence of processing conditions on the mechanical and thermal properties. The aim of the work has been to understand the inherent compatibility between ABS, HIPS and PP without added compatibilisers, in order to investigate the recycling potential of a real recyclable WEEE plastics fraction. Favourable processing conditions with respect to tensile properties of the virgin blend were found at intermediate screw rotations (40 to 80 min(-1)) and relatively low barrel temperatures (170 to 220 degrees C), which can be understood from the low onset of thermo-oxidative degradation at 200 degrees C. The recycled blend and recycled ABS, HIPS and PP showed higher stiffness and yield stress, but lower elongation at break than the corresponding virgin materials. The stiffness and yield stress of the blends were found mainly to follow the rule of mixtures of their components while the elongation at break exhibited adverse characteristics indicating incompatibility between ABS, HIPS and PP. The significant variations in the elongation at break of the blends appeared to be due to the ABS component. Differential scanning calorimetry showed an additional melt peak for the recycled blend compared to the virgin blend, otherwise the transitions were similar. The additional peak could be assigned to polyethylene in the PP component. The onset of the thermo-oxidative degradation was found to be at almost 190 degrees C in the case of the recycled blend, which was high considering that it was close to that of the virgin blend and higher than expected from the rule of mixtures of the recycled components.
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| 9. |
- Vahlund, C. F., et al.
(author)
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Squeeze flow rheology of glass mat thermoplastic (GMT) in large tools and at high closing velocities
- 2002
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In: International polymer processing. - : Walter de Gruyter GmbH. - 0930-777X .- 2195-8602. ; 17:2, s. 158-165
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Journal article (peer-reviewed)abstract
- Rheological measurements on materials with fibre-like inhomogeneities will be significantly affected by sample size when the in-plane dimensions of the sample are comparable with the length of the fibres. In this paper, a 310 t hydraulic press has been modified for squeeze flow rheology studies so that large tools that will minimize the influence of sample size can be used in combination with high closing velocities. Isothermal squeeze flow rheology experiments of GMT have been performed for closing velocities up to 30 mm/s corresponding to maximum closing forces of 1000 kN. Successful power law fits of closing velocity versus closing force have been performed for the velocity interval. Four different analytical models have been fitted to the experimental data and the accuracy in these has been investigated. The force prediction of the biaxial extension model is acceptable for the major part of mould closure, but better fits during the last part of mould closure were obtained using an additive model incorporating both shear and extensional flow.
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| 10. |
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