Christian Bonten

Analysis of a Single Screw Extruder with a Grooved Plasticating Barrel – Part I: The Melting Model

Abstract Single screw extruders with barrier screws, grooved feed zones and grooved melting zones were introduced to the European plastics industry in 1999. These extruders have an improved melting and conveying capacity among other advantages, such as a lower melt temperature, less wear, less torque and less energy consumption. The aim of this paper is to present a mathematical model for predicting the melting rate in this type of extrusion system. Based on the classical melting mechanism observed in conventional extruders, it was possible to study the effect of the geometry of the grooved barrel on the melting rate of a polymer. It was shown that the grooves on the barrel notably increase the melting rate, when compared to conventional single screw extruders. A good agreement between theory and experimental data was found.

Software-aided measurement of geometrical fidelity for 3D printed objects

ABSTRACTThis research evaluates the geometric fidelity of 3D printed objects by utilizing digital image analysis techniques on consumer grade 3D printers. ISO 527-2 Type B specimen are modeled using Houdini Software, then positioned on the virtual print-bed and sliced in 0.3 mm thickness layers utilizing MiracleGrue slicer. The specimens are printed on a Makerbot Replicator2X 3D printer with an X-Y resolution of 0.011 mm. The test set is divided into three where the first object set (Test set A) is printed with their longest side parallel to the X axis, the second object set (Test set B) with their longest side oriented at an angle to the X axis and the third object set (Test set C) as a control with a different material type and structure. The test includes objects with parallel patterns of 0, 5, 10, 30, 45, 60 and 90 degree resulting in toolpaths along the parallel lines. For the second test set the orientation angle is chosen to match the parallel pattern degree. The objects are analyzed with a softwar...

Extruded zeolitic honeycombs for sorptive heat storage

Energy conservation is very important nowadays. For an optimized re-utilization of waste heat and heat from regenerative energy sources, an improved storage system with a minimum loss is required. Hydrophilic zeolites are suitable materials for this purpose. Currently they are used as packed beds. The main disadvantage of such packed beds is the high pressure loss for the flow of the heat transferring medium through such a bed. This reduces the efficiency of such a system clearly. Zeolitic honeycombs can overcome this problem. At the IKT these honeycombs are produced on a twin-screw extruder known from plastics engineering. In this way, two process steps (compounding and shaping) can be integrated into one step: The compound is mixed in the machine and directly extruded through an appropriate die. Such a compound of mineral based zeolitic honeycombs consists of zeolite, a binder, a plasticizer and water. The first three components can vary in type. To get good mechanical properties, green bodies of such a...

Influence of the phase morphology on the weldability of PLA/PBAT-blends by using butt-welding

The material development in the field of bioplastics is steadily increasing. It is important to examine the processability but the Investigation of further process steps is also very important. In this paper the weldability of bioplastics is discussed. Compounds of Polylactide (PLA) and Polybutyleneadipate-terephthalate (PBAT) are produced by a twin screw extruder with different mixing ratios. Tensile specimens are produced by injection moulding and the tensile tests are carried out. In order to verify the weldability, some tensile specimens are cut in halfes and butt welded. Afterwards a tensile test is performed with the welded samples and the results are compared with the values of the unwelded samples. For understanding the results, the morphology of the welds were examined and correlated. It has been found that blends with a mixing ratio of 50:50 have the lowest welding factor, because of the immiscibility of PLA and PBAT. Weld images show segregated areas that reduce the force transmission.

Production of continuous fiber thermoplastic composites by in-situ pultrusion

The constructive design in the automotive industry, but also in many other industrial sectors has changed steadily over the past decades. It became much more complex due to e.g. increased use of hybrid materials. Combined with the desire to minimize the weight of vehicles and thus the CO2 emissions, the use of low density materials and especially fiber-reinforced plastics is increasing. E.g. Continuous fiber thermoplastic composites are used to reinforce injection molded parts. Low viscosity monomers like caprolactam, which is used to produce polyamide 6 by anionic polymerization are able to easily impregnate and penetrate the textile reinforcement. After wetting the fibers, the ring-opening polymerization starts and the matrix is becoming a polymer. At IKT, a method based on the RIM process (reaction injection molding) was developed to produce continuous fiber thermoplastic composites with high contents of continuous glass fibers. The anionic polymerization of polyamide 6 was now combined with the pultru...

Autoclave foaming of chemically modified polylactide

Polylactide has emerged as one of the most promising biopolymers due to its good mechanical properties, as reflected by the continual increase in its production volume per year. However, one of the main drawbacks of polylactide is its low melt strength, which is disadvantageous in terms of foaming. To overcome this issue, in this study, several chemical modifiers that induce crosslinking, chain extension or grafting were incorporated by reactive extrusion, which greatly affected the foaming process by increasing the molecular weight and thereby the melt properties of polylactide. By means of gel permeation chromatography, an increase in the molecular weight was observed in the modified polylactides. Elongational viscosity measurements indicate a dramatic viscosity increase for polylactide modified with a multifunctional epoxide and an organic peroxide. With pressure-induced batch foaming, almost all modifications, with the exception of styrene maleic anhydride, led to a decrease in foam density compared to the neat polylactide.

Modified standard polylactic acid (PLA) for extrusion foaming

Polymeric foams are used in disposable packaging because of their low density, high impact resistance and the low material consumption. Nowadays they are often made of petroleum-based extruded polystyrene foam (XPS). The use of biodegradable and biobased polymers in short-living packaging could be an ecological benefit. One of PLA´s shortcomings is its poor melt viscosity and poor melt stiffness. To foam a standard, cost effective man-produced PLA, it must be modified to increase its low melt strength. In the presented work the effects of grafting, crosslinking and chain extension on the melt strength were investigated. The addition of different modifiers and the performance of the reaction were performed by means of reactive extrusion on a twin screw extruder. The rheological properties in shear and elongation deformation, the foam densities, the cell sizes and the morphology were examined. The melt viscosity was increased and could be correlated to a higher molecular weight and broader molecular weight ...

Melting rate of a single screw extruder with a grooved melting zone

At the IKT, a mathematical model was developed to calculate the melting rate of a single screw extruder with a grooved melting zone. The shear thinning behavior of the polymer melt was considered. With the help of simulations, it is possible to determine the complex relationship between process variables, extruder geometry and plastic properties. The results were validated with experimental measurements from the literature.

Improvement of mechanical properties by additive assisted laser sintering of PEEK

The additive assisted laser sintering was recently developed at IKT: A carbon black (CB) additive is used to adjust the polymers laser absorption behavior with the aim to improve the interconnection of sintered powder layers. In this paper a parameter study, Polyetheretherketone (PEEK) samples were prepared with different contents of carbon black and were laser sintered with varying thermal treatment. The samples were mechanically tested and investigated by optical light and transmission electron microscopy. An influence on the morphology at the border areas of particles and intersections of laser sintered layers was found. Depending on the viscosity of the raw material and CB content, different shapes of lamellae were observed. These (trans-) crystalline or polymorph structures, respectively, influence the thermal and mechanical behavior of the virgin PEEK. Moreover, the thermal treatment during the sintering process caused an improvement of mechanical properties like tensile strength and elongation at ...

Extrusion-Based 3D Printing of Poly(ethylene glycol) Diacrylate Hydrogels Containing Positively and Negatively Charged Groups

Hydrogels are an interesting class of materials used in extrusion-based 3D printing, e.g., for drug delivery or tissue engineering. However, new hydrogel formulations for 3D printing as well as a detailed understanding of crucial formulation properties for 3D printing are needed. In this contribution, hydrogels based on poly(ethylene glycol) diacrylate (PEG-DA) and the charged monomers 3-sulfopropyl acrylate and [2-(acryloyloxy)ethyl]trimethylammonium chloride are formulated for 3D printing, together with Poloxamer 407 (P407). Chemical curing of formulations with PEG-DA and up to 5% (w/w) of the charged monomers was possible without difficulty. Through careful examination of the rheological properties of the non-cured formulations, it was found that flow properties of formulations with a high P407 concentration of 22.5% (w/w) possessed yield stresses well above 100 Pa together with pronounced shear thinning behavior. Thus, those formulations could be processed by 3D printing, as demonstrated by the generation of pyramidal objects. Modelling of the flow profile during 3D printing suggests that a plug-like laminar flow is prevalent inside the printer capillary. Under such circumstances, fast recovery of a high vicosity after material deposition might not be necessary to guarantee shape fidelity because the majority of the 3D printed volume does not face any relevant shear stress during printing.