Volume 29, Issue 5

This article proposes a novel extruder based on converging-diverging flow for polymer processing. The extruder is composed of four vane plasticizing and conveying units (VPCU) and three mixing units. The working principle of the new extruder is described in detail. Film was produced on this machine by using of CaCO 3 filled LDPE composites. The film's mechanical properties were studied in terms of tensile strength and tear strength. The microstructure of the composites was studied in terms of SEM. The thermo-mechanical history of the material suffered in this extruder can be remarkably shortened in contrast to a single screw extruder with the same maximum output. Experimental results showed that the die pressure has little effect on output. More CaCO 3 can be filled into the blend without degrading the parts performance.

A computational model for the description of polymer flow during the plasticating phase of the injection molding process is proposed. The polymer behavior is determined during the dynamic and static phases of the process. The model takes into account the backwards movement of the screw, the presence of a non-return valve and the conduction of heat during the idle times. Results for the dynamic and static phases of the plasticization are presented. The model is also used to study the influence of some important operative process parameters, such as, screw speed, backpressure, barrel temperatures and injection chamber length. The assessment of the computational results is made experimentally by comparing the average temperature calculated with measurements made in front of the screw nozzle using both, an IR camera and an IR thermometer. The differences between the computational and the IR camera measurements are below 5%.

In this study the viscosity behavior of the polymer-based drug delivery system (Soluplus-Fenofibrate) at high shear rates was investigated using (i) Computational Fluid Dynamics (CFD) methods and (ii) experimental data acquired with a high-pressure capillary rheometer. The barrel and capillary were rebuilt in the virtual domain by means of finite-volume methods and used for fluid dynamic simulations. Our primary focus was on validating the Carreau-Winter and Yasuda material models in the Open Field Operation and Manipulation program (OpenFOAM) and investigating their usefulness in this type of simulation. First, the models were fitted to experimental data from a well-known system – polystyrene type (145D, BASF). The results showed that the Yasuda model fit must be applied to obtain the correct material properties when simulating a non-Newtonian melt flow in a wide range of shear rates. The Carreau-Winter model was found to be valid only in the zero shear-rate viscosity region. On the basis of these findings, the Soluplus-Fenofibrate system was subsequently characterized and simulated. We observed that Fenofibrate (lipid-regulating agent) acts as a plasticizer in this polymer system and decreases system viscosity at lower shear rates compared to pure the Soluplus (polyvinyl caprolactam-polyvinyl acetate-polyethylene glycol graft copolymer) at the same temperatures. Our results show that the viscosity models can be implemented accurately even for processes with high shear rates, which also involve high temperatures.

The polypropylene (PP) mono-filament is an alternative material that can be used for insulation, packaging, and polymer composite applications. In this study, PP mono-filaments were prepared by extrusion free-fall at temperatures of 190, 200, and 210°C through a micro extrusion die with a diameter of 900 μm. The free-fall speeds of the filament were controlled by a gear pump driving at speeds ranging from 12.5 to 20.0 min −1 , and the extrudates were cooled at room temperature. The PP mono-filaments were subsequently foamed by a batch foaming process with sc-CO 2 as the blowing agent at foaming temperatures of 165, 170, 175 and 180°C. The thermal properties and crystallinity of the prepared filaments and their foams were investigated using a DSC. The foam morphology and isotropic foam properties were characterized by SEM micrographs. The results show that the various morphologies of the PP mono-filament foams deviated from the isotropic foam behavior and had isotropic foam index values in the range of 1.1 to 2.3. In addition, the PP mono-filament that was foamed at 175°C expanded in the longitudinal direction and exhibited the highest expansion ratio, but its degree of crystallinity decreased compared to the mono-filaments. PP mono-filament foam represented a narrow crystallization temperature range and crystallization time than mono-filament and tended to a faster crystalline growth.

The thermal, tensile and other properties of high density polyethylene films containing iron (III) acetylacetonate as pro-oxidant additive have been studied after exposure to UV irradiation for up to 300 h. The effect of photooxidation on polyethylene films with and without pro-oxidant was estimated by Fourier transform infrared spectroscopy, X-ray diffraction analysis, Differential scanning calorimeter measurements and the tensile properties. It was observed that UV irradiation had almost no effect on the melting temperature of the different samples. After exposure, the degree of crystallinity increased from 69% to 72% for the initial polyethylene samples without pro-oxidant additive and by 3% for the samples containing iron (III) acetylacetonate. It was found that the increase in the carbonyl index of initial HDPE was not significant even after 60 h exposure to UV irradiation while samples with pro-oxidant suffered substantial degradation still for 35 h. It was observed that the decrease of the tensile strength is more pronounced for the samples with pro-oxidant under irradiation for 60 to 70 h. The films containing pro-oxidant lose ∼90% of its initial elongation at break after 35 h exposure.

Thermoplastic vulcanizates (TPVs) based on high impact polystyrene (HIPS)/styrene-butadiene-styrene block copolymer (SBS)/styrene-butadiene rubber (SBR) blends were prepared by dynamic vulcanization, with the TPVs being reinforced by carbon black (CB). Experimental results indicated that mechanical properties of dynamically vulcanized HIPS/SBS/SBR blends were enhanced remarkably by the incorporation of CB. The fracture surface morphology of the reinforced HIPS/SBS/SBR/CB TPVs was relatively flat. The Mullins effect could be observed in the stress-strain curves of HIPS/SBS/SBR TPVs and HIPS/SBS/SBR/CB TPVs during the uniaxial loading-unloading cycles. Compared with HIPS/SBS/SBR TPVs, CB-reinforced HIPS/SBS/SBR TPVs had the relatively higher stress, residual strain and internal friction loss.

Roll to roll (R2R) UV micro-imprinting lithography was investigated by both experimental and numerical methods. A maximum imprinting velocity without bubble defects was found through experiments and numerical simulations. This velocity changes while the imprinting processes were conducted without cleaning the imprinting roll. The processes of resin filling into patterned cavities were simulated at various resin viscosities, contact angles of resin on substrate and on the roller. The predicted velocity showed a good agreement with experimental measurement. The results indicated that a larger imprinting velocity can be used with lower viscosity resin. It also showed that bubble trapping was affected by the contact angles between resin and mold (substrate). Finally, the influences of pattern aspect ratio in the filling processes were also studied.

This work aims to propose an annular rotating-die technique which is specifically designed and constructed in order for the mandrel to rotate in the stationary barrel during extrusion. The annular rotating-die was employed to study the effect of the mandrel rotating speeds on the extrudate swell behavior of HDPE parison in single screw extruder at a test temperature of 210°C. The results of experiment found that rotation of mandrel caused significant change in dimension of HDPE parison after it flowed out from the annular rotating-die. It was also found that at the same apparent shear rate, the diameter swell decreased with increasing mandrel rotating speed whereas the thickness swell yielded opposite results. These results could be explained by the change of flow direction during the flow of HDPE melt in the annular rotating-die. Furthermore, the annular rotating-die technique proposed in this research could be applied in adjusting size of diameter and thickness and in predicting thickness of HDPE parison during extrusion with no need to change any production parameter in the polymer extruder.

High pressure is involved during injection molding operation, especially in the packing phase. Cracks in the mold often occur as a result of high cavity pressure. In this study, the structural analysis of an injection mold was performed to investigate the stress concentration in injection mold. The structural analysis included stress distributions and stress concentration according to cavity pressures and mold designs. The causes of cracks were investigated through the computational results for stress concentration locations and the magnitude of stress. Two commercial programs were used and various boundary conditions were applied to obtain reliable results. This study found that the locations of high stress concentrations were coincident with the locations of cracks and that the weak mold design was responsible for these cracks. Mold designs such as interlocking designs exerted a strong influence on the robustness of the mold. It was verified that the analysis method used in this study can be applied to evaluate the robustness of injection molds.

We report on the development of a novel non-invasive ultrasonic measurement system for determining the melting behavior in a single-screw plasticization unit (35/22D) and on a modified drag-induced melt removal model that builds upon that by Tadmor and Gogos (2006). The solid bed to melt pool ratio is quantified using a non-invasive ultrasonic system based on reflection measurements. Automated analysis of the reflected pulses – measured at different axial positions along the barrel – allows the melting process to be monitored online. Our analysis of the delay section incorporates viscous dissipation into Tadmor's drag-induced melt removal model. We link temperature profile and melt film thickness via differential equations and consider viscous dissipation. By segmenting the delay section in the axial direction, the temperature dependency of the thermo-physical material properties is also considered. Using the melting behavior measured for different materials, we verified the mathematical model. Additionally, the effect of reduced screw length on the plasticization process, important for the injection molding process, was investigated.

Vibration casting method was developed for making polyetherimide (PEI)/Cloisite 30B nanocomposite. Towards this, a vibration casting apparatus was designed and developed. Vibration casting apparatus provided vibrational energy and heat, simultaneously. The processing parameters were established for vibration casting in terms of frequency of vibration, temperature, time and viscosity of casting mixture. Casting mixture of PEI/Cloisite 30B/N,N-dimethyl acetamide (DMAc) was made by dissolving PEI in DMAc and then mixing Cloisite 30B in this solution. The viscosity of PEI/Cloisite 30B/DMAc mixture was optimized for casting by controlling the volume fraction of PEI in DMAc. Morphology of PEI/Cloisite 30B nanocomposite was examined by wide angle X-ray diffraction, transmission electron microscopy, scanning electron microscopy and contact angle measurement. Mechanical and thermal properties of PEI/Cloisite 30B nanocomposite were also compared with that of neat PEI to ascertain the efficacy of vibration casting method.

In this paper, numerical simulations of flows in a co-rotating intermeshing twin-screw extruder are performed using a previously presented 3D finite elements model. Some numerical improvements recently introduced are presented. The computations are performed for several processing conditions and screw arrangements. Values of specific energy, pressure and filled length are compared to the results issuing from the 1D Ludovic software in order to compare both approaches. The 3D simulation method is found to be more accurate to describe the effect of varying staggering angle and thickness of kneading discs. On the other hand, 1D model provides very satisfactory results for flows in screw elements.

An extensive study has been presented on the polymer melt flow in a closely intermeshing counter-rotating twin screw extruder. A fully three-dimensional non-Newtonian FEM computations have been performed to design the screw pumping characteristics which may be implemented into the composite model of the process. ANSYS Polyflow software has been applied to model the melt flow in the machine. An analysis has been performed for the flow in the C-chamber, and the leakage flows have been identified over the calender gap, tetrahedron gap, flight gap, and side gap. Screw pumping characteristics have been calculated and modeled for screw elements at various power law indices. It has been observed that a thick flighted element due to the positive displacement effect has got high pumping capacity increasing with an increase of the power law index. A shearing element has got no pumping capacity, and in this case a pressure gradient must be applied to push the material through an element, and the gradient increases with an increase of the power law index. Negative pressure gradient has been observed for thick flighted elements at some simulation data, and a respective reorientation of the velocity flow field has been seen.

Thermoplastic matrix composites enable production in short cycle times suitable for high volume production of lightweight design parts. While heating fully consolidated semi-finished products (“organo-sheets”) internal stresses from their production emerge, thus causing voids. Such de-consolidation must be undone or obviated for void-free parts. In this article the influence of moisture and the laminate setup on the de-consolidation behavior of twill-weave PA6/GF laminates is investigated. The results show that moisture leads to a higher void content during de-consolidation. The laminate setup in terms of fiber-volume content preponderances the influence of moisture on the de-consolidation.