The SPE Library contains thousands of papers, presentations, journal briefs and recorded webinars from the best minds in the Plastics Industry. Spanning almost two decades, this collection of published research and development work in polymer science and plastics technology is a wealth of knowledge and information for anyone involved in plastics.
Today’s machine capability in injection molding is at a high standard and the variation of material properties are within a small range. Nevertheless variation in material properties and conditions influence the process- and product-quality. Examples are residual moisture or drying conditions by varying material handling. With respect to surface properties especially the injection-phase has a large influence on the part quality. By a recently developed process adapted pressure control during the injection phase a compensation of variations in the rheological behavior of the material is possible within the processing. Combined with a control of the switch-over point and packing-pressure, the quality of the process can be improved. Process variations by, for example, varying residual moisture content of the material are compensated by this new control strategy.
A batch process can be viewed as a 2-dimensional (2D) system with a time dimension within each batch and a batch dimension from batch to batch. In this paper, a 2D control algorithm that combines the iterative learning with the predictive functional control (PFC) which is the third-generation of model predictive control (MPC) is proposed based on the characteristics of batch processes. The proposed control scheme is tested experimentally through the implementation to an injection molding which is a typical batch process. The result shows the good performance of the proposed control algorithm.
Ghost marks is an appearance defect that appears in injection molding parts. Particularly, ghost mark presents an uncertain visual darkness depending on watching angles. This tiny defect is often omitted conventionally but couldn’t be ignored nowadays when considering a high quality appearance. The paper presents the causes of ghost marks through experimental study of injection molding a tensile-testing-sample and improves them with exterior gas-assisted holding pressure. The injection mold is peculiarly designed to enable executing exterior holding pressure on the in-molded part surface. Additionally, the surface qualities of testing samples are digitized through a proposed image processing approach in this research. Experimental results depict that a setting of high mold/melt temperatures as well as high injection speed/pressure enables to reduce the defect. Moreover, employing exterior gas-assisted holding pressure above 30 kgf/cm2 has a significant effect on reducing ghost marks.
A variety of average, or “bulk”, flow models have been developed to simulate twin-screw extrusion performance [1-6]. While these models cannot accurately predict all critical process variables for many polymers, blends or alloys over a wide range of operating conditions, they do provide important insights into compounding operations. Following an approach described for troubleshooting single screw extrusion processes , this paper illustrates how such models can be used to diagnose problems and provide options for making design or operational improvements on co-rotating, intermeshing twin-screw machines. Three examples are presented to illustrate the value of employing flow simulations in process development and troubleshooting activities. Polyolefin/TiO2 masterbatch compounding was studied to validate the flow model on a laboratory extruder. The effects of throughput and screw wear on pumping efficiency were examined to diagnose vent port flooding. The flow model was used in the investigation of a reactive extrusion safety incident in order to determine the physical state in a critical process region and to identify factors contributing to a catastrophic failure.
In this work, a mini-emulsion technique is used to prepare aqueous surfactant-stabilized suspensions of bio-based and optoelectronic polymers. Doctor blade coating is used to prepare films of controlled thickness. The relationship between colloidal suspension properties, processing parameters and film morphology is determined. This versatile wet coating process is appropriate for a large variety of applications, and the use of water instead of organic solvents improves the environmental profile of coating preparation. The required coating procedures and resulting properties are studied for two polymers: poly(3-hexylthiophene) and poly(butylene succinate), which find applications in polymer electronics and degradable packaging, respectively.
This paper presents an effort to use physics based simulation techniques to model the Selective Laser Sintering (SLS) layering process. SLS is an additive manufacturing process that melts thin layers of extremely fine powder; we use powder with an average diameter of 58 microns. In the numerical model, each powder particle is a discrete object with 632,000 objects used for the SLS layering simulation. We first performed an experiment to measure the angle of repose for the polyamide 12 (PA 650) powder used in the SLS process. This measurement was used to determine the correct friction parameters and calibrate the numerical model. Once calibrated, initial simulations for the SLS layering process were performed to measure the changes in the surface profile of the powder. Future work will study the effect that different powders and roller speeds have on the surface roughness of a newly deposited powder layer along with determining the changes to density and porosity in the final part.
The present work compared the year-long ageing at 23°C of roto-molded fuel tanks prepared with crosslinked polyethylene versus similar tanks with a polyamide-11 inner liner for their compatibility with biodiesel at different concentrations blended with low sulfur diesel. Analysis of the fuel itself showed few peroxides formed, even after a year. Mechanical properties based on tensile testing found no evidence of oxidative damage occurring with these tanks; however, reducing material stiffness was attributed to fuel absorption. The barrier properties of the polyamide layer meant to resist fuel absorption were not apparent due to sub-micron pores being evident from incomplete sintering.
A full 3D finite volume analysis system has been developed to simulate a Metal Injection Molding (MIM) filling process. In the MIM industry, the so-called black lines are frequently observed in the surface inspection of the final sintering products. Such a critical appearance defect is attributed to powder-binder phase separation. Powder concentration is used as an indicator for phase separation. In this work, it is necessary to numerically predict the powder concentration distribution during mold filling and discuss the phase separation issue.
The development of a phased array ultrasonic system specifically for inspecting both butt fusion (BF) and electrofusion (EF) joints in polyethylene (PE) pipes of diameters up to 1000mm (39 inches) is described, including development of the inspection techniques, procedures and equipment. Also described are the trials that were carried out to assess the prototype inspection system in both the laboratory and in the field. This paper describes a European-funded research project, called TestPEP, which involved 17 organizations from seven countries, to design, manufacture and validate a site-rugged phased array ultrasonic testing (PAUT) system for inspecting pipe-to-pipe and pipe-to-fittings (elbows, bends, reducers and tees) BF and EF joints in PE pipes.
Implantable thermoplastic polyurethanes (TPU) have been utilized in the medical industry for decades due to their combination of biocompatibility, abrasion resistance, and processability. The present review attempts to establish the main factors that affect the long term biostability of TPUs, based upon multiple in vitro and in vivo studies. TPUs present two main degradation modes: oxidation and hydrolysis, which accelerate under mechanical stress. Siloxane-based TPUs seem to be most resistant to biological degradation. In addition, their complex morphology makes accelerated in vitro predictions based on time-temperature superposition inaccurate.
The resin viscosity is an essential parameter to characterize the performance of injection molded products. However, it is very difficult to properly measure the viscosity of fiber reinforced composites during the injection molding process. In order to characterize the melt viscosity of fiber reinforced composites, capillary meters or rheometers are normally used. But the actual melt viscosities of composites in the injection molding process are not properly measured by those methods because shear rates realized by those methods are not high enough to mimic the shear rate during the injection molding process. In this study, an original molding tool is used to measure the melt viscosity of carbon fiber reinforced composites in the actual injection molding process. As a result, the influence of carbon fibers used in composites on melt viscosity during the injection molding process were properly characterized.
In this experimental series the influence of the initial moisture content of the materials in the extrusion-technical production of Polylactide Cellulose Fiber Compounds are examined. The target values in the tests are the mechanical properties (such as impact strength and tensile strength), the rheological behavior, the color, and the molecular weight of the produced compounds. The compounding was done by using a co-rotating twin screw extruder. The results show a significant effect of the variation of initial moisture of the materials on the tensile and flexural strength and the discoloration of the compounds as well as the melt temperature during compounding. Furthermore, it was found that the rheological properties of PLA-cellulose fiber compounds are linearly dependent on the material moisture before experiment. The other target values show no dependence on the moisture of the raw materials.
The aim of this work was to study the enhancement of the impact resistance of polypropylene via the addition of the thermoplastic elastomer styrene-butadiene-styrene, and fumed silicon dioxide nanoparticles. Polypropylene/styrene-butadiene-styrene silica nanocomposites were prepared using a twin screw brabender plasticorder, the weight percent of the SBS was varied at (0, 5, 10, 20 and 40) wt%, and the silica content was varied at (0, 0.05, 0.1, 0.5, 1 and 2) wt%. Throughout this study it was observed that increasing the SBS content lead to a drastic improvement in the impact strength, with over a 6-fold increase at maximum. It was an obvious conclusion that, contra to expectation, the silica nanoparticles didn't significantly enhance the impact property. This is most likely due to the poor dispersion of these powder nanoparticles in the polypropylene/SBS matrix. Therefore, the SBS properties had a greater effect on the enhancement of the impact properties than the silica.
Mechanical properties of fiber-reinforced thermoplastic products have a deep dependence upon flow-induced variations in fiber structure, involving fiber orientation, fiber length, and fiber concentration. However, few numerical studies have been done on fiber concentration to date. Using the suspension balance model of particle migration, the objective of this work is to perform the concentration calculation in mold filling of a center-gated disk. Consequently, the predicted concentration distribution of short glass fiber filled polybutylene terephthalate (PBT) with an average volume fraction of 0.177, through the thickness measured at the lubrication region of the disk, agrees well with related experimental results.
Injection molding is a typical batch process that transforms polymer granules into various high-value-added products. The aim of this paper is to improve the batch process control performance in the two-dimensional (2D, within batch and batch to batch) and hybrid frameworks by exploring the repetitive and multi-phase nature of batch process. This research involves a 2D hybrid prediction model, comprised of a 2D step response model and a piecewise affine model. With this prediction model, a novel 2D hybrid dynamic matrix control strategy is proposed. Application to the injection molding process shows the effectiveness of the proposed control algorithm.
Polyurethane (PU) foams were prepared using synthetic and bio-based polyol. In both cases, isocyanate content was reduced and cellulosic nanofibers and lignin were incorporated to achieve the desired rigidity. The experimental results indicated that the mechanical properties of 100% bio-based polyol PU foams exhibited higher performance compared to 100% synthetic polyol PU foam. The odor concentration of bio-based and synthetic PU foams showed in similar level. A automotive bumper energy absorber prototype has been developed from lignin and nanocellulose enhanced bio PU foams with reduced isocyanate content.
The visibility and shape of sink marks is an important criterion for the quality of a variety of injection molded parts. Due to necessary geometrical features on technical parts, the formation of sink marks is mostly inevitable. The aim of this work is to present a study on the influence of processing conditions, especially rapid heat cycle molding (RHCM), on the sink mark geometry. Several process settings were tested for enabling the recognition of the most influential process parameters. The Pseudo-Voigt distribution model, a superposition of the Gaussian- and the Lorentz-distribution was found to deliver an accurate mathematical description of the sink mark cross-section shape. For this work, specimens were measured via confocal microscopy to gain the sink mark shapes. Two different sample geometries were used. This enables to investigate various base-to-rip-thickness ratios as well as the dependence on the flow-path length. By applying RHCM, the mold surface temperature could be introduced as important factor. The Pseudo-Voigt-Model was then fitted on the measured sink mark shapes, resulting in several fitting parameters. These fitting parameters were then correlated with the process settings. The results show strong correlation of both, holding pressure and mold surface temperature, on the sink mark topography.
The onset of bubble formation or in other words the degassing pressure is an important value for the designing of a die for extrusion foaming. Therefore, the effect of flow channel geometry on the degassing pressure was examined with a newly developed slit die concept. The determination of the onset of bubble nucleation was carried out with an optical spectroscopy technique. In this study we used four different flow channel geometries to determine the degassing pressure for different flow conditions. Additionally simulation experiments were used to compare the different flow channel geometries in terms of shear rate, pressure drop rate and velocity changes to gain data for the scale-up. It was shown, that the degassing pressure is a function of the flow conditions. With increasing shear rate, elongation rate and pressure drop rate the degassing pressure increases.
Recent advances in processing-structure-property relationships of micro- and nanolayer polymeric systems are presented. Coextrusion via a series of layer multiplying dies has enabled the production of films of with two or more materials that contain tens to thousands of layers with individual layer thicknesses from the micro- to the nanoscale. Nanolayered films were demonstrated with improved gas barrier through confinement of a crystalline polymer layer. In addition, unique films with layer thickness dependent optical properties including novel reflective characteristics have been developed. Redesigned layer multiplication dies we have produced gradients layer thickness films including film-foam structures resulting in unusual properties.
New wear resistance (WR) thermoplastic co-polyester elastomers (COPE) deliver improved performance over a wide range of speed and load conditions in sliding or moving applications. These elastomers have excellent cold temperature impact strength and work well at a broad range of temperature and humidity conditions, primarily in injection molded articles. Various grades with wide range of hardness are suitable for applications requiring excellent tribological properties. These elastomers provide outstanding ductility combined with the excellent chemical and environmental resistance properties of polyesters. The unreinforced and higher flexibility COPE grades fill the property gap between standard thermoplastic polyester urethanes and vulcanized rubbers by providing excellent fatigue strength and hence an increased operational lifetime. These elastomers are easy to process, recyclable and retain their impact strength down to -30 °C.
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