SPE Library
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.
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Conference Proceedings
Evaluation of High Flow Poly Ether Imide Resins Using Structure-Property-Process Relationships
Melt stability of polyetherimide based resins were evaluated as a function of time and temperature to determine their respective processing temperature ranges for injection molding applications. The study identified temperature ranges where four experimental materials demonstrated equivalent (or nearly) thermal stability as commercial polyetherimide. Additionally, the entanglement density of the experimental materials was determined using van Gurp-Palmen plots to understand rheology and impact properties. The material with the lowest entanglement density showed the least thermal stability with reduction in toughness properties
Development of an Analytical Mathematical Modelling Approach for a More Precise Description of Disperse Melting
The melting behaviour in single-screw extruders is of significant importance. For a high-quality extrusion product, a completely molten and thermal homogeneous, in case of a compound or the use of fillers also uniform concentrated, polymer melt is necessary. Due to the striving for the highest possible economic efficiency of the process, screws which can achieve a higher throughput at the same extruder size through higher screw speeds are often used. In these, however, melting no longer takes place in the classical way with a subdivision into melt eddy and solid bed, as was researched in the 1950s and 1960s by MADDOCK and TADMOR and successively extended by many more. Much more the solid bed breaks up into individual solid particles due to high forces or special screw geometries introducing disperse melting. The mathematical description of this process is not as mature as that of classical melting and is therefore the subject of this paper. An analytical mathematical model is presented which allows the calculation of the temperature development in the particle and the variable melting rate in addition to the actual melting process of the disperse melting. The temperature input by dissipation as well as by barrel temperature is considered. By means of an iterative procedure, complete screw geometries can be checked for the melting behaviour. Furthermore, a statistical experimental design based on the model is used to show which factors favor or impair disperse melting.
Evaluation of the Distributive Mixing Quality Based on Particle Tracking and Delaunay Triangulation
In addition to conveying and melting, one of the core tasks of a single screw extruder is the homogenization of the material. Since conventional conveying screws in single screw extruders usually have an inadequate mixing effect, mixing elements at the end of the screw are commonly used to increase the homogenization performance. The melt homogeneity at the end of the screw is very important because it correlates strongly with the product quality and is therefore also directly related to reject rates in the production. However, characterization of the mixing quality is often very difficult because there are many degrees of freedom. In this paper, a new method for characterization of the distributive mixing quality on the basis of 3D CFD simulations is presented. In order to be able to assess the mixing quality, the particle trajectory of an initially defined particle distribution at the inlet of the flow must first be calculated with a particle tracking method. Subsequently, the homogeneity can be characterized by the change in the particle distribution at the end of the flow area. Bin counting is often used for this purpose. However, this method has considerable weaknesses, which will be shown. Consequently, a new characterization method based on the Delaunay triangulation has been developed and implemented in MATLAB. The new method will be demonstrated using selected fictitiously generated as well as simulated particle distributions of some different screw geometries.
Nonlinear Rheological Behavior Carbon Nanotube-Filled Polypropylene Nanocomposites: Modeling and EXP
The rheological behavior of multi-walled carbon nanotube (MWCNT)-filled polypropylene (PP) nanocomposites with different filler loadings was experimentally studied and simulated using constitutive modeling. Rheological behavior was characterized in small amplitude oscillatory shear (SAOS) flow, large amplitude oscillatory shear (LAOS) flow, startup of shear flow, steady shear flow, and stress relaxation after the imposition of a step shear strain. Virgin PP and PP with CNT loadings of 1, 3, and 5 wt% were used. The formation of a rheological percolation network was observed at these loadings. The Leonov and Simhambhatla-Leonov (SL) models were used to simulate the rheological behavior. In the linear region, the simulations provided good predictions of the experimental data for both the unfilled and filled PP. In the nonlinear region, the simulations also provided good results for the virgin PP and satisfactory results for the PP/1wt%CNT nanocomposite under most flow conditions. However, for the other two nanocomposites the model showed mixed results.
Analysis of Leakage Flow in Pressure-Generating Melt-Conveying Zones
In many extrusion analyses, the pumping capability of the extruder screw is overestimated. This is usually due to the effect of the flight clearance being omitted in the mathematical model. The clearance between flight land and barrel surface enables the polymer melt to leak across the flights, thereby reducing the effectiveness with which the screw can pump the polymer melt forward. A few studies have proposed modifications to the widely known pumping model to account for the effect of leakage flow. While most of these consider Newtonian fluids, less attention has been directed towards shear-thinning polymer melts. We propose approximate equations to predict the flow of power-law fluids through the flight clearance of pressure-generating melt-conveying zones. Rather than correct the net material throughput of the single-screw extruder, we locally describe the two-dimensional flow between the flight tip and the barrel surface. Our novel models, which predict the flow rate and viscous dissipation, increase the understanding of the flow of shear-thinning polymer melts across the flights. Implemented in our screw calculation routine (introduced in [1-4]), they also serve as the basic equations for the network elements positioned over the screw flights.
Improved Polypropylene Thermoformability Through Polyethylene Layering
While the flow forces governing primary melt-based polymer processing techniques, such as extrusion and injection molding, have been extensively studied, characterization of forces in secondary processes such as thermoforming is limited. In this work we utilize multilayer coextrusion to create an extruded film with 100s of alternating linear low density polyethylene (LLDPE) and isotactic polypropylene (iPP) layers; and by extension, 100s of interfaces. The combination of LLDPE, iPP, and these interfaces decreases the elastic storage modulus (E’) and broadens the rubbery plateau observed via dynamic mechanical analysis (DMA). The broadening of the rubber plateau is correlated with an observed improvement in LLDPE/iPP multilayer thermoformability compared to the homopolymer LLDPE and iPP films.
Characterization of Polycarbonate Blends: Executive (FT-IR) Compared To Rheology
This work was mainly focused on examining the viscosity and FT-IR for the same samples at the same temperatures. The characterizations were run in three stages. The first stage: The polycarbonate resins were melt-blended using (Coperion) a Co-rotating twin-screw extruder (SB). In the second stage, the same material was included; the same compositions were blended in steps of eleven in a Thermo Haake Mini Lab II twin-screw micro compounder (ML). The steps (%PC1/%PC2) were (100%/0%), (90%/10%), (80%, 20%)… (0%/100%) which resulted in eleven batches. In the third stage, the same polycarbonate blends samples were characterized by Fourier transform infrared spectroscopy (FT-IR) spectra analysis. The research aims to identify a comparative characterization study for the viscosity and FTIR. The results have a significant fundamental science by steering a systematic effect on viscosity and dispersion. This technique is particularly useful since it allows identification and localization of compounds to study and identify chemical groups or chemical compounds when the sample absorbs infrared radiation. The focus was extended to the polymer grade to extract the impact of the rheological characteristic, FTIR and to study their correlations in the viscosity data and their bearing effects on color output
Mitigating Resin Degradation Via Nitrogen Inerting for Single-Screw Extruders
Resin degradation can reduce the value of a product, especially for polyethylene (PE) films. Most of the degradation occurs in the final processing operations using single-screw extruders. There are many reasons why degradation occurs, and screw design is considered the first and best opportunity to mitigate it. The elimination of atmospheric oxygen is the next best option. This paper describes a method for mitigating resin degradation via nitrogen purging at the hopper. Extrusion data are provided that demonstrates the effectiveness of nitrogen purging for PE resins.
Viscous Heating Correction for Polymer Melts in Capillary Viscometry
Viscous heating in polymer melts can be a disturbing factor in high-shear-rate viscosity measurements. The present study employs an iterative algorithm that we recently developed to improve the accuracy of the shear viscosity from a capillary rheometer [1]. A generalized Newtonian fluid, along with the Cross-WLF model for shear viscosity, was used to simulate the contraction flow in the capillary rheometer by Moldex3D flow solver. According to the proposed algorithm, the simulated temperature rise and shear rate were used to iteratively correct the corresponding nominal data, so as to obtain the optimized parameters in the Cross-WLF model. The predicted pressure drops based on the proposed methodology were shown to be in better agreement with the capillary experiments, with an average relative error reduced by ~20% for the melts studied.
Experimental & Analytical Investigation of Incomplete Filling Defects During Hot Runner Based Inject
A novel processing innovation called Rheodrop technology is introduced for hot runner based injection molding. The goal is to enable both optimized processing and properties of final molded parts. The technology applies a controlled shear rate to the polymer melt during and/or in between injection molding cycles by rotating the valve pin inside a hot drop nozzle. Doing so can eliminate defects such as incomplete filling which was focused on during this study. This issue was investigated through both simulation and experimental analysis. Moldflow software was utilized to study the effect of melting temperature on cavity filling. Acrylonitrile Butadiene Styrene (ABS) was chosen as a focus material, and three different melt temperature levels were selected. The cavities are perfectly filled at the highest melt temperature level with incomplete filling resulting at the lower levels. Implementation of the Rheodrop technology then produced consistent and complete filling throughout the melt temperature range studied.
Large-scale extrusion-based 3D printing for highway culvert rehabilitation
A significant problem associated with repairing deteriorating highway culverts is the resultant lowered flow capacity. This can be mitigated by the use of culvert diffusers. Current culvert diffusers are made using fiberglass reinforced thermosetting epoxy polymers, which require custom made molds. This research work explores the use of large-scale 3D printed thermoplastic polymer composite to manufacture culvert diffusers. The research work shows that 3D printing technology reduces the manufacturing time as well as the cost of culvert diffusers. Large-scale 3D printing technology is well-suited for the manufacture of individualized culvert diffusers with unique geometrical designs without the need for molds. 3D printing technology is also capable of using different materials according to environmental requirements. The use of segmental manufacturing in conjunction with large-scale 3D printing enables the manufacturing of culvert diffusers larger than the build envelope of the 3D printer. Different post-processing techniques used for cutting, finishing, and joining the 3D printed segments are discussed.
Fused Filament Fabrication Feedstock Characterization via In-Line Rheology
An instrumented hot end has been developed to monitor the pressure in Fused Filament Fabrication, and is used as an in-line rheometer to characterize the viscosity of an acrylonitrile butadiene styrene (ABS) material. Additional analysis was performed on the transient pressure data to consider compressibility effects and nozzle drool. The range of flow rates was identified at which the pressure in the hot end was most stable. Stabilization time given compressibility effects was also evaluated.
Investigation and Realization of Watertight FDM Structures Made of Ultem 9085 in Pressurized Systems
Fused Deposition Modeling (FDM) parts generally show a fluid permeability due to their specific and characteristic strand structure. Therefore, an application including contact with water is difficult and limits the areas of application of this Additive Manufacturing (AM) technology. In this paper the aim is to determine the water tightness of FDM manufactured Ultem 9085 structures in a pressurized system using a suitable test setup. Based on the results, optimization approaches such as parameter modification, variation of the specific part thickness and a surface treatment shall identify if a complete tightness can be realized. For the validation of the results, analysis methods such as CT-scans and macroscopic images are used to determine the component surface.
Effect of Carbon Fiber On the Fracture Toughness of Fused Filament Fabricated CF/ABS Composites
This study reports the effect of carbon fiber (CF) on the fracture toughness of 3D printed carbon fiber/ acrylonitrile butadiene styrene (CF/ABS) composites. Chopped carbon fiber was compounded with ABS to prepare CF/ABS filaments containing 0-25 wt.% CF. Compact tension specimens were designed, 3D printed, and tested to measure the composites’ mode-I fracture toughness, KIc. The results showed CF/ABS composites can be made with up to 25 wt.% loading without any drop in their fracture toughness. In fact, ABS’s KIc increased by ~22% with an introduction of 10 wt.% CF. There was a slight drop in KIc, once the CF content was increased to 15 wt.%. Further increase in CF content from 15 to 25 wt.% did not cause any significant change in KIc and it was found to remain similar to that of the neat ABS. The fracture toughness trend with CF content was qualitatively explained in terms of two competing mechanisms, namely increased actual fracture surface area and less perfect interlayer adhesion at the presence of CFs.
Simulative Analysis of the Filling Process in the Two-Component-GITBlow-Process on Organo Sheets
The combination of different special processes allows the production of complex hybrid component structures with simultaneous function integration, thus opening up a large portfolio of possibilities. One example of this is the combination of back-injection of thermoformed organo sheets with the GITBlow process. An organo sheet is back-injected by two components, whereby one of the two components is additionally formed by the GITBlow process. The separation of the two cavities during the filling process by the formed organo sheet is a challenge not to be underestimated. The investigations refer to the simulative analysis of the filling process of the cavities. Here, the melt displacement into the secondary cavity during the first gas injection and the influence of the separation of the two cavities are considered. Investigations show that the melt temperature, the gas pressure and the injection speed have the greatest influence on the filling of the cavity separation.
Evaluation of Pressure Reduction for Various Materials at Various Length to Thickness Ratios Using An iMFLUX® Constant Pressure Process
This paper will show that an iMFLUX® constant pressure process can significantly reduce molding pressure requirements compared to conventional velocity controlled injection molding while molding a part with an equal length to thickness ratio. A significant pressure reduction is observed for all materials; regardless of material type or family. All comparisons in this paper are based on the maximum achievable flow length of a conventional velocity controlled process for each material.
Investigate on the Degree of Assembly for Components in an Injection Family Mold System
The main target for Design for Manufacturing and Assembly (DFMA) is to integrate multiple components with multiple functions to minimize cost and efforts. In addition, a family mold system has been utilized in industrial manufacturing to make a series integrated components for years. However, there is very few information to the degree of assembly for a single component or components. In this study, we have tried to investigate the degree of assembly using a family mold system with two different components. The study methods include numerical simulation and experimental observation. Firstly, we have adopted packing pressure as the practical operation parameter to affect the variation of degree of assembly. Then the pre-defined characteristic lengths can be utilized to catch the degree of assembly. Results showed that when a higher packing pressure applied in injection molding, it will results in more difficulty in the assembly for Part A and B by numerical prediction. Furthermore, the experimental validation on the degree of assembly based on the characteristic lengths has also performed. The tendency is quite consistent for both numerical simulation and experimental estimation. However, there is some gap between simulation prediction and experimental measurement for the same operation condition setting. It is necessary to make further study in the future.
Characterization of In-Mold Shrinkage Using a Multi-Variate Sensor
The design of a multivariate sensor is detailed that incorporates a spring-biased pin for measuring in-mold shrinkage. The sensor also includes a piezoelectric ring for measurement of polymer melt pressure and an infrared detector for measurement of the polymer melt temperature and the local mold temperature. As a result, the multivariate shrinkage sensor can accurately measure cavity pressure, melt temperature, ejection temperature, various event timings, and in-mold shrinkage to closely estimate the total shrinkage. The performance of the sensor is validated with a design of experiments for a high impact polystyrene (HIPS) and polypropylene (PP).
Influence of Chemical Blowing Agents on the Filling Behavior of Wood-Plastic-Composite Melts
A major challenge in the injection molding of wood fiber reinforced thermoplastics, so-called Wood-Plastic-Composites (WPC), lies in the flow anomalies that occur during the cavity filling process. The melt front is brittle and breaks open at unpredictable points. Particularly at wood contents above 40 % by weight stream flow (jetting phenomenon) caused by wall slipping occurs more frequently, which in turn leads to undesired weld lines. In this study, an analysis method is presented, which allows a quantitative evaluation of the filling process. The methodology is applied to different WPC formulations. Higher wood content, low viscous matrix polymers and coarser particles lead to poorer filling behavior overall. In order to reduce the flow anomalies, chemical blowing agent is added to the WPC. This should reduce the viscosity and thus the elasticity of the melt. It has been shown that reducing the viscosity has no positive influence on the filling behavior. An improvement could only be achieved with the lowest viscosity formulation. However, the explanation for this is seen in the comparatively lower resistance of the melt to the expansion of the blowing agent, as a result of which the melt is pressed more strongly against the mold wall and wall slipping is thus rather suppressed.
Enabling Mechanically Adaptive 4D-Printing with Cellulose Nanocrystals
Additive manufacturing of stimuli-responsive materials is an area of 4D-printing that is continuing to gain interest. Cellulose nanocrystal (CNC) thermoplastic nanocomposites have been demonstrated as a water responsive, mechanically adaptive material that has promise to generate 4D-printed structures. In this study, a 10wt% CNC thermoplastic polyurethane (TPU) nanocomposite is produced through a masterbatching process and printed using fused filament fabrication (FFF). A design of experiments (DOE) was implemented to establish a processing window to highlight the effects of thermal energy input on printed part mechanical adaptivity (dry vs. wet storage modulus). The combination of high temperatures and low speeds result in thermal energies that induce significant degradation of the CNC/TPU network and reduced absolute values of storage moduli, but the mechanical adaptation persisted for all the printed samples.
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