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.
Injection molding, a typical batch process with two-dimensional (2D) dynamics along the time direction as well as batch direction, is a widely used polymer processing technology transforming plastics into products of various shapes and types. Despite of fast development of hardware, computational load has to be considered in injection molding control system. Meanwhile parameters of control algorithm should be easy to tune and separately relative with control performance like set-point tracking and disturbance rejection. In this paper, a fast and effective 2-dimensional (2D) control algorithm combining model predictive control (MPC) and 2D error prediction is proposed based on the characteristics of injection molding processes, all parameters are normalized within 0 and 1, and separately related to control performance. The proposed control scheme is tested experimentally through the closed-loop control of a key process variable, packing pressure. The result shows the good performance and verifies the previous designs.
During the extrusion of polymers, it is generally necessary to provide heating and cooling capabilities at the extruder barrel for start-up and temperature control during operation. The most common solutions used, are electric resistance heaters in combination with air-cooling by radial blower fans. These heaters are usually grouped in zones to allow the setting of temperature profiles along the barrel. Although this well-established solution benefits from several of its properties, there is one major disadvantage. At certain operating points, it is unavoidable that cooling is applied to keep the processing temperature within the given limits. By the use of air-cooling, the extracted heat is wasted and the energy efficiency of the extrusion process decreases.
The main goal of the presented approach is to preserve this extracted energy inside the system and make it utilizable at another location in the process. This is achieved by a fluid heating system using thermal oil as heat transfer medium. The system provides two global temperature levels of thermal oil and uses bypasses for each zone along the barrel of the extruder. These bypasses allow the setting of a specific desired feed temperature for every single zone without the requirement to provide an independent fluid heating system respectively. The return flow is distributed back to the global fluid streams based on the fluid temperature after the zone. Depending on the specific operating conditions, this distribution leads to a decreasing power demand of the complete temperature control system by utilizing extracted process heat to minimize the additional global heat requirement.
Runner based shear imbalance has been existed since the beginning of the related polymer injection molding development. The major phenomenon of the shear imbalance is the non-unique filling results in the molding cavities, even if the cavities are balanced in space and position. Researchers have been studying the shear imbalance problems, such as shrinkage or warpage, and the associated solutions for years. However, there is not such a solution that could be universally accepted by all industries or research academies. In some previous studies, a novel technology, Melt Rotation Technology, has been studied and developed theoretically and experimentally, providing persuasive evidence that the melt flow shear gradients developed in the runner system during traditional injection molding process is mainly responsible for the imbalance filling results, and Melt Rotation Technology was able to overcome the shear induced problem and modify the thermal, physical or mechanical properties of the molded specimens. In the current study, polymer samples molded with and without Melt Rotation Technology were tested and compared logically. Specimens from higher shear melt flow regions exhibited higher crystallinity as well as higher melting temperatures due to the localized shear rate variation. New molding trials were implemented and more experimental results have been found to support the effectiveness of Melt Rotation Technology.
In this research, direct fiber feeding injection molding (DFFIM) technique was used to produce PC/ABS/PC oligomer blends composites reinforced Glass Fiber. The continuous roving of glass fibers were fed into the vented barrel directly and mixed with matrix. The number average fiber length of 10 wt% oligomer composite is longer than that of 0 wt% oligomer composite. Oligomers reduce viscosity of matrix, fiber attrition is reduced. The tensile strength of specimen containing oligomer is limited by about 115 MPa in case that fiber volume content is over 12 %, because increasing amount of fibers is facilitated attrition of fibers. From observation of scanning electron microscope, interfacial adhesion is poor, because of gap between matrix and fiber. The effect of oligomers is nothing to tensile properties.
Draping simulation tools improve virtual prototyping for Fiber Reinforced Plastics (FRP) by eliminating a costly trial and error development process. While the mechanical in-plane properties, i.e. tensional and shearing behavior, of FRP are widely studied, the out-of-plane bending is not well understood. The bending stiffness of a thermoplastic pre-preg was determined in dependency of temperature, fabric orientation and bending length, using a modified cantilever test. Simulation tools were used to validate the results. As the thermoplastic matrix and textile matrix interactions were expected to have a significant influence on the bending behavior, DMA was performed to account for viscoelastic effects during deformation.
A set of edge-gated and center-gated plaques were injection molded with long carbon fiber-reinforced thermoplastic composites, and the fiber orientation was measured at different locations of the plaques. Autodesk Simulation Moldflow Insight (ASMI) software was used to simulate the injection molding of these plaques and to predict the fiber orientation, using the Anisotropic Rotary Diffusion and the Reduced Strain Closure models. The phenomenological parameters of the orientation models were carefully identified by fitting to the measured orientation data. The fiber orientation predictions show very good agreement with the experimental data.
Hexagonal boron nitride (h-BN) nano-particle composites were prepared with Bismaleimide (BMI) resin and low concentrations of filler to compare their thermal and mechanical properties. Silver was used as a filler to increase the thermal conductivity and to see the effect in the dielectric strength. Thermal conductivity values in the axial and radial direction were measured. The dielectric strength, dielectric constant, and the Tg were compared and analyzed among the different concentrations and particles sizes of the BN in the BMI resin. The thermal conductivity values increase as the concentration of the h-BN particles increase, and the axial and radial thermal conductivity gradient increases as the concentration increases due to the orientation of the particles as they become more closely packed. The Tg has remained constant among the different h-BN particle sizes. The dielectric strength shows improvement with the boron nitride particles as filler. Silver decreases the dielectric strength considerably. A Nova NanoSEM was used to precisely analyze the orientation and dispersion of the h-BN particles.
Physical morphology, mechanical and thermal properties of potential drug delivery devices and scaffold structures were examined. PCL and PBAT were selected because of their biodegradable and biocompatible nature. Properties of electrospun single component PCL and PBAT meshes were compared with coaxial fibers of PCL as a sheath material and PBAT as core. DMA test results indicate that the stiffness of the coaxial fiber sample has increased significantly diminishing the flexibility of the mesh. DMA results also reinforced that the strength of the coaxial fibers increases many fold as compared to individual fibers spun.
Beginning in June 2014, a small group of students at the Polymer Engineering Center at the University of Wisconsin-Madison collaborated with Kleiss Gears, Inc. in an effort to provide a fundamental understanding of the viscoelastic behavior of high-speed polymer gearing in heavy-duty applications. The project has the following ongoing objectives: material characterization, injection molding simulation, thermal-mechanical simulation, and experimental validation. The goal of this paper is to present the first look at a methodology for creating a robust viscoelastic material model that can be utilized by ANSYS? for precise simulation of thermal and mechanical behavior in polymer gears made from polyetheretherketone (PEEK).
The manufacture of polymeric foams with high cell densities with injection molding is of great interest to industry, primarily because of the flexibility and cost-effectiveness of the technology. Nonetheless, achieving high cell density foams with foam injection molding is inherently challenging due to process constraints. In our earlier work , we showed that by controlling the cooling and crystallization time within the mold cavity, foams with cell densities as high as 1010 cells/cm3 were attainable. In this work, we investigated the use of a crystal-nucleating agent in controlling the crystallization behaviors of the polypropylene and studied its influence on the foaming behavior during foam injection molding.
Novel three-dimensional (3D) open-celled carbon scaffolds (CS and CS-GR) anodes were prepared by carbonizing the microcellular polyacrylonitrile (PAN) and PAN/graphite composites (PAN-GR), which were obtained by means of foaming via using supercritical carbon dioxide as physical foaming agent. Both anodes were assembled in microbial fuel cells (MFCs) based on Escherichia coli (E. coli). The improved performance for the CS anode is ascribed to remained ?C=N group resulting in considerably improved hydrophilicity and biocompatibility after carbonization and the 3D open-celled scaffold structure contributing to the substrate transfer and internal colonization of E. coli bacteria. Meanwhile, the superior performance for the CS-GR anode is mainly attributed to increased specific surface area and active reaction area resulting from the addition of graphite. This work provides an effective method to develop a 3D open-celled biocompatible CS-GR anode, which facilitates the extracellular electron transfer for high-performance MFCs that are promising for practical applications on a large scale.
Medical devices in contact with blood require engineering plastics with reduced or negligible thrombosis or blood clotting properties. Other than the blood itself and the flow rate, the material is one of the most important variables affecting blood coagulation. A relatively new family of engineering plastics is Eastman TritanTM copolyester, which offers significant advantages to the medical industry due to excellent optical clarity before and after radiation sterilization, toughness, and chemical resistance to a variety of medical disinfectants and oncology drugs. In this paper, we describe a fibrinogen ELISA testing protocol that was developed to evaluate the fibrinogen binding behavior of various commonly used plastics including Tritan copolyesters. Surface-adsorbed fibrinogen directs cell adhesion and therefore plays a crucial role in thrombosis formation. These studies illustrate that Tritan MX731 and MX711 copolyesters exhibit low fibrinogen adsorption, indicating potential for reduced thrombosis compared to other engineering plastics.
The effect of the dispersed phase morphology on the foaming ability of a blend of polyethylene (PE) and polypropylene (PP) is investigated. Two blends of PE/PP are prepared, one with the PP phase exhibiting spherical domains and the other with the PP phase exhibiting fibrillar domains. The morphological features of the PE/spherical-PP and PE/fibrillar-PP are identified using SEM. Batch foaming is conducted to show the effect of the blend morphology on the foaming ability. Measurements of the uniaxial extensional viscosity of the two types of blends are made. The crystallization kinetics is investigated using small amplitude oscillatory shear test. Changes in foaming ability are explained in terms of the differences in extensional viscosity and crystallization kinetics.
In conductive polymer composites (CPCs), the alignment of fibers play a key role in determining the functional properties such as electrical conductivity, thermal conductivity, electromagnetic interference shielding, and dielectric behavior. However, in CPC foams, the evolution of fiber alignment caused by cell growth is not well understood. In this work, the interactions between carbon fibers (CF) and growing cells were in-situ visualized in a high-pressure foam injection molding process using polystyrene (PS)/CF as a model material system. The carbon fiber content, foam processing conditions, and visualization set-up were identified in a way that the interactions between individual fibers and cells can be captured. The results clearly demonstrate that the fibers in the vicinity of cell nuclei exhibit both translational and rotational movements upon the growth of the cells and the degree of rotation is a function of the cell size, initial fiber angle, and its distance from the cell nucleus. The results of this work provide a better understanding of the mechanisms by which foaming influences the functionalities of CPC foams and gives insight into the development of new orientation models that can accommodate foaming effects.
The ability to prepare various foams with a fixed relative density or a fixed cell size opens the possibility for decoupling the effects of cell size and cell density on the properties of foams, especially electrical conductivity. In this work, the PS/MWCNT composite foams were selected as a model system and various foamed samples were prepared by one step batch process with supercritical carbon dioxide (scCO2). Processing conditions were determined to produce polystyrene (PS)/multi-walled carbon nanotube (MWCNTs) composite foams that have the same relative density with significantly different cell sizes. Different cellular structures were achieved by controlling the saturation temperature, pressure, and time. The microcellular structure and relative density of PS-MWCNT nanocomposites were then characterized. Around the relative density of 0.48, the cell size varied from 4.5 -103 ?m.
Nanocellular foams of isotactic polypropylene (iPP) containing clarifying agent were prepared through batch foaming process with supercritical carbon dioxide (CO2). Clarifying agent, Millad NX8000, which has been introduced as a new generation of sorbitol derivatives to enhance the clarity of PP, was used to promote cell nucleation. The samples of iPP/sorbitol were prepared using twin-screw micro-compounder. Thermo-gravimetric analysis (TGA) was performed to assess the thermal degradation status of the materials during processing and characterization tests. Crystallization behavior of neat iPP and iPP/sorbitol was studied using differential scanning calorimetry and polarized optical microscopy. Cellular structure of the foams was also characterized. Depending on the foaming condition, foam structure was obtained in both micro and nano scales. Nanocellular foams with a cell density of ~1015 cells/cm3 was achieved by controlling crystallization kinetic of iPP in the presence of sorbitol. An optimum foaming temperature was found wherein the smallest cell size with highest cell density could be produced.
In this research, a Monte Carlo model is built to examine the effects of compressive and tensile strains on the percolation threshold of fibers in polymer composites. Uniaxial strain was applied in the vertical direction in a system containing fibers with an aspect ratio of 10. The strain effect was modeled by introducing its corresponding alignment effect on the fibers. The critical volume fraction èc was then analyzed in both normal direction (vertical, èc?) and parallel direction (planar, èc?) to that of the cross-section plain. The results showed that the introduction of fiber alignment, caused by strain changed both the èc? and èc?, albeit with different trends. With the increase of tensile strain, èc? reached a minimum value first before starting to rise, while èc? continuously increased. On the other hand, under compression, with the increase of strain, èc? showed a minimal behavior before rise while èc? always increased. The results of this study confirm that the percolation threshold in a particular direction of interest can be decreased via a proper choice of applied strain.
Surface quality remains one of the biggest problems when manufacturing products using selective laser sintering (SLS). Several experiments were performed using different SLS input variables in order to manufacture samples with different surface characteristics. The effect of virgin or recycled powder, the laser power utilized, and the roller speed were studied and related to surface defects. An Alicona metrology system, with a 4th axis for rotating and imaging tools system was utilized to analyze samples. The three main quantities investigated were average surface roughness, root mean square roughness and ratio of areas. Bearing area curves were also examined.
Limiting failure mode for long term performance of High Density Polyethylene (HDPE) pressure piping is slow crack growth (SCG), which is governed by the sustained stress levels (pressure and axial loads), and increases exponentially with elevated temperatures. Preliminary findings indicated the much lower resistance to SCG exhibited by HDPE butt-fusion pipe joints when compared to the parent pipe material. The integrity of HDPE pipe joints and the critical flaw size evaluation has now become a focus for the nuclear industry, regulators, and the plastic pipe industry. The ASME Boiler and Pressure Vessel Code Committee Sections III, IX, and XI address the use of HDPE piping in nuclear safety related applications. This current study is a summary of the findings till date on the crack driving force (Stress Intensity Factor), material fracture resistance (SCG tests on butt-fusion pipe joint materials), and service life prediction models for critical flaw size determination.
Injection moldable thermoplastic polyurethanes (TPUs) have been used in golf ball cover layers since the 1980s and can provide an attractive combination of formulation flexibility, performance, ease of processing, and overall lower cost when compared to cast thermoset polyurethane and polyurethane-urea systems. In developing raw material specifications for TPU and in their polymerization at the material supplier, melt flow index (MFI) is often used as a means to target certain processing and property requirements. However, using MFI as the only metric for quantifying a given TPU formulation can lead to problems as it does not capture polymerization and thermal history dependent structural variations inherent to these materials. In this study, final golf ball performance attributes, mechanical properties, thermal properties, dynamic mechanical properties, and dynamic rheological properties of two batches of TPU with identical composition and MFI were compared and contrasted. The results will be used to illustrate why TPU copolymer segmental structure and both temperature and time dependent morphology are important in the processing characteristics and properties of these versatile materials.
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