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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Modeling of Dispersive Mixing in a Twin-Screw Extruder with Three Parameter Residence Stress Distribution
In twin-screw extrusion compounding processes, dispersive mixing has a significant effect on final properties. Due to the complex flows that develop in a twin-screw extruder, prediction of dispersive mixing is difficult. The Residence Stress Distribution (RSD) is an in-line, experimental method to quantify the stress in a melt that induces dispersion. The RSD method uses the percent break-up (%BU) of stress-sensitive micro-beads to quantify the stress history in a twin-screw melt at any set of operating conditions. Using the %BU information across an operating condition domain, a predictive equation is generated to estimate the stress level in a melt as a function of operating conditions. In the following paper, predictive equations are generated with the variables of screw speed, specific throughput, and barrel temperature. Results show that increases in screw speed and specific throughput increase the %BU, while increases in barrel temperature decrease the percent break-up. In addition, the effect of screw speed and specific throughput is lessened as the barrel temperature increases. These equations allow for prediction and control of a twin-screw compounding process with three separate operating conditions.
Trouble Shooting Hot Tip Induced Polycarbonate Splay
Splay is a primary source of fallout when injection molding parts using polycarbonate. Elimination of splay is a difficult proposition, but maintaining acceptable baseline fallout across production is crucial to keeping waste under control and shipment of defects to customer to a minimum. Overall splay was reduced from 1.8 to 0.9 percent on parts running in excess of 1.4 million annually. The analysis provided in this paper shows how the extent of splay waste was identified, root cause analysis conducted, corrective action implemented, and results verified for one source of polycarbonate splay in a production environment.
Getting to Compliance: A Guide to Setting up a Medical Plastics Processing Operation
Navigating the highly regulated world of medical manufacturing and clean room operations can be a daunting, time-consuming task. Regulations and standards, developed by such organizations as the U.S. Food & Drug Administration, the International Organization for Standardization (ISO) and others, are many and complex. For those who want to begin manufacturing medical plastic products and components, understanding the regulatory requirements is only the first hurdle to be overcome. Then specialized facilities, including cleanrooms (Figure 1), white rooms and hybrid rooms, need to be designed and built, and processing equipment needs to be sourced with special attention not only to performance, efficiency and quality, but also to cleanliness, calibration, maintenance and record-keeping. Mistakes can result in delayed start-up, lost production, quarantined parts, rework and lack of process validation. This paper will review the standards and regulations that apply to medical plastics processing, and discuss the complications involved in setting up a compliant operation and resources available to simplify the process.
The Effect of Hot Melt Extrusion Operating Conditions on Degradation and Water Content of a Pharmaceutical Solid Dispersion
The processing of pharmaceuticals using twin-screw extrusion has many benefits over alternative manufacturing processes. However, several failure modes may develop as a result of the extrusion processing. In this paper, the effect of extrusion on degradation of an active pharmaceutical ingredient is considered, as well as the effect on water content of the extrudate. These properties were measured across an operating condition range of screw speed, specific throughput, and barrel temperature. From the property response, predictive equations for degradation and water content were generated as a function of the significant operating conditions. Results showed that as barrel temperature increased, the degradation increased while water content decreased. Increasing specific throughput decreased degradation and increased water content. Changes in screw speed did not significantly affect the water content and had competing effects on degradation. When designing a pharmaceutical extrusion process, this analysis can generate predictive equations that allow for evaluation of the tradeoffs between degradation and water content across the operating domain.
Accurate Three Dimensional Cooling Simulation of the Gas-Assisted Plastic Injection Molding Process
The simulation of the cooling phase of the gas assisted plastic injection molding process has not been extensively implemented for true 3D models. Gas assisted injection molding has become a mature process where an inert gas is injected into the core of a hot polymer part driving the polymer into the mold until it is completely filled. After the filling phase, the gas driven packing and cooling phase occurs before part ejection. This process requires lower injection pressures, lower clamp forces, smaller injection molding machines and shorter cycle times while requiring less material to manufacture parts. This results in cost savings. Early tests on midplane models and process observations indicate that the position of the gas core and the temperature of the surface of the mold were strongly dependent upon each other. In order to simulate cooling for the gas assisted injection molding process on 3D meshes the mold and the part domains were combined into a single temperature matrix with the flow and cooling phase simulated together in order to get the most accurate temperature solution. This paper outlines the implementation of a simulation method for the cooling phase of gas assisted injection molding. Finally results are demonstrated on real world models.
Application of Air Gap to Enhance Acoustic Performance of Biobased PLA Foams
There is an increasing need for lightweight, biodegradable and efficient sound absorbers in various industries. Polylactic acid (PLA) open cell foams have been previously identified as an effective sound absorber. This study investigates the integration of air gap to enhance acoustic performance of PLA foams. PLA foams of two different cell sizes were characterized and tested for the frequency range of 800-6300 Hz. It was identified that increasing the gap caused an increase in maximum absorption and a shift in peak frequency to lower values. The data recorded will allow for determination of parameters such as pore size and air gap for acoustic solutions in the industry.
Foaming Effects on the Percolation Threshold in Conductive Polymer Composites: A Systematic Analysis
In this research, a systematic analysis was conducted to clarify the foaming effects on the electrical percolation threshold of rod-like conductive fillers in polymer composites. In order to decouple the volume exclusion and the cell growth effects, instead of using the “final” volume content of filler in foamed samples the “initial” volume concentration of filler was considered in the analysis. This provided a means to investigate the sole effect of cell growth action. By independently analyzing the effects of void fraction and cell size on the filler orientation and inter-connections, and the subsequent electrical conductivity, a clear understanding of the filler motion in conductive polymer composite foams was obtained. The results of this study provide a useful theoretical guideline for future research.
Effects of Injection Molding Processing Parameters on Experimental Fiber Length Distribution of Glass Fiber-Reinforced Composites
Effects of injection speed on the experimental fiber length distribution of long, semi-flexible glass fiber-reinforced polypropylene composites using an end-gated plaque geometry exhibiting a complex 3-dimentional flow field were quantified. Three injection speeds were considered with constant mold and screw temperatures. Samples were subsequently used to obtain experimental fiber length distribution data. Fiber length distribution data was obtained using the epoxy method, which is a technique for fiber population selection. Injection speeds of 1, 2, and 4 seconds were used with a mold temperature of 79oC. Fiber length data at the middle of the plaque were obtained and compared. Preliminary results suggests that the fiber length data does not change considerably for each injection time being considered. More data is needed to conclude whether fiber lengths are changing significantly as a function of varying injection times.
Measurement of Hot Melt Extrusion Thermal Residence Distributions
Hot Melt Extrusion (HME) is a technique for converting insoluble active pharmaceutical ingredients (API) from a crystalline to amorphous form, by dissolving the API into a melted polymer, with the aim of increasing solubility and improving bioavailability.1 ,2 ,3Development of an HME process includes determining the region of acceptable product quality, which is typically bounded by two primary modes of failure. The first mode of failure is incomplete conversion of the crystalline API and polymer into a single phase amorphous dispersion, which can occur when the process fails to achieve a high enough temperature or has inadequate time at elevated temperature. At the other end of the spectrum, extended time at very high temperatures can cause excessive chemical degradation of the API. The region between these two failure modes results in product of acceptable quality and contains the processing space. When these two failure modes overlap, the HME process is not viable for the given API.4 ,5 ,6 ,7
In this work, we disclose a method of using a thermally sensitive molecule with well-known degradation kinetics to interrogate the average bulk thermal history of the extrudate. This method can capture effects of localized shear heating that are not easily interrogated by single point measurements at the die of the extruder. This internal thermal probe was utilized to interrogate extrusion processes with two pharmaceutical polymers, Copovidone and hydroxypropyl methylcellulose acetate succinate (HPMC-AS).
Coating Trials for an Antimicrobial Coating Containing Nisin Using Gravure and Flexographic Converting Processes
Nisin is a GRAS (generally recognized as safe) approved antimicrobial peptide that has been found to be effective against Gram positive microorganisms. Implementation of nisin into antimicrobial packaging has the potential to extend product shelf life through inhibition of spoilage microorganisms. This study found that it is possible to produce an antimicrobial coated material using large scale production processes such as gravure and flexography. The coated material produced using flexography resulted in material with potential to be sealed and did not delaminate like that of the material produced during the gravure trial. Both trials produced materials that maintained antimicrobial efficacy against M. luteus when control films were compared to treatment films. (P<0.0001)
Recycling of PP/LDPE Blend: Miscibility, Thermal Properties, Rheological Behavior and Crystal Structure
Blending of plastics used in packaging is an interesting approach for recycling or upcycling. Therefore, this study focused on the effects of processing on the properties of recycled PP and PP/LDPE blends. MFI measurements, Differential Scanning Calorimetry (DSC) and hot-stage polarized optical microscopy techniques were used to investigate the miscibility of PP/LDPE blends based on the thermal properties, degree of crystallinity, crystallization and morphology development in the blends. The MFI indicates, that PP and PP/LDPE blends are marginally sensitive to degradation at common processing conditions. The degree of crystallinity of the blends decreases with an increase of the LDPE content. Furthermore, the spherulite growth rate and crystal size of PP decrease with an increase of LDPE content.
The shifts of crystallization temperatures from the DSC measurement, in conjunction with the crystallization kinetics, indicate that PP/LDPE (25 wt% LDPE) is partially miscible.
Fabrication and Characterization of Bio-based PCM Microcapsules for Thermal Energy Storage
Bio-based phase change microcapsules (MicroPCM) consist of polylactic acid (PLA) shell and butyl stearate core were fabricated by emulsion evaporation method. Scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), and differential scanning calorimeter (DSC) were employed to characterize the morphology, the chemical structures, and the thermal properties of the fabricated MicroPCM. The results indicated that higher energy input during the emulsion step, utilized a sonicator, is critical to fabricate microPCM with smaller size (i.e., 10-12 ?m) and narrower size distribution. In short, the experimental results demonstrated the possibility to fabricate 100% bio-based MicroPCM with enhanced environmental sustainability for thermal energy storage applications.
Dupont's Renewably Sourced High Performance Polymers
Renewably sourced, also commonly referred as biobased, materials are an integral part of DuPont’s commitment to sustainable growth. DuPont is a market leader in high performance renewably sourced polymers for engineering applications. These include products based on polyamide, polyester and thermoplastic elastomers and contain between 20 to 100 percent renewable carbon by weight. By tapping innovative technology and strategic partnerships, DuPont has created novel methods of manufacturing high-performance materials from renewable resources. This new generation of materials, derived from biomass instead of petroleum, reduces the environmental footprint without compromising performance. This paper will provide an overview of renewably sourced engineering polymers and examples of commercial products in various applications.
Endurance Regression Testing: A Method to Replace ASTM D2992
After decades of use it is becoming evident that the standard practice ASTM D2992 and referenced Standard test Method ASTM D1598 may not consistently produce the intended results. Like the current practices, the goal of “Endurance Regression testing” is to obtain the Hydrostatic Design Basis for “Fiberglass” (Glass Reinforced Thermosetting Resin Pipe, Fittings, and Joints). “Endurance Regression Testing” will similarly measure, plot, and extrapolate the long term hydrostatic strength (LTHS) of fiberglass components upon exposure to a controlled and constant set of aging conditions. The control of these aging conditions is the primary departure from ASTM D2992 methods.
The choice of long term aging conditions shall take into account that there exist critical thresholds that should not be exceeded if one plans to predict performance of a similarly undamaged fiberglass component. The tested components are intended to “Endure” a pre-determined maximum design condition, intentionally set at levels believed to be below that of permanent damage. Essentially we will separate the regression testing into two stages: 1) aging or degrading the composite and 2) failure testing – measuring the effect of aging conditions. We will determine a (HDB) and/or Pressure design base (PDB) depending on the component type, and identify the component’s regression gradient for use in subsequent qualifications of similar components in shorter term testing.
Experiments with Hot Tool Joining of HDPE to Mild Steel
Joining of dissimilar materials like metals to plastics and polymeric composites is needed to make structures lighter for automotive and aerospace applications. In this work, HDPE was joined to mild steel sheets in a lap shear configuration using a heated tool. The steel sheets were sanded with and orbital sander and chemically surface treated prior to joining. The metal substrate was heated for a preset time by pressing it against a hot tool while the HDPE sheet was heated using non-contact heating with a gap of 1 mm from the hot tool. Then the steel sheet, HDPE and the hot tool were retracted, and the heated HDPE sheet was pressed against the hot metal surface for a preset time resulting in flow of thermoplastic into roughened area and joining the parts. The heating time was varied from 10s to 30s with 20s of heating producing the strongest joints. Three surface preparations of the steel sheets were investigated. The sanded steel sheet with a coarser finish prepared with pickling solution had the highest joint strength among all the tests.
Plastics and Composites Joining Laboratory Department of Materials Science and Engineering The Ohio State University
This work presents an analytical heat input model or Friction Riveting joints. Case-study friction-riveted joints were produced with unreinforced polyetherimide (PEI) and aluminum alloy AA2024 to validate the analytical model. Due to physical and phenomenological process similarities, principles from the heat generation in spin welding and metal friction welding were applied to describe heat generation in Friction Riveting. The proposed general formulation for total heat input considered both frictional and normal force contributions. However, experimental validation results indicated that the normal force contributions for the total heat input were very small (0.08% - 0.13%). Therefore they may be neglected for simplification. Furthermore model validation results showed that the viscous dissipation component of the frictional contribution varies from 91.5% to 94.7%. This shows the importance of internal shearing in the molten polymer as a mechanism of heat generation.
Generating Ultrasonically Welded Parts with Improved Strength and Reliability for Critical Applications in Medical Device Manufacturing by Utilizing Advanced Melt Flow Controls of Servo Driven Ultraso
Ultrasonic welding of thermoplastics is widely used by many industries to fuse together two parts in a short time without additional consumables. The development of servo-driven ultrasonic welders introduces unique levels of control. This study pursues previous research and investigates the capabilities of servo-driven welders to produce stronger welds. It focuses on developing a more robust and better controlled joining process for medical devices that increases the strength and reliability of welds without fully collapsing the joint or creating excessive weld flash. Experiments were completed in which the weld velocity was varied, and the resulting strength and appearance of the welds were evaluated against the intense requirements of the medical industry. Analysis of weld cross sections suggests that higher weld strength was associated with a linearly increasing weld velocity profile.
Thermography and Weld Strength Characterization of Thermoplastic 3D Printing
In fused filament fabrication (FFF), a material extrusion additive manufacturing (AM) method, thermoplastic filament is extruded though a rastering nozzle on prior layers building a 3-dimensional object. The resulting strength of the FFF produced part is limited by the strength of the weld between each layer. While numerous factors can affect the weld strength, the temperatures of the extrudate and the previous layer dictate the amount of interdiffusion and thus the weld strength. To investigate the relationship between the FFF processing conditions, extruder temperature and feed rate, and final build strength, infrared cooling profiles and weld fracture strengths are compared.
Feed Mechanism for Improvement in Scale up from Small Laboratory Reciprocating Kneaders
Industrial laboratory extruders need to have a minimum size to guarantee accurate scale up. For reciprocating kneaders the bore of the machine is required to be between 45 mm and 60 mm. The fundamental restriction preventing accurate scale up is the feeding capability of smaller machines where area available for feeding and de-aeration is limited.
An alternative feed section was tested. The new feeding zone allowed for accurate scale up from a 30 mm TriVolution compounder. The solution provided can be easily retrofitted into any kind of reciprocating kneader. Furthermore the new feed zone reduced investment when compared to a standard kneader zone.
Stability of Poly (Etheretherketone) and Poly [2, 2’ (M-Phenylene- Bibenzimidazole] Blend under Harsh Environments
The objective of this work is to investigate the degradation mechanisms and property changes of a blend of poly (etheretherketone) (PEEK) with poly [2, 2’-(m-phenylene-5, 5’-bibenzimidazole] (PBI) upon exposure to water at temperatures up to 288 °C. The molecular scale damping behavior of PEEK/PBI blend was probed using dynamic mechanical analysis (DMA). Atomic Force Microscopy based nanomechanical mapping has been used to assess the moduli profile near the interface of PEEK and PBI with various environmental exposure histories. The results demonstrate that the incorporation of water influences the compatibility behavior of PEEK and PBI through enhanced interfacial adhesion. Fracture toughness of the PEEK/PBI blend is significantly reduced by hot water exposure at 288 ºC.
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