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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Isothermal Cure Rheology and Chemo-Physical Correlation of a Medical Grade, Two-Part Epoxy-Amine Adhesive System
A series of isothermal, rheometric, cure experiments were conducted in small-amplitude oscillatory shear (SAOS) rheology mode at various temperatures of interest in an effort to probe relevant cure rheological behaviors of a two-part, reactive epoxy-amine adhesive system. Based on the measured rheograms, various characteristic cure times and physical transitions were quantitatively identified. A nonisothermal, calorimetric cure experiment was carried out by using a differential scanning calorimeter (DSC). The results were further utilized to analyze the “instant” chemo-physical changes at various partly-cured states of the adhesive system under simulated isothermal or non-isothermal cure conditions by using the StepScan™ DSC method. The chemo-physical correlations between the rheologically-measured physical transitions and calorimetrically-measured chemical changes are established for the purposes of understanding relevant mechanisms that govern isothermal cure processes of the adhesive system and providing practical engineering insights for advance process development in making medical devices.
Enhanced Thermal Conductivity of Ultra-High Molecular Weight Polyethelene (UHMWPE) Films through Strain-Induced Fibrillation
Thermally conductive polymers have emerged and considered as low-cost and lightweight alternatives to traditional metal and ceramic for thermal management applications. In this context, this study presents an industrially feasible processing strategy to develop and fabricate highly thermally conductive ultra-high molecular weight (UHMWPE) thin films, through extensionally mechanical stretching, to promote the fibrillation of polymer films. Key parameters (i.e., strain level and strain rate) during the stretching process were investigated, and structural characterization (DSC and SEM) and thermal conductivity measurement were conducted, to derive the processing-structure-property relationship. With an optimal strain level and a high strain rate, UHMWPE films with a maximum in-plane thermal conductivity of 1.52 W/(m·K) were fabricated. This corresponded to a thermal conductivity that was approximately three times higher than that of compression-molded films.
Thermoplastic Polyurethane Foaming through Extrusion Using a Blowing Agent
This study investigated a process of making thermoplastic polyurethane (TPU) foam using Expancel® as blowing agent during an extrusion process. For this purpose, different let down ratios (LDRs) of blowing agent were implemented in TPU. The study employs X-ray micro computed tomography (µCT) in order to see effect of the changing LDR on expansion ratio and cellular structure of the foamed TPU. The results reveal that LDRs and pressure significantly influence both the expansion ratio and the morphology of the phases present in the foamed TPU. Also the viscosity of TPU at different LDRs was measured using a custom-made in-situ capillary rheometer, which was mounted to an extruder.
Thermoplastics Viscosity Measurement Combining Experimental and COMSOL Simulation Results
Present study discusses a new method of how to apply COMSOL-Multiphysics® numerical simulation to improve the accuracy of polymer melts viscosity measurements. The main emphasis is placed on to evaluate the effects of entrance and exit geometry of a capillary rheometer on viscosity measurement. By combining experimental and COMSOL® simulation results, an accurate Bagley correction factor was found for a low density polyethylene (LDPE) and polypropylene (PP) - a stable power-law polymer melt. The results showed the Bagley correction factor based on COMSOL simulation was different from the experimental results. The method which combines experimental and simulation data can give an optimized value for Bagley correction factor for thermoplastics. And it will be used to precisely predict polymer melt viscosity for online rheometers attached to an extrusion line.
Three-Dimensional Numerical Flow Simulation of Resin Transfer Molding Process with Draping Analysis
In this paper, the numerical flow simulation of thermoset materials in resin transfer molding (RTM) process with draping analysis is described. It gives an introduction, theory and methods of analysis for the flow and draping. Then, two example cases are shown. One is a simple case where the accuracy of the solution can be checked against analytical solutions. Another is the case where the effect of using draping analysis in the RTM flow simulation is shown. The simulation results in this study are in good agreement with analytical solutions where analytical solutions are available. They also verify the significance of considering draping analysis results in RTM flow simulations.
Steps to Overcome Flow Problems
Every bulk solids handling process is prone to unreliable flow resulting in a negative effect to the bottom line of the processing unit. Understanding the cause of the flow issues is the first step in troubleshooting the problem. Next, measuring the material’s flow properties is critical in providing the design data required to develop a comprehensive scientific solution. Or in the case of a new installation, the design data is required to prevent flow problems from occurring so that the new equipment works correctly from start-up. The flow property data can also provide the design parameters for a purge system to strip out residual volatiles and produce safer, higher value, and customer pleasing products.
Degradation of PBSA in Water
The degradation of poly(butylene succinate-co-adipate) (PBSA), a biodegradable polyester that can be made from renewable feed stocks, was investigated in this work. PBSA-starch-furfural blends of up to 20 wt% corn starch and up to 15 wt% furfural were made to determine if these systems could be used to deliver a control amount of furfural, a known nematicide, for agricultural applications. The PBSA-starch-furfural blends were aged in distilled water for up to 30 days. There was only a slight downward trend in molecular weight of the PBSA and PBSA-starch blends over the 30-day aging period. Changes in the total weight of samples and the concentration of furfural in the water surrounding the pellets indicated that furfural was quickly released from the pellets and a total furfural release of 92% was achieved by day 10 of degradation.
Optimization of the Devolatilization Process in the Injection Molding Cylinder
In the recent years, many of the past demerits and all vent up problems that the past vent-type injection molding machines had were solved, so such a vent-type injection molding machine is being focused. However, the plasticization process of vent-type molding is not solved theoretically and systematically. In order to use a vent-type molding widely in the future, the technology needs to be built systematically by theoretical break-through of the devolatilization of gas and moisture, and by studying the influence on the molding materials. In our study, PA6 materials with dry pellets and water absorption pellets were molded by the normal barrel and the vent barrel injection molding. The systematic construction of the technology studied by grasping injection molding parameters which would influence the devolatilization of gas and moisture in the cylinder during the plasticization process for the vent-type molding by the system optimizations using Quality engineering .
Sterilization Effects on the Mechanical Properties of Laser-Welded Polymer Specimens of Polypropylene and Polycarbonate
Microorganisms on components need to be removed through sterilization in order to ensure the safe use of medical products for patients. Therefore, polymer parts are typically treated with gamma radiation, ethylene oxide or superheated steam; such treatment may result in a modified structure or the degradation of the polymer. The present paper shall demonstrate how the mechanical properties of test specimens and welded samples of polypropylene and polycarbonate change during the sterilization procedure. The resulting changes in the structure and the degradation respectively will be analyzed by Fourier transform infrared spectroscopy (FTIR) and Differential Scanning Calorimetry (DSC) and structural property relationships shall be derived. The analyses showed that the changes in the mechanical properties depend on the sample, the sterilization procedure and the corresponding polymer; and that those changes must be considered when designing the respective products.
Bonding of Plastic Parts with Dispersion Adhesives – Film Formation via Diffusion Processes
Bonding of plastic parts poses some challenges e.g. regarding wettability, adhesion or the choice of a suitable adhesive system. Often cost-intensive, chemically setting adhesives such as epoxy resin adhesives are used. In the furniture and paper industries, porous materials such as wood or paper are bonded with dispersion adhesives which are regarded as ecologically friendly and, due to the high water content, are cost-effective. In the context of combining wood and plastic, for example with WPC (Wood-Plastic Composites), hybrid joints of wood/WPC or wood/plastics are becoming more and more important for industrial applications. The investigations in this paper show a possibility to bond non-hygroscopic parts with dispersion adhesives. Through perforation of one bonding partner, the water in the wet adhesive can be removed from the adhesive layer. The process of film formation is analyzed considering diffusion processes, capillary forces and deformation of the particles.
A Basic Experimental Study of Cast Film Extrusion Process for Fabrication of Plastic Microlens Array Device
This paper reports a highly effective method for fabrication of plastic microlens array device based on a cast film extrusion process. In this method, a thin steel mold with a micro-circular hole array pattern is fabricated by photolithography, and a wet chemical etching process. The thin steel mold was then wrapped onto a metal cylinder to form an embossing roller mold. During the cast film extrusion process operation, the molten polymer film was extruded and immediately pressed against the surface of the embossing roller mold. Under the proper processing conditions, the molten polymer will just partially fill the micro-circular holes in the mold and due to surface tension form a convex lens surface. A continuous plastic film with a microlens array pattern was fabricated. This technique shows great potential for the mass production of large-area plastic microlens array device with high productivity and low cost.
Optimizing the Warpage of Injection Molding Parts Using 3D Volume Shrinkage Compensation Method
Injection molding has been applied to manufacturing for various products for years. However, due to the requirement of high precision for modern products, the product development is still very challenge. Conventionally, people used to utilize the packing pressure technology (either enlarge packing pressure or extend the packing time) to enhance the dimension quality, but it is not always useful. In this study, first we have applied Computer-aided Engineering (CAE) technology to analyze why the conventional packing pressure is not always effectively. The reason is that the compiled injection system with different thickness along the product will cause non-uniform shrinkage all the time. It is not easy to compensate using packing pressure skill. Furthermore, we have applied 3D volume shrinkage compensation method (3DVSCM) to reduce the warpage defect based on a mobile phone benchmark. Results show that through various packing pressure operations the dimension deviations at different regions can be compensated simultaneously. It is also verified under various operation conditions, such as different injection times, melting temperatures, mold temperatures, and so on. The modification is always so effectively. That means the high dimension quality demand is possible obtained utilizing 3DVSCM under suitable process condition setting.
Online Measurement of Polymer Melt Viscosity in Injection Molding
Melt viscosity, determined by the shear rate, barrel temperatures, and pressure during plasticization, greatly affects the flow ability of polymer melts as well as the quality of injection-molded parts. In particular, the consistency of molding qualities is highly relevant to the plasticizing quality at each cycle (i.e., injection molding requiring a high yield rate highly relies on the stability of polymer melts). However, numerous factors affect the plasticizing quality, including the geometry of injection screws, processed polymer materials, processing parameters of plasticization such as the feeding rate, screw rotational speed, barrel temperatures, back pressure, and screw backward speed. The conventional approach of plasticization in injection molding machines uses a single reciprocating screw for conveying, melting, and metering polymer melts. The plasticizing quality is roughly adjusted by indirectly controlling barrel temperatures; thus, the melt viscosity varies. An in-suit approach of assuring melt quality is to measure the melt viscosity variation online, which is a more suitable indicator of the plasticizing quality than temperature. This study thus monitored the melt viscosity variations in polymer melts by using in-mold pressure sensors. Furthermore, the effects of the injection velocity and mold temperature on the melt viscosity variations were examined.
The Different Viscosity Arrangement Effects on the Variation of Interface between Skin and Core in Co-Injection Molding
Co-injection molding, one of the multi-component molding methods, is commonly used in our daily life product. However, there are too many combinations of designs and parameters, how to properly control of co-injection is very challenge. Furthermore, co-injection with multi-cavity system is still not fully understood yet. In this study, we have focused on a nonsymmetrical multi-cavity system. First, we tried to find out how the different viscosity arrangement effects on the variation of the interface between skin and core layers in co-injection molding. Specifically, we have assigned three types of material arrangements, say A/A (low viscosity-to-low viscosity), A/B (low viscosity-to-high viscosity), and B/A (high viscosity-to-low viscosity). In A/A system, with a unique skin-to-core ratio and a fixed flow rate, general operation parameters have no significant effect on the change of the interface between skin and core. In A/B system, it generates longer and narrower locus than that of A/A system. It might be due to the higher viscous core material has higher inertia force to push in flow direction. On the other hand, in B/A system, it generates shorter and wider locus than that of A/A system. It might be due to less viscos core material has lower inertia force to push core melt in perpendicular to flow direction. Moreover, in the presence of flow rate variation, as flow rate increased, the penetration distance of interface between the skin and core is reduced for A/A system. This reduction phenomenon on the penetration distance of the interface is also observed in A/B and B/A systems. Finally, the experimental study is also performed to verify the numerical predictions on the different viscosity arrangement effects. Specifically, in the presence of flow rate variation, the numerical prediction on the interface between the skin and core is in a good agreement with the experimental data in trend.
Study on the Micro-structures of Long Fiber through Runner and Cavity in Injection Molding for Reinforced Thermoplastics (FRT)
Lightweight technology has been applied into many industries especially for automotive to enhance the fuel efficiency. One of most famous methods is applied fiberreinforced thermoplastics (FRT) technology, it includes short and long fiber-reinforced thermoplastics (FRT) to support lightweight technology. However, the enhancement mechanism by the microstructures of the fibers in FRT is still too complicated to understand. In this study, we designed a benchmark to study the fiber microstructures based on ASTM D638 with dog-bond system. First, we have tried to study how the geometry of cavity influences the fiber orientation during the injection processes. Furthermore, we have paid the attention on the variation of the fiber length distribution as the injection molding processing. Results show that the geometry of cavity has significant effect on the fiber orientation during the injection processes. Since the system has contraction and expansion structure, the orientation tensor component a11 corresponding to the flow direction, will be enhanced and then decreased along the cavity. Moreover, the fiber lengths have dramatically sharp distribution on skin layer when melt goes through the gate into the cavity. It will allow almost 90% lengths are broken through the skin layer. Meanwhile, using numerical visualization from runner to cavity through core layer, there is about 30% length broken during the journey in runner section. Finally, some fiber orientation results are compared with some literature’s. Results showed that our numerical predictions are matched with that of literature quite well in the trend.
Effect of Ethylene Content on Maleic Anhydride-Grafted Polypropylene Based Block Copolymers
This paper reports an alternative approach by incorporating ethylene segments into polypropylene backbone, that is, ethylene propylene (EP)/isotactic polypropylene (iPP) block copolymers, to mitigate the chain scission issue during the free radical initiated maleic anhydride (MAH)-grafting reactive extrusion of polypropylene. 13C-labeled MAH was used to study chemoselectivity by 13C Nuclear Magnetic Resonance (NMR) spectroscopy. Results showed that MAH was selectively grafted onto ethylene sites of copolymers. The MAH-grafting reactive extrusion conducted on a 25-mm twin-screw extruder indicated that increasing ethylene contents in EP/iPP block copolymers from 15 wt% to 46 wt% not only significantly improved MAH-grafting efficiency but also dramatically reduced the molecular weight degradation and low molecular weight fraction in the resultant functionalized polymers. This method can be also leveraged to other free radical-based functional polypropylenes.
Preparation of Three-Dimensional Poly(e-Caprolactone) Porous Tissue Engineering Scaffolds by a Combination of Microcellular Injection Foaming and Polymer Leaching
Three-dimensional (3D) interconnected porous poly (e-caprolactone) (PCL) scaffolds with desirable pore sizes and porosities have been prepared by utilizing both microcellular injection foaming and polymer leaching techniques. The incorporation of water-soluble poly(ethylene oxide) (PEO) served as a porogen to improve the porosity and interconnectivity. Highly oriented and elongated pore structures were obtained from the scaffolds via microcellular injection foaming. It was found that the pore diameter variety and the porosity increased with PEO. The compression modulus of the porous PCL scaffold decreased from 68.2 MPa for neat PCL to 46.7 MPa for 50%PCL (i.e., 50%PCL/50%PEO blend by volume) with an increase in porosity, which may render these scaffolds suitable for a variety of medical and tissue engineering applications. 3T3 fibroblast cell culture was performed to confirm the biocompatibility and cell viability of the scaffolds, which revealed that the cells proliferated the best on the 50% PCL scaffolds, as compared to the other three scaffolds, due to the more elongated and spindle-shaped pore structures, indicating favorable cell–scaffold interactions. Therefore, this novel method offers an effective means for scalable fabrication of tissue engineering scaffolds.
Research and Application of Gas Counter Pressure Technique to the Strength of Co-Injection Molding
With people’s daily life full of various plastic products, many molding technologies are developed in order to reduce production cost, increase product strength, improve product appearance, and adhere to environmental protection. Co-injection molding is also known as sandwich molding, producing composite plastic products with a multilayer structure through one injection procedure. Most manufacturers use secondary recycled material or high strength plastics as the core material to reduce material cost and increase product strength or utilizes an appropriate proportion of materials to improve product strength and surface quality. This study employs the GCP(Gas Counter Pressure) technique in the co-injection molding process to increase product strength. As co-injection molding has two flow front behaviors of melt, the skin layer thickness distribution and core penetration length are difficult control, and the fountain flow effect results in an unstable injection of core melt. Therefore, the gas counter pressure technique in co-injection molding can inhibit the flow front behavior. This study discusses the effect of the gas counter pressure technique on core penetration and mechanical strength as well as the effect of penetration length and penetration section of core melt on mechanical strength under different gas counter pressure intensities. The experimental results show that the gas counter pressure mechanism enhances core material penetration stability, changes the penetration length and penetration section of core material, and effectively enhances the end product strength.
Exploration of Annealing Effect on Pore Formation of Polyethylene Films
This paper reports the exploration of annealing effect on the pore formation of semicrystalline homopolymer, polyethylene (PE) films. Differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), and wideangle X-ray diffraction (WAXD) techniques were used to gain fundamental understanding of the change in the crystalline structure of a PE film during the annealing process. Mercury porosimetry was employed to characterize the pore structure of PE porous films under different annealing conditions. The result showed that annealing was critical for the pore formation in PE films. Longer annealing time not only resulted in larger crystalline lamellae and higher crystallinity, but also promoted the pore formation leading to larger porosity and pore size in PE films. Porous films with 49.5% porosity and an average pore size of 96.5 nm were achieved when the annealing time was 24 hours.
Synthesis and Characterization of Microcellular Injection and Injection-Compression Molded PPgMA/Graphene Nanocomposites
Maleated polypropylene (PPgMA) and Graphene (GP) nanocomposites were prepared directly by microcellular injection and injection-compression molding. Synthesized PPgMA/GP nanocomposite dispersion morphology was confirmed by X-ray diffraction (XRD) and Transmission Electron Microscope (TEM) analysis. Thermo-mechanical and electric properties of PPgMA/GP composites were also reported. Furthermore, electromagnetic interference (EMI) shielding effectiveness was investigated by injection molding (IM), foamed injection molding (FIM), injectioncompression molding (ICM), and foamed injection compression molding (FICM) methods.
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