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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Rheological and Chemical Modification of Polypropylene with Inorganic Clays
Polymer composites were produced by mixing an inorganic clay hydrotalcite (HT), stearate coated (HTC) and uncoated (HTU) at 5 and 30% by weight with polypropylene and modified polypropylene. Torque profiles from blending in a batch mixer indicated significant viscosity changes depending on the type of the particular clay/polymer components. FTIR, MFI, DSC and TGA data suggested corresponding structural changes in the composites. The results showed that coated hydrotalcite produced the highest melt viscosity when added in the modified polypropylene. Tests are underway on flammability and rheology to shed more light into the interactions of the clay and the polymers.
Cross-Linked LDPE as a Rheological Modifier for LLDPE
Melt strength tests were conducted for blends of linear low density polyethylene (LLDPE) with cross-linked low density polyethylene (xLDPE) to study the effect of rheological modification on the development of low density, LLDPE foam with improved processability during extrusion foaming. Blends of LLDPE containing various concentrations of xLDPE, cross-linked with peroxide, were prepared in a Brabender batch mixer. Melt strength tests of the prepared blends were conducted through a capillary rheometer. It was found that melt strength increased with respect to increasing concentrations of xLDPE, suggesting optimum foamability at specific xLDPE content.
On the Deformation of a Slender Bubble in a Carreau-Yasuda Liquid in an Extensional Flow
The deformation of a slender bubble in a Carreau-Yasuda liquid in a simple extensional and creeping flow has been theoretically studied. With the assumption of a constant pressure in the liquid, the deformation problem can be described by an ordinary differential equation, which was numerically solved. Analytical expressions for the local radius were obtained close to the center and the end of the bubble. The results for the shape of the bubble are presented as a function of four governing dimensionless numbers. The relevance of this work to polymer devolatilization and foam plastics is discussed.
Non-Reactive Process for Recycling of Cellular Phones
The use and production of cellular phones have skyrocketed within the last decade, with the average use lifetime between 1 and 3 years. So, the ability to dispose of and recycle the phones is a pressing issue. These phones are composed of a variety of materials, including thermoplastics (six different types), metals, rubber, and epoxy. This work pertains to the grinding of cell phones, separation of thermoplastics and epoxy from the bulk ground material, and subsequent compounding of the desired materials in an intermeshing, co-rotating, twin screw extruder. Tensile and Izod impact tests were performed on the immiscible blends, whereas SEM and AFM analyzed the fracture surfaces. Dynamic mechanical thermal analysis show how thermal properties of the blends change as a function of blend composition. A polyolefin elastomer (PE) was incorporated into the blend and was shown to improve impact properties.
Reactive Process for Recycling of Cellular Phone Housing
The front cover of the cellular phone housing was ground to be as the same size as the original particles before use using the knife mill and the undesired materials were separated with the sink-float process in water and salt. The unprinted glass fiber reinforced epoxy circuit boards were size reduced and pulverized using both the knife mill and the hammer mill. The separated epoxy powder and glycidyl methacrylate (GMA) were added as the additive and the reactive species for the reactive process using the batch mixer and the twin screw extruder, respectively. Izod impact strength at various temperatures, tensile test, particle size distribution analysis for the ground circuit board, SEM on the fracture surface, and dynamic mechanical spectroscopy were performed to characterize the reactive polymer alloys and mixtures compounded by the batch mixer and the twin screw extruder.
Morphology Development and Rheology of HDPE/PBT Blends
High density polyethylene and a small amount of poly (1,4-butylene terephthalate) (PBT) have been blended in a twin screw extruder, and its rheology as well as morphology has been investigated as a function of extrusion condition. When the blend was extruded slightly below the melting temperature (Tm) of PBT, the dispersed phase forms a curved sheet morphology, and turns into fibril and finally into droplet structure as more shear is applied. On the contrary, when the material was blended at the higher temperature, the dispersed phase forms only droplet structure.Even though the blend contains as small as 5wt% PBT, the moduli as well as shear viscosity of the blend with the sheet structure increases significantly. However, the droplet structure does not show enhancement of rheological properties unlike the case of curved sheet. This means that we can control the blend morphology as well as its rheology, and can enhance the rheological properties by inducing the microstructure like a curved sheet.
2D Composite Models of Modular Tangential Counter-Rotating Twin Screw Extruders
A new 2D composite model with hybrid FEM/FDM formulation was developed for simulating the fully filled and starved regions with the associated pressure profiles of a modular tangential counter-rotating twin screw extruder. 1D composite models combine the screw characteristic curve of individual element to analysis flow of an entire modular screw and the flow fields of the whole domain are not calculated again. Based on the linear relationship of the drag flow rate and the screw rotation speed under the single screw extrusion theory, the new mesh with artificial screw rotation speed boundary conditions was used to simulate the entire flow fields for the counter-rotating twin screw extrusion process in our 2D composite models.To demonstrate applicability, the predictions of individual screw elements via hybrid FEM/FDM agree well with Nichols's experimental studies. The pressure and filling factor profiles in a modular LSM34-34 extruder provided by 2D composite models show good agreements with those of 1D composite models.
The Effect of Different Batches of the Same Polymer on the Flow in Flat Coextrusion Dies
Rheological and molecular characteristics (MWD) were experimentally determined for different batches of LDPE. The results show that extensional viscosity may significantly vary for different batches even if shear viscosities and MWDs are very similar. FEM analysis was consequently performed to determine the stability of the coextrusion flow in the flat die for different batches of the material and the effect was found considerable. A recently proposed ‘TNSD sign criterion’ (Zatloukal et al, Int Polym Proc., 16(2) 198-207 2001), which quantifies the relative stretching of the layers in the merging area, was used for this purpose.
An Intelligent Knowledge-Based Plastic Injection Mold Design System
This paper presents an intelligent knowledge-based plastic injection mold design system, 'IKB-MOLD', which was developed based on the analysis of injection mold design process and collection design rules from plastic injection mold design companies. A plastic injection mold object and knowledge representation is propose for detailed injection mold design. Since such representation considers both relationships for assembly and relationships for functional, it is possible for automatically generating assembly tree while satisfying the functional requirement during design process. IKBMOLD integrates the proposed object and knowledge representation with many developed tools in a commercial CAD/CAM software environment. And it has been testified in plastic injection mold design company that IKB-MOLD system can speed up the design process and facilitates design standardization.
Evaluation of Flow Instabilities Using Simulations
Three-dimensional simulations were used to gain insight into the jetting instabilities. With 3D meshing and Navier-Stokes equations, flow instabilities were observed in 3.2-mm thick parts. Inertia produced significant flow instabilities in simulations of polycarbonate and polyacetal. For these materials, this unstable flow correlated with jetting that was associated with slippage of melt along the mold walls. Gravitational effects reduced these instabilities in most materials, but produced highly unstable flow in PBT. No significant instabilities were predicted for polystyrene, polypropylene, polyamide-6, and ABS. In these materials, jetting is usually associated with elastic effects, rather than frictional characteristics. This suggests that the 3D simulations can be used to predict these defects. A viscoelastic constitutive equation should produce more reliable results.
Comparison of Approaches for Optimizing Molding Parameters
The effects of two molding parameter optimization techniques, a manual technique and an automated (software-based) method, were compared with respect to the processing conditions, process stability and reproducibility of the molded parts, and the stress retained in those parts. The software-based process optimization resulted in molding conditions that led to more consistent part weights and dimensions than a manual technique. The parts from the former method, however, exhibited somewhat higher retained stress. This was attributed to the low injection velocities and the packing method recommended in the optimization process. The fully automated process optimization was sometimes limited by the software’s selection of injection velocities and shot size increments that could not be achieved in practice.
Automated Design for the Gate Location of Injection Molds
In injection molding, the placement of a gate is one of the most important variables of the total mold design. In this paper, a methodology that automatically predicts the “optimal” gate location for single-gate injection-molds was developed based on the minimization of the maximum equivalent flow length difference between different fundamental flow paths. The objective of optimization is to achieve a balanced filling pattern design within minimum time. A genetic algorithm was used to search the optimal gate location. The models analyzed demonstrate that the proposed method is promising and the computation time is gratifying.
Evaluating Factors Affecting Shrinkage Predictions
The effects of selected assumptions on shrinkage predictions were determined using two materials, polycarbonate and poly(butylene terepthalate). The linear shrinkage of polycarbonate parts increased with melt temperature, but the shrinkage of PBT exhibited little sensitivity to processing conditions. Although none of the simulations provided linear shrinkage results that reflected these trends, volumetric shrinkage did. Modified flow rates had little effect on the predicted linear shrinkage, but incorporating temperature dependent specific heat and thermal conductivity values produced small changes. Three linear shrinkage models incremented or decreased the shrinkage by 10%, with no model matching linear shrinkage at all processing conditions.
Process Identification of Barrel Temperature Control in Injection Molding: A MIMO Approach
Melt temperature is a key variable in injection molding that has to be continuously controlled during the molding process. Its control is generally simplified due to the dynamic characteristics of the melting process and the barrel zones interactions. Therefore, a thorough understanding of these process dynamics is required to achieve accurate control of melt temperature. Multi-input-multi-output (MIMO) deterministic models were derived and employed for predictive control of melt temperature. Simulations and experiments showed that MIMO model could be used as a good physical representation of the overall system.
Understanding the Effect of Processing Parameters on the Mold Temperature
The mold temperature is one of the most important injection molding parameter, affecting both productivity and quality on the molded plastic parts. The data sheet for various raw materials always give the recommended mold temperature. However, the molds are becoming more and more complex, and as a result it is getting ever more difficult to create proper conditions for effective temperature control. Quite a few researchers have demonstrated the importance of the mold temperature, but, in general, a practical way to determine it is rarely presented. In this work, the software MoldFlow was used to perform cooling analysis with three different injection molds, with different molding conditions, in order to investigate the parameter setting for mold temperature. The analysis of the simulation results showed that cooling water temperature was the most significant parameters to the mold temperature. Empirical model between this factors and the mold temperature was also built. Such model seemed to be effective to estimate the temperature of all the studied molds.
Microstructures of Injection Molded Glass Fiber Reinforced PC/ABS
Microstructure of the injection molded glass fiber reinforced PC/ABS was investigated in the present study. Two types of glass fiber were used to compound with PC/ABS and the compounded materials were injection molded with three moulds of different configurations, respectively. It was found for the specimen molded with the 2 mm-thick sheet mould at the injection speed of 250 mm/s, the glass fibers didn't always flow with the polymer matrix together in the core zone. It was also found the fibers treated for adhesion to ABS appeared to be bound to ABS, while the fibers treated for adhesion to PC/ABS appeared to be bound to PC.
Crystallization Behaviors of Nylon 66 and Nylon 6 Copolymers at High Supercoolings
Crystallization kinetics and morphology of a series of random copolymers of Nylon 66 and Nylon 6 (up to 21 wt%) have been investigated. Optical microscopy with rapid cooling apparatus was employed to measure growth rate at higher supercoolings. Results indicated that the rates of crystallization of Nylon 66 copolymers were reduced with increasing content of Nylon 6 comomoner, and crystallization temperature were moved to lower temperatures. Final spherulites morphology of Nylon 66 and copolymers could be changed from impinged spherulites to isolated spherulites with decreasing size until total amorphous with increasing supercoolings. The melting temperature, crystallinity, and crystal structure of the Nylon 66 copolymers from different cooling conditions were studied with Differential Scanning Calorimetry (DSC) and Wide Angle X-ray Diffraction (WAXD). Crystallinity and melting temperature were found to be lower at higher supercoolings.
Simulation of the Time-, Temperature- and Stress-Dependent Elastic, Viscous and Retarded Creep Behavior
The creep behavior of polymeric materials has been studied, with emphasis on dividing the total deformation into an elastic, viscous and retarded part via a 4-elements-model. It was found that the long-term creep behavior can be satisfactorily predicted based on creep experiments up to 1000h loading duration. An extrapolated Findley-approximation up to a predetermined criterion delivers data-points for long time intervals. The models developed allow a comprehensive description of the creep behavior. With that approach, the simulation of e.g. isochronous curves for arbitrary stresses and temperatures was possible with very good accordance to the real creep behavior.
Photo Degradation Mechanisms of Layered Silicates Polymethyl Methacrylate Nanocomposites
The use of advanced lightweight materials to improve combat survivability has been of crucial interest to the U.S. Army for a number of years. The design, development, and performance testing of these advanced materials is critical for enabling Future Combat Systems and the Objective Force Warrior. Specifically, hybrid organic/inorganic polymer matrix nanocomposites show promise in providing many of the physical properties required (ie. lightweight structure, rugged abrasion resistance, high ballistic impact strength). However, as with any polymer system, these materials are susceptible to degradation over time when exposed to various environmental (i.e. sunlight, moisture, temperature) conditions. This structural degradation (1-4) will eventually comprise the original integrity of the materials’ desired properties. The focus of our research is to exploit nano-technology through incorporation of layered silicates for property enhancement.In this study, the impact of accelerated weathering upon newly developed polymethyl methacrylate-layered silicate nanocomposites materials was investigated. The silicate loading varied from 0 - 5 % by weight. A fluorescent ultraviolet (UV)/condensation weathering tester was selected for the exposure study. The materials were characterized by UV/VIS spectroscopy and FT-IR spectroscopy. The results reveal that the acrlyate linkages undergo a scission reaction upon UV exposure thereby compromising the original properties of the material. Furthermore, these scissions produce a yellowing of the polymer matrix which can inhibit its use where optical clarity in important.
Simulations of Scratch Resistance and Recovery in One and Two-Phase Polymers
We have used molecular dynamics to simulate the behavior of polymers in scratch tests. We start by creating a material on the computer consisting of chains with varying molecular mass, orientation and second phase concentration.Scratching is simulated by moving a force along the surface of the material. We measure the resulting deformation and we study penetration depth and recovery. We find that these depend on the local structure of the material as well as on the distribution of the second phase.Our simulations allow us to better understand scratching and scratch recovery. This helps in the creation of materials with improved tribological properties.
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