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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The Effect of Mold Temperature on Morphology and Mechanical Properties of Injection Molded Hdpe Structural Foams
In this study, HDPE structural foams were produced by injection molding under different mold temperatures to study the effect of this variable on average cell dimension, cell density, and skin thickness ratio. Samples were also produced by setting independently the temperature of the fixed and moving plate of the mould to detect the sensibility of foam structure to a temperature gradient in processing. The resulting foams were also characterized in terms of mechanical properties including impact and flexural tests. It was found that for homogeneous mold temperatures, symmetrical skin thicknesses were obtained, which increased with decreasing mold temperature. On the other hand, by keeping one mold face at a constant temperature and varying the second one, asymmetric skin thicknesses were obtained. The degree of asymmetry was found to increase as the temperature difference between both molds increased. Furthermore, decreasing mold temperature produced a small increase in average cell sizes and reduced cell density. In general, both impact strength and flexural moduli of the structural foams increased with increasing skin thickness. For the particular case of asymmetric foams, the moduli were slightly dependent on the direction of the applied force (surface on which the stress is applied). Higher impact strength was obtained when the falling weight stroke the samples on the face having the smaller skin thickness, whereas for flexural tests, the reverse was observed.
Optimizing Pad Printing Efficiency with Stepper Motor Technology
Technology tends to advance in fits and starts, and pad-printing equipment is no exception. New machinery is developed by manufacturers either as a means to overcome specific technical hurdles or in response to competitive pressures. In this paper we'll look how the old technology of pad-printing has learned new tricks when confronted with both of these issues. And we'll explore how improved equipment designs are opening doors for the pad-printing process in industrial-imaging applications. In particular, we'll consider large-format applications involving consumer appliances, where new pad-printing machines are making the technology viable as an alternative to in-mold decorating, heat transfers and pressure sensitive labels.
An Optimization Approach for Polymer Sheeting Die Design
An optimization approach for the polymer sheeting die design based on the finite element simulation and genetic algorithm was studied in this paper. The optimization model was established according to the flow balance principle where the outlet flow distribution uniformity was taken as the optimization object and the die structure parameters were the design variables. The results of FEM simulation on the polymer extrusion process were adopted for the calculation of the objective function. The genetic algorithm was used for the fitness evaluation and the search of optimal design variables. The above optimization approach is applied for the optimal design of a fish-tail sheeting die whose result shows that it's feasible and reasonable.
Rheological and Crystallization Behavior of Linear and Branched PBT
Rheological and thermal characteristics of PBT resins were investigated with potential applications in low density foaming. The branched PBT was produced by extrusion modification with a tri-functional modifier, whereas the linear PBT was processed under the same condition without the modifier. The presence of branched molecules resulted in increased elasticity and slower crystallization kinetics due to higher concentration of entanglements and/or increased interchain interactions. Degradation by processing for both resins produced shorter chains, and involved reduced shear viscosity and faster crystallization kinetics, in particular, at high temperature.
Thickness Characterization of Thin Polymer Nanocomposite Oxygen Barrier
Thin films of sodium montmorrilonite clay and cationic polyacrylamide have been produced by alternately dipping a plastic substrate into dilute aqueous mixtures containing each ingredient. After 30 clay-polymer layers have been deposited, the resulting transparent films exhibit an oxygen transmission rate below the detection limit of commercial instrumentation (< 0.005 cm3/m2/day). This level of oxygen barrier, which is unprecedented for a clayfilled polymer composite, is believed to be due to a nanobrick wall microstructure comprised of completely exfoliated clay in a polymeric mortar. This brick wall creates an extremely tortuous path at thicknesses below 500 nm. Thickness measurement of these thin films is very challenging, requiring several techniques to confirm accuracy. Ellipsometry, weight measurement, and electron microscopy were used in the present study to obtain accurate thickness. With an optical transparency greater than 90% and potential for microwaveability, this thin film composite is a good candidate for foil replacement in food packaging and may be useful for flexible electronics packaging.
Polyurethanes from Soybean Oil-Based Polyols with Mixed Primary and Secondary Hydroxyls
Soybean oil was converted by epoxidation and hydroformylation to polyols with varying ratio of secondary and primary hydroxyl groups while keeping hydroxyl content approximately constant at about 200 mg KOH/g. Polyols with secondary groups were solid at room temperature. Their consistence changed gradually to liquids as the content of hydroformylated OH groups increased. Reactivity of polyols with diisocyanates was studied by viscosity increase with time. Glass transition of resulting polyurethanes with the same functionality of polyols varied linearly with the content of primary groups being lower for the higher content of hydroformylated hydroxyls. This was explained by the larger molecular weight of network chains, Mc, of hydroformylated polyols due to extra carbon atoms introduced by the process. The effect of crosslinking density, primary hydroxyl content and polyol reactivity on properties is discussed.
Investigation on Warpage and its Behavior in Sequential Overmolding
Sequential overmolding is one of the great methods to fabricate the modern injection products. Due to its complicated nature and the unclear physical mechanism, trial-and-error method can not address and manage the warpage and its mechanism effectively. In this study, various parameters including product geometrical effect and material selection have been conducted both theoretically and experimentally. Results showed that the product geometries and molded materials will affect the warpage of final products significantly. It can be the good guidelines to help people understand the mechanism and make the proper design for fabricating the modern multi-component molding products.
Analysis of Rotational Moulding Process Parameters and Warpage on Cycle Times
The analysis of heat transfer in the rotational moulding process is a non-linear multi-dimensional problem, which involves a number of process conditions and thermal parameters. This study, mostly involves dimensional analysis, the changing effects of the process parameters and conditions on the process times for different processing circumstances. The modelling helps to further identify and understand the dependence of key thermal parameters due to external heating, external cooling, external-internal cooling and warpage on cycle times of the rotational moulding. This study shows that for the external cooling process, the warpage formation for thicker parts does have a considerable influence on prolonging the total cycle time, also the external-internal cooling method significantly improves the cycle time.
A Constitutive Model for Creep Lifetime of PBO Braided Cord
A constitutive model to describe the creep lifetime of PBO braided cord has been developed and fit to laboratory data. The model follows an approach proposed for p-aramid cord in similar applications, and has an Arrhenius-type representation that arises from consideration of the failure phenomenon mechanism. The data were obtained using a hydraulic-type universal testing machine, and were analyzed according to Weibull statistics using commercially-available software. The application of concern to the author is NASA's Ultra- Long Duration Balloon and other gossamer spacecraft, but the motivations for the related p-aramid works suggest broader interest.
The Reinforcement of Poly(Lactic Acid) Using High Aspect Ratio Calcium Carbonate Based Mineral Additive
As a sustainable alternative to petrochemical-derived products, poly(lactic acid) (PLA) is gaining a lot of interest in recent years. PLA has good optical clarity and high stiffness, but it is also intrinsically brittle. In this paper, the comparison between a specially engineered high aspect ratio mineral-EMforceTM Bio calcium carbonate, mica and talc in reinforcing PLA was performed. It was found that EMforceTM Bio calcium carbonate was extremely effective in improving the low temperature impact toughness as well as increasing the stiffness of PLA. Further the addition of EMforceTM Bio calcium carbonate to PLA does not hinder its compostability at elevated temperatures.
Insert Coating as a Pre-Processing Approach for Improvement of Adhesive Bonding in Plastic-Metal Hybrid Structures
Improvement of adhesive bonding between plastic and metal components by means of surface coating pretreatment has been investigated. Metal inserts have been coated with polymer-based film then overmolded with reinforced polyamide-6 in an injection molding process. Experimental work has included the characterization of the adhesive bonding strength and the influence of the coating film on the mechanical behavior. FE-Simulation has been conducted to analyze the local shear stresses. Aging influence has been evaluated using climate change test.
ION/Polymer Interactions in Polyelectrolyte Gels
We report results from experimental studies performed on polyelectrolyte gels to understand the volume transition induced by multivalent cations. Macroscopic osmotic and mechanical measurements are made to determine the effect of ion binding on the elastic and mixing contributions of the network free energy. Small-angle neutron scattering is used to reveal the role of multivalent ions in the organization of the polymer segments. We demonstrate that combination of scattering and osmotic measurements allows us to determine the characteristic size of the structural elements that contribute to the osmotically driven concentration fluctuations, and yields important information on the effect of ions on the structure and thermodynamic properties at both molecular and supermolecular levels.
Effect of Strain Rate on Tensile Properties of Carbon Nanofiber-Reinforced SC-15 Epoxy
In this study, tensile tests were performed on carbon nanofiber reinforced epoxy at different strain rates. Tests results showed that both the elastic modulus and the tensile strength of the materials increased with higher strain rates, but the failure strain decreased with higher strain rates, indicating that the composite is a strain rate-dependent material. Experiment results also showed an even distribution of CNFs in the 1 wt% and 2 wt% systems and an agglomeration of CNFs in the 3 wt% system. Therefore, the 2 wt% CNF-infusion system exhibited maximum enhancement, compared to other systems.
Clear Barrier at Atmospheric Pressure – the Second Phase
The barrier properties of transparent layers deposited on flexible plastic substrates are of interest to many in the packaging industry. Numerous methods have been used to manufacture transparent barrier coatings with varying degrees of success to address evolving environmental laws requiring the reduction or elimination of volatile organic compounds (VOCs), which are the byproduct of curing liquid topcoats. There is also a consumer preference to visually inspect packaged products through packaging prior to purchase. This paper will present new evidence since the 2006 SPE FlexPack Conference of the potential for clear barrier at atmospheric pressure through the use of plasma processing as integral steps in a composite, or several stage, process for deposition and polymerization of functional barrier coatings. XPS analysis of polymerized film showed presence of silicon, carbon and oxygen in ratios different from the monomer, and in fact approaching a Si:O atomic ratio of 1:2 confirming cross linking effects, and the plasma polymerized organo-silicon films displayed good functional barrier properties without the environmental concerns of VOCs.
Mini Mixing Devices for Specialty Nano-Strucured Blends and Composites: Evaluation of Flow, Mixing and Morphology
A 1:20 downscale of an internal batch mixer (60mL total volume), the Minibatch mixer (3 mL total volume), requiring only 2g per blend sample, has been developed for small-scale blending of specialty polymers and nanocomposites. The morphology of samples processed by this new miniature mixer is compared to other labscale equipment such as the 60mL internal batch mixer and the Alberta Polymer Asymmetric Minimixer (APAM). Immiscible blends showed a spherical dispersed phase structure and uniform distribution throughout the blend; however, the dispersed phase particle size was large in comparison to the other mixers. Vapor grown carbon fiber (VGCF) nanocomposites were better dispersed and more homogeneous compared to those prepared using the 60mL batch mixer and the APAM. The large surface to volume ratio of this new mixer plays an important role in the heat transfer mechanisms and thus may affect flow patterns occurring in the Minibatch mixer. Simulations using Polyflow software showed that the flow pattern in the 3mL Minibatch is similar to the 60mL batch mixer but that the temperature rise due to viscous dissipation is not as large for the new miniature mixer.
Comparison between Amorphous Metallic Alloy and Silicon as Molding Insert for Micro Injection Molding of Polymers
The mass-production of microfluidic devices must be done in a reliable manner. In this study, toolings used to reproduce microfluidic features on cyclic-olefincopolymer (COC) and polymethyl-methacrylate (PMMA) polymers by amorphous metallic alloy and silicon inserts were compared. Both toolings were used in micro injection molding. Findings indicate that the alloy was mechanically more suitable as mold inserts, whereas silicon had better surface roughness. COC samples showed comparable geometrical replication of microfluidic features compared to PMMA.
Solids Compaction and Conveying in a Single-Screw Extruder by Discrete Particle Modeling
To improve our understanding of granular flow in the solids-conveying zone of a single-screw extruder, a discrete particle model has been developed. The discrete particle approach allowed us to simulate polymer compaction without using the isotropic stress assumption used by continuum models. An elastic-fully plastic contact force displacement model was validated by simulating HDPE and PS under compaction in a batch cell and comparing against reported data in the literature. The particle model and experimental results showed good agreement for PS which exhibited elastic behavior up to the tested limit of 12 MPa. The simulation for HDPE showed marked deviation above 4 MPa, over predicting the plastic dissipative losses. The extruder simulations showed exponential pressure development along the axial length of the screw, similar to continuum models, but indicated that bulk density in the screw was affected by attributes of the flow field besides just pressure. The nonisotropic stress distribution of the solids in the screw was examined, with the stresses found to be concentrated at different boundaries depending on pressure development.
Scale up Rules for Profile Geometries in Extrusion Dies and Options to Adjust Surrounding Flow Channels to Avoid Transverse Flow
The design of extrusion dies is frequently based on knowledge and experience of the designers. One very simple, rapid and low-cost means of designing a profile die is the use of scale-up rules. This paper deals with an approach to develop scale-up rules which make it possible to scale-up or scale-down existing profile geometries by means of simple equations. The following profiles are observed: rectangular channel, annular gap and pipe channel. Allowance is also made for a change in material properties in order to achieve the greatest possible variability in the die design. Neighboring areas are examined and revised by iterative procedures to avoid transverse flow between the flow channels.
Effects of Structural Constraint and Impact Energy on Fracture Behavior of a Flexible Composite Tubing
By using scanning electron microscopic analysis, we fractographically examine failure modes of flexible, braiding-reinforced composite tubes under impact energy pulses. The tubes are subjected to different extents of structural constraint imposed by other catheter components. The effects of impact energy pulses and structural constraints on failure modes are qualitatively evaluated. It is practically shown that under certain extents of structural constraint, minimal impact energy input can introduce catastrophic, brittle fracture mode dominant over either fatigue fracture mode or ductile failure behavior. In an attempt to identify the root causes for the formation of observed brittle fracture phenomena, various material characterizations, including differential scanning calorimetry (DSC), thermo-gravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR) are conducted on the thermoplastic elastomer material of the tubes to attest material integrity after fabrication.
Melting Behavior of a Poly(Ether-Block-Amide) Copolymer Melt-Crystallized under Isothermal, Quiescent Condition
The melting behavior of a poly(ether-block-amide) copolymer melt-crystallized under various quiescent, isothermal conditions was studied using differential scanning calorimetry (DSC). The structure of the crystallized copolymer was characterized at ambient temperature using wide-angle X-ray diffraction (WAXD). It was found that the hard, crystalline microdomain of the melt-crystallized copolymer only exhibited ?- or (???) crystal form associated with hexagonal habits. It was determined based on the DSC and WAXD results that the multiple melting endotherms were attributive to different origins, including the short-range ordering effect at the late stage of crystallization and the melting-crystallization event that occurred during the DSC heating scan.
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