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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Blends of Starch with Poly(Vinyl Alcohol)/Ethylene Copolymers for Use in Foam Containers
The use of foamed polymer packaging such as polystyrene (PS) cups, bowls and clamshells has decreased in recent years because of perceived environmental disadvantages. Blends of starch with poly(vinyl alcohol-co-ethylene), PVOH, a degradable, water-resistant polymer, were processed into viable alternatives to PS providing degradable polymers from renewable resources. Modulated DSC and X-ray crystallography were used to characterize the miscibility and morphology of extruded starch/PVOH blends that contained a series of plasticizers. These included combinations of water, glycerol, triacetin, citrate esters, and amino acids. The optimal blend formulation, based on miscibility, strength, aging characteristics, and capability to replace PS foam was--60-65% wheat starch, -25 -30% PVOH, and -5-10% plasticizer.
Numerical Investigation of the Continuous Electronic Laminate Processing
The continuous electronic laminate processing method is a novel method which addresses the major industrial concerns: solvent elimination, void removal, dimensional consistency, and economics. To better understand its process mechanism, modeling and numerical simulation is implemented on resin flow, heat transfer, and conversion process. In this study, the problem of resin flow and heat transfer through the composite channel is analyzed. The channel is assumed to be a two-layer system, one filled with a resin saturated porous medium and the other with a clear resin. The Brinkman - Forchheimer - Extended Darcy equation is utilized for the glass fiber matrix porous region. The viscosity effect accompanied by the resin curing process is coupled into the flow model. For the heat transfer analysis, a uniform heat flux is imposed at the copper plate, and the heat diffusion effect in resin cure is also considered. The laminate thickness variation and the curing degree profile can also be obtained using the numerical simulation.
Use of Cavity Pressure Sensors to Build Viscosity Data for Flow Simulations
Mold filling analyses are frequently used in the design of a part or mold, but are rarely validated to verify the assumptions used in the simulation. This includes assumptions about the accuracy of the material property database(s). The purpose of the proposed study was twofold: 1. to reconstruct viscosity data for a material using actual process data from a standard mold geometry; and 2. to validate the data by comparing simulation results with actual cavity pressure data. Validation was performed using different analysis models and processing conditions, and showed promising correlation with actual process results.
Automatic Design for Parting Line on Injection Mold
This study discusses a method for the automatic design of a suitable parting line, which enables a reduction in flash, which occurs at the front edge of the parting line, a molded defect in injection molding. The amount of flash is estimated by the size of the gap, which is calculated at the front edge of the parting line, using numerical analysis by the non-linear finite element method. The parting line is automatically determined, using heuristic search methods of a genetic algorithm. As for the application of this algorithm, its validity will be examined in the following steps in the process of a numerical experiment : encryptation of individuals expressing parting line, the definition of the fitness function to evaluate such individuals, and genetic operation (selection, crossover, and mutation) for the individuals. Our study found determination of a parting line, which almost satisfies the size of the gap and effective stress given as targeted values, and its possibility of automatic design.
Effect of Processing Parameters on Bond Strength for Multicomponent Injection Molding
TPVs already have a number of successful applications in many multiple component parts. Part consolidation and integration resulted in cost saving and added value. Useful attributes, such as soft touch for ergonomics, contrasting color for better consumer appearance and marking for corporate recognition, can be achieved along with better quality and performance. In those parts, TPVs play a very important functional role, as such integrated seals & gaskets for water tight applications, soft touch grips for kitchen wares, living hinges and/or energy absorption elements. Co-process fabrication technology takes advantage of the melt-processibility of TPVs and the heat fusion bonding to a compatible substrate. These multi-material techniques have been creatively used in co-extrusion, tri-extrusion, insert molding, two shot molding and even co-injection .
TPEs in Hot Runner Systems: An Elastic Entity
Hot runner systems have been around since the early 1960's. They have provided users with runnerless, finished parts for many technically exciting applications. In producing these parts, materials play an important role in the type of hot runner system used to fabricate them. Hot runner systems lend themselves to multi-shot molding applications, which eliminates the need for three-plate cold runner systems. Hot runner systems are used for a variety of reasons, the main ones being a runnerless system with zero scrap, fast cycle times and, in many cases, improvement of part quality. There are no gates to trim. Cycle times are based on the part itself, and smaller gates can be used to improve the molded part appearance. While all this paints a rosy picture, disadvantages in hot runner systems do exist. Higher mold costs and longer learning curves, along with added personnel training, tend to make using these systems more costly. For high volume production, these systems are ideal and they can improve the ability to engage in a lights out" operation for best efficiencies. In our review we will touch briefly on standard hot runner systems for thermoplastics but the focus will be on hot rudder systems for thermoplastic elastomers (TPEs) and thermoplastic vulcanizates (TPVs)."
Ballistic Impact Measurements of Polycarbonate Layered-Silicate Nanocomposites
The effect of layered-silicates on the impact response of polycarbonate (PC) nanocomposites against the .22 caliber fragment-simulating projectile was determined. The amount of nanoclays incorporated appears to be critical in the overall ballistic performance. For example, nanocomposites consisting of 5 wt.% nanoclays exhibit brittle mode of failure, while ductile deformation is observed for the nanocomposites containing 2.5 wt.% of nanoclays as well as for the PC control. Stress whitening, which is not observed in the pure PC, is apparent in the 2.5 wt.%-PC nanocomposites. This is consistent with their quasi-static mechanical response, and is attributed to good interfacial bonding and proper stress transfer between the matrix and layered-silicate reinforcements.
A Potential Screening Method for Interface Stability in Particulate Filled Dental Composites
This study involves in-vitro simulation and characterization of the degradation process of dental composites. Composite formulations with different silane contents on filler surfaces were prepared. Cylindrical test specimens of 6mm in diameter and 3mm in depth were prepared using visible light curing system. Cured specimens were treated with an aqueous solution of 0.1N sodium hydroxide (NaOH) at 60°C for various time intervals. They were then neutralized with hydrochloric acid (HCl) solution followed by 24 hours immersion in distilled water and air- dried. The radial surface of each specimen was polished and the depth of degradation was measured using an optical microscope. Specimens with optimized silane content exhibited the lowest degradation, and those with unsilanated fillers displayed the highest.
Printing on Vinyl-Part II, FTIR and TOF SIMS Studies
Earlier surface analysis studies suggested that, at least in some situations, the print adhesion properties of barium/zinc stabilized, stearic acid lubricated, PVC are influenced by the migration (exudation) of a barium/zinc stearate complex. This paper expands the previous study in attempts to reproduce the effects observed on samples of commercially produced films, explain the origin of the migrating specie and to identify the variables which influence the extent to which the phenomenon occurs. The effects of different lubricants, stabilizers and processing conditions are studied. Mechanistic work suggests that a revised hypothesis is appropriate and that the hydrolyzed complex is actually formed in the PVC matrix and not at the surface.
Comparison of the Mechanical Performance of Extruded Blown and Cast Polyolefin Thin Film
Thin mono-layer films of metallocene catalysed polyethylene, linear low density and conventional low density polyethylene, as well as polypropylene, were produced from a 38mm extruder through a 75mm diameter blown film die and a 600mm cast film die. By using the same die gap on each die to achieve equal draw-down ratios, the influence of orientation from the two processes on the mechanical properties of each film was investigated. Tensile strength at break, Young's Modulus, percentage elongation at break, tear propagation resistance, in both machine and transverse direction all gave significant differences in properties with cast film when compared to different blow-up ratios for blown film. Differential Scanning Calorimetry was used to measure the percentage of crystallinity in each film. Differences were found to show that the cooling process as the melt exits the die has a significant effect on the percentage of crystallinity.
Novel Process for the Production of Long Glass Fiber Reinforced Composites
Twin screw extruders have been used successfully to incorporate glass fibers in polymer melts. However, during the compounding step, the fiber attrition can be high, resulting in poor physical properties of the finished product. In order to obtain a high overall fiber length and a gentle treatment of the fiber, the glass roving has to be impregnated with melt prior to entering the extruder. The patented Berstorff solution presented in this paper is based on two counter rotating rolls, that feed the fibers to the extruder and impregnate them with melt. The impregnating unit is designed in a compact manner and can be sandwiched between two barrel sections of a co-rotating twin screw extruder.
Feeding and Processing of Compacted Fillers on a Reciprocating Single Screw Kneader Compounding System for Automotive and Masterbatch Applications
Fillers are used in plastics to achieve a variety of beneficial structural and performance properties. These properties are maximized by using fillers in the form of powders with fine particle sizes and specific aspect ratios. The goal is to preserve these properties after compounding. Unfortunately, low bulk density materials like these tend to bring a significant amount of entrained air into the extruder that takes up volume, hampering, among other things, throughput rates. As an alternative to these powdered forms of fillers, compacted fillers can be used which significantly reduce the level of entrained air. As a result, processing and handling of these materials are much less labor intensive. Using a reciprocating screw kneading system, a number of talc filled formulations used for automotive and masterbatch applications were compounded over a variety of conditions. The results will show improvements in throughput rates when split feeding the powdered talc and marked improvements in handling, throughput rates and overall compounding performance when using the compacted talc.
Streamline Die Design for Complex Geometries
Severe tolerances of profiles in the plastic industry require a simple and accurate die design method. In this paper, we present a method taking simultaneously into account the flow-balancing problem as well as the complex dimensional changes occurring after the die exit. A network model is used to predict the flow behavior within the profile die. The model is non-isothermal and includes accurate sidewall effects. Experiments with capillary and slit dies were done to determine the swelling as a function of shear rate, residence time and temperature. Several die designs for a PVC profiles were realized. Tests conducted for rectangular PVC profiles confirmed the validity of the model.
Reinforced Plastic Design: Tensile Versus Flexural Fatigue
Glass fiber reinforced thermoplastics are being used in applications where fatigue life is important. Although conventional S-N or Wohler curves can be adequate for design purposes, the inherent anisotropy of these materials is often not accounted for if one uses standard molded test bars. An additional factor, generally not recognized, is the difference between fatigue data generated in tension versus flexural loading. This paper will present fatigue data for several glass reinforced materials showing the relative influence of these effects. Simple rules of thumb to estimate the appropriate fatigue data for design pruposes are also provided.
Rheology and Crystallization in Fiber Optic Cable Jacket and Conduit Extrusion
Rheological tests measure melt-state polymer flow, delineating molecular structure and predicting extrudability. Rheology of compounds used in fiber optic (FO) cable jackets and in the conduits that contain such cables will be our focus. Polyolefin-based jackets strengthen the FO cable and protect internal components, while the conduit provides long-term strength and protects the cables against environmental stresses. High density polyethylene use in these applications is growing rapidly, spurred by FO cable growth. Important properties in both applications include melt-state processability, stress crack resistance and solid-state stiffness. Melt rheology directly influences processability, combining with crystallization behavior to dictate final solid-state properties.
Reinforced Plastic Design: Microstructure and Stiffness of Tensile Bars
The majority of mechanical property data reported for reinforced thermoplastics and available to a part designer is based upon testing end-gated injection molded tensile bars. ASTM Type I injection molded tensile bars were molded of ~30 wt% glass-filled polybutylene terephthalate, polycarbonate, and nylon-66. Detailed microstructural evaluations of the lengths and orientations of the glass-fibers were made. The experimental elastic moduli are predicted to within 4% using micromechanics. As a general observation, the simulations reveal that the modulus for a 30 wt% short glass fiber-filled thermoplastic tensile bar is 50 to 70% that expected from a composite of unidirectional fibers of infinite lengths.
Phase Morphology and Cure State Characterization of Soft Thermoplastic Vulcanizates (TPVs) by Using Atomic Force Microscopy (AFM)
AFM shows comparable capability to transmission electron microscopy (TEM) for characterization of TPV phase morphology. Phase imaging by tapping mode AFM scanning gives good contrast between the rubber phase, plastic phase, and filler in a TPV. In addition to TPV phase morphology characterization capability, it can quantitatively distinguish the cure state difference of the rubber in TPVs. A procedure for the analysis on phase imaging data is demonstrated and a good correlation is observed between AFM data, weight gain, and modulus at 100% elongation.
Tear Resistance of INSPiRE Performance Polymer Blown Films
Tear resistance is critical for Polypropylene (PP) blown film in packaging applications and has been widely evaluated by several ASTM standard test methods. However, for characterization and differentiation of the tear resistance of blown films, these factors should be considered: tear behavior, tear propagation trajectory, film thickness, and tear speed. The tear strength of several mono- and multi-layer INSPiRE performance polymer films was analyzed by several test methods in this paper. The effect of film orientation, loading speed, failure mechanism, and sample geometry on tear strength will be discussed. Some uniqueness of the tear behaviors and advantages of the INSPiRE performance polymer blown films will also be discussed.
Injection Molding Long Glass Fiber Reinforced Thermoplastic Composites
Long Glass Fiber Reinforced Thermoplastic (LGFRT) Composites are produced by a proprietary pultrusion process rather than conventional extrusion compounding. This pultrusion process provides a high level of fiber impregnation in the pellets with no fiber damage compared to conventional short glass compounding. The result is injection moldable pellets containing fully wetted fibers equal in length to the pellet, typically 11 mm. This longer, initial fiber length translates into improved properties in molded parts when processing with optimized molding equipment and conditions that preserve the higher aspect ratio. As a class, long fiber composites exhibit overall higher mechanical properties, better elevated temperature performance, lower wear, and improved creep and fatigue endurance. This paper will examine the advantages of long fiber composites, properties of long vs. short fiber, equipment, tooling and processing conditions to maximize fiber length in the molded part and resultant mechanical advantage. In addition, alternative processing techniques including structural foam, injection compression & gas-assist, types of thermoplastic materials used and typical applications will be discussed.
Dependence of Melting Behavior on Melt Index
The dependence of dissipative melting behavior of solid bed on melt index ([MI]) was studied experimentally for polystyrene (PS) and high density polyethylene (HDPE). Melting occurs primarily by the heat generated in the melt film in dissipative melting. The melting rate and the shear stress were expected to decrease with increasing [MI] because of decreasing viscosity. For PS, the shear stress decreased as expected but the melting rate increased with increasing [MI]. For HDPE, both the shear stress and the melting rate did not show a simple dependence on [MI]. HDPEs with very low [MI] values exhibited unstable melting mechanism and their melt did not coat the metal surface. Such unstable melting mechanism is probably responsible for high screw wear. Shear stress depends on the viscosity in the melt film. [MI] only indicates the viscosity at low shear rates, far below the shear rates in the melt film, and by itself cannot indicate the viscosity in the melt film. Melting rate depends on the viscosity and also the velocity profile in the melt film. The viscosity and the velocity profile in the melt film depend not only on the [MI] but also on the shear and the temperature sensitivities in a complex way.
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