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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Flow-Induced Morphological Changes Inpoly(Styrene-Co-Maleic Anhydride)/Poly(Methyl Methacrylate) Blends
The effects of shear flow on the phase behavior of a polymer blend with high glass transition temperature, Tg, constituents possessing large viscosity difference were investigated in the linear and non-linear regime using shear and capillary rheometry. This was complemented by differential scanning calorimetry and analysis of the extrudates with scanning electron microscopy. The blend is a lower critical solution temperature polymer mixture of a random copolymer of styrene and maleic anhydrite, SMA (Tg=178°C), and poly (methyl methacrylate), PMMA (Tg=105°C). The methodology presented here for the determination of the shear-induced phase diagram should be applicable to any industrial mixture. The activation energy analysis in the phase separated SMA/PMMA(50/50) blends predicted cylindrical domain morphology in the non-linear regime. The latter was confirmed by SEM of the phase separated SMA/PMMA(50/50) extrudates, associated with high shear rates, where fibrillar domain structure was observed in the shear direction.
The Effect of the Boron Mitride Type and Concentration on the Rheology and Processability of Molten Polymers
The influence of a new processing additive (a composition of fine particles of boron nitride) on the rheology and processability of molten polymers is studied. The equipment used includes both an Instron capillary rheometer with special annular dies (Nokia Maillefer wire coating crosshead) attached to the rheometer and a parallel-plate rheometer. A metallocene polyethylene and Teflon FEP with several types of boron nitride varying in particle size distribution are tested at various concentration levels. The additive with the finest particle size has the greatest influence in crosshead dies and tips. As a result, its use eliminates surface melt fracture and postpones the critical shear rate for the onset of gross melt fracture to significantly higher values depending on the additive concentration. The influence of the boron nitride type and its concentration on the polymer rheology is also discussed. It is found that the activation energy for flow of Teflon FEP scales with the BN concentration.
Laser Sintered Short Run Tooling for Injection Molding
Direct prototyping of a mold using a laser sintered (SLSa) polyamide/copper (Cu/PA) compositeb allows the production of a limited number of prototype injection molded parts from production materials such as PP, PE, and ABS. The tooling is produced without doing reverses from patterns typical of prototype tools. The paper details the process including production of the tool, typical parts from such tool, and best use of such parts, tolerances, feature details, and cosmetics. The process is benchmarked against CNC tools and epoxy/composite tooling to compare durability, lead time, and accuracy. Whereas the material is not touted to be a production tooling substitute, the copper/polyamide facing with epoxy based tooling may be an option for parts with low volume, quick turnaround requirements, medium tolerance requirements, and fine detail and feature refinements. However, prior to processing, the Cu/PA tools have several criteria that must be incorporated into the design of the tool in order to effectively utilize the process.
Using Traditional Machine Shops Versus CNC Machining Centers
The paper examines traditional and CNC machining for fabrication of molds and prototypes. Factors examined include: • Delivery • Cost • Equipment • Tolerances • Technical competence • Cosmetics Conventional machined tooling is more appropriate where high finish, extremely high precision and high feature density is required, but CAD data is not available or is not converted easily to CNC cutter paths. Traditional machined prototypes may be more cost effective, delivered faster, and include better feature definition and surfaces for small part volumes. Leaving CNC out of the manufacturing cycle may be beneficial for the OEM, injection molder, and designer in low volume applications and for high precision molds where the feature definition of the part is critical and parts costs must be considered.
High Performance Crosslinkable Thermoplastic Elastomers for Medical and Electronic Applications
A family of thermoplastic elastomers have been developed that when crosslinked by irradiation are shown to have improved thermo- mechanical properties and chemical resistance at elevated temperatures. These materials can be easily injection molded and extruded into thin wall parts and tubing as well as wire and cable coatings. This processing can be performed on conventional thermoplastic processing equipment. They offer design engineers capabilities not previously available. This paper will present an overview of thermoplastic elastomer families and markets where thermoplastic elastomers are used. We will review the advantages of the irradiation crosslinking process and the improvements imparted to plastics and elastomers by this process. We will more specifically introduce the application of the irradiation crosslinking process and its improvements to a specific family of thermoplastic elastomers. That family being the COPA family of thermoplastic.
Decision Diagrams Aided Conceptual Mold Design
The conceptual mold design for injection molding of thermoplastics represents one of the most important phases in mold designing. In practice, the solutions for this phase are often based only on the designer's experience, which may cause severe faults in the finished mold. One of the possibilities in solving this task during the mold design is to apply the decision diagram for a principled selection of the solution for single partial functions of the mold. Such decision diagrams may be very simply checked in practice, the necessary corrections made, and they may be then developed into an adequate computer program - knowledge base, which is of special significance to the less experienced mold designers.
Single Cycle-Twin Sheet Thermoforming for Technical Precision Parts
One feels as we address the dawn of the 21st century that there should be some revolutionary process-something radical-some brilliant new discovery that, as we speak today in the spring of 1999, will create history. Unfortunately, developments as radical are not spawned from the Roman calendar or our individual ambitions to become famous. They are borne of a need, an idea to solve a problem, and so, ultimately, today’s solution is destined to become tomorrow’s technology. I am sure that, being active members of thermoforming and plastics related industries, you are familiar with the simplistic concept of TWIN SHEET thermoforming. The forming of a 3D product from two separate sheets of plastic material is, in broad concept terms, a simple matter. The complexity and technology required too create a similar product of uniform strength and acceptable aesthetic appearance requires much more skill and process technology before it could reach the market. In this presentation we will review the use of single cycle thermoforming machines dedicated to the production of very high precision parts of extreme dimensional accuracy and total quality repeatability.
Hot Fillable Containers Manufactured from New Polymeric Compounds Based on PET/PEN Copolymers and Blends
Copolymers and blends of PET containing NDC units, owing to their favorable combination of properties, may find applications in areas of beverage and food containers of high performance requirements. Copolymer of PET with sizable increase of NDC content has been processed in Injection Stretch Blow Molding (ISBM) in a sort of unique controlled one stage cycle process, which was developed to produce the microstructure necessary to overcome high thermal resistance of hot filling of liquids at up to 95°C accompanied with high barrier properties. PET/PEN blends, which attracted even greater attention, were initially produced and investigated on a scale of experimental system and at later stage produced by an ISBM process into bottle containers. The properties of both type of materials in a form of ISBM produced containers, has found to be depended on their composition and microstructure, which can be tuned by controlling the production parameters. These properties, namely the Tg, the strain induced and the thermal crystallization, were monitored by DSC and DMTA thermal analysis techniques throughout the investigation. The results of this study are promised and may provide the way to a range of new material formulations with a capability of improved properties for ISBM made heat stable containers.
Predicting Flow Length of Spiral Melt Flows in Injection Molds by a Semi-Empirical Model
A spiral-shaped mold of nearly rectangular cross-section with height and width in the order of a few millimeters is often used to classify injection molding materials according to their flowability. The length of the solidified plastic in the spiral, known as flow length, is taken as a measure of the flowability of the resin concerned. The parameters involved in the flow process are, mainly, resin viscosity, melt temperature, mold wall temperature, axial screw speed, injection pressure and geometry of the mold. To minimize the number of experiments required to determine the flow length, a semi-empirical model based on dimensional analysis has been developed. The modified dimensionless numbers used in this model taking non-Newtonian melt flow into account are Graetz number, Reynolds number, Prandtl number, Brinkman number and Euler number. Comparison between experimental data obtained with different thermoplastic resins and the model predictions showed good agreement , confirming the applicability of the approach for any injection molding resin.
Study of the Influence of the Injection Molding Processing Parameters on Molded Part Properties Using the Full Factorial Design
Due to a large number of processing parameters involved in injection molding of thermoplastic melts, a systematic investigation of their main effects and interactions is indispensable in order to achieve the optimum quality of the molding. In this study, the main adjustable influencing factors have been varied, such as melt temperature, injection pressure, cavity wall temperature and coolant rate. The experiments were carried out by applying the factorial design 24 and the following properties were analyzed: weight, dimensions, surface waviness and tensile strength of the molding.
Mechanochemistry Effects in Recycled Polypropylene and its Blends during Solid-State Shear Pulverization (S3P)
On-going research focuses on understanding the mechanochemistry during Solid-State Shear Pulverization (S3P) of recycled polypropylene (PP) and its blends. Free radicals formed during this process act as compatibilizing agents for ordinarily incompatible polyolefin blends. It was observed earlier with Nuclear Magnetic Resonance spectroscopy that each S3P cycle converts a small portion of polypropylene chains from isotactic to atactic stereoregularity. Small amounts of such atactic chain segments impart additional levels of toughness, which offset, in part, the damage associated with the inevitable chain scission. We determined how many processing cycles S3P-made recycled PP can endure without significant loss of mechanical properties.
New Uses for Electroless Nickel in Mold Building and Design
This paper describes electroless nickel and the scope for its many applications in mold making, maintenance and repair. While most mold builders are familiar with nickel solution for rust prevention in cooling water lines, many have remained unaware of the different formulations of electroless nickel plate and its capabilities as an engineering or functional coating applied by techniques firmly established in the electronics, fire-arms, automotive and other industries. Case histories of in-mold performance illustrate correct usage, proving that electroless nickel can offer properties equivalent to hard chrome plate, yet without the problems of thickness variation, anode deployment or the ever-rising environmental penalties and costs associated with chrome plating.
Designing with L-" and "U-" Shaped Snap Fits"
Snap-fit designs for assembly of thermoplastic-based products provide many benefits. However, when the strain caused by the deflection of a typical cantilever snap fit cannot be designed below the allowable strain of the intended material, conventional designs must give way to alternative snap-fit designs. In these cases, a U-" or "L-" shaped snap usually reduces the strain to an acceptable level without sacrificing the cost and performance benefits of the typical cantilever snap fit. These alternative designs can accommodate very large deflections without inducing high strains at the base of the snap-fit finger. Formulae for both the "L" and the "U" have been derived to allow for maximum deflection for a given geometry. Detailed examples of the application of these formulae which were confirmed using finite-element analysis are given in this paper."
Experimental Investigation of Fracture Toughness in Injection Molded Long Fiber Reinforced Thermoplastics
The variations of fracture toughness Kc in injection molded 50% E-glass long fiber reinforced polypropylene are investigated. Plaques at different sets of processing conditions have been produced and specimens have been obtained at preselected spatial locations, both in the in-flow and cross-flow directions. The effect of part morphology, which consists of through-thickness layers, was evaluated experimentally by measuring the fracture toughness at locations where a crack initiation is produced prior to the measurement. The results show a strong effect of processing conditions and spatial locations on the fracture toughness as a result of variations in the through-thickness layered structure.
The Effect of Ionic Strength Variation on Patterned Self-Assembled Monolayers Using Infrared Reflection Absorption Spectroscopy
The morphological properties of polymeric thin films deposited on self-assembled monolayers are closely related to the orientation of the macromolecular chains on the surface. In one such system where ionic polymers are involved, the orientation is highly influenced by the presence of an electrolyte and it depends in particular on the ionic content of the initial solutions. In the study presented here, infrared reflection absorption spectroscopy was used to elucidate the effect of salt concentration variation on the orientation of polymeric thin films of alternating bilayers of sulfonated polystyrene and poly (diallyl-dimethyl-ammonium chloride) (SPS/PDAC).
Viscoelastic Behavior of HDPE under Tensile Loading
The time dependent mechanical behaviour of high density polyethylene has been examined. Creep experiments with an endurance of eight weeks were performed. The creep strain can be described properly by the Leaderman model using engineering stresses and strains if the strain remains below approximately 2% strain. By expressing the Leaderman model in terms of true stress and true strain it is possible to improve the accuracy at higher strain levels. A good fit of the creep data up to approximately 5% strain can then be obtained. At strains above this value of 5% the creep strain gets an upward curvature, indicating the beginning of the secondary creep stage with plastic flow dominant. This can not be described yet. Results from tensile straining experiments show good agreement with the model predictions. Therefore the Leaderman model is capable of giving good predictions for the mechanical response of this HDPE for creep as well as for tensile straining conditions.
Time-Dependent Strain Distribution in Polymers under Complex Stress History: Experimental Study by Moire Fringe Method and Finite Element Predictions
A combination of experimental and computational methods are developed, for predictions of nonlinear viscoelastic creep of polymers in sheet form, subjected to inhomogeneous stress states and stress history. A recently proposed multiaxial constitutive model for glassy polymers was implemented in a commercial finite element (FE) package. The model was tested by means of creep experiments on PMMA at elevated temperature, using specimens with a central circular hole. The experiments were performed using a tensile creep machine, and the geometric Moire fringe method was employed for measuring strain distribution. The results obtained from the experiment and FE analysis were compared.
Integrated Simulations of Gas Injection Molding Process and Part Structural Performance under a Unified CAE Model
Integrated simulations of gas injection molding process and part structural performance under a unified CAE model were carried out. An analysis algorithm based on DKT/VRT elements superimposed with beam elements representing gas channels of various section geometry was first developed to evaluate the structural reinforcement of gas channel in the design stage. During melt/gas filling process, a mixed control-volume/finite-element/finite-difference method combined with dual-filling-parameter technique was implemented to trace the advancements of melt and gas fronts. For the prediction of secondary gas penetration, flow model of isotropic-shrinkage origin was introduced. Mold cooling analysis was executed utilizing cycle-averaged boundary element method considering the cooling system. Both cooling channel and the hollowed core gas channel were modeled using line-source approach. Thermal residual stresses calculated from part temperature distribution were then combined with the structural analysis to predict part warpage. The monitor support was used as the case study. The analysis accuracy from this unified model of 2 1/2-D characteristics were examined experimentally. The only difference between process simulation and structure/warpage analyses is that different values of equivalent diameters assigned to a circular pipe representing gas channel should be used, respectively.
Waxs Modeling of the Liquid State of Polyethylenes: Implications for Phase Analysis, Glass Transition, and the WLF Constants in Thermoplastic Elastomers
Waxs studies of melts of branched copolymers with varying comonomer content revealed a temperature and branch dependence of the low angle amorphous halo (LAH). Numerous studies in real space suggested a semi-quantitative method for the deconvolution of the LAH. Two linear relations for the temperature dependence (low/high branch content) were observed. The WLF constant, C2, is derived from the slopes and the Tg° from the convergence temperature. The quantity fo of C2 is ca. 4.1x10-4/K. Proper representation of the liquid state scatter (and its temperature dependence) are crucial in quantitative phase analysis, including: interfacial content, latent heat, and crystal microstructure with increasing chain defects.
Elastomeric Polypropylenes from Unbridged Metallocenes
The present work describes properties of a series of experimental polypropylene polymers prepared with unbridged 2-arylindene group IV catalysts. Compositions span a broad range of isotactic content and have molecular weights typically used for extruded polypropylene films and fibers. Mechanical properties encompass elastomers with moderate recovery to highly ductile soft plastics. Compared to ethylene based copolymer elastomers with similar room temperature elastic modulus and tensile properties, these polypropylene elastomers have higher softening and melting temperatures but also higher glass transition temperature.
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