SPE Library

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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Conference Proceedings

The Effect of Contraction Angle on the Entrance Pressure Loss

Evan Mitsoulis, Savvas G. Hatzikiriakos, May 2001

The excess pressure losses due to end effects in the capillary flow of a metallocene linear low-density polyethylene (m-LLDPE) were studied both experimentally and theoretically. They were first determined experimentally as a function of the contraction angle (8° to 150°). It was found that the excess pressure loss function increases with increasing contraction angle from 8° to about 30° and consequently decreases up to contraction angles of 150°. Numerical simulation using a multimode K-BKZ viscoelastic equation and a purely viscous equation (Carreau model) have shown that the excess pressure loss function decreases monotonically with increasing contraction angle, an observation that contradicts the experimental results. The origin of this disagreement is also discussed.

A New Non-Reactive Polymer Processing Additive (PPA) for Use with HALS and Other Chemically Interacting Additives

Steve E. Amos, Maria P. Dillon, Susan S. Woods, William Coggio, Joyce Kunde, May 2001

Polymer processing additives are used to reduce melt fracture, increase the processing window and eliminate die lip build-up and gels in polyolefins. There are additives that can interfere with the performance of the PPA by four main mechanisms - adsorption, abrasion, site competition and chemical reaction. Strong bases such as hindered amine light stabilizers (HALS) can cause the PPA to lose effectiveness due to both site competition and chemical reaction. Introduced is a next generation, non-reactive PPA that has improved performance compared to conventional materials.

Failure Analysis of Hinges: Case Studies, Part One

Rabeh H. Elleithy, May 2001

Plastic hinges are subjected to different types of stresses during service. Some case studies are presented in this paper to show the effect of service history, processing conditions, and part design on hinge failure. Microscopic analysis was used in these investigations to identify the fracture features. Additionally, Finite Element Analysis was used to estimate the stresses on the hinges during service. The first case shows mainly the effect of adverse service history on the hinge performance. The second case illustrates primarily the importance of appropriate processing conditions in preventing hinge failure. The third case describes essentially the combined contribution of end-use and part design on limiting the hinge lifetime.

Combining Boron Nitride with a Fluoroelastomer: An Enhanced Polymer Processing Additive

Manish Seth, Franky Yip, Savvas G. Hatzikiriakos, May 2001

The effect of a new processing additive (boron nitride powder in combination with a fluoroelastomer) on the rheology and processability of molten polymers is studied. The equipment used include an Instron capillary rheometer equipped with a special annular die (Nokia Maillefer wire coating cross-head), a twin screw extruder equipped with a blow moulding unit, and a parallel-plate rheometer. Metallocene polyethylenes with and without boron nitride (BN) and fluoroelastomer are tested in extrusion and conventional high density polyethylenes with and without BN with fluoroelastomer are tested in Blow moulding operations. First, it is demonstrated that BN is a superior processing aid compared to conventional fluoropolymer ones. Secondly, it is found that the combination of BN powders with a small amount of a fluoropolymer improves even further the processability of molten polymers (melt fracture performance).

Valve Screw Design - A New Concept on Screw Design Optimization

Peter N. Wang, May 2001

Adding valve" means to a screw is a concept of screw design optimization in a way of matching four normally concerned processing functions. The four processing functions are conveying melting mixing and pressurizing. This paper discusses the relationships between these four functions and promotes design ideas as to how to change them individually. A design called "valve screw" which contains a screw body groups of shear rings and a tube shaped tip are proposed. The shear rings and tube tip serve as valve means controlling / enhancing mass flow rate melting rate and mixing rate. Pressurizing is also indirectly controlled. A high efficiency overall optimized operation is therefore achieved."

Shear Ring Screw Design - A Design against Barrier Screw Design's Philosophy

Peter N. Wang, May 2001

Barrier screw design follows a design philosophy as to keeping melt separate from solid. This leads to ununiform shearing, i.e. all shearing takes within the place of the thin film between the solid bed and the barrel inner surface while the main body of the solid bed has been left no shear at all. The present shear ring screw" breaks the solid bed into small pieces (or individual pellets) at early stage of melting. This would be achieved by using shear rings with series of angled flow through ports which makes the ring self-driven by fed material. "Drag induced melt removal melting mechanism" [12] or "laminar segregated melting mechanism" [3] converts to "pulse dissipative mix-melting mechanism". It is proved theoretically as well as experimentally by Chung and Wang [6] that the heating time required for melting decreases exponentially with decreasing the pellet size and the heat transfer coefficient h (cal/cm2-s-°C) increases substantially due to convections around pellets. These are roots of current design."

Blends of Polypropylene (PP) and Polyamide 6,6 (Pa 6,6) with Functional Polyolefin Elastomer (FPOE) as a Compatibilizer

Hui Tang, Charles L. Beatty, May 2001

The objective of this study is to evaluate the effects of functional polyolefin elastomer (FPOE) on the morphology, and mechanical properties of the blends of polypropylene (PP) and polyamide 6,6 (PA 6,6). PP was blended with different weight concentration of PA 6,6 and functional POE. All blends were carried out in a reactive twin-screw extruder. The mechanical properties of the blends, such as tensile strength at yield (?y), modulus of elasticity (E), and elongation, were examined. Moreover, their morphological behavior was investigated through scanning electron microscopy (SEM). It is clearly indicated that the morphology structure can be controlled through functional POE. It was found that the morphology of the cryogenic fracture surface of the blends was dramatically changed, from micron fibers in the mechanical blending to sub-micron fibers in the reactive blending. The tensile strengths at yield (?y), and modulus of elasticity (E) of the blends with functional POE are increased relative to mechanical blends. However, the elongation of the reactive blends is decreased. These results illustrated that the functional POE can be employed as a effective compatibilizer in the blends of PP and PA 6,6. It stands to reason that functional POE can reduce interfacial tension preventing the blends from agglomerating as well as leading to smaller domain size and better dispersion of PA 6,6 phase in the PP matrix.

The Blends of Polypropylene (PP) with Functional Polyolefin Elastomer (FPOE) for Recycling of Xerographic Toners

Hui Tang, Charles L. Beatty, May 2001

This paper presents experimental results on the blends of polypropylene (PP) with functional polyolefin elastomer (FPOE) for recycling of xerographic toners. All experiments were carried out in a co-rotated reactive twin screw extruder. The investigation of the mechanical properties and morphology for different blends consist of PP, xerographic black toners and functional POE (FPOE) through reactive compounding. It is of interest to note that the notched Izod impact resistance of the blends with functional POE (FPOE) is significantly improved relative to physical blends. However, tensile strength at yield (?y) and modulus of elasticity (E) of the reactive blends are reduced. The reason why the impact properties should be so is clearly shown by the stress-strain behavior of the blends. Morphology of the cryogenic fracture surfaces of the blends was studied through scanning electron microscopy (SEM). The results of morphological studies indicated that not only the domain size of the phase of black toners could be reduced but also the interfacial adhesion could be enhanced through proper functional POE (FPOE). The phase morphology of the blends also illustrated that better dispersion of black toners could be obtained through using FPOE whereas serious agglomeration of black toners was found in the physical blends. It is elucidated that the functional POE could be an excellent candidate of compatibilizer for recycling xerographic black toners.

Training of Operators in Extrusion and Stretch Blow Molding

Ottmar Brandau, May 2001

The current lack of qualified operators in the blow molding industry and its effects on blow molding operations is described. The need for the training of blow molding operators is illustrated. Different methods of training are described and evaluated with respect to their effectiveness. The reasons for the lack of trained operators are shown and from there new training methods are developed overcoming some of the shortcomings of other methods. It is shown that only training material closely resembling the actual plant conditions is well accepted by trainees. Engineering concepts need to be translated into understandable training materials. Retention levels are improved by giving short tests challenging the trainees into thinking about the material presented. Given the right methods, one can teach more complex relationships between material properties, machine functions, and settings.

Reciprocating-Screw Injection Molding Machine for Microcellular Foam

Jingyi Xu, David Pierick, May 2001

The reciprocating-screw (RS) injection molding machine for microcellular foam has been successfully developed. It creates the necessary conditions for a single-phase solution with a specially designed plasiticizing unit. An overall system is the key for successfully implementing a microcellular foam process. The important components for the microcellular foam molding machine system including a plasticizing unit, injection unit, hydraulic unit, clamp unit, gas unit, are discussed in this paper. The general guidelines to design an injection molding machine for microcellular foam are listed as the conclusions.

Transient in the Mold Measurements of Thermal Diffusivity Using Injection Molded Cylinders

Boris L. Serebrennikov, Nick R. Schott, Miftahur Rahman, May 2001

The thermal properties of polymers such as thermal conductivity, k, heat capacity, Cp, and thermal diffusivity, ?, are important properties that affect polymer processing economics due to their critical influence on cooling time and cycle time (1). For cooling calculations one needs the physical properties of k, ?, and Cp to calculate the thermal diffusivity. These vary with each resin and also with the additives, fillers and reinforcements. The task of collecting these data is almost insurmountable since the U.S. has about 8000 resin grades recognized by UL (Underwriter’s Laboratories) and a total of about 30,000 grades are commercially available. By injection molding and experimentally determining the thermal diffusivity under actual molding conditions one can eliminate the individual measurements of k, ? and Cp and instead measure the thermal diffusivity directly. The objective of the study was to show that this is a practical approach to the evaluation of the thermal diffusivity for injection molding cooling calculations.

Optimizing the Mechanical Performance in Semi-Crystalline Polymers: Roles of Melt Temperature and Skin-Core Crystalline Morphology of Nylon

N. Sanjeeva Murthy, Val A. Kagan, Robert G. Bray, May 2001

Crystalline texture and mechanical (tensile and flexural) properties of injection molded nylon 6 were evaluated to understand the influence of one of the key-processing variable, the melt temperature (Tmlt). We find that mechanical properties are sensitive to Tmlt only below ~ 250°C. Rapid quenching of the surface produces a skin with lower crystallinity than the core, which cools more slowly; this difference in the rate of cooling produces ? crystalline form in the skin and ? crystalline form in the core. Higher tensile strength at yield, lower elongation at break and higher flexural strength were observed in specimens molded at lower Tmlt. These characteristics are associated with thicker and less ordered skin, and a lower crystallinity core. The role of the Tmlt on micro-structure and mechanical properties of injection molded nylon 6, the development of skin and core morphologies, and the role of the residual stresses in the core are discussed.

Simulation, Implementation and Evaluation of the Production of a Gas-Assisted Long Part

Nikos G. Pantelelis, Andreas Malikopoulos, Andreas Kanarachos, Nikos Efentakis, May 2001

At this paper the simulation of a gas-assisted injection molded part will be studied. Several gas injection strategies will be developed and simulated using the C-Mold software. As the Gas-Assisted injection molding is a complicated process with many parameters to tune, a detailed analysis of the effects of each processing parameter at the final product will be simulated. Furthermore, a test mould for a commercial product has been constructed and the simulated results will be compared to the real outcome of each strategy. In this way, the accuracy of the simulations according to each production strategy will be evaluated and guidelines will be drawn according to the outcome of these evaluations.

Comparison of Electrical, Thermal, and Mechanical Properties of Carbon Filled Resins

Matthew L. Clingerman, Jeremiah P. Konell, Erik H. Weber, Julia A. King, Kirk H. Schulz, May 2001

The conductive properties of polymers can be improved by adding carbon fillers. The effect of filler content on the mechanical properties must also be considered. High filler concentrations used to maximize thermal and electrical conductivity can degrade mechanical properties. In this study, chopped and milled Polyacrylonitrile PAN-based carbon fibers, nickel coated PAN-based carbon fibers, and a synthetic graphite were added to nylon 6,6 to determine filler amounts needed to obtain acceptable conductivity and mechanical properties.

Miscibility of Poly(Aryl Ether Ketone Ketone) and Thermotropic Liquid Crystalline Polymer

Younggon Son, R.A. Weiss, May 2001

Poly(aryl ether ketone ketone) was melt-blended with a thermotropic liquid crystalline aromatic copolyester, Vectra 950A. A miscibility of the blend was investigated by dynamic mechanical analysis and differential scanning calorimetry. These polymer blends were found to form partial miscible blends. Glass transition temperature (Tg) and crystallization behavior of each phase in the blends were found to be affected by counterpart component. Tgs of each phase in the blends shifted toward each other compared to those of pure polymers. Slight depression of Tm of both component was observed in the blends. When the crystallization temperature is above the melt temperature (Tm) of LCP, the crystallization rate of PEKK in the blends decreased while it increased at the temperature below Tm of LCP. This result was discussed in terms of phase separated nucleation effect.

Dispersive and Distributive Mixing Characterization in Extrusion Equipment

Winston Wang, Ica Manas-Zloczower, May 2001

Mixing is a key step in almost every polymer processing operation. The traditional methodology for improving machinery performance has relied more on users' experience and trial and error experiments. Recently, the fast development of advanced computing resources has enabled the use of numerical modeling as an alternative and more efficient approach in studying the influence of design and processing conditions on equipment mixing performance. In this work using numerical simulations we record the flow history of a number of tracers in the equipment and use them in conjunction with dispersion kinetics models to evaluate minor component size and concentration distributions.

Flow Balancing of Profile Extrusion Dies

J.M. Nóbrega, O.S. Carneiro, F.T. Pinho, P.J. Oliveira, May 2001

In this work a methodology to automatically balance the flow in profile extrusion dies is used. For this purpose a computational code, based on the finite-volume method, was developed and used to perform the required three-dimensional numerical simulations of the flow. The methodology is illustrated using two case studies, each one leading to the adoption of a different constructive solution (with and without flow separators). In order to evaluate the quality of the automatically generated die geometries, an objective function, that takes into account the flow balancing and the ratio L/t of the parallel zone, is proposed.

Hot Plate Welding of Glass Reinforced Polypropylene

M.J. Oliveira, F.M. Duarte, D. Tchalamov, A.M. Cunha, May 2001

The reinforcement of thermoplastics with short glass fibers is a common way for obtaining composites with high strength and stiffness. These materials are amenable for welding by the hot plate method, although a drop in the mechanical strength is observed. In this paper 20% glass reinforced polypropylene (GRPP) was injection molded in mono-material and bi-material (PP/GRPP) ISO-type tensile testing specimens and welded using the hot-plate technique. Morphological analysis and mechanical testing were used to investigate the effect of the processing parameters and type of molding on the weld behavior. It was found that the welds made with PP/GRPP moldings are stronger than if only GRPP is used in the moldings.

Design of Extrusion Screws Using an Optimisation Approach

A. Gaspar-Cunha, J.A. Covas, May 2001

The design of a screw for polymer extrusion based on scientific principles is still a challenging task, which has received relative little attention in the literature. Prior to the definition of the geometric parameters of the screw, the designer has to decide about general features, such as the type and location of mixing zones, which is mainly based on empirical knowledge. Once the main process criteria are identified (e.g., pressure generation capability, mixing efficiency, power consumption), the design is then carried out on a trial-and-error basis. In the present work we consider screw design as an optimisation problem where the aim is to maximise the value of an objective function that describes quantitatively the process performance. A design methodology incorporating this approach is presented. The relevance of the solutions and the sensitivity of the method to changes in the criteria considered are demonstrated with various examples.

Polyethylene Die Deposit-Measurement, Formation Mechanism and Routes to Reduction

Choon K. Chai, Gordon Adams, Jason Frame, May 2001

Die deposit (sometimes known as die drool, die lip build-up, etc) occurs in melt extrusion of polyolefins. It is an undesirable build-up of material, normally on the lip or open faces of extrusion dies. In commercial scale polyethylene extrusion processes (e.g. blown or cast film, fibre spinning, etc), die deposit can have a significant influence on productivity, through the need to shut down processing line periodically to clean the die, and on the end-product quality. There are a wide range of factors or sources that lead to the formation of die deposit as its mechanism is not understood, these include low molecular weight species and volatiles, die swell, die design and polymer structure. This paper investigates, through laboratory-scale extrusion and rheology evaluations, some of the key relationships in the die deposit formation process. A deposition mechanism is thus proposed from these studies, with some suggestions for its reduction.