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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

Anticipated Electrical Guidelines for the Upcoming Mold Safety Standard
Thomas P. Linehan, May 2000

The Society of Plastics Industry (SPI) has a working committee to address safety issues with injection molds. Part of this committee's work is to address electrical aspects of safety. To do this, a Mold Electrical Safety Sub Committee has been created under the Committee on Mold Safety specifically to review electrical standards for injection molds. Proper design of hot runner system wiring is one of the key areas of focus because of the adverse environment these systems operate in. This paper will seek to give a heads-up" in what to expect in one part of the electrical safety standard that is to be released in the next couple of years. A proposed method for proper selection of heater conductors (wires) will be reviewed as there are no existing guidelines for applications that expose wire to this high a temperature and conductor bundle size (number of conductors)."

The Effect of Feeding Mode on Dispersive Mixing Efficiency in Single-Screw Extrusion
P.H.M. Elemans, J.M. van Wunnik, May 2000

In the case of dry colour compounds, where polymer granules are coated with a pigment powder, the latter tends to form agglomerates during extrusion, due to the hydrostatic pressure that prevails in the screw channels. In single-screw extruders, this pressure is due to the Coulombic frictional transport in the solids conveying zone. The formation of agglomerates can be prevented to a considerable extent by operating the extruder in an underfed mode. This result has emerged from a study of the problems encountered when dispersing pigments in poly(butylene terephthalate) (PBT), but can also be applied in the case of numerous compounds where a fine dispersion of solids in polymers is required.

Enhancing Dry-Colour Efficiency in Starve-Fed Injection Moulding
P.H.M. Elemans, May 2000

As in the case of extrusion, the formation of agglomerates can be avoided to a significant degree in the injection moulding of dry colour compounds by starve-feeding the machine. This involves dispensing of the granules (powder-coated with pigment in these tests) to the screw by means of a vibrating trough while the screw is rotating; during the injection phase, the feed is zero. A measure of the filled length is the plasticating time, which is greater in the case of starve-feeding than if the machine were to be operated in a flood-fed mode. Experiments reveal that, using a plasticating unit having a standard three-zone screw, products can be obtained which have a good (albeit still not perfect) pigment dispersion, which is markedly better than in the case of conventional injection moulding. This process offers application possibilities in the field of coloured formulation development.

Electron-Beam Processing of Plastics: An Alternative to Chemical Additives
Michael Stern, May 2000

Modifications in polymeric structure of plastic materials can be brought about either by conventional chemical means, usually involving silanes or peroxides, or by exposure to ionizing radiation from either radioactive sources, or highly accelerated electrons. Chemical cross-linking typically involves the generation of noxious fumes and sensitizing by-products of peroxide degradation. Increased utilization of electron-beams (e-beams) for modification and enhancement of polymer properties has been well documented over the past forty years. Of specific interest to the plastics industry has been the use of e-beam processing (EBP) to improve thermal, chemical, barrier, impact, wear, and other properties of inexpensive commodity thermoplastics, extending their utility to demanding applications typically dominated by higher-cost engineered materials. EBP of cross-linkable plastics has yielded materials with improved dimensional stability, reduced stress cracking, higher service temperatures, reduced solvent and water permeability, and significant improvements in other thermomechanical properties. The purpose of this paper is to review the basic effects EBP on polymers, as well as to highlight several specific recent cases of its utilization to improve key properties of selected plastic products.

The Three-Level Stack Mold
Joseph R. Klanfar, Henry Rozema, Vincent Travaglini, May 2000

Development of new technologies is crucial for the injection molding industry as a whole. This is especially true when Rigid Thin-Walled Disposable Packaging is concerned. Increased competition in this market has led to the evolution of stack molds. The goal: to produce a product of higher quality, in a shorter time and at a lower price. In this industry, where profit margins are measured by fraction of a second, innovation is the key to success.

Production of Profiles from Thermoplastic Composite Towpregs
J.N. Mota, J.P. Nunes, A.S. Pouzada, May 2000

The production of towpregs of continuous fibers and thermoplastic matrix is a convenient way of impregnating thermoplastics in fiber tows. The processing of these towpregs brings about technical difficulties when producing end user products. A pultrusion head was developed and tested for the producing of a U-shape profile of continuous carbon fibers and polycarbonate matrix. The methodology and theoretical models used to design pultrusion head and the results of preliminary tests made to pultruded the U-shape profiles are presented and discussed.

The Advantages of Direct In-Line Compounding Systems
Marvin J. Voelker, Charles D. Weber, May 2000

Composite Products, Inc. has commercialized in-line compounding technology to produce thermoplastic composites. Turnkey systems continuously compound thermoplastic resin with reinforcements i.e. ½ inch chopped glass, carbon or natural fibers to produce finished composites with outstanding toughness. Coloring, recycling of plant regrinds and use of recyclates are accomplished in-line with the molding process. The patented technology provides molders the ability to contain costs and simplify complex scheduling logistics to meet Just-In-Time shipping schedules.

Backmixing in Screw Extruders
Chris Rauwendaal, Paul Gramann, May 2000

Mixing is a critical function in most extrusion operations. One of the most difficult mixing tasks is backmixing. An extrusion operation where good backmixing is very important is when a low percentage color concentrate, CC, is added to a virgin polymer. In this case, the initial distance between the CC pellets may be 100 mm or greater. If the final striation thickness needs to be reduced to the micron level, the reduction of the striation thickness needs to be at least five orders of magnitude - this is quite a tough task! This paper will analyze how the velocity profiles, axial mixing, and residence time distribution are related. It will be shown why simple conveying screws have poor axial mixing capability. New mixer geometries that are specifically designed to improve backmixing will be discussed. Results from extrusion experiments will be presented.

Non-Return Valve with Distributive and Dispersive Mixing Capability
Chris Rauwendaal, May 2000

The screw of the plasticating unit of an injection molding machine (IMM) typically consists of a single stage, single flighted conveying screw with a non-return valve at the end. Mixing sections are usually not incorporated into the screw design. One reason for this is the fact that most plasticating units a relatively short; the typical length-to-diameter ratio is 20:1 in IMMs. This does not leave much space to incorporate a mixing element. Another reason may be the mistaken believe that mixing is not very important in the injection molding process. A convenient method to improve the mixing capability of the plasticating unit of an IMM is to design the non-return valve (NRV) such that it has mixing capability. Such a dual-purpose NRV allows an increase in mixing capability without affecting the melting and conveying capability of the plasticating unit. This paper will describe a NRV mixer based on the CRD mixing technology developed for single screw extruders.

Role of Thermal Degradation of Polyethylene under Natural Weathering Conditions
Syed Halim Hamid, May 2000

UV-B portion of solar radiation adversely affects the physical, chemical, and mechanical properties of exposed plastics and thus their lifetimes are reduced. Mostly polymers used in outdoor applications have UV-stabilizers incorporated in their formulations. The crucial role of temperature on the weathering of polyethylene (PE) was studied. In this paper, polyethylene film samples were exposed to the outdoor weather of Dhahran, Saudi Arabia as well as in low temperature set up maintained at 15°C at all times. The combined effect of high temperature and UV-B radiation on the polyethylene film sample was evaluated in terms of drop in tensile properties and increase in carbonyl absorbance. Higher UV-B together with high temperatures encountered in this region cause faster degradation of polymeric materials.

Design Sequential Gating for Family Mold
A. Pipino, G. Boero, G. Bertacchi, May 2000

The paper illustrates the results of the first phase of a project investigating the area of major interest for sequentially operated valve gates, followed by the developments of a procedure for their implementation in family molds applied to very dissimilar parts. The activity covered the use of computer simulation to determine location, dimension and actuation time of gates during filling and holding phases. Some results are checked by molding on a specially designed mold. The methodology can exploit the potential of this technology to reduce tooling and molding costs with the added benefit of the best color matches of molded parts.

Fractography of Metals and Plastics
Ronald J. Parrington, May 2000

Fractography is critical to failure analysis of metals and plastics. Fractography of plastics is a relatively new field with many similarities to metals. Utilizing case histories, various aspects of failure analysis and fractography are compared and contrasted. Common failure modes include ductile overload, brittle fracture, impact and fatigue. Analogies can also be drawn between stress corrosion cracking (SCC)/stress cracking, corrosion/ chemical aging, dealloying/scission, residual stress/frozen-in stress, and welds/knit lines. Stress raisers, microstructure, material defects, and thermo-mechanical history play important roles in both cases. Key fractographic features for metals and plastics are described.

Factorial Design Approach Applied to Electrically Conductive Nylon 6,6
Julia A. King, Erik H. Weber, Matthew L. Clingerman, May 2000

Prior work by Michigan Technological University showed that for nylon 6,6 based resin there was a synergistic effect on electrical conductivity due to the combination of electrically conductive carbon black, milled synthetic graphite, and PAN-based carbon fiber. The purpose of this present study was to conduct an experimental design to quantify the effects of these three different fillers (carbon black, synthetic graphite, and carbon fiber) on the electrical properties of the resulting nylon 6,6 composites.

Mixing Silica and Other Fillers into Elastomers and Their Agglomerate Breakdown during Mixing in an Internal Mixer and Their Rheological Behavior
Kwang-Jea Kim, James L. White, May 2000

The rate of silica particles agglomerate breakdown in an laboratory internal mixer were measured and compared with carbon black, calcite, talc and zinc oxide particles. Silica agglomerates exhibited the highest agglomerate size. The rheological behavior of each compound was investigated. Small silica particle filled system exhibited highest viscosity level.

The Foaming Mechanism in Rotational Molding
James Throne, May 2000

Rotational molders are lightweighting their parts by adding chemical blowing agents to their polymers. However, they are finding to their dismay that it is just as difficult to produce controlled voids as it is to eliminate voids. This paper highlights the mechanism of cell formation as an aid to those struggling with foam production.

Gloss Control in Rigid PVC-Part II: Effect of Processing Variables on Gloss of Rigid PVC Profiles
Elvira Rabinovitch, Deanna Harshbarger, May 2000

This paper describes the results of the study on the effect of extrusion conditions on gloss of rigid PVC profile. Extrusion variables investigated in this study are: extrusion melt temperature, extruder temperature settings, extrusion rate and the die/sizer metal surface condition. It is hoped that this information will help PVC profile manufacturers to optimize their process for achieving desirable gloss.

PEEK / Carbon Fiber Composites: An Evaluation of Particle Size and Processing Method on Composite Properties
T.A. Bullions, J. Morin, R.H. Mehta, A.C. Loos, May 2000

This study examines the effects of particle size on the consolidation quality and mechanical performance of carbon fiber-reinforced composites fabricated from dry powder coated carbon fiber tow (towpreg). Poly(ether ether ketone) (PEEK) powder was sieved to produce three different particle size distributions; a minimal polymer powder deposition system was used to coat carbon fiber tow with these distributions and unsieved polymer. Unidirectional composite panels were manufactured from these four batches of towpreg and APC-2 (PEEK / AS4) prepreg using an identical processing schedule. Poor consolidation quality of some panels limited conclusions. However, these results did bring forward several questions concerning the effects of powder particle size distribution on the processing of composites from PEEK/G30-500 towpreg that may be addressed in future studies.

Microcellular Foam Molding: Advantages and Application Examples
Kai Jacobsen, David Pierick, May 2000

The MuCell® molding technology is a proprietary manufacturing process for producing microcellular foamed plastics. The microcellular foam process uses supercritical fluids (SCFs) of atmospheric gases to create evenly distributed and uniformly sized microscopic cells throughout a polymer. Suitable for injection molding, this breakthrough foam process enhances product design, improves processing efficiency, and reduces product costs. This foam process does not require chemical blowing agents (CBAs), hydrocarbon-based physical blowing agents, nucleating agents, or reactive components. The microcellular foam molding technology permits molders to reduce raw material consumption while producing strong, lightweight products, extending considerably the applications of foamed polymers. This paper describes those benefits, shows the effect of processing conditions on cellular structure and reviews some successful applications of the technology.

Model-Based Techniques for Improving Part Development
A. Attar, L. Pecora, R. DiRaddo, N. Bhuiyan, V. Thomson, May 2000

In this work, optimization strategies that employ model-based technologies are developed for minimising the overall weight and improving thickness distribution of an extruded blow moulded part. The part studied is a plastic dumbbell for the recreational sector. Process simulations and preliminary experimental trials are simultaneously performed to assist in the development of the part. Once the numerical modelling methodology is functional, one can perform a process optimization based on a desired objective function, such as uniform part thickness distribution and/or minimal part weight. The optimization is performed in two sequential steps (weight optimization followed by thickness optimization) by the systematic manipulation of the operating conditions, such as the parison dimensions. Furthermore, a commercial procedure modelling technology (i.e. FirstSTEP™) is employed for demonstrating the reduction in the part development time with the new model-based approach.

Anisotropic Electrical Percolation and Electrostatic Dissipation in Chaotically Mixed Carbon Black Filled Polyethylene Composites
S.G. Kasliwal, A.A. Ogale, D.A. Zumbrunnen, May 2000

The electrical resistivity and electrostatic charge dissipation characteristics of carbon black (CB) filled low-density polyethylene (LDPE) thermoplastic composites processed by three-dimensional chaotic mixing were investigated. These properties are reported as a function of carbon black concentration and are related to novel microstructures that have been shown to reduce percolation thresholds. Microscopic analysis of emerging structures is correlated to electrical properties of the composite. Electrical conductivity exhibited anisotropy indicating preferred orientation of aggregates formed in situ.

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