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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A Plasticating Screw Design for the Reprocessing of Multi-Layer or Multi-Material Plastic Formulations
Recycling or reprocessing of “multi-layer” or “multi-material” plastic products is a particular problem for plastic compounders or recyclers. Examples of multi-layer plastic products include painted or coated plastic items, such as automotive body panels, or multi-layer plastic packaging, such as that used in high barrier applications. In each of these cases, the coating or multi-layer structure is utilized to enhance either the product's overall performance or appearance. Unfortunately, the presence of other material layers will generally have a negative impact on the recyclability of the primary thermoplastic material as they often act as incompatible contamination. For example, most of the paints or coatings used in the automotive industry are thermosetting in nature and act as solid particulate inclusions in the recycled matrix material. Methods to remove coatings from coated plastic parts have been developed, but are not always cost effective. As an alternative, these complex material constructions can sometimes be effectively recycled if the contaminating layers can be reduced in particle size and effectively mixed into the continuous thermoplastic matrix material. A single screw mixing or “grating” section has been designed and evaluated experimentally in this study. Experimental trials were conducted using reground, painted thermoplastic olefin automobile bumpers. The reground bumper scrap was extruded using a single screw equipped with this grating sections, and several more conventional extrusion screw designs. The paint flake size distribution of the extrudate, and the physical properties of samples molded from the extrudate were evaluated for each screw design, both with and without melt filtration.
Plastic-Metal Hybrid - A New Development in the Injection Molding Technology
Plastic/Metal Hybrid technology is an innovative approach in designing structural systems to save both cost and weight while improving quality. The use of this technology reinforces thin open metal profiles with a strategic placement of thermoplastic ribs. The rib structure prevents buckling of the metal profile and maintains the original steel section properties. The weight benefit is realized by designing secondary structures and complex geometry in plastic while using steel only where necessary. The cost benefit is delivered by the potential to integrate many functions into one component. Part quality is improved through increased dimensional stability and reduced tolerances. Successful applications in automobile structures have opened the technology to new markets such as furniture, consumer, and information technology.
The Plastics Resources for Educators Program (PREP) - Phase 2, Dissemination and Evaluation
The Plastics Resources for Educators Program (PREP) has been developing instructional materials including multimedia, illustrations, and processing simulators for educators in Plastics Engineering Technology. We have made these materials available at our Internet website (www.pct.edu/prep) to faculty interested in using these instructional materials. The mission of the PREP initiative has now evolved to focus more on dissemination and evaluation of the instructional materials we have produced. The purpose of this paper is to outline how instructional materials can be obtained from PREP and how individuals can submit their work to PREP for inclusion on the PREP bookshelf.
PMF®Fiber Processed Mineral Fiber High Performance Reinforcement for Thermoplastics
The performance of Processed Mineral Fiber (PMF®FIBER) as a reinforcing agent is compared to both milled and chopped glass fibers in polypropylene, nylon 6, and nylon 66. The influence of method of mixing and partial replacement of glass fibers by PMF®FIBER on properties of 30% filled composites is investigated.It has been determined that the PMF®FIBER composites properties are less sensitive to method of mixing. Even untreated 0.20 mm long PMF®FIBER performed better in nylon and similar in polypropylene than eight times longer milled glass fibers (1.58 mm). Replacing up to 50% of chopped glass fiber by PMF®FIBER seemed to have no significant effect on impact strength or heat distortion temperature. Longer, surface treated PMF®FIBER can be economical alternative to glass fibers.
Poly(3-Hydroxybutyrate) Porous Structure for Tissue Engineering Applications
Biodegradable polymeric supports (scaffolds) have been used in tissue engineering in order to regenerate damage or lost tissue and organ structures.In this work scaffolds of poly (3-hydroxybutyrate) (P3HB), a natural polyester produced by bacterial fermentation process, were prepared by solvent - casting / particulate - leaching where the polymer was dissolved in organic solvent and mixed with salt particles of different sizes, followed by controlled solvent evaporation and water dissolution of the salt.The interconnected pore structure was evaluated by Scanning Electron Microscopy (SEM). Differential Scanning Calorimetry (DSC) was used to determine the thermal properties of P(3HB) / salt. SEM micrographs revealed the presence of interconnected pores for all ranges of salt particles. Thermal analyses showed that the degree of crystallinity for the porous structures was higher for lower salt particle size compared with P(3HB) dense film.
Polyethylene Obtained with 1,3-Xylylene-Cp2ZrCl2 / Methylaluminoxane Catalyst System
Development of polyethylene thermoplastic was stimulated by the advent of metallocene catalysts. New catalyst systems were obtained to improve polyethylene synthesis and polymer properties. In this work polyethylene was synthesized with an asymmetric metallocene system. This system is composed by 1,3-xylylene- bis(cyclopentadienyl) zirconium dichloride and methylaluminoxane (MAO). An experimental planning was carried out in order to study the effect of ethylene pressure and polymerization temperature on the catalyst activity and polymer properties.
Nanometer scale platy materials were exfoliated into polymers for better performance. Layered double hydroxides, LiAl2(OH)7 (LAH) and MgAl(OH)5 (MAH), were modified by ion exchange with organic acids and salts. The organic modifier compatibilizes the hydroxide surface to polymer matrices and spaces the crystalline layers apart to minimize the energy needed for exfoliation during the compounding process. The storage modulus of the polyethylene elastomer containing 5% organic modified MAH is better than that filled with 20% micron size talc particles. The performance of PP, ABS, Nylon 6,6 and PC nanocomposites will also be discussed.
Polyolefin Nanocomposites Using Maleic Anhydride Modified Polyolefins
Nanocomposites comprised of montmorillonite clays and maleic anhydride grafted polyethylene (PE-g-MA) were prepared by melt blending. The presence of maleic anhydride (MA) derived groups grafted in PE promoted strong interaction between polymer matrix and clay, leading to complete exfoliation and dispersion of clay platelets. The non-isothermal crystallization behaviour, rheology and mechanical properties of the nanocomposites were investigated. The non-isothermal crystallization of the PE phase was strongly accelerated by the presence of clay. The viscous and elastic properties increased significantly with increasing clay content. The tensile strength of nanocomposites was improved as compared to pure PE and PE/clay mixtures, but elongation at break decreased considerably.
Porous Implants Based on UHMW Polyethylene for Biomedical Applications
A novel generation of porous implants based on Ultra High Molecular Weight Polyethylene (UHMWPE) for knee and hip joints has been developed. These porous, rather than solid (non-porous) commercial PE implants, could help to provide internal lubrication with synovial fluid to reduce wear and erosion of implants. The porous structure has been developed by a non-foaming, leaching (washing-out) technique using commercial water-soluble mineral salts as fillers (porogens). The size, shape and content of the salts determine the size, shape and amount of interconnected pores in the samples produced by compression molding process. The porous structure and mechanical properties have been studied and compared with non-porous UHMW-PE materials.
Porous Polyethylene Films via Template-Leaching Method: Preparation, Characterization, and Tensile Properties
In this work, porous polyethylene films were prepared by the template-leaching method. The leachable component was tapioca starch, which was blended with low density polyethylene (LDPE) to respectively produce blends of 2, 4, 6, 8, 10, and 12% by weight of starch. Each blend was melt-extruded to obvtain LDPE/starch films having thicknesses of 50, 80, and 100 ?m. The porous structure of the films was then formed by removing starch particles from the films via either acidic or enzymatic hydrolytic leaching techniques. For acidic hydrolysis, the films were immersed in solutions of HCL, H2SO4, and HNO3 under various conditions while a solution of ?-amylase was employed for enzymatic hydrolysis. For acidic hydrolysis, starch particles were best removed using 5 N HNO3 at 65°Celsius corresponding to a reduction in the starch level of ca. 85%, whereas, for enzymatic hydrolysis, the reduction was much lower at ca. 35%.
Powder Flow during Rotational Molding
For about the first-third of the rotational molding heating cycle, the polymer free of the mold surface flows as a powder. Although it appears that the powder is cohesionless at room temperature, there is strong evidence that there is increasing cohesion during heating. This changes the nature of powder flow from avalanche to block flow with frictional or shear flow occurring between the mold surface and the powder layer against it. Stress analyses on the powder bed show that shear forces between powder particles and between the particles and the mold surface are linearly proportional to the normal force on the powder, and yield two fundamental powder properties, powder cohesiveness and particle-to-particle coefficient of friction. The parameters that affect these relationships and methods of measuring them are discussed.
Practical Approach to Modeling Multiple Reactor HDPE Process
Instantaneous Property Predictive Models are very valuable in the operation of a multiple reactor high-density polyethylene (HDPE) process. The purpose of these models is to accurately predict resin physical properties, such as density, melt index (MI2) and molecular weight distribution (MWD) from reactor synthesis conditions. This paper describes how a predictive model was developed by regressing Gel Permeation Chromatograms (GPC) deconvolution constants versus reactor synthesis conditions. Briefly, the model generates a GPC trace of the resin produced in each stage of reaction; the data from all the stages are summed up to give a composite trace; the number average (Mn) and weight average (Mw) molecular weights are calculated from the composite. Previously published correlations (1) are then used to predict MI2, MWD and density from the composite Mn and Mw and comonomer concentrations. Predictive results for thirty-four resins are presented.
Practical Relationships for Calculating Pressure Drop in Injection Molds
The flow of melt in runner systems of injection molds takes place in channels whose cross section can be either circular, square, rectangular or of any other geometrical form. In order to obtain a uniform distribution of the melt at low pressures, knowledge of the pressure drop along the flow path is important. Based on the modern developments in rheology, this paper presents easily applicable relationships for calculating pressure drop in the flow channels of different geometry taking flow rate, resin type and melt temperature into account. Worked-out examples illustrate the use of the equations presented, which were found to agree well with the results in the practice.
Prediction of Anisotropic Shrinkage Behavior of Plastic Injection Molded Parts by Experimental Design Approach
The shrinkage behavior plays an important role in the determination of the final dimensions of plastic injection molded parts. Materials used, mold and part designs, and processing conditions all can have great influence on parts' final dimensions. In this study, the experimental design approach of L27 array is used to study the effects of three processing parameters (melt temperature, mold temperature, and holding pressure) on the shrinkage behavior (along-the-flow and across-the-flow directions) of injection molded parts of polystyrene. A multiple regression model is set up to predict the dimensions and the goodness of the model is verified by the confirmation data. Previous research results are reviewed and compared with.
Prediction of the Mechanical Properties with Part Weight Reduction for Injection Molding Microcellular Foam Parts
A microcellular plastic part with an injection molding method can be treated as a sandwich structure in which a foamed core encased by a skin frame. It is unique characteristics for microcellular plastic injection molding part because of a uniform cell distribution across the foamed section except the skin. The simple models based on this structure for prediction of mechanical properties of microcellular plastics are proposed and verified by the injection molding microcellular sample tests. The weight reduction percentage of the whole part and the skin thickness are used as input data to calculate the mechanical properties. The effect of skin-core ratio for the mechanical properties of foamed part is also discussed in this paper.
Pressurization and Energy Characteristics of Strainer Disk Elements CFD Calculations and Experimental Results
A study of pressurization and energy characteristics of strainer disk elements for different sizes of ZSK twin-screw extruder with PE-HD are presented. The work compares the results of a complex 3D CFD model of ZSK40 strainer disks with some experimental results. As the manual setup of such a complex CFD model is rather expensive, a method has been developed to decompose the complete model into two simple parts. These parts can be set up easily in a batch procedure. Finally the effect on the pressurization and energy characteristics is discussed when doing a scale up from a ZSK40 to a ZSK92 or a ZSK250.
A Procedure for the Design Optimization of Injection Molded Plastic Parts Using CAD/CAE Softwares
The objective of this work was the development of a procedure to establish the optimization design basis of plastic parts by using Computer Aided Design (CAD)/Computer Aided Engineering (CAE) software. An example is show applying the procedure on a specific problem where the part evaluated was a commercial compact disk (CD) case. The simulation results were obtained through a filling/cooling simulation program for the injection molding process and a three-dimension solid modeler program. After modifying the process conditions, gate dimensions and part design, a new case design was evaluated. The simulation results, maximum wall shear stress and shear stress in service showed a best behavior in use for the new proposal.
Process Capability Comparison of Various Switchover Modes from the Filling to Packing Stages in Injection Molding
Many sources of variation in the process can contribute to product inconsistencies among a batch of molded parts in the injection molding process. These sources include materials, machine control capability and conditions, human factors, and environment. This paper provides an overview of the means for measuring process capability and the methods for maintaining process robustness in injection molding. Furthermore, an experimental study utilizing statistical methods provides a simple and effective means of identifying capable switchover methods in the injection molding cycle to maintain the shot-to-shot process repeatability for injection molding operation. Five switchover modes are compared.
Process Control by NMR at Basell Polyolefins
Basell currently has over 25 polyolefin production lines at our various plants throughout the world utilizing NMR for advanced process control. These units include online units, which provide virtually continuous process feedback control as well as offline and laboratory units to provide checks of the various processes. Correlations have been developed to monitor a number of process variables of interest. The use of NMR for advanced process control has reduced the need for frequent wet" tests has reduced "off-spec" materials has improved product transition times and has allowed the reallocation of resources to other parts of the plants. The intent of this paper is to give a general overview of process control by NMR and in particular at Basell and how it is implemented."
Processing and Cell Structure of Nano-Clay Modified Microcellular Foams
Applications of nanometer-sized particles can facilitate the formation of microcellular foams in the continuous extrusion foaming process. Both intercalated and exfoliated polystyrene/nanoclay composites were foamed using CO2 as the foaming agent. The resulting foam structure is compared with that of pure polystyrene and polystyrene/talc composite. It is found that unique foam structure can be created by changing the content and the dispersion of nanoclay particles. The effects of nanoclay dispersion on the polymer melt rheology and the foaming process are discussed. Combining nanoclay compounding with microcellular foaming provides a new technique for the design and control of foam structure.
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