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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Phase Separation in a Homogeneous Shear Flow
Computational results of phase separation in a homogeneous shear field, based on a Galerkin type spectral element method have been obtained. The theory of Cahn and Hilliard, describing the free energy of a non-uniform system with local and non-local terms, is used in the framework of the theory of the non-classical thermodynamics described by de Groot and Mazur (1) to derive a complete set of equations that governs phase separation and hydrodynamic effects such as coalescence. This work is compared with results in which the velocity field is inserted directly into the convective term of the time-dependent Ginzburg-Landau equation. Logically the results of a coupled solution with high capillary number closely resemble those of a directly imposed velocity field. However, as a smaller capillary number is chosen the interfacial forces become more dominant over the viscous forces which results in different morpologies.
Phota Degradation Mechanisms of Layered Silicate-Polycarbonate Nanocomposites
The use of advanced lightweight materials to improve combat survivability has been of crucial interest to the U.S. Army for a number of years. The design, development, and performance testing of these advanced materials is critical for enabling Future Combat Systems and the Objective Force Warrior. Specifically, hybrid organic/inorganic polymer matrix nanocomposites show promise in providing many of the physical properties required (i.e. lightweight structure, rugged abrasion resistance, high ballistic impact strength). However, as with any polymer system, these materials are susceptible to degradation over time when exposed to various environmental (i.e. sunlight, moisture, temperature) conditions. This structural degradation (1-5) will eventually comprise the original integrity of the materials’ desired properties.Polycarbonate (PC) has outstanding ballistic impact strength, good optical clarity, and high heat distortion resistance. The Army has a continuous interest in research on PC for better chemical resistance and enhanced resistance to abrasion. The focus of our research is to exploit nano-technology through incorporation of layered silicates for property enhancement. Typical mica-like clays consist of stacked platelets with the thickness of each individual platelet on the order of 1 nm. (1-5) Because of the nanometer size and high aspect ratio characteristics, polymer-layered silicate nanocomposites with much lower volume fraction of clays exhibit properties significantly better than the conventional mineral-filled micro- or macro-composites.In this study, the impact of accelerated weathering upon newly developed polycarbonate-layered silicate nanocomposites materials was investigated. The silicate loading varied from 0-3.5 % by weight. A fluorescent ultraviolet (UV)/condensation weathering tester was selected for the exposure study. The materials were characterized by UV/VIS spectroscopy and FT-IR spectroscopy.The results reveal that the carbonate linkages
Photoelastic Measurement of Residual Stresses in Hot Plate Welded Polycarbonate
Formation of thermal and residual stresses during thermoplastic welding can have detrimental effects on the joint quality under both dynamic and static loading conditions. Residual stresses can reduce the solvent resistance of the polymers as well as the tensile strength and fatigue life. Therefore, it is important to be able to measure and predict the residual stresses that develop during welding and to relate process parameters to the stress level. Photoelasticity was used to measure the residual stresses in hot plate welded polycarbonate. It shows that stresses in the direction parallel to the weld are highest.
Photostabilization of Wood Flour Filled HDPE Composites
Wood/plastic composites are increasingly examined for non-structural building applications. As outdoor applications become more widespread, durability becomes an issue. Ultraviolet exposure can lead to photodegradation, resulting in a change in appearance and/or mechanical properties. Photodegradation can be slowed through the addition of photostabilizers. This study examines the performance of photostabilized HDPE/wood flour composites after accelerated weathering. A full factorial experimental design was used to determine the effects of hindered amine light stabilizers (HALS), a UV absorber (UVA), a colorant, and their interactions on the photostabilization of the composite. After 250, 500, 1000, and 2000 hours of accelerated weathering, color change and flexural properties were determined. The experimental results indicate that both colorant and UVA are more effective photostabilizers for wood flour/HDPE composites than HALS.
Physical Aging during Creep and Recovery of PET Bottle Grade Material
The effect of physical aging on long-term creep and recovery of PET bottle grade material was investigated at temperatures below glass transition temperature. Long-term experiments (time duration -840 hrs) were performed to probe the significance of temperature on the intensity of aging and its effect on the rate of creep and recovery. It was found that the effect of aging during the creep and recovery is significant at elevated temperature. This investigation is important for the packaging application. The paper provides information regarding the collapse of PET bottles over time and temperature and also provides quantitative design information for the assembly of the package. Furthermore, comparative study of recovery responses of PP (material for the closure) and PET (bottle grade material) over time and temperature was made.
Pipes from Recycled High Density Polyethylene Blends
This paper presents the results of the development of recycled HDPE blends with improved SCR for low pressure pipe containing the maximum possible portion of post consumer recycled HDPE. A post consumer recycled High Density Polyethylene (R-HDPE) was blended with virgin Medium Density Polyethylene (MDPE), over the composition range of 0-100%. The recycled HDPE has limited post-consumer applications due to its poor stress crack resistance (SCR). Resistance to SCR of the compositions was determined by the Notched Constant Tensile Stress Test (NCLS). Results indicate that there is potential to incorporate the use of Post consumer HDPE in low pressure pipe applications at composition greater than 50%.
Plastic Brighteners: Character and Application
The use of optical brighteners in the plastic industry is becoming more and more popular, as shown by a steady increase of consumption during the last two decades. The main application fields for the major plastics polyvinyl chloride, polyolefines, ethylene - vinyl acetate copolymers, polystyrene, polyester and polyurethane are presented. Performance characteristics such as high effectiveness and excellent fastness properties are required. End users and plastic manufacturers have to find ways to satisfy these demands. The individual characteristics of the polymer require the optical brightener to have a specific chemical structure of the optical brightener.The optical brightenersC.I.Fluorescent Brightener 184C.I.Fluorescent Brightener 236C.I.Fluorescent Brightener 367C.I.Fluorescent Brightener 368C.I.Fluorescent Brightener 378C.I.Fluorescent Brightener 393are illustrated. Their effectiveness in widely used polymers is reviewed indicating their preferred application. Selected properties such as the influence of TiO2 as well as that of light stabilizers and plastisizers are discussed. Migration problems with optical brighteners in the case of LDPE are discussed. Care must be taken when brighteners containing olefinic bonds are added to esterification process during polyester production.
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.
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