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.
Flow-induced migration of polyethylene-co-maleic anhydride (PE-co-MA) additives in a polyethylene (PE) melt is investigated using long-chain branched polyethylene covering a range of melt index. Attenuated total reflection infrared (ATR FTIR) spectroscopy and interfacial tension measurements were used to characterize surface composition of copolymer additives processed by a melt extrusion. Experiments covering a range of shear rates, die length/diameter and extrusion temperatures are described. The surface concentration of copolymer additives were changed from the bulk to the surface of extrude depending on the shear rate and temperature due to the shear-induced diffusion of macromolecules. A mechanism based on stress-induced diffusion is proposed to explain the observed surface migration phenomena.
By the year 2010, HCFC 142b will be banned for use as a foaming agent for extruded polystyrene (PS) foam in North America. Many blends of foaming agents have been patented as replacements to expand PS. In this study the optimal concentration of a previously unexplored blend of CO2 and 2-ethyl hexanol (2-EH) is shown to allow the production of PS foam of 30 kg/m3 density. The glass transition temperature reduction of the PS, due to the incorporation of 2-EH, is believed to be an important contributor to the success of this foaming agent blend. In long-term use of the foams, the 2-EH does not measurably diffuse out of the PS whereas the half-life of CO2 diffusion out of the foam is measured in weeks.
Medium and high density polystyrene foam moldings were produced by compression and injection molding. Polystyrene (PS) was first impregnated with HCFC 141b and pelletized. These impregnated pellets became the feedstock in injection and compression molding, with cycles typically lasting between 1 and 30 minutes in duration. The compression molding cycles were studied to optimize the mold release method and the cycle times ascribed to heating, pressure release and sample cooling. The lowest foam density reached was 196 kg/m3. While residual foaming agent in the matrix negatively impacts on the mechanical properties of the foam, the results of this work demonstrate that a physical foaming agent is feasible for compression molding and short-shot injection molding of PS. It should however be pointed out that HCFC 141b will be banned for use in the U.S. by the year 2003 and in Canada by 2010.
The fracture toughness, defined as Kc, of injection molded long fiber reinforced polypropylene with 50% E-glass and its variations is investigated. Rectangular plaques of different thicknesses at various sets of processing conditions have been fabricated. In order to assess the spatial variation of the fracture toughness, specimens aligned in the direction of the injection molding flow and perpendicular to it, have been obtained and tested at pre-selected locations. The morphology of the samples consisting of flow induced through-thickness layers was also evaluated experimentally and related to the fracture toughness, thus showing the effect of the part morphology on such mechanical property.
Thin-wall injection molding is a key technology allowing the low-cost mass production of microstuctures, such as devices with surface-relief microcomponents widely applied in micro-optics, micro-fluidics, medical and biotechnology. Research was performed in order to gain better understanding of important parameters in injection molding of thin-wall microstructures. A series of injection molding experiments were conducted with PC and PMMA, which are common materials in bio-MEMS (Micro Electro Mechanical System) applications. The rheological properties were characterized through dynamic, and transient shear viscosity measurement using a Rheometrics Mechanical Spectrometer. Micro-channels of different lateral and depth dimensions were obtained on thin wall substrates. The Scanning Electronic Microscope (SEM) photos were used to measure the fidelity and roughness of the replicated plastics. Birefringence was used to qualitatively examine the amount of residual stresses in the molded parts.
Fundamental scratch damage behavior in polymers was studied through investigation of a series of polycarbonate and polystyrene samples with different molecular weights. The constant load scratch test, based on a spherical indenter, was employed. Scanning electron microscopy and transmitted optical microscopy were performed to examine surface and subsurface damage during scratch. The plastic flow scratch pattern and the fracture scratch pattern are the two typical scratch patterns found in polymers. It is shown that shear yielding is the main mechanism for the plastic flow scratch pattern, while tensile-tear induced fracture on the surface and shear-induced fracture on the subsurface are the main damage mechanisms found in the fracture scratch pattern. The relationship between scratch resistance and material property relationship in polymers is discussed.
Everyone - color concentrate manufacturer, resin producer, compounder, molder, or extruder - understands delivering the right color the first time is crucial to customer satisfaction. Today, digital color communication technology ensures color specifications across approval points and within an increasingly complex cycle of tighter manufacturing tolerances and requirements, global competition, and just-in-time scheduling. By replacing physical sampling with digital, adjustments and approvals are made on screen, eliminating time, cost, and frustration among all points in the supply chain. This paper explores the profound implications this new technology has on the entire color cycle- from design to compounder to finished product.
Low density poly(ethylene-co-octene) foams were produced by injection molding compounded formulations consisting of resin, chemical foaming agent, activators, cross-linking agent and nucleating agent. The effect of the formulation on the foam density and morphology was examined for one set of processing conditions. The concentration of cross-linking agent must be geared to the initial resin viscosity to allow proper bubble growth. The foam will otherwise collapse or show little expansion. The results show that an optimized formulation along with proper processing conditions yield fine-cell foam of low density.
In this paper the mechanical, magnetical and rheological properties are analyzed. The influence of different magnetic powders onto a plasticized polvinyl chloride) were studied. The magnetic characterization of isotropic plastic bonded magnets, based on strontium ferrite (SrFe12O19) and plasticized polyvinyl chloride, as a function of composition was analyzed in a magnetometer at room temperature. In order to explain the dependence of the volumetric density and the saturation magnetization with composition, an additive model for these properties is considered. The intrinsic coercivity shows a decrease with increasing strontium ferrite content, which is due to the increasing interaction between the magnetic particles. The maximum energy product is lower than 1 MGOe and increases with the second power of the strontium ferrite content. The rheological properties were studied in a capillary rheometer; it was found that viscosity increased as the magnetic powder concentration increased in the composite.
Important appliances have arised from the study of polymer composites containing conductive particles (e.g., EMI shielding, antistatics, wire coatings for overcurrent prevention). The present work is concerned with dynamic properties related to the microstructural arrangements, as observed by Transmission Electron Microscopy (TEM), in an elastomeric blend system consisting of Polybutadiene (BR), EPDM and Carbon Black (CB). Based on changes in the viscous component signals of BR and from micrographs of samples stained with osmium tetroxide it was found that the CB was located mainly in the BR phase. Final behavior of the conductivity was found to have great dependece on this fact.
This study discusses the influence of molecular weight, melt temperature, mold temperature, and aging on the impact characteristics of molded PVC. Tensile impact (uni-axial), instrumented drop-dart impact (bi-axial), and Izod impact (tri-axial) methods were utilized to assess the impact properties of the material under investigation. It was found that the impact properties were affected by aging more than by the changes in the melt temperature or the mold temperature. Additionally, the molecular weight played a significant role in influencing the impact properties of PVC.
Some case studies are presented in this paper to show the effect of material choice and end-use on product failure. Microscopic analysis was used in these investigations to identify the fracture features. Additionally, mechanical analysis was utilized occasionally. The first case shows the importance of material choice and processing conditions on the failure of plastic products. The second case illustrates the negative effect of adverse end-use conditions on the failure of plastic parts. The third case describes the combined contribution of material choice and end-use to the plastic product failure.
In this work an improvement in mechanical perfomance of a general purpose reinforced unsaturated polyester resin, is attempted by using two different types of crosslinking systems to make composite materials by compression molding. Three resin layers separated by two glass fiber mat pieces conform the composites to be tested. Styrene, divinyl benzene and butyl acrylate in different proportions were used to crosslink the resin. Important variations in two formulation composition zones were found for tensile strength, impact resistence and dynamic properties. A formulation may be chosen to achieve enhanced performance in particular properties.
Industrial Technology is a field of study designed to prepare technical and/or management oriented professionals for employment in business, industry, education, and government. As a young industrial technologist it is my responsibility to understand both the technical aspects of world class equipment and more importantly, strategic application of these technologies for maximum corporate impact. Rapid prototyping and rapid tooling are technologies that if coupled with appropriate management strategies should allow companies to get their products to the market faster. This paper presents how a team of graduate students is using rapid prototyping and rapid tooling to reduce product changes and associated costs and accelerate product development.
The surface of a polymer film can be modified by allowing additives within the film to diffuse to the surface and accumulate there. Some of the most commonly used surface-property modifiers are slip, antifogging and antistatic agents. Erucamide is a slip agent widely used to reduce coefficient of friction (COF) of polymer films. This research focused on quantifying the relationship between erucamide surface concentration and COF of LLDPE films. The surface concentration was measured using surface washing, and results showed that there were significant COF changes in the surface-concentration range of 0 to 0.5 ?g/cm2.
The surfaces of a polymer film can be modified by allowing additives within the film to diffuse to the surfaces and accumulate there. To model the diffusion/accumulation process, it is necessary to accurately measure the diffusion coefficient of the additive in the polymer. We have attempted to characterize the diffusivity of erucamide in LLDPE through several means: mass sorption (diffusion in") and surface washing and ATR-FTIR ("diffusion out"). Experiments demonstrate that surface washing can provide inconsistent results. Mass sorption and ATR-FTIR provide comparable results although emphasis is placed on the ATR-FTIR technique because the migration process more closely mimics the behavior of commercial films."
The stress development during polymer processing of semi-crystalline polymers can cause stress-induced crystallization and changes in the crystallization kinetics. The integration of orientation entropy changes calculated by non-linear viscoelastic constitutive equations in crystallization thermodynamics gives us a proper physical model to describe the crystallization behavior in oriented polymer melts. Based on the model a new economic characterization procedure for stress-induced crystallization is put into application. The new model is used to simulate the stress-induced crystallization during the injection molding of isotactic polypropylenes. The results are compared with experimental data.
Knowledge about interfacial adhesion in thermoplastic/LCP blends is important for manufacturing self-reinforced composites with improved performance. Thus, in the present study, interfacial shear strength between different LCPs and thermoplastics was measured by using fiber pullout method. The LCPs employed were Vectra A - 950, Vectra B - 900, Ultrax KR - 4002 and Ultrax KR - 4003. The thermoplastics included were high density polyethylene, polypropylene, polycarbonate, polyphenylene oxide/polystyrene alloy, polybutylene terephthalate, polyethylene terephthalate, polyethylene naphthalate, polyetherimide and copolyester. Based on these measurements, the similarities and differences in interfacial behavior of various pairs have been found. In addition, ranking of various pairs of thermoplastic/LCP blends has been made concerning their interfacial shear strengths.
The dynamic properties of polystyrene (PS)/silica mixtures of various concentrations were investigated as a function of frequency and strain along with the flow curves. An abrupt change in the viscoelastic properties is noticed above 1% volume concentration. Observations by means of scanning electron microscopy (SEM) indicate the creation of a 3D network through bridging of filler particles by adsorbed polymer. The rheological behavior is simulated utilizing a double network created by the entangled polymer matrix and the adsorbed polymer. Both networks are represented by a Giesekus viscoelastic constitutive equation. The dependence of rheological properties on filler concentration is taken into account through the density of polymer-filler interactions and a hydrodynamic reinforcement. The relative contribution of both networks is computed through the energy balance consistent with the thermodynamics of the chemical interactions and fluid mechanics. This self-consistent approach allows one to predict the major features of the rheological behavior of such systems.
Resolution and sensitivity are two of the most important properties of thermal analyzers. Resolution can be described as the ability to separate and observe two events, which occur close to one another and sensitivity is the ability to detect very small effects. The ability to significantly shorten the overall experimental time and increase throughput, yet obtain data with improved resolution and greater sensitivity are highly desirable. In many labs involving thermal analysis of polymers, today's instruments provide a similar choice. In this paper, improved sensor design and firmware in Differential Scanning Calorimeters (DSC) will be discussed using few application examples.
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ANTEC 2016 - Indianapolis, Indiana, USA May 23-25, 2016. [On-line].
Society of Plastics Engineers
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