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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TRENDS IN RESEARCH ON POLYMER FOAMS
In recent years, concerns over environmental issues have led to a number of new regulations which have had a significant impact on the foams business in general and, in particular, for foams used in thermal insulation applications. Concerns over the depletion of the ozone layer and greenhouse gas emissions have led to the Montreal Protocol and measures to reduce the CO2 emissions. These regulatory issues in combination with traditional performance vs. cost issues are still driving changes in the global foams market today ' changes that are reflected both in the predictions of market growth as well as the technical demands placed on foamed products. In this paper, the expandable polystyrene (EPS) foam market is used to demonstrate the complex interactions of market forces versus technical progress when implementing successful foam products and processes for a wide-spread utilisation.
MISCIBILITY OF STATISTICAL AND BLOCK ETHYLENE-OCTENE COPOLYMER BLENDS
The miscibility of a statistical ethylene-octene copolymer (EO) with an ethylene-octene block copolymer (OBC) was studied. In general the EO/OBC blends were miscible if the octene content difference was less than about 7 mol% and immiscible above about 12 mol%. This contrasted to EO/EO blends where blends were miscible if the difference in octene content was less than about 10 mol% and immiscible above 13 mol%. Unexpectedly, OBC-rich blends (EO/OBC 30/70) displayed significantly more demixing than OBC-poor blends (70/30) even for constituents of about the same molecular weight. The octene content of the OBC soft block was varied in order to differentiate the effects of the average comonomer content from the effects of blockiness.
Comparison of Different Methods of Introducing Water as a Co-Blowing Agent in the Carbon Dioxide Extrusion Foaming Process for Polystyrene Thermal Insulation Foams
In this study, water is used as a co-blowing agent in the carbon dioxide (CO2) extrusion foaming process in a twin screw extruder. It acts as a co-blowing agent to generate larger cells and thus low density foams for thermal insulation applications. Different strategies have been studied in our group to introduce water into the foaming process. These methods include direct injection of water into the extruder with surfactants, the extrusion foaming of water expandable polystyrene (WEPS) beads, and feeding water containing activated carbon (WCAC)/polystyrene (PS) pellets. Morphology and properties of foams made by these processes are compared. It was found that WCAC/PS pellets provide the most stable and clean extrusion process, more uniform cell morphology, and better thermal insulation than other methods.
A COMPARISON OF LAYERED NANOFILLERS IN FLEXIBLE PVC
Previously, our group reported improved oxygen barrier in flexible PVC nanocomposites with 2 wt% Cloisite 30B, an organically modified montmorillonite nanofiller , and industrially relevant lead- and phthalate-free PVC / Cloisite 30B nanocomposite wire and cable formulations with enhanced acceptability . In this work, we begin with a flexible PVC formulation based on our wire and cable work but with all other fillers removed, and consider the effects of a constant loading level of 2 wt% of various commercial layered nanofillers on appearance, thermal stability and oxygen barrier. In addition to natural smectites and synthetic analogs, hydrotalcite nanofillers are investigated as well.
IMPROVING COMPATIBILITY OF BLENDS OF POLYSTYRENE AND POLY(METHYL METHACRYLATE) BY ORGANICALLY MODIFIED LAYERED-SILICATES
Equal volume fraction blends of high molecular weight PS and PMMA are thermodynamically unstable. In thin films supported on silicon, PMMA forms a continuous layer on the surface; while PS tends to move away from the surface and form discrete islands on top of the PMMA phase. The size of PS domains decreases with introduction of nanoparticles. For bulk blends, without nanoparticles, PS forms the matrix and PMMA forms the dispersed phase. For the case of 0.6 wt% silicate, in both thin film and bulk, the blend morphology converts from discrete to co-continuous.Electron micrographs reveal well dispersed silicate sheets locating at the interface between small PS domains in the PMMA phase.
ENCHANCEMENT OF SURFACE REPLICATION BY MICRO-GAS-INJECTION MOLDING
The quality of surface replication is very critical for polymeric micro fluidic devices. It, however, has been a great challenge to achieve perfect replication of micron or submicron features without creating sink marks in the injection molded parts. Gas assist injection molding (GAIM) has been employed to solve this problem with polypropylene and polymethylmethacrylate. This paper discusses the implementation of GAIM in these parts and replication as characterized using profilometry, scanning electron microscopy and confocal microscopy.
FOAMING BEHAVIOR OF MELT BLENDED POLYLACTIDE-CHITIN COMPOSITES
This study details the fabrication and foaming of melt blended polylactide (PLA) and chitin composites. The chitin used for compounding was as-received and in nano-whisker form, which were produced by an acidhydrolysis technique and their morphology was examined with Transmission Electron Microscopy. The composites were characterized for their thermal and rheological behavior. Chitin was found to decrease the thermal stability but increase the crystallinity of PLA. Addition of chitin was also found to reduce the viscosity of the composites even though chitin is a stiffer phase. The reason for this observation is believed to be due to the hydrolysis of PLA during melt blending of chitin in suspension. Foam samples were produced by a two step batch foaming technique and the expansion behavior was correlated with the visco-elastic observations.
ENHANCING THE GAS BARRIER PROPERTIES OF POLYLACTIC ACID BY MEANS OF ELECTROSPUN ULTRATHINZEIN FIBERS
Ultrathin fibers of 100-500 nm in diameter were obtained by electrospinning from an alcoholic solution of zein, a prolamine from maize. The ultrathin zein fibers generated were incorporated as a reinforcement to a poly(lactic acid)/polyethylene glycol (PLA/PEG) matrix by a proprietary method to generate a novel multilayer structure consisting of a zein fiber layer laminated in a sandwich to two PLA/PEG layers.As the zein nanofibers retained the ultrathin structure inside the resulting PLA/PEG matrix, the overall composite remained transparent and colorless. The incorporation of the zein did not significantly affect the thermal behaviour or the water permeability of the original PLA/PEG matrix, but surprisingly it did reduce the oxygen permeability of the matrix by ca. 70%. This technology could thus be potentially applied to obtain highly transparent PLA films with enhanced barrier properties of interest in for instance packaging applications.
CHARACTERIZATION OF POLYETHYLENE BLENDS IN CONSIDERATION OF EPE FOAMING
Blends of linear low density polyethylene (LLDPE), low density polyethylene (LDPE), and high density polyethylene (HDPE) have been characterized in this research work. The main purpose was to generate clear two-peaks from the expanded polyethylene (EPE) foam beads made out of these blends . The blends of 20 wt% of the minor components into LLDPE and a ternary blend of the three components were prepared in a twinscrew extruder at two levels of rotational speed: 5 and 50 rpm. The DSC measurement was carried out at two cooling rates, 5 and 50?§C/min. The results showed that blending with HDPE has a more noticeable effect on the DSC curve of LLDPE than with LDPE. Also, the rotational speed and the cooling rate affect the shape of the DSC curves and the percentage area below the onset point. DSC Characterization of the batch foamed blends revealed the existence of multiple peaks which may be mainly due to the annealing effect during the gas saturation process.
COMPARISON OF THE PREDICTED AND ACTUAL CELL DENSITIES IN STRUCTURAL FOAM MOLDING
There have been many studies on the cell nucleation behaviors in extrusion. In this paper, an effort is made to utilize the cell nucleation mechanism obtained from foam extrusion to describe that of the structural foam molding process. The mold pressure profile is recorded and used to determine the pressure drop (i.e., super-saturation) that is applied for cell nucleation during the structural foam molding process. The predicted data are compared to the actual obtained cell densities. The results indicate that a variety of cell nucleation technologies developed in extrusion foam can also be applicable to injection molding as long as cell deterioration is prevented.
COHESION-DRIVEN RECIRCULATION OF A POLYMER SOLIDS BED IN A SCREW SIMULATOR
This paper demonstrates a previously unnoted heat transfer mechanism for solids-conveying in an extruder which certain polymers exhibit. It was found in this study that polyethylenes readily demonstrate bed circulation in a geometry representative of a lid-driven cavity. This granular advective term for heat transfer in the heated chamber resulted in a more rapid rise in overall bed temperature compared to plug-like conditions. The mechanism for this circulation appeared to be a cohesiondominated phenomenon which requires adhesive forces at the rotating surface to exceed the internal cohesive strength of the solids bed. Conversely, other materials like polypropylene and polystyrene did not readily show this behavior except under more extreme conditions.
A NONLINEAR MODEL-BASED PREDICITVE CONTROLLER FOR INJECTION SPEED
In this work, a unique approach for designing a nonlinear regression model-based predictive controller (NRPC) for controlling the injection speed of 150 tonne injection molding machine. The innovation of this strategy is that the controller structure allows nonlinear open-loop modeling to be conducted while closed-loop control is executed every sampling instant. Consequently, the system matrix is regenerated every sampling instant using a continuous function providing a more accurate prediction of the plant. The proposed algorithm is implemented on controlling the screw speed for injecting plastic into a mold and controlling the temperature of three steel cylinders inside a barrel in order to melt the plastic. The experimental closed-loop responses of the proposed algorithm were compared to a multi-model dynamic matrix controller (DMC) with improved results for various setpoint trajectories. Good disturbance rejection was attained resulting in improved tracking of multi-setpoint profiles in comparison to multi-model DMC.
EFFECT OF BLENDING MODIFICATION WITH POLYETHYLENE ON CELL MORPHOLOGY OF POLYCARBONATE FOAM
This study is aimed at investigating the effect of blending modification with polyethylene (PE) on cell morphology of Polycarbonate (PC) foam. In this study, foamed PC was produced using a dynamic simulation foaming setup designed by ourselves, with supercritical CO2 as foaming agent. The cell morphology of the foamed samples was characterized using SEM. It was found while added appropriate content of PE in PC formulations, melt viscosity and strength of the mixture could decrease, which was beneficial in foaming of PC. But if excessive PE was added, the melt strength of PC/PE mixtures became too low to form cell structure.
TWO COMPONENT MICRO INJECTION MOLDING FOR MID FABRICATION
Molded Interconnect Devices (MIDs) are plastic substrates with electrical infrastructure. The fabrication of MIDs is usually based on injection molding and different process chains may be identified from this starting point. The use of MIDs has been driven primarily by the automotive sector, but recently the medical sector seems more and more interested. In particular the possibility of miniaturization of 3D components with electrical infrastructure is attractive. The paper describes possible manufacturing routes and challenges of miniaturized MIDs based on two component micro injection molding and subsequent metallization. The technology will be demonstrated by an industrial component.
PLUG MATERIAL AND SHEET TEMPERATURE EFFECT OVER THE FORCE PENETRATION CURVES UNDER BIAXIAL DEFORMATION
The main objective of this work is to study the variables affecting the force produced by a plug on a polymer sheet during the thermoforming process, under different testing conditions. The considered variables are: the sheet temperature, the plug speed penetration, and the plug material. The plug material selection, speed and the temperature of testing under biaxial deformation play an important role in the registration of the force and, at the same time, it shall has a strong effect on the experimental data used to set the parameters of the material to determine a constitutive equation.
AN EXTRUSION STUDY: EXAMINATION OF THE IMPROVED PROCESSING CHARACTERISTICS OF A PLA IMPACT MODIFIED BLEND
Biomax Strong is an impact modifier (IM) that is used to improve the physical properties of PLA produced in sheet extrusion applications. Its addition in the range of 1 to 4% into PLA has also been shown to improve the processing characteristics of PLA. Previous studies have shown a reduction in extruder drive power, lower melt temperature and lower extruder head pressure along with improved energy efficiency. This work investigates the processing characteristics of PLA, with and without the additive, in order to gain insight into the mechanisms leading to improved processing. A highly instrumented extruder was used to study how the impact modifier affects solids conveying, melting, melt conveying and power consumption.
ULTRASONIC SEALING AND CUTTING IN THERMOFORMING
In common thermoforming, filling and sealing applications the processes of sealing and cutting are performed in two separate steps. In order to combine sealing and cutting in one station a new device has been developed employing ultrasonic technology so that both functions can be executed simultaneously. The ultrasonic sealing and cutting station reduces sealing times, cutting forces, wear and tear as well as floorspace, facilitating fast format changes. Contaminated rims can be sealed without compromising the sealing integrity and thus preventing any exposure to the atmosphere so that neither food items are permitted to spoil nor medical items loose their sterility. This device provides data for logged sealing quality and is linked with the control system of the entire packaging line.
THE EFFECT OF FUNCTIONALIZATION ON POLYMER INTERCALATION AND PROPERTIES OF POLYSTYRENE/CLAY NANOCOMPOSITES
Polystyrene nanocomposites were prepared using the following compatibilizers: a block copolymer of styrene maleic anhydride (SMA) and various functionalized polystyrenes terminated (on one or both ends) with various polar functional groups (e.g. OH, COOH, acrylate). Solvent mixing was used to promote intimate contact between the organoclay and compatibilizer. A phosphonium surfactant was used to modify the montmorillonite, in order to obtain a thermally stable organoclay. Generally, the best mechanical and barrier properties were obtained with the SMA copolymer.
SHEAR AND EXTENSIONAL RHEOLOGY OF CARBON NANOFIBER/POLYSTYRENE MELT COMPOSITES
The rheological behavior and morphology of polystyrene / carbon nanofiber (PS/CNF) composites in their melt phase have been characterized through experimental measurements. Viscosity measurements of the PS/CNF composites in the linear viscoelastic regime show the ratio of the transient extensional viscosity to the transient shear viscosity to be greater than three, the Trouton ratio. This behavior is believed to be due to differences in the flow induced orientation of the CNFs in shear and extensional flow. The orientation development of the CNFs were analyzed by TEM and optical microscope and considered for the relationship to rheological behavior.
EFFECT OF MOLDING PARAMETERS AND ORIENTATION ON THE PROPERTIES AND SKIN-CORE STRUCTURE OF POLYPROPYLENE PLAQUES
The major objective of this work was the study of the injection molding process conditions (holding/packing pressure, injection temperature, injection speed) and the geometry of the mold over the mechanical properties, morphology, orientation and core-skin structure of polypropylene (PP) plaques. Tensile test type IV specimens were cut in MD and TD directions of injected plaques (100 x 100 x 1 mm) with a 1 mmthick fan gate. Two different behaviors were clearly observed: there were groups with strain at break lower than 25% while others exhibit strains at break higher than 700%.
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