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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Shape Memory Polymer Orthodontics
Shape memory polymers (SMPs) have been intensively investigated for multiple medical applications in recent years. In our lab, we have developed several SMPs with tailored transition temperatures, excellent shape fixing and shape recovery, and variable stiffness, with values ranging from > 1 GPa (hard) to < 1 MPa (soft). Recently, we have endeavored to apply two particular SMPs, a castable shape memory polymer (CSMP) and a shape memory rubber, to orthodontic appliances. We have measured the mechanical properties, water absorption, stain resistance, and stress stability and compared the results with currently used orthodontic polymers, revealing significant advantages. Prototype appliances are presently under evaluation. In this presentation, we will introduce the progress we have achieved and propose how SMPs can offer unique functionality to orthodontic appliances.
Development of a High-Pressure Slit Rheometer
In thin - wall injection molding processes, parts thinner than 1 mm are produced using high injection pressures and velocities. Modeling has not been successful in predicting process physics during molding. We have built a high pressure slit rheometer that enables us to measure the rheological properties of polymers at elevated pressures and temperatures. Measurements were done with polystyrene, and the results showed the effect of pressure and the effect of viscous heating on the viscosity. Results from such measurements will allow us to introduce viscosity pressure effects during mold filling of Thin-Wall Injection Molding.
Viscosity of Soy Protein Plastics as Determined by Screw Extrusion Through a Capillary Die
Processing of soy protein plastics using conventional methods (injection molding, extrusion) has met with some success. At this point the lack of data on fundamental flow behavior of soy protein plastics limits future advances. Previous work by Japanese researchers showed the effects of moisture content, temperature, and strain history on the viscosity of soy protein isolate at elevated temperatures. However, no studies to date have explored the viscosity of processable formulations that contain soy protein along with the necessary additives (e.g., glycerol and corn starch). Viscosities of several soy protein formulations are evaluated using screw-extrusion through a capillary die. The viscosities are found to conform to the power-law model, but are substantially higher than those of commodity petroleum-based resins.
Using Multilayer Films to Fabricate Reactive, Submicron Patterned Surfaces
Highly layered structures are important to microfabrication and nanofabrication technologies as tools for understanding and controlling surface structures through manipulation of chemical and physical interactions. A new approach is introduced to create submicron patterned surfaces with surface chemical functionality using multilayer polymer films. Alternating layer structures of two immiscible polymers, linear low density polyethylene (LLDPE) and ethylene-co-acrylic acid copolymer (EAA), were formed by co-extrusion with subsequent compression molding. Thin sections of the multilayer molded sheets were prepared by microtoming and the highly layered microstructure was verified by SEM, TEM, and polarized optical microscopy. Regionally confined chemical functionality was confirmed by grafting a fluorescent label selectively to the alternating layers of EAA.
Surface Modification of Ethylene-Acrylic Acid Copolymer (EAA) Films Using Various Linker Layers
Two reaction systems were developed to covalently graft polyethylene glycol (PEG) chains on ethylene acrylic acid copolymer (EAA) surfaces without significant penetration of reactants. The scheme involved surface grafting of link molecular l-lysine or link layer poly(glycidyl methacrylate) (PGMA), followed by covalent bonding of PEG chains. For the PGMA method, AFM images showed that large, isolated surface domains on the micron scale existed on the EAA surface because of phase separation during dip coating and drying of the PGMA. For the l-lysine method, NHS and EDC were used to activate the carboxylic acid groups of the EAA. After activation, l-lysine was grafted onto the EAA surface, followed by PEG grafting. Each step of the surface modification was followed by ATR-FTIR spectroscopy, XPS, and AFM.
Birefringence Distribution in Gas Assisted Tubular Injection Moldings
Flame Retardancy and Rheological Behaviour of Acrylonitrile-Butadiene-Styrene Copolymer (ABS) Composites Filled with Magnesium Hydroxide Sulfate Hydrate(MHSH) Whiskers
Flame-retardant ABS composites were prepared using MHSH whisker as a flame retardant. The morphology observation indicates that the addition of zinc stearate could lead to the uniform dispersion of the whisker and improvement of flame retardancy. With increasing whisker content, flame retardancy properties of the composites is improved, the viscosity and storage moduli of the composites increase at low frequency zone. The presence of zinc stearate leads to slight increases in the storage moduli.
Effects of Molding Conditions on the Conductivity Properties of Injection Molded Bipolar Plate Used for Fuel Cell
Fuel cell is an important energy source for the 21st century. Among fuel cell components, plastics have been chosen as a candidate material for bipolar plates which needs to fulfill the conductivity requirement. In this study, polymer polyphenylene sulfide (PPS) containing 50% carbon fiber was in injection molded and its conductivity was measured by the four point probe. The carbon fiber dispersion and orientation were examined by scanning electron microscopy (SEM). It was found that at high mold temperature, high melt temperature and lower injection rate, the carbon fiber distributed more uniformly leading to higher conductivity. High holding pressure closely tangled the carbon fiber, also increases conductivity. 3D-CAE simulations were also conducted to verify fiber dispersion and orientation under different molding parameters and show reasonable consistency.
Analysis and Experimantal Verification on the Optical Performance of Injection Molded Light Guide Plates with Micro-Feature Design
This study investigates the optical performance of light guide plates with micro-feature characteristics. The light guide plates are made of injection mold PMMA. Both one- and two-sided micro-feature designed patterns were conducted. The results reveal that the micro-feature with smaller interval of dot array would lead to better luminance. It is also found that the uniformity in luminance distribution can be greatly improved if proper geometry of micro-structure dot is arranged. In addition, the luminance can be improved as the elevation of the temperatures of melt and mold, filling speed and packing pressure. The luminance may achieve highest value under proper packing pressure.
Efficiencies of Various Mold Surface Temperature Controls and Their Effects on the Qualities of Injection Molded Parts
Various mold surface temperature control methods including mold surface coating, induction heating, infrared heating and suitable combinations of surface coating with different surface heating are utilized to achieve a rapid mold surface temperature controls. Surface coating with thermally insulated materials can introduce heat hysteresis effect and the plastics melt-mold surface contact temperature may sustain high temperature for about one second leading to the elimination of weld line marks for ABS parts. For rapid mold surface heating with temperature rise ranging from between 50° and 100° or higher, induction heating seems to be the most efficient method (within 2 to 4 seconds). Infrared heating combined with surface coating although can achieve the same effect as compared with that of induction heating, however; it takes longer time (about 15 seconds). Both heating methods can definitely eliminate weld line marks, reduce residual stress and enhance the associated weld line strengths. For molding micro-featured parts, induction heating also exhibits a significant assist in melt flow within micro channels and improves the molding accuracy in the micro-features.
Prediction of the Weld-Line-Induced Strength Reduction for Injection-Molded Plastic Parts
Weld-lines look like cracks on the appearance of plastic parts. Sometimes these visible features are not accepted esthetically in many applications. However, most importantly, the local mechanical strength in the weld-line area could be significantly weaker. It could be one of the most significant problems for structural applications due to the potential failure in the weld-line areas. Hence, how to prevent the weld-lines and guarantee the good quality are the major concerns to part/mold designers. In this paper, a numerical approach is proposed to predict weld-lines and weakened mechanical strengths. Furthermore, through the data link between mold-filling simulation and structure analysis, the effects of weld-lines towards part structure are predictable.
Characterization of Knitted Fabric Reinforced PP/PP and GF/PP Composites
This paper reports an experimental study to characterize impact behaviors of PP/PP and GF/PP composites. The plain knitted PP and GF textile fabric were combined with homo-PP matrices to fabricate flat composite panels using injection compression molding technique. The molding temperatures of the resin and the mold were varied in order to study the effects of processing conditions on the impact behaviors. It was found that at the low molding temperature, due to the integrity of PP fabric was preserved, even PP/PP composite showed the similar impact resistance as compared with GF/PP composite.
The Study of the Water Assisted Injection Molding Process
This study investigated the manufacture of a handle bar by the water-assisted injection molding (WAIM) process. WAIM is a new technology based on gas-assisted injection molding (GAIM). Both use fluid as the medium, but one uses water while the other uses nitrogen gas. Experimental studies were conducted to determine the effects of process parameters on the hollowed core ratio and the penetration length of the WAIM. Process parameters include melt temperature, water pressure, mold temperature, water injection delay time, shot size, and water temperature. Semi-crystalline material, PP, and amorphous material, ABS, were used for this study. The results show that PP and ABS have the same trend on the hollowed core ratio but have opposite effects on the penetration length.
Investigation of Polymer Injection Molded Packages for Optoelectronic Applications
Metal and ceramic packages have been the ultimate solution for maintaining a perfectly sealed environment around a device. Currently, the packaging of optoelectronics makes the use of a fiber optic network too costly for use in medium area networks and local area networks. Polymers offer a promising new way of producing packages at a lower cost. Some high performance polymers, such as Liquid Crystal Polymer (LCP), may be able to meet the hermetic needs required of optoelectronic packaging. LCP provides an excellent barrier against water vapor and oxygen, making it a prime candidate for hermetic packaging. Prototype packages made of short glass-fiber filled LCP were insert injection molded using various processing conditions. These packages were sealed using a Bisphenol-F Aminizol based adhesive. The resulting prototype packages were exposed to humidity at a constant temperature over a period of time. The packages tested resulted in various levels of moisture diffusion and relevant processing conditions affect ing the hematicity are identified.
Kinetics of Melt Crystallization of Polypropylene Using Kissinger's Method
Kissinger's method of kinetic analysis was applied to melt crystallization of polymers upon cooling. The rate of crystallization was expressed as a function of the un-crystallized component and the temperature difference between melting and crystallization. Using a modified expression for the rate constant, a relationship is obtained to correlate an apparent energy for crystallization with the cooling rate and the temperature difference between melting and crystallization. This relationship allows analysis of non-isothermal crystallization of polymer melt. Using differential scanning calorimetry (DSC) to obtain thermograms at different cooling rates, the kinetics of crystallization can be analyzed. The crystallization rate of some commercial polypropylene resins was compared. It was shown that this analysis correlates well with the resin characteristics from DSC.
Preparation and Characterization of Polyaniline/Carbon Nanotube Composites
This describes the synthesis of 1-D doped polyaniline composites containing multi- and single-walled carbon nanotubes via in situ chemical oxidation polymerization based on CNT template. Due to the ?-?* electron interaction between aniline monomer and CNTs, aniline molecules were adsorbed and polymerized on the surface of MWNTs and SWNTs. Structural analysis using FESEM and HRTEM showed that 1-D PANI/CNT composites are core (MWNTs and SWNTs)–shell (doped PANI) tubular structures with diameters of several hundreds of nanometer, depending on the template size and PANI content. Both Raman and UV-Vis spectra indicate that a site-selective interaction between the quinoid ring of doped PANI and CNTs. The conductivities of these 1-D PANI/CNT composites are higher than those of pure PANI without CNT template.
Ink Washout Problem of In-Mold-Decoration by Microcellular Injection Molding
In-Mold-Decoration (IMD) and Microcellular Injection Molding are two advanced processes in the plastics industry. IMD combines film technology and injection molding processes to improve the parts’ surface decoration and coloration. IMD also reduces the cost for secondary processing. The current problem with IMD is the ink washout effect by the melt polymer. The purpose of this project is to study the ink washout effect by microcellular injection molding. PC films of 0.1 and 0.125 mm thicknesses, coated with grid mesh, were used as the IMD devices and put on the perimeter of the gate of a grocery box of ABS material. Process parameters were changed to investigate the ink washout effect by the microcellular injection molding and the conventional injection molding processes. The results show that microcellular injection molding has less effect on ink washout than conventional injection molding. As melt temperature, injection speed, mold temperature, and shot size are increased; the ink washout problem is more severe. However, as the melt plasticizing pressure (MPP) is increased, the ink washout problem is less severe for microcellular injection molding.
Structure-Property Relationships in Pet Nanocomposite Fibres
Poly(ethylene terephthalate) (PET) resin has been compounded with various organoclay layered-silicates. Processing methods included double-pass compounding using single screw extrusion and injection moulding various test specimens. PET nanocomposite compounds were also melt-spun into fibres using a capillary rheometer at draw speeds of 80 and 800m/min. Morphology and mechanical properties of these nanocomposite fibres have been analysed. The results show that organoclays can be incorporated into PET fibre matrix with good interclation and exfoliation, showing significant improvements in mechanical performance.
Conformational Dynamics and Entanglement Phenomenon of Polymer Chains During Glass Transition
This study investigated glass transition characteristics of polymers by using molecular dynamics simulation. The simulation modeled the polymeric fluid with the shifted Lennard-Jones potential theory, and the polymer bond stretching/bending/torsion was simulated with Hook-like model. By cooling the system temperature from melt state to room temperature, we could determine the glass transition temperature. The causes of glass transition can be explained by monitoring the chain energy and structure variation during the cooling process. Different chain length and deformation dynamics of polymeric chain systems were also illustrated. All simulation results were found to be in good qualitative agreement with related experimental and theoretical investigations.
Scanning Probe Microscopy of Complex Polymer Systems: Beyond Imaging Their Morphology
Scanning probe microscopies provide important contributions to the study and optimization of polymer properties. In particular, in dynamical force techniques, the phase measurement yields in many cases to images reflecting tiny variations of the local properties of the sample surface. On that basis, it is possible to extract useful information for samples showing compositional heterogeneity at small scale, for instance blends of hard and soft materials.Here, we present the major morphological features observed with SPM in a series of polymer systems of growing complexity: polymer blends, block copolymers, and hyperbranched polymers.
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