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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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.
Rheological Characterization of Compatability & Degradation of Polycarbonate/Polybutylene Terephthalate Layered Silicate Nanocomposites
The linear viscoelastic oscillatory shear properties of a polycarbonate PC and polybutylene terephtahalate PBT, 60/40 by respective weight, blend and its nanocomposites with various concentrations of organically modified organoclay and clay surface treatment were evaluated. The decrease in properties is attributed to a decrease in molecular weight. A 70% decrease in complex viscosity over all angular frequencies is observed. A relatively small decrease in Tg is observed and is attributed to increased compatibility.
Investigating How Stress will Affect the Weatherability of Plastic Materials
The increased use of polymeric materials having outdoor exposure has created a need for a better understanding of the effects of Ultraviolet (UV) Radiation. Many plastics do not perform well when exposed to UV radiation. The exposure to UV radiation significantly affects the physical, chemical, and mechanical properties of plastics materials, thus reducing their life expectancy. Not much research has been done to investigate how stresses will affect the weatherability of plastic materials in outdoor exposure. This paper will show that exposure and/or internal stresses will decrease the displacement and maximum stress.
Effect of Preparation Method on the Rheological Behavior of Waterborne Polyurethane Dispersion
Two classes of environmentally-friendly polyurethane dispersions have been prepared via prepolymer emulsification process and acetone process. Rheological behavior of these dispersions has been studied as functions of PU-concentration, degree of post-neutralization and temperature. At a critical volume fraction of PU (? ~0.43), a dramatic increase in the reduced zero shear viscosity was detected for the two dispersions. Co-occurrence of thermal-induced gelation and liquid-liquid phase separation was observed for the prepolymer process, while, only liquid-liquid phase separation was discovered both rheologically and morphologically for the acetone process.
Molecular Dynamics Simulation of Nanoimprinting at Different Process Condition
Nanoimprint Lithography (NIL) can fabricate sub-50 nm fine structure precisely. However, the processing problems for imprinting include the control of imprinting velocity, polymer flow behavior, the thermal shrinkage of materials at cooling stage and the friction force at releasing step. All of above-mentioned factors will affect the fabrication of nanostructure significantly. Except for investigating these factors experimentally, molecular dynamics (MD) simulation can be adopted to study the effects at different process conditions and obtain further detailed process information. In this article we focus on the effect of different imprinting velocity and the friction at demolding step. And in the future this simulation technology can be further applied to study the making of high-density compact disk, plastic optical nano-device, DNA chip...etc.
Improving the Efficiency of the Calibration Stage in the Production of Extruded Profiles
During the production of extruded profiles, the calibrator should cool down the profile both swiftly and uniformly. The main difficulty to be faced in the design of these tools arises from the fact that these two objectives are conflicting, i.e., conditions leading to a lower average temperature generally promote a lower temperature homogeneity and vice-versa. There are few ways to improve simultaneously both criteria. As shown in previous works, the most effective alternative is the division of the cooling length into several cooling units separated by annealing zones. In these zones the extrudate temperature distribution homogenizes and, as a consequence, its surface temperature increases (increasing also the thermal energy removal in the subsequent cooling unit), hence leading to improvements in both conflicting objectives.In this work, an optimization methodology (encompassing a numerical simulation code, an objective function and an optimization routine) is used to optimize the lengths of the individual cooling units and of the annealing zones with a view to improve the thermal efficiency of the calibration stage.
Functionalization of Polypropylene with Sulfonyl Azide through Reactive Blending
The functionalization of polypropylene (PP) by 4-carboxybenzene sulfonyl azide (CBSA) was investigated in a batch mixer. The degree of grafting was studied through FTIR, 1H-NMR and XPS spectroscopy using varying levels of CBSA. Under different reaction temperatures, the grafting degree showed a maximum point at 190°C. The degree of grafting increased with feed azide content initially and then leveled off. The rheological properties of the functionalized PP were also evaluated by oscillatory shear measurements and were found to correlate with the grafting degree results. Finally, the adhesion of functionalized PP to aluminum substrates was found to increase significantly.
Biomimetic Mineralization of Collagen with a Calcium Phosphate Polymer-Induced Liquid-Precursor Phase
It is the aim of this project to distinguish the functionalities of collagen that allows it to attract a Polymer-Induced Liquid- Precursor (PILP) phases to Calcium Phosphate (CaP) and stimulates biomineralization. The system investigated mimics the electrostatic interactions present in collagen through testing surfactants with varying end groups. Self-assembled monolayers micro-contact printed unto gold is used as the substrate for mineralization. Results obtained thus far have been analyzed through optical microscopy, scanning electron microscopy (SEM) and electron dispersive spectroscopy (EDS).
Effect of Heat-Sealing Temperature and Holding Time on Mechanical Properties of Heat-Sealed Poly (Lactic Acid) Films
Heat-sealing process is often employed in packaging applications of polymeric films, especially for plastic bags. In this study, effects of heat-sealing temperature and holding time on mechanical properties of heat-sealed parts of poly (lactic acid) (PLA) films were investigated. Peel tests, double edge circular-notched tension (DECNT) tests, and center cracked tension (CCT) tests were conducted with the heat-sealed PLA films. The thermal properties of the heat-sealed parts obtained by differential scanning calorimetry (DSC) were also investigated.
Rheology Studies of Two-Phase Gas-Polymer Suspensions During Mold Filling
In thermoplastic foaming, phase separation (i.e., bubble nucleation and growth) occurs due to a sudden change in pressure during mold filling that has significant effects on the rheology of polymer flow. An instrumented mold cavity has been designed to capture rheological measurements of the eventual two-phase gas-polymer suspensions. Experimental results for low density polyethylene (LDPE) and thermoplastic polyolefin (TPO) with two types of chemical blowing agents indicated that the rheological properties of two-phase gas-polymer suspensions were sensitive to shear rate, blowing agent concentration, melt temperature and mold temperature. The viscosity of gas-polymer suspensions was reduced in the presence of gas bubbles. A model has been proposed that yields good agreement with our experimental results for estimating the viscosity of two-phase flow in the mold cavity of the injection molding machine.
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