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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The Consequences of Approximating the Classical Nucleation Theory in Simulation of Polymer Foaming Process
According to the homogeneous classical nucleation theory, the nucleation free energy barrier in the foaming process can be calculated by W =16??3/3(Pbubble – Pmelt)2. Currently, almost all the simulation results simply substitute the bubble pressure, Pbubble, with the saturation pressure, Psat, and the curvature-dependent surface tension, ?, with the experimentally measurable surface tension, ??. This paper engages a brief discussion of the above two approximations. The consequence of substituting Pbubble with Psat on the free energy barrier will be considered with respect to equations of state. The effect of the curvature dependence of surface tension on the prediction of free energy barrier for bubble nucleation, and thereby on the calculation of nucleation rate is explored using the recently proposed scaling function approach.
Polylactic Acid (PLA)-CO2 Foams at Sub-Critical Conditions
Solubility and diffusion coefficients of Carbon Dioxide (CO2) in polylactic acid (PLA) (poly-L-lactic acid (PLLA) and poly-DL-lactic acid (PDLLA) copolymer) have been measured at room temperature and pressures up to 5.8 MPa. Based upon x-ray diffraction analysis it was found that CO2 induced crystallinty in the samples. The results indicated that the crystallinty increased with processing pressure with the largest increases noted at pressures between 2.1 and 2.8 MPa under room temperature conditions. These findings were used to investigate the effect of different saturation conditions on the cellular structures of foams produced using various processing temperatures. Samples saturated at 2.8 MPa and room temperature for two days, followed by foaming at 100°C gave a uniform cellular structure with a cell diameter in order of 30-40 ?m and a cell density of 7.93x107 cell/cm3.
Improved Scratch Resistance of Polymer Nanocomposites
The susceptibility to mechanically-induced surface damage in neat and clay-reinforced polymer nanocomposites is examined by combining the lateral resolution of scanning electron microscopy and vertical resolution of atomic force microscopy. The surface damage in neat polymers is characterized by ‘psiloma-type’ morphology indicative of compressive plastic deformation, while in clay-containing nanocomposites, ‘ironing,’ a less severe surface damage was dominant. Also, clay-reinforced nanocomposite experience significantly reduced stress whitening, and characterized by lower change in gray level in the stress-whitened zone. This behavior is attributed to the effective reinforcement by clay particles that increase the tensile modulus of the composite and restricts plastic deformation of the polymer matrix.
Reduced Fiber Breakage in an Injection Molding Machine
An experimental investigation of the flow behavior of a glass fiber reinforced polypropylene in an injection molding machine revealed that it was possible to reduce the extent of fiber breakage occurring through the addition of a blowing agent. With the increased addition of a chemical blowing agent, from 0 to 5 wt%, the fibre length distribution was found to increasingly resemble the virgin resin. Rheological study of this phenomenon with an inline rheometer showed that the blowing agent changed the pseudoplasticity of the composite. As a result of the change in pseudoplasticity, less glass fibers were exposed to shear flow and therefore did not experience rotation normally leading to fibre breakage.
Elastic-Plastic-Creep Analysis of Lead and Lead-Free Solder Bumps in FC
Lead-free has been the trend of electronic product. In this study, the thermal-mechanical behaviors of lead bump 63Sn/37Pb and lead-free bump 96.5Sn/3.5Ag under temperature cycle test are investigated. The elastic-plastic-creep analysis are performed and decoupled for comparisons. The results show that 96.5Sn/3.5Ag have the better performance on creep, but the plastic strain is higher. However, since the lead-free material 96.5Sn/3.5Ag has the higher melting point than 63Sn/37Pb, it needs higher reflow temperature during reflow process. Furthermore, for higher cycling temperature with loading rang -55 - 155 ° C, the lead-free bump 96.5Sn/3.5Ag still has good performance on creep.
Shear-Induced Morphology Prediction in Injection Moulded Semi-Crystalline Thermoplastics
The prediction of the development of the microstructure in semi-crystalline thermoplastic parts offers new options in the integrative simulation of their mechanical behaviour depending on the chosen process parameter. A good correlation between simulation and reality is shown in simulation results of a cross-section which crystallizes quiescent computed by the self-developed software SphaeroSim. The next step will be the initial simulation of shear-induced structures under injection moulding conditions. In this paper a selection of approximating methods for the prediction of shear-induced morphology distribution in moulded semi-crystalline thermoplastic parts are presented and discussed in focus to an application in the software SphaeroSim.
CFD Study of Flow Pattern and Heat Transfer in Miniature Mixers Using a Generalized Newtonian Fluid
The Alberta Polymer Asymmetric Mixer (APAM, 2ml) and a mini-batch mixer (MBM, 3ml) built in our lab are used for polymer blends and nanocomposites processing. Before a new product is scaled up, the miniature mixers are usually used for polymer processing because they require small amount of material and can be flexibly designed [1-2]. The MBM is a scaled down version of the laboratory internal mixer with roller blades. Previous experimental study has shown that the APAM is effective in mixing polymer blends and nanocomposites . Here we use CFD software, Polyflow 3.9 from Fluent Inc, to model transient non-isothermal processing of polystyrene in APAM and in MBM. The flow fields inside APAM and MBM were characterized using velocity profiles. The velocity profiles show the co-existence of shear flow, converging flow and recirculation. The temperature inside both mixers increased due to viscous dissipation. Thermal steady state was reached after 12s and 25s respectively for MBM and APAM. The melt temperature results from simulation were verified by experimental measurement in the MBM. Finally, the global mixing performance of the miniature mixers was quantified in terms of spatial distributions of shear rate and shear stress.
The Processibility and Properties of the Nano-CaCO3/Polypropylene Composite for Rotomolding
The aim of this project was to investigate the ability of nano-scale calcium carbonate (nm-CaCO3) to improve the impact strength of rotational molded polypropylene (PP) parts. Two different types of compatibilizers were also investigated: acrylic acid (AA) and dicumyl peroxide (DCP).Results show that the addition of nm-CaCO3 leads to an increase in modulus and impact properties. The largest increase in impact properties at room temperature is found at 0.3% contents while the peak at low temperature are determined to be at 1% content. Moreover, the inclusion of AA and DCP improves this property even further.
Optical Simulation of a Plastic Lens Reflecting Injection Molding Effects
The present work covers a new ray tracing method of an injection-molded plastic lens linked with CAE analysis of injection molding processes. The traditional ray tracing schemes have been based on the assumption that optical property of the lens is homogeneous throughout the entire volume. However, this assumption is quite unrealistic since material properties vary at every point due to injection molding effects. In order to consider non-homogeneous property of a lens, a modified ray tracing method is proposed in connection with finite element analysis of injection molding. Through the injection molding simulation, we can obtain the distribution of refractive indices of the lens. This information is then applied to the proposed ray tracing scheme based on finite element meshes. The effect of mold temperature is investigated through injection molding simulation, and the relevant optical quality is evaluated through the proposed ray tracing simulation.
Melting Phenomena in Polymer Blending
This paper focuses on melting process in polymer blends. A barrel sliding mechanism and a perturbation method were used to study melting behavior of polypropylene/polystyrene, PP/PS blends in a twin screw extruder (TSE). It was found most melting occurred in the transition from partially filled region to fully filled region. Numerical modeling was used to obtain heat transfer coefficient of a solid polymer pellet in another polymer melt. A good match between simulation and experiment was found after taking thermocouple dynamics into account. The deformation and breakup of PC drop in PE melt under shear flow was studied experimentally and numerically. Stress peaks at the interface explained the “erosion” mechanism found in the experiment and simulations.
Advanced Micromolding Applications
Micromolding parts with feature sizes less than a micron is anything but practical nor does micromolding follow conventional practices used for decades in conventional or macro molding. As miniature molded parts approach micro or nano in size, several challenges exist to molding them in a production environment. This paper explores some of these challenges such as part handling, part degating methods, and overall micro part quality out of the gate.Custom-built micromolding systems will be case studied that provide the type of single-source solutions this rapidly growing sector of the marketplace demands. Costly learning curves can be avoided to produce the complex microscopic parts or microscopic design features on larger parts in a variety of applications, including medical devices such as catheters, microfluidic nozzles and chips, MEMS and micro sensors, resorbable implants, electronics, and tiny pumping mechanisms.
Proccessing Solutions and Market Applications for Mixed ABS
Electronics reclaimers are generating rising volumes of mixed ABS plastics from the processing of computer equipment and televisions. This flow represents a large market opportunity. Within our research we are investigating the processability of this scrap material and the properties of the resulting material. We found that the mechanical behavior of the reclaimed material was fairly repeatable, with the exception of impact properties. However, better compounding will result in even more consistent properties. We are also focusing on potential processing solutions and market applications for this mixed ABS scrap.
Anisotropic Shrinkage in Injection Moldings of Semicrystalline Polymers: Simulation and Experiment
A novel approach to predict anisotropic shrinkage of semicrystalline polymers in injection moldings was proposed using the flow-induced crystallization, frozen-in molecular orientation, elastic recovery and PVT equation of state. The anisotropic thermal expansion and compressibility affected by the frozen-in orientation function and the elastic recovery were used to obtain the in-plane anisotropic shrinkages. The elastic recovery and frozen-in stresses and birefringence were obtained by a non-linear viscoelastic model. The flow-induced crystallization was described via the elevated melting temperature affected by entropy production with modified kinetics of the crystallization. Numerous injection molding runs on polypropylene were carried out by varying packing time, flow rate, melt temperature and mold temperature, and anisotropic shrinkage of moldings were measured. The experimental results were compared with the simulated data.
Modeling the Infrared Sheet Heating in Roll-Fed Thermoforming
The heating stage is of primary importance in the thermoforming process. Computational methods using the finite element technique for modelling the radiation heating stage of thin gauge, roll-fed plastic sheet is presented and discussed. The theoretical approach as well as the experimental validation is also presented. The proposed approach takes into account the dynamic effects of sag and the displacement of the sheet inside the oven. The volumetric power absorption representing a heat generation term, which is critical in the case of semitransparent materials, is also integrated by using Beer’s absorption law.
Control of Thixotropicity of Polymer Melts by Disentanglement Processing
It is well known that thixotropicity of polymer melt is determined by the chemical nature of the bonds and the length of the macromolecules, more specifically the molecular weight distribution. Little is known of the influence of processing on thixotropicity. As a matter of fact, governing theories predict that processing variables (temperature, pressure, strain rate) should have no visible influence on melt pseudoplasticity or thixotropicity. The Carreau’s equation of viscosity describes well this tendency for a polymer melt to shear-thin at higher strain rate, and also incorporates the effect of temperature and pressure (via the pressure dependence of Newtonian viscosity). In terms of the simpler power law model, pseudoplasticity is described by the melt index, which is found from the slope of Log (Stress) vs Log (Strain Rate). As already said, it is generally accepted that neither the melt index, nor the Carreau’s parameters, are a function of the processing conditions.
Exfoliation of Nanoclays in Concentrates of LDPE
Masterbatch concentrations of nanoclay filled polymers are in high demand, but they have proven to be difficult to produce because of difficulties achieving homogeneous dispersion, exfoliation, and intercalation, especially in the case of polyolefins. This paper covers the use of disentanglement processing technology [1,2,3] to mix and disperse nanoclay concentrates (up to 30%) into LDPE resins. The prescribed treatments employed for the experiments covered by this paper were TekFlow technology by Stratek Plastic Ltd. These treatments extensively shear-thin polymeric melts, under conditions of non-linear viscoelasticity, producing disentanglement. Also, the high success in obtaining fully intercalated, exfoliated high concentration nanoclay blends is assumed to arise from the unique ability of the disentanglement processors to laminate the melt at very low temperature without rising pressure.
Cure Optimization of Layered Silicate Polynanomers
The mechanism of exfoliation in layered silicate - epoxy nanocomposites has been investigated using ex-situ x-ray diffraction (XRD) measurements taken during dynamic and isothermal curing cycles. Cure temperature ranges have been determined by differential scanning calorimetry (DSC) to coincide with the termination of the exotherm peak observed during cure. During cure, samples are sequentially removed from the heating system and immediately quenched to slow the polymerization reaction and lock-in the layered silicate morphology. The quenched samples are exposed to XRD analysis so that silicate d-spacing may be determined as a function of cure advancement. The changes in silicate morphology are correlated to the thermal events measured using DSC. Ultimately this approach is being used to develop specific cure cycles to control and optimize the properties of montmorillonite filled nanocomposites.
Implant Induction Welding of Nylon 6/6
The implant induction welding technique utilizes a heating element material at the joint interface to generate the heat. In this study, three factor two level full factorial design of experiments were performed to evaluate two different types of Nylon 6/6, denoted as A and B, in a lap shear joint geometry. It was found that weld time was the most dominant factor in affecting the weld strength followed by power and pressure. It was also found that the weld strength was proportional to the heating time at constant power and constant pressure. In addition, final sample thickness was inversely proportional to the lap shear strength. Bending of the joint during testing was the major failure mode. The maximum achievable strength for material B is 15% higher than that of material A. Furthermore, vibration welding of these two materials was also performed for comparison. It was found that material B achieved 80% higher weld strength than material A using vibration welding.
Novel Phillips Loop-Slurry Based Polyethylene Resins Using Modified Chromium Oxide Catalysts for High Performance Pipe Applications
Novel high density polyethylene resins made in the Phillips Loop-Slurry Process (single-reactor), using a catalyst of chromium on modified aluminophosphate, were developed with unique structural attributes that make them especially suitable for high performance pipe applications. These structural attributes include high molecular weight (MW), very broad molecular weight distributions (MWD), effective levels of short chain branching in polymer chains with MW > 1,000,000 g/mol, and reduced levels of long chain branching (LCB). In particular, pipes made from these ethylene 1-hexene copolymers satisfy the performance requirements of PE100 specifications; in addition, these resins also offer outstanding slump (or sag) resistance for large diameter (> 24 inch) pipe processing. In this paper, a brief description of these catalyst systems is presented along with the unique molecular aspects of the resins. The physical properties of these resins and their fabricated pipe processing/performance properties are compared to several “bimodal” type resins.
Continuous Process for Melt Intercalation of PP-Clay Nanocomposites with Aid of Power Ultrasound
A continuous ultrasound assisted process using a single screw extruder with an ultrasonic attachment was developed to prepare PP/clay nanocomposites of varying clay concentrations. The feed rate that controls the residence time of the polymer in the ultrasonic treatment zone was varied. Die pressure and power consumption were measured. Rheological properties, morphology and mechanical properties of the untreated and ultrasonically treated nanocomposites were studied. An intercalation of polymer molecules into clay galleries and a partial exfoliation, which occur at short residence times (on the order of seconds), were observed as evident from measurements by X-ray diffraction and transmission electron microscopy. The obtained results indicate a possibility of the rapid intercalation and partial exfoliation of PP/clay nanocomposite without the matrix being chemically modified.
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