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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Morphology of HDPE/PS Blends along the Axial Position in a Novel Co-Rotating Non-Twin Screw Extruder
In this study, a novel co-rotating non-twin screw extruder with a clam-shell barrel was designed and invented. Then, the visualization of mixing an 80/20 (wt%) ratio HDPE/PS blend was carried out after the barrel was opened. The morphological development of HDPE/PS blends in this non-twin screw extruder was studied. Two groups of operating conditions were employed when the ratio of the screw speed to the feed rate was kept constant. The effects of the screw speed on the morphological development of the HDPE/PS blends along the axial direction during extrusion were discussed. The results revealed that coalescence happened during extrusion, and increasing the screw speed resulted in a smaller droplet size and a narrower size distribution of the product. The dispersive mixing was stronger in the nip zone than in the screw channel. In addition, it was found that the morphology pattern changed considerably and the particle size decreased sharply and became more uniform after the blend went through the holes of the die.
Numerical Simulation for the Viscoelastic Effects on the Birefringence Variation for an Injected Optical Lens
Recently, polymeric optical lens have been utilized in many fields and electronic devices, such as camera, mobile phone, tablet, and other optical devices. The quality is the key for the main suppliers to keep competition, however, how the material’s viscoelasticity influences the optical features is still not fully understood yet. In this study, we have investigated the viscoelastic effects on the optical property of a lens made of Zeonex COP 480R material by the traditional injection molding, simulated with n = 0.4 and ?* = 217,000 Pa in the Cross model for the melt viscosity. Results show that if the power-law index (n) was varied from 0.1 to 0.6, the total fringed order has no significant difference, but the fringed patterns were varying dominantly in the perpendicular direction, instead of the flow direction for the case at n = 0.4. This situation was matched with the distribution of the flow-induced residual stresses. Moreover, if the ?* in the Cross model was varied from 100,000 Pa to 300,000 Pa, the total fringed patterns were apparently changing from being dominated in the flow direction to being in the direction perpendicular to the flow. The influenced width of the fringed patterns was almost linearly increased with the increasing ?*. The results can be applied as some guideline for either the further material modifications or the new material developments.
3D-Simulation of Gas-Assisted Injection Molding
The gas-assisted injection molding (GAIM) process is so complicated that increasing reliance has been placed on CAE?Computer Aided Engineering?as a tool for both mold designers and process engineers. In this paper, a 3D theoretical model and numerical scheme is presented to simulate the GAIM process, in which an equal-order velocity-pressure formulation method is employed to eliminate the pressure oscillation. In addition, the whole flow field is calculated with the gas pressure as a boundary condition to obtain the gas penetration, and a 3D control volume scheme is employed to track the flow front of the melt and gas. Finally the validity of the model has been tested through case studies and experimental verification.
Thermal Analysis of the Rotational Molding Cycle Followed by Internal Air Temperature Profiles: An Application for Foamed Polyethylene
In this study, temperature profiles for the air inside the mold was measured to analyze the thermal behavior of a polymer for a complete rotational molding cycle. Foamed and unfoamed linear medium density polyethylene (LMDPE) parts were produced by biaxial rotational molding. A chemical blowing agent (azodicarbonamide, ACA) was used at different concentrations (0, 0.25, 0.50, and 1.0 % wt.). The temperature profiles inside the mold were measured for different oven temperatures (260-320 °C). The analysis proposed is based on the temperature profiles and their derivatives to better determine the different temperature transitions occurring in a complete molding cycle.
Effect of Residual Chlorine on Durability of Plastic Pipes Used for Hot Water Supply
Recently, polymer electrolyte fuel cell (PEFC) cogeneration systems using plastic pipes for hot water supply have been commercialized in Japan. However, it is expensive and difficult to replace these plastic pipes if they are damaged. Therefore, it is important to evaluate the durability and to predict the life expectancy of these pipe materials and systems. In this study, the immersion test was used for polybutylene (PB) and double-layer crosslinked polyethylene (PEX2) pipes to evaluate their long-term performance in the residual chlorine solutions at 80 °C for 30,000 consecutive hours. The mechanical and thermal properties of these pipes were investigated using tensile test and DSC. Based on the tensile test results, it was found that the elongation at break rather than the yield stress had a strong correlation with the melting enthalpy (?H) of the PB and PEX2 pipes. On the other hand, the DSC results revealed that the oxidation induction time (OIT) at the inner surface of the PB and PEX2 pipes decreased significantly with immersion time, in which the OIT of the PB pipe decreased more rapidly than that of the PEX2 pipe. The difference in the OIT behavior was discussed in terms of the influence of the residual antioxidants in these pipes.
The Mixing of Flame Retardant Polymer Materials in a Novel Co-Rotating Non-Twin Screw Extruder
The mixing process of a halogen-free intumescent flame retardant ABS composite was carried out to examine the priority of a novel co-rotating non-twin screw extruder (NTSE) over the traditional twin screw extruder (TSE). The homogeneity of the flame retardant additives of the composites processed by NTSE and TSE under the same operating condition was characterized qualitatively using mechanics performance, LOI and UL-94 tests, and quantitatively using FTIR and TG analysis. All the results suggested that NTSE could achieve better mixing of the flame retardant additives in the polymer matrix than in TSE, which was further clarified by the SEM analysis.
Blends Characterization by Thermal Techniques
Thermal analysis (TA) techniques are indispensable tools for polymer characterization and root cause analysis of various problem such as contamination and part failure. Thermal analysis were carried out using Thermo-Gravimetric (TGA), Differential Scanning Calorimeter (DSC) and Hot Stage Microscopy techniques were used to study compatibilization of blends. This study related Polyethylene terephthalate (PET) as major phase) with minor amounts of Polycarbonate (2%PC) and Polyethylene-liner-low-density (3-5% PE-LLD). PC is fully miscible with PET in a molten state or when it exists in infinitesimal domains. The binary (PET/PC) blend’s matrix yields a homogeneous phase in thermal analysis. Degradation kinetics (single degradation peak) suggests that PET/PC is a binary miscible blend. On the other hand, PE-LLD is immiscible with PET even in a minor concentration; a pronounced skin-core effect was observed in hot stage microscopy and a doublet degradation peak was observed in TGA. In a ternary blend (PET, PC and PE-LLD), surprisingly the PC acts as a compatibiliser for the PE-LLD in the blend matrix. The degradation doublet peak in ternary blend due to PE (TGA) was minimized and crystallinity of ternary blend (DSC) was increased than the binary blends. Therefore, ternary blend appears as a homogeneous matrix in all three TA techniques used.
Evaluating Rigid and Semi-Flexible Fiber Orientation Evolution Models in Simple Flows
As American vehicle fuel efficiency requirements have become more stringent due to the CAFE standards, the auto industry has turned to thermoplastic-fiber composites as replacements for metal parts to reduce weight while simultaneously maintaining established safety standards. Furthermore, these composites may be easily processed using established techniques such as injection molding and compression molding. The mechanical properties of these composites are dependent on, among other variables, the orientation of the fibers within the part. Several models have been proposed to correlate fiber orientation with the kinematics of the polymer matrix during processing, each using various strategies to account for fiber interactions and fiber flexing. However, these all require the use of empirical fitting parameters. Previous work has obtained these parameters by fitting to orientation data at a specific location in an injectionmolded part. This ties the parameters to the specific mold design used. Obtaining empirical parameters is not a trivial undertaking and adds significant time to the entire mold design process. Considering that new parameters must be obtained any time some aspect of the part or mold is changed, an alternative technique that obtains model parameters independent of the mold design could be advantageous. This paper continues work looking to obtain empirical parameters from rheological tests. During processing, the fiber-polymer suspension is subjected to a complex flow with both shear and extensional behavior. Rather than use a complex flow, this study seeks to evaluate and compare the effects of shear and extension on two orientation models independently. To this end, simple shear and planar extension are employed and the evolution of orientation from a planar random initial condition is tracked as a function of strain. Simple shear was imparted using a sliding plate rheometer designed and fabricated in-house, and a novel rheometer tool was developed
Effects of Blend Morphology and Operating Parameters on Foaming of Polylactic Acid/Thermoplastic Polyurethane
The effects of blend composition and foaming conditions on polylactic acid (PLA)/thermoplastic polyurethane (TPU) blend foams were studied. Thermal behavior of the blends showed that TPU weakened crystallization ability of PLA. It was found that foam morphology was impacted by the blend composition and foaming conditions used in the study. PLA and PLA/TPU (80/20) did not demonstrate any significant foaming behavior while PLA/TPU (50/50) foamed at high temperature and pressure conditions. TPU foam morphology demonstrated temperature and pressure dependence. Interestingly enough, PLA/TPU (20/80) showed pore formation at all the operating conditions with either open cell or closed cell structures.
On the Successful Fabrication of Auxetic Polyurethane Foams: Key Insights from Materials Science and Polymer Processing Perspectives
This paper aims to provide fundamental understandings in several issues critical to the fabrication of auxetic polyurethane (PU) foams: auxetic structure fixation mechanisms, materials characteristics essential for the successful auxetic conversion, and optimal conditions for auxetic conversion. The chemistry, microstructure and thermomechanical properties of starting PU foams for auxetic foam manufacturing were thoroughly analyzed. This is followed by the auxetic convertibility study of these three foams. Mechanisms for fixing the structure were elucidated and the windows for processing were interpreted in the context of polymer relaxation. Guided by these understandings, we finally report an ultrafast, room-temperature process for auxetic PU foams manufacturing that can be completed in as little as several seconds.
Evaluating the Effect of Nanoclay and Recycled HDPE on Stress Cracking in HDPE Using J-Integral Approach
This study employed the J-integral approach to investigate the effect of recycled HDPE and nanoclay contents on the long-term stress cracking behavior of pristine HDPE. This behavior was conventionally approached by using stress intensity factor K, which defined the stress cracking behavior as two failure mechanisms: creep and slow crack growth (SCG). Unlike the conventional approach, the J-integral method identified the short-term failure prior to the creep failure. By integrating the short-term and SCG failure behavior, this study derived a correlation between Jc and SCG. The SCG behavior of recycle-blended materials without nanoclay was governed by Jc which decreased as the recycled contents increased. The decrease of Jc led to a reduction in SCG failure time. In contrast, the addition of nanoclay (up to 6-wt%) reduced Jc and stress relaxation of the material, subsequently extending the SCG failure times.
Effect of Gas Counter Pressure(GCP) on Shrinkage and Residual Stress
This study set out to apply gas counter pressure (GCP) in the injection molding process. By importing gas through the ends of the cavity, the melt was exposed to a melt front pressure, which, together with the packing pressure from the screw, is supposed to reduce product shrinkage. The aim was to investigate the impacts of GCP on the process parameters via the changes in machine feedback data, such as pressure and the remaining injection resin. This study also used a relatively thin plate-shaped product and measurements, such as the photoelastic effect and luminance meter to probe into the impacts of GCP on product residual stress, while a relatively thick paper-clipshaped product was used to see the impacts of GCP on shrinkage in thick parts. According to the experimental results, the addition of GCP resulted in increased filling volume, improvement of product weight and stability, as well as effective reduction of section shrinkage, which was most obvious at the point closest to the gas entrance. The shrinkage of the sections parallel and vertical to the flow direction was proved to be reduced by 32% and 16%, respectively. Moreover, observations made via the polarizing stress viewer and luminance meter showed that the internal residual stress of a product could be effectively reduced by a proper amount of GCP.
Polymer Multilayer Films for High Temperature Dielelctric Applications
Advanced film capacitors require polymers with high thermal stability, high breakdown strength, and low loss for high temperature dielectric applications. In order to fulfill such requirements, two polymer multilayer film systems were coextruded via a forced assembly technique. High glass transition (Tg) polycarbonate (HTPC) and polysulfone (PSF) were layered with poly(vinylidene fluoride) (PVDF), respectively. The PSF/PVDF system was more thermally stable than HTPC/PVDF system. For dielectric properties at high temperature, PSF/PVDF system exhibited higher breakdown strength and lower hysteresis compared with HTPC/PVDF system. These results demonstrated that PSF/PVDF was a superior system to HTPC/PVDF for high temperature dielectric capacitors.
Reducing Thermal Conductivity of Polymeric Foams with High Volume Expansion Made From Polystyrene/Expanded Graphite
Radiative thermal conductivity has long been recognized as an important heat transfer mechanism. In the literature, a heat transfer of 20% to 40% through low density thermal insulation materials has been reported. Adding particles such as carbon nanotubes can significantly reduce the radiation by absorption and scattering. In addition to its cost effectiveness and easy processability, the expanded graphite was expected to absorb thermal radiation more efficiently than carbon nanotubes with the same volume content. Using the Rosseland approximation, we quantitatively undertook a first-time study of how expanded graphite significantly reduces the radiative thermal conductivity. We found that particle-added polystyrene foams with a 0.018%vol of expanded graphite nanoplatelets and a 25-fold volume expansion ratio could block 92% of the overall thermal radiative thermal conductivity. A 19.6 mW/m.K of the total thermal conductivity of these foam composites was experimentally achieved. This was due to the extremely high volume expansion (>40- fold) and to the efficiency in attenuating the thermal radiation via the polymeric foams. When we used the Glicksman model for thermal conduction together with the Rosseland approxiamtion, the calculated values of the total thermal conductivity were all in good agreement with the experimental data, and the tolerance was less than 5% (<2 mW/m.K).
Mechanical Properties and Effects of Additives of Cellulose-PLA Composite
Mechanical properties and thermal properties of cellulose- PLA composites were measured. The relation between molecular structure of additives and an addition effect on cellulose-PLA was investigated. By examining for combination of three kinds of cellulose material and four kinds of additive of different features, effects of additives to PLA and cellulose and their mechanism were revealed. It was found there was the most improvement of mechanical properties using hydrophobic additives with many functional groups. It was assumed that reactive additives made a crosslinked structure in cellulose-PLA composite.
Welding of Incompatible Thermoplastic Polymers
Due to the wide range of properties of plastics (e.g. low density), more and more conventional materials are substituted by polymer materials. Complex requirement profiles on technical parts increase the demand for joining processes that enable the reliable joining of otherwise incompatible thermoplastics. In this case, material bonded connections are approaching their limits. In the following study two incompatible thermoplastic polymers were welded by using polymer blends that are compatible to both components. Industrially relevant thermoplastics polyethylene (PE) and polyamide 12 (PA12) were chosen to demonstrate the potential of an innovative joining technology.
Influences of the Variation of Process Parameters on the Pole Length of Multipolar Bonded Magnets
Polymer bonded magnets are mainly used in sensor or electric drive applications. Depending on the particular application, certain requirements of the multipolar magnets, such as high peak flux density or accurate pole length of each pole, must be assured. Multipolar bonded magnets can be economically produced in the injection molding process. Several parameters, such as the compound composition, the mold design and the processing properties affect the final properties of these magnets.
This paper deals with the influences of processing parameters on the magnetic properties, in particular the pole length and maximum radial flux density, of poleoriented molded rings. It can be shown that the pole length in the area of injection points and weld lines is strongly influenced by their existence. Further, the accuracy of the pole length is influenced by the investigated processing parameters.
Preparation and Characterization of Biodegradable Polylactide/Ethylene Methyl Acrylate Copolymer Blends
The poly(lactic acid)/ethylene methyl acrylate copolymer (PLA/EMA) blends were melt blended with by a twin-screw extruder. The phase morphologies, mechanical, and rheological properties of the PLA/EMA blends with three weight ratios were investigated. The results showed that the addition of EMA improves the toughness of PLA at the expense of the tensile strength to a certain degree. All the PLA/EMA blends display typical droplet-matrix morphology, and different characteristic linear viscoelastic properties in the low frequency region, which were investigated in terms of their complex viscosity, storage modulus, and Cole-Cole plots. The interfacial tension between the PLA and EMA is calculated using the Palierne model conducted on the 80/20 PLA/EMA blend, and the calculated result is 3.3 mN/m.
Towards the Prediction of the Wall Thichkness for Technical Parts Manufactured in Extrusion Blow Molding
Extrusion blow molding is an efficient way to produce hollow parts with complex geometry. In this paper a jounce bumper geometry is investigated and numerical simulations are compared with experimental data. In addition a parametrical study is performed to visualize the influence of the processing conditions on the resulting wall thickness distribution. An analytical procedure is derived to correct overestimation of stretching during inflation. This is caused by the membrane approximation approach that is implemented in the simulation software. Accuracy of the simulation results is within the variation of the measurements for thin areas and shows 5 % up to 15 % underestimation in thick areas. Furthermore, a parameter study is employed to correlate initial parison geometry with final wall thickness distribution. Thus the choice for suitable processing conditions in terms of initial parison geometry aiming for a certain wall thickness distribution is accelerated.
Simulation and Experimental Validation of a Conformally Cooled Injection Mold
Conformal cooling systems are an effective method of removing heat from an injection mold. Careful consideration is required with respect to its design to ensure an adequate flow rate through all sections and an even mold temperature distribution achieved. Using simulation to predict the complex thermal environment of a conformally cooled mold can therefore become an important design tool.
In this work experimentally measured temperatures from within a conformal cooled mold insert are compared to that predicted by an Autodesk Moldflow Insight transient cooling analysis for a number of materials. The results showing that the key mold temperature trends can be accurately predicted, enabling its use as a design tool for complex conformal cooling geometries.
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