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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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.
Joining Investigations of Polymer-Metal-Hybrids for Permanantly Non-Leaking Applications
The demand for light-weight construction and economic efficiency has led to the development of light-weight construction strategies, i.e., multi-material design, in many areas of industry. Here, the property profiles of the composite partners are utilized synergetically. Plastic-metal hybrid composites possess a large amount of potential in this regard owing to the weight reduction that can be achieved in the composite and the simultaneous enhancement of the mechanical properties.
Hybrid components have already proven their potential in large structural components for the bodies of cars, and are already employed in series.
A particular difficulty arises in the case of applications where sealing is required between the composite materials. Achieving a firmly bonded connection between the differing materials is a tough challenge, especially since exposure to different temperatures and media can alter the composite properties significantly. This was examined and evaluated in expansive test series.
The Influence of Blend Composition and Additive Type on the Properties of LDPE-PA6-Blends
The aim of this work was to investigate the effects of the composition on the properties of LDPE-PA6 blends with an emphasis on the addition of EVA, because this material is often used as interlayer in packaging films. Furthermore, also the effects of additional compatibilization on the blend properties should be investigated.
We found, that the addition of EVA alone shows some compatibilizing effects in blend properties, like impact strength and viscosity. Further improvements can be gained by adding prefabricated additives, like maleic anhydride grafted polyethylene and ethylene vinyl acetate, while the in situ production of such additive shows some reduced effects, likely due to some reduced accessibility of the EVA component for the in-situ grafting. Nevertheless all the investigated approaches show some effectiveness in compatibilisation, which will help to reuse such materials in other applications.
Effect of Rubber Addition on Structure and Property Distribution of Thin-Wall Injection Molded Polypropylene
In this research, rubber with two different molecular weights was added to thin-wall injection molded polypropylene (PP). The effect of rubber addition on structure and property distribution of these thin-wall injection molded polypropylene (PP) samples was investigated using Polarized Optical Microscopy (POM), Differential Scanning Calorimetry (DSC), Wide Angle X-ray Diffraction (WAXD), a high speed tensile test, and a micro-cutting method. The thin-wall injection molded PP with high molecular weight with rubber exhibited the higher crystalline orientation and ?-crystalline fraction as compared to other samples. Micro cutting method results revealed that the addition of rubber to PP samples led to lower shear strength. The relationship between structure and property distribution of thin-wall injection molded PP is discussed on the basis of these results.
Differential Scanning Calorimetry (DSC) Quantification of Polyamide 12 (Nylon 12) Degradation during the Selective Laser Sintering (SLS) Process
Selective laser sintering, a 3-dimensional printing technique, converts powdered thermoplastic resins, e.g. polyamide 12 (nylon 12), into end-use parts by using a laser to melt and fuse the particles. In this layer-by-layer additive manufacturing process, the powder is both the raw material and the mold. Therefore, unsintered powder can be recovered and recycled in subsequent builds to significantly decrease net costs. To improve blending protocols, the powder quality, i.e. the degree of degradation, was quantified using differential scanning calorimetry. Contrary to the work of others, the results suggested that the sensitivity of differential scanning calorimetry to small changes in molecular weight could reproducibly detect small changes in oven-aged (degraded) powder.
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