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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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.
Molecular Weight Analysis of Polyethylenimine Using Dynamic Light Scattering and Gel Permeation Chromatography with Multi-Angle Light Scattering Detector
It has been challenging to characterize the molecular weight distribution of water soluble cationic polymers, such as polyethylenimine (PEI), due to intramolecular electrostatic interactions, adsorption, ion exchanges, ion exclusion and ion inclusion. In this study, several commercial PEIs with various molecular weights and architectures were examined using Gel Permeation Chromatography (GPC) with online multi-angle light scattering (MALS) detection. Good GPC separation for medium-to-low molecular weight (< 100 kDa) PEIs was achieved by using a cationic column set in an acidic buffer condition. However, for high molecular weight (> 500 kDa) and branched PEI, non-ideal GPC separation, manifested by anomalous late elution of high molecular weight chains, was detected by MALS at longer elution times. Dynamic light scattering was utilized to examine the solution behavior of PEIs in the GPC buffer condition.
A Through-Process Modeling Approach for Anisotropic Performance and Lifetime Evaluation of Fiber Reinforced Thermoplastic Parts
Fiber reinforced thermoplastic (FRTP) materials offer great potential for, among others, weight and cost reduction in a wide range of applications. In this paper, consequences of fiber orientation-induced anisotropy (due to injection molding process) in the development of FRTP parts as well as predictive engineering techniques for part performance evaluation are discussed. A coupled simulation methodology, referred to as Through-Process Modeling, will be used to predict the processing-morphology-properties relation in FRTP parts. This method enables taking morphological information into account and results in improved simulation accuracy and, ultimately, an accelerated development cycle.
Non-Destructive Characterization of Hygrothermally Aged Polymers
Numerous established procedures exist for non-destructive material testing; the goals of such tests typically include detecting material defects, such as cracks or pores. However, material aging, which has a significant influence on a material’s properties, is also critical to consider for polymers in particular . In order to establish the existence of possible aging effects, corresponding characteristic values are determined with destructive tests ; such methods, however severely limit the possibility of preventative maintenance procedures. Therefore, the following contribution will introduce a method with which the effects of aging on polymeric materials can be determined non-destructively. To do so, the hygrothermal effects on samples of artificially aged Polyamide 6 will be investigated and macromolecu-lar changes identified using ultrasonic testing.
Improved Model of Thermal Diffusivity for Semicrystalline Polymers as a Function of Temperature, Temperature Gradients, Cooling Rate and Injection Molding Process Conditions
An improved model of thermal diffusivity for semicrystalline polymers is proposed. This model is the result of an evolution of a previous model which was based on the part thickness position, temperature and typical injection molding conditions. One-dimensional simulations with the new and the original model were performed obtaining good agreement between the results. The new model used the cooling rate and temperature gradient as parameters, instead of the thickness position, increasing its applicability in injection molding simulation software.
Enhanced Properties of Oriented Multilayer Polypropylene Film/Foams
This research work presents an understanding of structure-property relationship in uniaxially oriented multilayer polypropylene (PP) film/foams. Multilayer PP film/foams having 16 layers have been produced by using a unique coextrusion and multiplication technique. A post-uniaxial drawing process at a certain temperature has been carried out to orient the multilayer film/foams in extrusion direction. Oriented film/foam samples were collected at different draw ratios (DR). Bulk density of oriented samples decrease with increasing draw ratio of film/foams up to a DR of 2.5 (?DR=2.5 = 3.0 g/cm3) and then increases slightly at higher DR. In addition, the modulus and fracture stress increase with increasing draw ratio. Thus, a light weight and strong composite structure comprising alternating layers of PP film and foams have been successfully fabricated.
Continued Studies of the Effects of Metallic Pigment Dispersions on the Physical Properties of Thermoplastics
Metallic pigments continue to serve an important part in the coloration and function of thermoplastics. In particular, aluminum flake pigments play a prominent role in expanding plastics markets such as automotive, electronics, and appliances. The use of in-mold and inprocess coloration for paint replacement is growing as result of market drivers that require low volatile organic content (VOC) coloration, lower process costs, and reduced manufacturing times.
As the amount of plastic used for high-profile applications increases, the need for physical property trends becomes more useful. Impact strength and tensile properties of polymers play an important part of material selection, and the addition of colorants and additives affect those properties. Previous studies1,2 involving aluminum flake-pigmented polycarbonate (PC) and acrylonitrile-styrene-acrylate (ASA) noted the effect of carrier types, flake particle size, geometries, and concentration levels on impact and tensile properties. As a result, physical property trends for additional polymer types are of interest.
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