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3D printing is used for various medical applications, such as the manufacture of guides for surgical operations, custom medical instruments, and low-cost medical applications. In few of these studies that have been performed, the effect of sterilization on these parts has not been considered yet. The fused filament fabrication process (FFF), which is the most widely used today, is used for the making of these guides and instruments. One of the most used materials in the FFF process is polylactic acid (PLA) due to its ease of printing, however, this could be degraded with the sterilization processes by steam heat and dry heat and lose its dimensional accuracy and resistance, something required for medical applications. The purpose of this study is to determine the effects of the steam heat and dry heat sterilization processes on the mixture of PLA and hydroxyapatite (HA) to check whether this mixture can be used in medical applications that are not implantable in the human body. The percentage by weight of hydroxyapatite used is 5%. To study the effect of sterilization processes already mentioned, 3D specimens were printed for flexural, tensile, Shore Hardness and impact mechanical tests. Thermogravimetric analysis (TGA), Differential scanning calorimetry (DSC) and Dynamic mechanical thermal analysis (DMTA) tests were also performed. It is concluded that the blend of PLA and hydroxyapatite increases its resistance to temperature but decreases its mechanical characteristics.
Polymer producers and converters are continuously evaluating potential options to reduce costs by producing faster, reducing energy consumption, reducing scrap and improving article properties. Recently, however, sustainability and overall environmental impact have also become prominent themes for converters, as a result of the pressure to minimize the footprint of the plastics industry on the environment. Polyolefin blown film and injection molding are large polymer conversion market segments that have received significant attention in terms of equipment improvements and formulating principles. Processing aides are commonly used in blown film extrusion and injection molding. Specifically in injection molding, silicone spray is used to ease the removal of the article from the mold, thereby saving cycle time. Silicone spray is, however, difficult to remove from the final part. An alternative is to use higher molecular weight Fischer-Tropsch (FT) hydrocarbons as a polymer processing aide and mold release agent due to good compatibility with the polymer compound matrix. This paper gives an overview of the use of FT hydrocarbons as processing aides in injection molding. Examples of more than 15 years of experience in the global marketplace, ranging from the production of small to large articles, are shown. Formulating with these hydrocarbons allows the converter to reduce cycle time, produce faster to reduce labor, to reduce energy consumption and improve certain properties of the injection molded article. Ultimately FT as a polymer processing aide could be an important tool to a converter to reduce manufacturing costs and improve quality.
Because of their versatile properties multi-layer polymer products have a high industrial relevance. Process understanding and prediction of the flow characteristics of co-extrusion, hence, is of major importance. When the shear-thinning behavior of polymer melts is to be included in modeling, there is no alternative to numerical solution methods. We present a numerical solver that is based on the shooting method to predict two-layer co-extrusion flows of non-Newtonian fluids within rectangular ducts of infinite width. The pseudo-plastic flow behavior of polymer melts is modeled by the power law according to Ostwald and de Waele. We carried out a dimensional analysis of the governing equations based on the theory of similarity, and identified four independent dimensionless parameters that fully describe the problem. To solve the dimensionless governing equations, we developed a numerical solution procedure. Additionally, we conducted an extensive parametric study by varying these independent dimensionless quantities over a wide range that covers almost all applications in industry. The numerical results offer insights into the influence of the independent parameters on, for instance, pressure gradient, (interfacial) shear stress, velocity profile, and viscosity distribution.
A new carbon black product was developed at Birla Carbon with ultra-high jetness and bluish undertone for high color applications in plastics. The new product was demonstrated with improved jetness in various polymer systems over the existing high color products, especially achieving a 40% improvement in polyamide 6. The new product shows great potential for ultra-high jetness plastics applications including automotive, household appliances, and consumer electronics.
Introduction of surface textures has long been used to improve the hydrophobicity of solid materials. This study focusses on understanding the effects of various micro-texture geometries on the hydrophobicity of textured polymer surfaces. Square pillar, cylindrical, hemispherical and conical surface features, both protrusion and cavity, are considered in this study for two polymers. Employing the well-known models, the study shows that introducing textures on polymer surfaces generally increases the contact angle and, therefore, improves the hydrophobicity of polymers. The effect of surface texture on hydrophobicity significantly varies with texture geometry and dimension. The study provides useful guidelines for improving hydrophobicity of polymers by introducing textures on the surface.
With advances in computing technology, applications of computer-aided engineering (CAE) technology are becoming widespread in diverse industries. Specifically, machine learning is now being applied to fields such as that of materials design and production which is the field within which this study focuses. However, problems in implementing this technology arise in regard to lengthy analysis times and a lack of suitability in regard to on-site, real-time judgments during some production processes. This study addresses these issues in regard to the problems of applying CAE to the injection molding production process where quite complex factors inhibit its effective utilization. In this study, an artificial neural network, namely a Back Propagation Neural Network (BPNN), is utilized to render results predictions for the injection molding process. By inputting the plastic temperature, mold temperature, injection speed, holding pressure, and holding time in the molding parameters, these five results are more accurately predicted: EOF pressure and maximum cooling time, warpage along Z-axis, shrinkage along X-axis and shrinkage along Y-axis. This study first uses CAE analysis data as training data and reduces the error value to less than 5% through the Taguchi Method and the Random Shuffle Method which we introduce herein, and then successfully transfers the network which CAE data analysis has predicted to the actual machine for verification with the use of transfer learning. Of particular interest, is this study's use of a Back Propagation Neural Network (BPNN) to train a dedicated prediction network through using different, large amounts of data for training the network, which is proven fast and that can predict results accurately using our optimized model.
A novel additive manufacturing technique has been developed in the Manufacturing Science Laboratory at Lehigh University.The technique utilizes an extrusion based 3D printer, which has the ability to regulate the areaof the polymer flow inside the extrusion head, thus, allowing precise control over shear rate applied to polymer melt. The controlled shear alters the melt rheology, which in turn controls the evolution of crystallinity in the printed parts. The temporal control of shear translates to spatial control of melt rheology. Thus, the localized evolution of molecular orientation and nucleation/crystallization kinetics as well as the mechanical and optical properties can be precisely controlled during the additive manufacturing process. In this research, a semi crystalline poly-lactic acid (PLA)was utilized to validate the developed technique of controlling the shear rate while printing. The confinement will induce shear on the polymer the degree of which can be controlled by the gap between the conical cavity and theconical extruder tip. The analytical modeling results indicate that this strategy can increase the induced shear rate. Preliminary experimental analysis validated an increase incrystallinity percentage up to 16%.
Solid-State Sheer Pulverization (SSSP) is acontinuous processing technique in which low-temperature application of shear and compressive forces impart changes in structure and properties to different thermoplastics. In this paper, SSSP is applied to post-industrial ultra-high molecularweight polyethylene (UHMWPE) materials for a technical feasibility study of mechanical recycling of high-molecular weight, high-melt viscosity polymers. The SSSP process is able to effectively reduce the particle size while also mechanochemically enhance the crystallization behavior of the polymer.
Despite the evolution of several new die concepts since the invention of spiral mandrel dies in the 1960s, the basic geometry of the spiral grooves themselves remained unchanged. The cross section of the groove is u-shaped, i.e. consists of a rectangular and a semi-circular area. Typically, the spiral grooves abruptly merge into the annular gap, forming sharp edges. These edges negatively affect process performance e.g. by potentially damaging the polymer chains or provoking deposits. Rounding off these edges ease the effect to some extent, but alternating the general shape of the cross section has obviously a much better potential to influence the process characteristics of the die. This paper systematically investigates spiral mandrel dies with channels of different cross-sections: type I is u-shaped, as it is normally used for spiral dies, type II is u-shaped with one side inclined at 45 degrees and type III is a wider variation of the u-shape. To calculate the pressure drop along channels with such cross-sections, it is common practice to use correction factors. These so-called flow coefficients correct the error introduced by the geometrical simplifications necessary to obtain analytical solutions. This paper presents flow coefficients calculated from CFD results for the given cross-sections.
The effect of glass fiber on the viscoelastic properties, thermal stability, permittivity and volume resistivity, as well as stress relation behavior of poly(ether ether ketone) (PEEK) was investigated using dynamic rheology, TGA, broadband dielectric spectroscopy and DMA over a wide range to temperature. The complex viscosity of PEEK filled glass fiber with 30 wt.% increases by one order of magnitude at 360 oC compared to the unfilled PEEK indicating that the glass fibers inhabited the polymer chains motion and reduced the free volume at high temperature in the melt. The viscosity and dynamic moduli (G′ and G″) of both PEEK and 30 wt.% glass fiber filled PEEK were not very sensitivity to the temperature variation (i,e.; the viscosity, G′ and G″ slightly decreased with increasing temperature). The angular frequency dependence of complex viscosity was found to be well described by Carreau–Yasuda model. It was also observed that the thermal stability of PEEK improved significantly by adding glass fibers. In addition, the relaxation modulus master curve at 200 oC reference temperature for glass filled PEEK is significantly higher than that of pure PEEK due to the excellent reinforcement effect of the glass fibers.
PA6-based in-situ nanofibrillar composites, containing polyphenylene sulfide (PPS) nanofibrillar domains with average diameter around 60 nm, were produced combining melt compounding and hot stretching. Then, effect of this fibrillar network on the crystallization behavior of PA6 composites was investigated using differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), and polarized optical microscopy (POM). Results indicated no significant increase in the composite’s crystallinity due to PPS nanofibrils; however, the nanofibrillar network did induce a significant difference in the crystallization curve with the evolution of a high temperature crystallization peak. The impact performance of nanofibrillated PPS-PA6 was improved with 3 wt.% PPS nanofibrils, which was explained by the interconnected fibril network and the formation of transcrystalline structures and small crystal size in the presence of the fibril network.
A fundamental aspect of a polymer weld is the presence of intermolecular diffusion between the two joint surfaces. Without the movement of polymer chains across the melt interface, then the bond achieved is merely adhesive, and not a true weld. Therefore, it is essential to be able to determine where diffusion has occurred in order to properly evaluate weld quality. One of the simplest methods to do so is via cross section and heat treating of a weld section. The scientific basis for this process and the experimental method to complete it is presented here.
This paper will treat to expose the complexity of stabilization of plastics in automotive applications. First, we will review some basics on stabilization, the use of phosphites and phenolic antioxidants. We will cover the different aspects of polymer stabilization: during processing and along the service life of the parts. This will involve discussion around light stabilization too. Along this paper, we will see some examples of outstanding chemistries than can lead to combine several benefits to achieve the performances required by OEMs.
Continuously increasing demands on the component functionality as well as the demand for efficient production processes are causing a change of multi-component injection molding from a special process to a key technology in plastics processing. However, the possibilities of the process are limited due to the complex interactions in adhesion. Innovative product solution ideas are limited by limiting material factors or by excessive process costs due to necessary process steps. The use of the atmospheric pressure (AP) plasma process can extend the compatibility of polymer materials. Nevertheless, a complete integration into the injection molding process has not yet been achieved. With the development of the InMould-Plasma treatment a process has been developed which integrates the plasma activation of plastic surfaces into the injection molding cycle. In this study it is shown that original incompatible materials, like polypropylene (PP) and thermoplastic polyurethane (TPU), have a long-term stable bond under different aging conditions, by using the InMould-Plasma technology. Due to their relevance in the automotive sector, the aging conditions are based on test standards of German car manufacturers. These include aging in an oven up to 120 °C, cold storage down to minus 40 °C, water storage and climate change tests. For testing the bond strength, the samples were peeled apart according to the standard VDI 2019. The influence of the aging of the individual components was supplemented by tensile tests. The test specimen are tensile rods according to DIN EN ISO 3167 and were subjected to the same conditions as the composite. It is shown that the InMould-Plasma process enables a long-term stable bond between originally incompatible materials and withstands the aging conditions in accordance with test standards of German car manufacturers.
Many products and assembled systems of different products require the use of threaded plastic to threaded metal connection to provide the mechanical integrity required for the service application. While there are design guidelines and industry acceptable standard specifications related to the design of the different thread profiles used in the connection of plastic to plastic or connection of metal to metal threaded components, there is very limited information available for designing a plastic to metal threaded connection. Generally, designing a mechanical connection between a plastic threaded component and a metal threaded component is discouraged. However, in some applications this cannot be avoided and as such the lack of understanding related to plastic to metal threaded connection leads to product failures when such connections are made or designed improperly into products. This paper reports two case studies of product failures where plastic to metal threaded connections contributed to product failure that caused either personal injury or personal property loss. A failure analysis investigation was conducted to evaluate the thread design in two products in which plastic to metal threaded connections were involved in the product failure. In the first case-study, the thread connection was found to be insufficient in the mechanical strength and in the second case study the root cause of failure was determined to be excessive tightening of the female threaded plastic component onto a male threaded metal component.
Acrylonitrile Butadiene Styrene (ABS) is widely used in additive manufactured part production due to its widespread availability and ease of manufacturing, but unfortunately its structural and thermal performance limits its use in industrial applications. The addition of fiber reinforcements, specially chopped carbon fiber to the ABS matrix has the potential to enhance its structural performance while simultaneously reducing dimensional variations during thermal changes. The quantification of the fiber orientation in the processed ABS bead is important to understand its correlation to the mechanical and structural properties of the processed thermoplastic. This study presents the sample preparation and acquisition of images of fiber orientation and void measurements through optical and scanning electron microscopy of an additive manufactured bead with 13% by weight carbon fiber reinforced ABS. The images are then analyzed, and the fiber orientation is measured using the method of ellipses. The method of ellipses poses a problem of ambiguity for the direction of fiber orientation. With the SEM images the ambiguity problem can be solved using an electrical shadowing technique and the orientation of the fibers in the ABS matrix can be determined. The results for the orientation from the two methods are contrasted, and a discussion is provided on the impact the fiber orientation has on the final part performance. The results also indicate the presence of voids caused by the deposition process that is unique to the currently employed additive manufacturing process which will hamper the final part performance.
The motivation for this work was to increase the economic life of recycled poly(lactic acid) (rPLA) (30 wt%) by utilizing it with virgin PLA (70 wt%) in the presence of a fiber-based reinforcing filler, micro-crystalline cellulose (MCC) and an epoxy-based chain extender. A conventional melt extrusion technique was used to fabricate the strands with and without MCC and chain extender in the PLA/rPLA blend matrix. It was observed that the complex viscosity of rPLA was improved significantly after the addition of the chain extender, which resolved the issue related to excessive polymer flow during processing and hence made it possible for use in fused deposition modeling (FDM)-based 3D printing. The addition of the chain extender improved the impact strength of 3D the printed PLA/rPLA specimens. The voids in the 3D printed material contributed to the reduced weight of the developed sustainable composites. The modulus and tensile strength of the 3D printed sustainable biocomposites were improved significantly, and impact strength increased by ~10% by reinforcing the blended matrix with 5% of MCC.
This article shows the effect of melt mixing parameters such as temperature and time on the macromolecular chain structure of Recycled Poly(ethylene terephthalate) using a batch mixer. The objective was to develop a pretreatment of PET to reduce molecular weight and crystallinity in preparation for microbial degradation. A depolymerization kinetic model was built to understand the irreversible structural changes caused via melt processing of RPET. Chain scission reaction occurred faster at higher temperatures, as evidenced by molecular weight calculated from intrinsic viscosity measurements.
Demand for increased recycled content in various applications has driven innovation toward incremental step change in recycled material quality. In pursuit of increasing recycled content usage in extrusion blow molding applications, considerations must be made for the preservation of mechanical properties via the prevention of thermal and oxidative degradation during both the recycling and molding processes. In order to understand the importance of timely implementation of solutions like stabilizer blends, a set of experiments was run on extrusion blow molded articles to illustrate the rate of performance decay that occurs between the recycler and the molder. This analysis proposes pathways to improve upon current recycled content utilization while simultaneously improving end-use properties.
Low gloss finishes (≤2 GU at 60°) are a demand across a variety of industries. These low gloss finishes must provide scratch, mar, and burnish resistance to maintain physical and visual integrity over the lifespan of a product. This can present unique challenges within interior automotive, where low gloss finishes are expected to provide luxurious aesthetic characteristics as well as support the need for anti-glare application for driver safety. The high traffic of automotive cabins requires the low gloss finishes to be highly resistant to chemical and abrasion resistance throughout the lifetime of the vehicle. Continuous evolution in the methods used to evaluate interior automotive materials has led to the development of new, innovative coating technologies that exceed previous scratch and chemical resistance expectations for interior finishes. The performance capabilities of new coating technologies and the supplemental benefits they bring enable designers to achieve low gloss, quality finishes that exceed Original Equipment Manufacturer (OEM) testing demands for performance and quality while remaining cost-effective.
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