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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Sandwich Injection Molding - Core Breakthrough and Flow Imbalance Studies
We presented numerical simulations concerning two important defects encountered in the sandwich molding process: the core breakthrough in a thin-walled part and the flow imbalance in a multi-cavity mold. The part thickness largely determines how far the skin melt front advance before breakthrough happens. This limits the size of the part and the maximum core ratio. The skin and core advancement in the multi-cavity system is complex due to the temperature imbalance and pressure resistance variation encountered in the runner. An understanding of the melt flow mechanism through simulation is helpful for the part designer to fully utilize the benefits of the sandwich molding process.
Transformation of Measured Viscosity Data of Special Plastic Materials Into Moldflow Software
Special applications in plastic engineering require new different polymers. Therefore new polymers and additives are constantly being developed. A lot of these special polymers are not available in databases and cannot be used in simulation software. But it is becoming more and more important to know as much as possible about polymers in order to avoid problems in product development and the manufacturing process. So the polymers have to be tested. This paper shows a possibility of measuring points of flow curves and transforming them into a mathematic model to do molding simulation with the specific material afterwards.
Role of Simulation in Analyzing Root Cause Failure
Understanding root cause failure mechanisms for plastic packaging is becoming more important. This need has become critical due to new packaging materials, faster production speeds, lighter weight packages, creative designs and challenging product formulations. Often there is a need find and eliminate the cause for failure and come up with a more robust package. Replicating and analyzing failures via simulation can provide rapid feedback and optimal solutions in a shorter time frame than traditional methodologies. This paper looks at some of the common failure mechanisms and not so common analysis and detection procedures. Practical case study examples will be presented.
A Study of Rolling Resistance of Electrospun Polymer Fabrics
Rolling resistance contributes to 6-10% of the overall fuel consumption of vehicles. Little is understood on the relationship between rolling resistance and surface characteristics such as adhesion, surface asperities and topology. In this study, we evaluate the rolling resistance using a free oscillation of a pendulum. Different substrate materials such as asphalt, rubber, wood, high-density polyethylene (HDPE), nylon, polycaprolactone (PCL) and poly(vinylidene fluoride) (PVDF) were tested by a laboratory fabricated pendulum steel roller. The damping factor is examined using an envelope analysis technique based on Hilbert transform methodology. The rolling resistance is found to depend on viscoelastic properties, adhesion and surface characteristics. The damping factor is the highest for asphalt and the second highest for rubber. The damping factor of electrospun polymer fabrics lies somewhere in between those pertaining to asphalt and more rigid substrates such as steel and copper
Key figures for describing and comparing the energy consumption of injection molding processes
This paper deals with energy consumption data for a broad variety of injection molded parts. An analysis shows that key figures can be derived for comparison and reference purposes and allow the evaluation of the energy efficiency in a part dependent production process. The key figures comprise material properties and part geometries to build a focus relative to these particular part characteristics independent of category or application. This approach goes beyond the widely applied method of examining a machine specific energy consumption data. A significant potential of energy reduction for most analyzed injection molding processes is expected.
Microcellular injection molding of in-situ modified Poly(Ethylene Terephthalate) with supercritical nitrogen
The microcellular injection molding (commercially known as MuCell) of in-situ polymerization-modified PET (m-PET) was performed using supercritical nitrogen as the physical blowing agent. Based on design of experiment (DOE) matrices, the influence of operating conditions on mechanical properties of molded samples were studied systematically for two kinds of m-PETs, namely, n-m-PET and m-m-PET synthesized using pentaerythritol (PENTA) and pyromellitic dianhydride (PMDA) as modifying monomers, respectively. The optimal conditions for injection molding were obtained by analyzing the signal-to-noise (S/N) ratio of the tensile strength of the molded samples. The specific mechanical properties, especially the impact strength, of the microcellular samples under these conditions increased significantly. Scanning electron microscope (SEM) analyses showed a uniform cell structure in the molded specimens with an average cell size of around 35 ?m. The m-m-PET modified with PMDA generated a slightly finer cell structure and a higher cell density than the n-m-PET.
Equipment and Material Considerations for Microcellular Foaming
Microcellular foaming processes are now proven technologies and integral part of the “mainstream” in polymer conversion operations. The present paper is a joint effort between two companies (Dow and Mucell) to address key aspects necessary to achieve a more efficient use of materials and resources via physical foaming. The paper reviews in detail all aspects that influence performance, paying special attention to the synergies that arise between hardware and material selection. A comparison of performance between chemical and physical blowing is analyzed, highlighting the advantages of microcellular foaming.
High Temperature Aesthetic Grade Liquid Crystal Polymers for Consumer Applications: Not Just For Connectors Anymore
For many years the use of high flowing engineered resins, such as Liquid Crystal Polymer (LCP), have been used for very detailed and intricate parts in the electronics and connector industries where function and performance far outweigh any need for coloristic attributes. Today we find the uses of such resins extending out to more visible consumer products that need the performance and functionality of the LCP with the additional demand of excellent aesthetics. This paper looks to show where the coloring of LCP and the producing of aesthetically pleasing parts has brought LCP’s from behind the scenes to center stage for the consumer products industry.
Simulating the directionality of liquid crystalline polymers
In this paper a practical method of modeling directionality of crystals in liquid crystalline polymers (LCPs) is studied. The main components of this method represent the effects of shear on crystals, the effects of crystals on each other and the effects of movement of crystals with the flow. The implementation of this simulation is done by coding a user defined function (UDF) in ANSYS® FLUENT®. The results of the simulation are shown in two and three dimensions. The presented results show promising closeness to the physical phenomenon associated with the directionality of LCPs. The proposed method can be used as an estimation of the directionality of crystallines during the processing.
Crystallographic Analysis of Electrospun Poly(?-caprolactone) Nanofibers by 2-D Wide-angle X-ray Diffraction (2D WXRD)
The crystalline morphology of electrospun PCL nanofibers was studied. Random and aligned nanofibers were obtained by a conventional plate collector and a two-parallel-conductive-plate collector, respectively. Scanning electron microscopy (SEM) and 2D wide-angle X-ray diffraction (2D WXRD) were employed to characterize the nanofibers. The degree of crystallinity of aligned nanofibers was higher than that of randomly aligned nanofibers. The crystallites in the nanofibers were highly oriented along the nanofiber axis, as were the molecular chains. The estimated crystallite size in the nanofibers suggested that a single nanofiber was composed of dozens of nanofibrils and a nanofibril was further composed of crystallites along the nanofiber axis with an amorphous region of extended PCL molecular chains between neighboring crystallites.
Mechanical Properties of Interconnected Porous Elastomers Fabricated by a Microsphere-Templating Casting Process
The mechanical properties of interconnected porous polysiloxane elastomers under tension and compression were studied in this work. The porous elastomer was found to be highly deformable and had non-affined tensile deformation. The increase of pre-set strains and strain rates in cyclic tension and compression resulted in an increase of stresses at pre-set strains and hysteresis. The permanent sets after unloading process non-linearly decreased as the strain rates were lowered in cyclic compression while the strain rates seemed to have very limited influence over permanent sets in cyclic tensile testing.
Crystallization of Polypropylene: The Effect of Shear and Temperature
The final mechanical properties of a plastic product which is made of semi-crystalline polymers depend significantly on the molecular properties and the applied processing conditions. Particularly, the formation of flow induced structures via polymer crystallization plays a major role in defining the final attributes of the product. In this paper, the effects of shearing and temperature on the flow induced crystallization of several polypropylenes are examined using rheometry. Generally, strain and strain rate found to enhance crystallization in simple shear at temperatures between the melting and crystallization points. The effects of molecular weight and its distribution are also examined and observed to have a strong influence on flow induced crystallization structures.
Microcellular Foaming of Poly(lactide acid)/Nanosized Calcium Carbonate Composites
This article focused on the study of the effect of nanosized CaCO3 on foam morphology of PLA using CO2 as the foaming agent. The thermal properties were investigated through the TG and DSC methods. The presentation of CaCO3 acted as nucleation site to facilitate the crystallization of PLA that resulted the greatly increase of PLA crystallization up to 69.14%. The SEM results showed that the addition of CaCO3 significantly improved the foam morphology, cell size decreased and cell density increased greatly. When the content of CaCO3 is 30wt%, they are similar to the content of 20wt%. Because of the incompatibility of CaCO3 and PLA, the addition of CaCO3 decreased the mechanical properties of PLA.
Foaming Morphology of Microcellular Injection Molded Parts - Simulation and Experimental Characterization
We present the morphological study of microcellular injection molded product using amorphous and semi-crystalline polymers with nitrogen. The cellular structure and cell distribution probed by scanning electron microscope (SEM) were compared with three-dimensional simulation of cell size and density distribution. The morphological comparisons between SEM photos and simulations were analyzed for three different locations along the flow direction. Good agreement between simulation and real molded part prove the capability of commercial CAE software in 3D prediction of microcellular foaming process; furthermore, expensive morphological study from SEM can be economically assisted by simulation tool for industrial application.
Preparation an dMicrocellular Foaming Investigation of Poly (Lactic Acid)/Talc Composites
This study investigated the influence of talc content on the mechanical/thermal properties and crystallization behavior of PLA/talc composites. Talc was compounded with poly (lactic acid) (PLA) via a triple screw extruder, and the foaming properties of the blends were investigated by using a homemade foaming device. Carbon dioxide was used as the blowing agent. The impact strength were significantly increased (by 10%-31%) at the expense of a certain degree of reduction of tensile strength. Owing to the nucleation effect of talc, the 5% talc blends received the maximum crystallinity (43.8%). Furthermore, when the talc content was 10%, the foaming sample obtained the maximum cell density and the minimum cell size.
A Nanoscaled Three Dimensional Structure Created By Using Electrospun Poly(?-Caprolactone) (PCL) Nanofibers and Induced PCL Crystallization
A nanoscale, three-dimensional structure consisting of poly(?-caprolactone) (PCL) nanofibers covered by periodically spaced PCL crystal lamellae was successfully created using a self-induced crystallization method. The shish-kebab structure was obtained by inducing PCL crystallization on electrospun PCL nanofibers immersed in a PCL solution followed by solvent evaporation. The resulting structure highly resembled the nanotopography of natural collagen nanofibrils in the extracellular matrix (ECM) of natural tissues and thus could be a good in vitro model for tissue engineering scaffolds.
Use of a Stack Mould to Increase the Productivity and the Quality in the Injection Molding
The main objective of this research was to study the effect of the injection process conditions over the quality and final properties of plastic parts made in stack moulds. For that, there were used CAD/CAE tools. As a result, it was obtained that when the melt and mold temperatures are increased, the volumetric shrinkage of the molded parts is also increased, and this coincides with the obtained results in hot runners’ moulds. By other hand, when the holding/packing pressure is increased, it is observed a decrease in the parts volumetric shrinkage, as well as in cold and hot runners’ moulds. When the melt temperature increased and the injection velocity decreased, the residual stress in the plastic parts are reduced.
Injection Molding of Rigid Vinyls
Rigid Polyvinyl Chloride and Chlorinated Polyvinylchloride are highly viscous materials that are susceptible to thermal degradation. This combination makes them very challenging to process consistently and often require temperature conditions that are quite a bit different than what someone who has processed other thermoplastics is used to. Also, these materials require some special modifications to the molding machine to facilitate processing. By understanding how the polymer is responding to the process conditions imposed on it, a stable, repeatable process can be established that will produce consistent, high quality parts
Processing effects on permanent electrically conductive HDPE- Conductive Carbon Black composites
Conductive carbon black is still today the most used solution to give permanent electrical conductivity to plastic materials. Electrical conductivity of the final material is known to be affected by processing history and especially final transformation processes as they can induce changes in the filler properties or distribution. In a recent work we highlighted the large difference in the percolation curves of the electrical resistivity of compression and injection molded samples of conductive and extraconductive carbon black loaded HDPE. Such difference can be addressed to different effects such as surface induced segregation, carbon black structure reduction or different crystallization of the polymeric matrix. In this work we investigate by simple but specific tests the relative importance of these factors evaluating their contribution to the modification of the final electrical properties of the material.
Thermo-Mechanical Property Prediction for Long Fiber-Filled Thermoplastics Composites
Following on from the long fiber orientation and long fiber breakage model implementations in the past, long fiber enhanced polymer composite property calculation models have been implemented for long fiber-filled injection moldings. These long fiber composite properties are useful in terms of residual stress calculation, warpage prediction and subsequent structural analysis. Major differences between long fiber and short fiber composite property enhancements include the non-uniform fiber length distribution across injection molded parts and possible de-bonding between fiber and matrix. This paper addresses these differences by presenting a recently implemented micro-mechanical models specific to long fiber composites, which makes use of calculated long fiber orientation and fiber length distributions. A case study on fiber orientation distribution (FOD), fiber length distribution (FLD) and subsequent long fiber composite property distributions are given for injection molding simulation.
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