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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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.
Injection Molded Asymmetric Spur Gear Tooth Deflection: Numerical and Experimental Investigation
In the recent years, asymmetric gear tooth profiles are being considered for the unidirectional power transmission applications due to the advancement in gear manufacturing techniques. Additionally, the advancement in material development makes polymer and polymer composite gears to replace the metallic gears for the motion as well as power transmission applications. Number of researches has been carried on asymmetric steel gear as well as symmetric polymer gears using numerical techniques. This work attempts to understand the structural behavior of asymmetric polymer spur gears with the aid of experimental and numerical investigation. Four tooth 3mm module, 4mm face width, 18 number of teeth of asymmetric (34°-20°) and symmetric (20°-20°) polypropylene gears were considered for this work. An experimental test rig was developed to simulate gear mesh and torque was applied through dead weights and gear tooth deflection was measured with the aid of rotary encoder. The effect of pressure angle at drive side matches well with the experimental values. Asymmetric gear tooth profile having larger pressure angle (34°) at drive side exhibited least deflection and symmetric gear with 20° pressure angle at both drive and coast side exhibited maximum deflection.
Improving Adhesion between Kevlar®129 Fibers and Natural Rubber Matrix Using Morphological Treatments and Coupling Agents
Kevlar fibers are known for their exceptionally high tensile strength, and hence used in a wide variety of high performance applications ranging from military to aerospace and civil applications. However, the expected strength of composites fabricated using Kevlar fibers has not been reached due to poor interfacial adhesion between the fiber and matrix of the composite. This poor interfacial adhesion has been attributed to the highly crystalline and oriented molecular structure of the fiber.
Herein, we present new methods to improve the adhesion between Kevlar fibers and natural rubber matrix. Pre-treatments were used to create new surface morphologies on the fiber. The pre-treated fibers were then subject to treatments with coupling agents. The coupling agents were soaked also in the presence of supercritical carbon dioxide (scCO2). Treated fibers were embedded in rubber matrix and adhesion was measured by fiber bundle pull-out adhesion test. Adhesion was found to improve by around a 100%. Comparative results are reported for both untreated fibers and a range of pre-treatments. Failure analysis of fiber surface revealed a suppression of interfacial failure. The effect of pre-treatments on fiber properties are also characterized, and the optimization between fiber properties, fiber-matrix interface properties, and overall composite properties are discussed.
Use of Core Retraction to Achieve Low Density Foams in Microcellular Injection Molded Polypropylene Parts
Core retraction was used with the conventional microcellular injection molding (MIM) process to foam thick polypropylene (PP) parts with high density reductions of 30% and 55%. The cavity volume was changed by changing the retraction distance, which resulted in varying density reductions. The lowest densities were achieved with a core retraction-aided microcellular injection molding (CRMIM) process, the results of which could not have been achieved by the conventional MIM process alone. The effects of delay time and weight reduction on the microstructure of the core and skin layer were investigated. It was shown that the CR-MIM process yielded a better microstructure and a higher tensile modulus than the conventional MIM process. Use of core retraction also yielded more consistent densities and tensile properties at different distances from the gate location.
Simulation of Long Semi-flexible Fiber Orientation during Injection Molding
This work is concerned with the effect of fiber length on the performance of the Bead-Rod fiber orientation model which takes into account the flexibility of semi-flexible fibers. Different averaging techniques are used to represent the average fiber length for the population, which give different fiber length parameters for the Bead-Rod model. The sensitivity of the Bead-Rod model is evaluated with regard to the fiber flexibility parameter k and length parameter ????. Fiber orientation simulation is conducted for the Center-Gated-Disk (CGD) geometry and compared with experimental data.
Comparative Analysis of Low-Smoke, Zero-Halogen Compounds for Wire and Cable Applications
The choice to use low-smoke, zero-halogen cable jackets is becoming increasing popular in certain applications, allowed by advances in materials expertise that overcame many of the historical difficulties of this class of cable jacket. Test method optimization has occurred in order to better predict how the jacket will perform in the field, and these tests have been used to understand how certain filler and polymer choices affect the jacket performance. These same sets of tests are also used to compare commercially available low-smoke, zero-halogen jackets, in order to evaluate how well the different jackets balance the potentially conflicting property requirements. Analyzing various jackets highlights the variation in properties and quality that can be seen.
Backflow Compensation for Thermoplastic Injection Molding
Minimization of fail parts save companies time and money. Therefore, the injection molding process has to be optimized regarding part quality, cycle time and fault frequency. Machine and process capability are a measurable property of a process to the specification and compare the output of an in-control process to the specification limits. Through process control on different levels of machine control, a high part- and process-quality is achieved. It involves both machine operation and the behavior of plastic. To accomplish these goals and to improve existing machine technology, an alternative injection concept is developed and examined to improve the process and machine capability using a reciprocating screw without moving, locking elements at the screw tip (Figure 1).
Nonwoven Microfilters Produced by a Novel Melt Coextrusion Process
Fibrous filters were fabricated using a novel melt co-extrusion and two-dimensional multiplication technology combined with a high pressure water jet delamination technique. The filters made from polypropylene (PP) / polyamide 6 (PA6) system exhibited micro to nano scale fibers having uniform fiber distribution and superior mechanical properties. Effects of film draw ratio upon co-extrusion on the final filter characteristics were investigated. It was found that increasing the film draw ratio significantly improves the filter’s surface area and porosity, and decreases the mean pore size. This melt-based, versatile technology is applicable to any melt-processable polymers to produce fibrous filters having tunable properties for various filtration applications.
Impact of Pigments on the Dimensional Stability of Plastics
Shrinkage and Warpage phenomenon are common issues faced by injection molders in the plastics industry. These dimensional stability issues are more prevalent in semi-crystalline polymers such as HDPE. Formulation of organic pigments into semi-crystalline polymers impact the nucleation rates and can lead to further shrinkage and warpage. Dimensional instability with the organic pigments can be can be minimized or eliminated through processing steps as well as through surface treatment of the pigments. This paper will describe the shrinkage and warpage distortions, test methods for determining warpage, and recommend solutions.
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