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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Optimization of PVDF Extrusion to Produce Electroactive Filament for FFF
The development of Poly(vinylideneflouride) (PVDF) material with high electroactive properties is of great interest for its use in energy harvesting. This study is concerned with producing PVDF filaments to be fed into a Fused Filament Fabrication (FFF) 3D printer to broaden the horizon for printing complex energy harvesters. An extrusion process followed by post treatments was applied and the processing conditions were varied as they play a crucial role in altering the phases within PVDF and its crystallinity. The correlation between the parameters and the resultant properties of the PVDF filament was made using combination of Fourier-transform infrared spectroscopy (FTIR) and Differential Scanning Calorimetry (DSC) characterization techniques. The optimized processing conditions were found to be 230 ᴼC for extrusion temperature and 4.5 – 6.5 stretching ratio. This led to the fabrication of an electroactive PVDF filament with 80% β-phase content and 50 to 55% degree of crystallinity.
Analytical Characterization of Acid Copolymers and Ionomers
Ethylene-methacrylic acid (EMAA) copolymers are converted to ionomers (ionic functionality) through the partial neutralization of their carboxylic acid groups. These ionic groups are randomly distributed along the polymer backbone, and various cations (i.e., Na, Zn, Mg, Li, etc.) can be incorporated into the ionic functionality to modify their properties. Some unique properties that these ionomers exhibit include high melt strength, excellent toughness and optical clarity. These desired properties make the ionomers ideal for applications that include packaging, decorative perfume and spirit caps and capstock decking. This study was focused on the use of Fourier-Transform Infrared (FTIR) spectroscopy to study EMAA copolymers partially neutralized with Zn cations. FTIR was also used to measure the degree of neutralization of ionomers. The % neutralization method was developed internally, and it was applied to extract the experimental neutralization values with comparison to theoretical values for EMAA–Zn ionomers. The values were in good agreement with the expected neutralization levels. Chemical mapping of the acid band (C=O stretch) and carboxylate band (COO- stretch) in EMAA–Zn ionomer indicated that their distribution on a micro-scale in the selected cross-section were homogeneous. The FTIR method was also used to study EMAA copolymers neutralized by mixed metal Zn and Na cations and compare with EMAA ionomers neutralized by single metal cation. For the mixtures, a new carboxylate band appeared around 1569 cm-1, which was assigned to the COO- stretch. Based on the unique peak position, it suggests that there are interactions between the zinc and sodium cations.
Influence of Processing Parameters on Fiber Length Degradation During Injection Molding
This work is focused on investigating the influence of processing parameters on the fiber breakage in the plasticizing unit of an injection molding machine. To determine the fiber length reduction, an injection molding machine is equipped with a special cylinder which can be opened over a length of 700 millimeters. This makes it possible to measure the fiber length along the screw channel and to analyze the influence of the melting behavior. Fiber length degradation is investigated for short fiber reinforced polypropylene with different fiber fractions under the variation of the processing parameters screw speed, barrel temperature and back pressure. The results show a negative influence on the fiber length for an increase in screw speed and back pressure as well as for a reduction of the barrel temperature.
Study on the Flow-Fiber Coupling and its Influence on the Shrinkage of FRP Injection Parts
The fiber-reinforced plastics (FRP) material has been applied into industry as one of the major lightweight technologies, especially for automotive or aerospace products. The reason why fibers can enhance plastics is because of their microstructures. One of those microstructures is fiber orientation distribution. Since the fiber orientations inside plastic matrix are very complex, they are not easy to be visualized and managed. In addition, there might be some interaction between flow and fiber during the injection molding processing, but not fully understood yet. In this study, the flow-fiber coupling effect on FRP injection parts has been investigated using a geometry system with three ASTM D638 specimens. The study methods include both numerical simulation and experimental observation. Results showed that in the presence of flow-fiber coupling the melt flow front advancement presents some variation, specifically at the geometrical corners of the system. Furthermore, through the fiber orientation distribution (FOD) study, the flow-fiber coupling effect is not significantly at the near gate region (NRG). It might result from too strong shear force to hold down the appearance of the flow-fiber interaction. However, at the end of filling region (EFR), the flow-fiber coupling effect tries to diminish the flow direction orientation tensor component A11 and enhance the cross-flow orientation tensor component A22 simultaneously. It ends up with the cross-flow direction dominant at the EFR. This orientation distribution behavior variation has been verified using micro-computerized tomography (micro-CT) scan and images analysis by AVIZO software. Finally, the flow-fiber coupling effect also verified based on the tensile stress testing and the shrinkage of the injected parts through different flow domains.
Physical Analysis of Multifunctional Aerogels Made of Polymerized Silica Precursors With Stiff and Flexible Backbone
Aerogels made of polymerized silica precursors are an evolving class of porous materials with the potential to get functionalized by embedding graphene materials in their structure. Owing to their unique features they have shown promises for a wide range of applications namely electronics and biomedical devices. The mesoporous structure of these aerogels is defined during the sol-gel transition process which can be tailored by optimizing processing parameters. In this study, the main effort is to examine the comparison of the properties of the aerogels made of polymerized silica precursor with and without graphene nanoplatelets (GnP) and graphene oxide (GO).
Monitoring Degradation of Nuclear Cable Insulation Subjected To Sequential And Simultaneous Thermal
Predicting useful remaining life of cables in nuclear power plants is a topic of growing interest as plants continue to age. A typical electrical cable consists of polymeric materials, such as the cable jacket and insulation, which are susceptible to degradation due to exposure to both elevated temperatures and gamma irradiation over decades of service. In this work two insulation materials, crosslinked polyethylene (XLPE) and ethylene propylene diene (EPDM) elastomer, were characterized to quantify aging using total color difference and indenter modulus. Since the effects of thermal and gamma radiation are not additive but coupled, the effects of different aging scenarios including sequential and simultaneous aging were also evaluated. In the case of sequential aging, two aging scenarios were explored where the order in which thermal and gamma radiation received were altered. Total color difference of XLPE showed that sequentially aged insulation specimens, which received radiation first, degraded slightly more at maximum exposure than specimens which received thermal first. Similarly, in the case of EPDM, the extent of degradation evaluated using total color difference was found to be most severe in the case of sequentially aged insulation specimens which received radiation first. Indenter modulus was found to be insensitive to aging for XLPE but trended for EPDM. The largest variations were observed for the sequentially aged insulation specimens which received radiation first, similar to what was observed for total color difference.
Foam Injection Molded Lightweight PP Composite Foams Reinforced by Fibrillary PTFE With Outstanding
A facile way was reported to produce lightweight and strong foamed PP/polytetrafluoroethylene (PTFE) components. First, in-situ fibrillated PP/PTFE composites were prepared using a co-rotating twin-screw compounder. SEM analysis showed nanoscale reticular PTFE fibrils uniformly dispersed in PP matrix. DSC combined with online optical microscopy observation, and rheological analysis demonstrated PTFE fibrils pronouncedly improved crystallization and viscoelasticity, respectively. Thus, PP/PTFE foam showed obviously refined cell structure compared with PP foam. Thanks to the promoted crystallization and cellular morphology, PP/PTFE foam exhibited superior mechanical properties. PTFE fibrils facilitated to improve PP foam’s tensile strength and modulus. Therefore, lightweight and strong PP/PTFE foam, achieved by the flexible, efficient, and scale-up FIM technology, exhibits a promising prospect in applications.
Study of Mechanical and Machinability Behaviour of Natural Fibre Composites
This study aims to investigate the mechanical and machinability behaviour of three polypropylene (PP) based natural fibre reinforced composites (NFRCs) – Rice husk (RH)/PP, jute/PP and kenaf/PP composites. ASTM standards have been used to evaluate the mechanical properties of NFRCs. Scanning electron micrographs have enabled the assessment of fractured surfaces to understand the interaction at fibre/matrix interphase. Furthermore, cutting experiments have been performed to examine the machinability features concerning the surface roughness (Ra) and delamination (Fd). Among the NFRCs, kenaf/PP composites evidently displayed the best mechanical and machining performance. The generated mathematical models for predicting the machinability output responses have envisaged good accuracy.
New Concept for Melting in Single Screw Extruders
In the late 1950’s Union Carbide’s research engineer, Bruce Maddock, ran several single screw extruder experiments. He established a method to reveal the melting profile in the screw by stopping the screw at speed and quickly cooling it to freeze the polymer. Then he reheated it to create a melt film on the barrel surface so he could pull the screw out. The condition of the polymer in the screw flights was studied. This revealed what Bruce called the solid bed melting mechanism. He showed that at the end of the feed section there was a tightly packed mass of solids in the screw channel. Melting occurred at the barrel surface as the conventional transition section decreased in depth. The melt was scrapped off the screw barrel surface by the rotating screw flight which deposited it into the rear of the screw channel. Thus, the solid bed melting mechanism was discovered. This mechanism has been the basis of all screw designs since. This paper will disclose an alternate melting mechanism which does not use the solid bed theory.
Development of an Analytical Mathematical Modelling Approach for a More Precise Description of Disperse Melting
The melting behaviour in single-screw extruders is of significant importance. For a high-quality extrusion product, a completely molten and thermal homogeneous, in case of a compound or the use of fillers also uniform concentrated, polymer melt is necessary. Due to the striving for the highest possible economic efficiency of the process, screws which can achieve a higher throughput at the same extruder size through higher screw speeds are often used. In these, however, melting no longer takes place in the classical way with a subdivision into melt eddy and solid bed, as was researched in the 1950s and 1960s by MADDOCK and TADMOR and successively extended by many more. Much more the solid bed breaks up into individual solid particles due to high forces or special screw geometries introducing disperse melting. The mathematical description of this process is not as mature as that of classical melting and is therefore the subject of this paper. An analytical mathematical model is presented which allows the calculation of the temperature development in the particle and the variable melting rate in addition to the actual melting process of the disperse melting. The temperature input by dissipation as well as by barrel temperature is considered. By means of an iterative procedure, complete screw geometries can be checked for the melting behaviour. Furthermore, a statistical experimental design based on the model is used to show which factors favor or impair disperse melting.
Evaluation of the Distributive Mixing Quality Based on Particle Tracking and Delaunay Triangulation
In addition to conveying and melting, one of the core tasks of a single screw extruder is the homogenization of the material. Since conventional conveying screws in single screw extruders usually have an inadequate mixing effect, mixing elements at the end of the screw are commonly used to increase the homogenization performance. The melt homogeneity at the end of the screw is very important because it correlates strongly with the product quality and is therefore also directly related to reject rates in the production. However, characterization of the mixing quality is often very difficult because there are many degrees of freedom. In this paper, a new method for characterization of the distributive mixing quality on the basis of 3D CFD simulations is presented. In order to be able to assess the mixing quality, the particle trajectory of an initially defined particle distribution at the inlet of the flow must first be calculated with a particle tracking method. Subsequently, the homogeneity can be characterized by the change in the particle distribution at the end of the flow area. Bin counting is often used for this purpose. However, this method has considerable weaknesses, which will be shown. Consequently, a new characterization method based on the Delaunay triangulation has been developed and implemented in MATLAB. The new method will be demonstrated using selected fictitiously generated as well as simulated particle distributions of some different screw geometries.
Analysis of Leakage Flow in Pressure-Generating Melt-Conveying Zones
In many extrusion analyses, the pumping capability of the extruder screw is overestimated. This is usually due to the effect of the flight clearance being omitted in the mathematical model. The clearance between flight land and barrel surface enables the polymer melt to leak across the flights, thereby reducing the effectiveness with which the screw can pump the polymer melt forward. A few studies have proposed modifications to the widely known pumping model to account for the effect of leakage flow. While most of these consider Newtonian fluids, less attention has been directed towards shear-thinning polymer melts. We propose approximate equations to predict the flow of power-law fluids through the flight clearance of pressure-generating melt-conveying zones. Rather than correct the net material throughput of the single-screw extruder, we locally describe the two-dimensional flow between the flight tip and the barrel surface. Our novel models, which predict the flow rate and viscous dissipation, increase the understanding of the flow of shear-thinning polymer melts across the flights. Implemented in our screw calculation routine (introduced in [1-4]), they also serve as the basic equations for the network elements positioned over the screw flights.
Improved Polypropylene Thermoformability Through Polyethylene Layering
While the flow forces governing primary melt-based polymer processing techniques, such as extrusion and injection molding, have been extensively studied, characterization of forces in secondary processes such as thermoforming is limited. In this work we utilize multilayer coextrusion to create an extruded film with 100s of alternating linear low density polyethylene (LLDPE) and isotactic polypropylene (iPP) layers; and by extension, 100s of interfaces. The combination of LLDPE, iPP, and these interfaces decreases the elastic storage modulus (E’) and broadens the rubbery plateau observed via dynamic mechanical analysis (DMA). The broadening of the rubber plateau is correlated with an observed improvement in LLDPE/iPP multilayer thermoformability compared to the homopolymer LLDPE and iPP films.
Mitigating Resin Degradation Via Nitrogen Inerting for Single-Screw Extruders
Resin degradation can reduce the value of a product, especially for polyethylene (PE) films. Most of the degradation occurs in the final processing operations using single-screw extruders. There are many reasons why degradation occurs, and screw design is considered the first and best opportunity to mitigate it. The elimination of atmospheric oxygen is the next best option. This paper describes a method for mitigating resin degradation via nitrogen purging at the hopper. Extrusion data are provided that demonstrates the effectiveness of nitrogen purging for PE resins.
Experimental & Analytical Investigation of Incomplete Filling Defects During Hot Runner Based Inject
A novel processing innovation called Rheodrop technology is introduced for hot runner based injection molding. The goal is to enable both optimized processing and properties of final molded parts. The technology applies a controlled shear rate to the polymer melt during and/or in between injection molding cycles by rotating the valve pin inside a hot drop nozzle. Doing so can eliminate defects such as incomplete filling which was focused on during this study. This issue was investigated through both simulation and experimental analysis. Moldflow software was utilized to study the effect of melting temperature on cavity filling. Acrylonitrile Butadiene Styrene (ABS) was chosen as a focus material, and three different melt temperature levels were selected. The cavities are perfectly filled at the highest melt temperature level with incomplete filling resulting at the lower levels. Implementation of the Rheodrop technology then produced consistent and complete filling throughout the melt temperature range studied.
Large-scale extrusion-based 3D printing for highway culvert rehabilitation
A significant problem associated with repairing deteriorating highway culverts is the resultant lowered flow capacity. This can be mitigated by the use of culvert diffusers. Current culvert diffusers are made using fiberglass reinforced thermosetting epoxy polymers, which require custom made molds. This research work explores the use of large-scale 3D printed thermoplastic polymer composite to manufacture culvert diffusers. The research work shows that 3D printing technology reduces the manufacturing time as well as the cost of culvert diffusers. Large-scale 3D printing technology is well-suited for the manufacture of individualized culvert diffusers with unique geometrical designs without the need for molds. 3D printing technology is also capable of using different materials according to environmental requirements. The use of segmental manufacturing in conjunction with large-scale 3D printing enables the manufacturing of culvert diffusers larger than the build envelope of the 3D printer. Different post-processing techniques used for cutting, finishing, and joining the 3D printed segments are discussed.
Fused Filament Fabrication Feedstock Characterization via In-Line Rheology
An instrumented hot end has been developed to monitor the pressure in Fused Filament Fabrication, and is used as an in-line rheometer to characterize the viscosity of an acrylonitrile butadiene styrene (ABS) material. Additional analysis was performed on the transient pressure data to consider compressibility effects and nozzle drool. The range of flow rates was identified at which the pressure in the hot end was most stable. Stabilization time given compressibility effects was also evaluated.
Investigation and Realization of Watertight FDM Structures Made of Ultem 9085 in Pressurized Systems
Fused Deposition Modeling (FDM) parts generally show a fluid permeability due to their specific and characteristic strand structure. Therefore, an application including contact with water is difficult and limits the areas of application of this Additive Manufacturing (AM) technology. In this paper the aim is to determine the water tightness of FDM manufactured Ultem 9085 structures in a pressurized system using a suitable test setup. Based on the results, optimization approaches such as parameter modification, variation of the specific part thickness and a surface treatment shall identify if a complete tightness can be realized. For the validation of the results, analysis methods such as CT-scans and macroscopic images are used to determine the component surface.
Effect of Carbon Fiber On the Fracture Toughness of Fused Filament Fabricated CF/ABS Composites
This study reports the effect of carbon fiber (CF) on the fracture toughness of 3D printed carbon fiber/ acrylonitrile butadiene styrene (CF/ABS) composites. Chopped carbon fiber was compounded with ABS to prepare CF/ABS filaments containing 0-25 wt.% CF. Compact tension specimens were designed, 3D printed, and tested to measure the composites’ mode-I fracture toughness, KIc. The results showed CF/ABS composites can be made with up to 25 wt.% loading without any drop in their fracture toughness. In fact, ABS’s KIc increased by ~22% with an introduction of 10 wt.% CF. There was a slight drop in KIc, once the CF content was increased to 15 wt.%. Further increase in CF content from 15 to 25 wt.% did not cause any significant change in KIc and it was found to remain similar to that of the neat ABS. The fracture toughness trend with CF content was qualitatively explained in terms of two competing mechanisms, namely increased actual fracture surface area and less perfect interlayer adhesion at the presence of CFs.
Simulative Analysis of the Filling Process in the Two-Component-GITBlow-Process on Organo Sheets
The combination of different special processes allows the production of complex hybrid component structures with simultaneous function integration, thus opening up a large portfolio of possibilities. One example of this is the combination of back-injection of thermoformed organo sheets with the GITBlow process. An organo sheet is back-injected by two components, whereby one of the two components is additionally formed by the GITBlow process. The separation of the two cavities during the filling process by the formed organo sheet is a challenge not to be underestimated. The investigations refer to the simulative analysis of the filling process of the cavities. Here, the melt displacement into the secondary cavity during the first gas injection and the influence of the separation of the two cavities are considered. Investigations show that the melt temperature, the gas pressure and the injection speed have the greatest influence on the filling of the cavity separation.
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