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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Optimizing Mechanical Behavior of Basalt-Natural Fiber Hybrid Injection Molded Composites
Environmental consciousness is driving modern research and development in the automotive sector to target the advancement of feasible green materials in automotive applications. Basalt fiber has shown to be a robust competitor against glass and carbon fiber and is more eco-friendly manufacturing processes. Reinforcing polypropylene with basalt fiber and hemp hurd using maleic anhydride-grafted polypropylene (MAPP) as a coupling agent, has shown to contain similar mechanical properties to its competitors. A mixture model was implemented to optimize the mechanical properties of a variation of fiber ratios and MAPP to compare against a controlled GF mixture. Scanning Electron Microscope (SEM) analysis of fracture surfaces show the variation in fiber–matrix adhesion based on addition of MAPP. This study concludes that the addition of MAPP improves the mechanical behaviors of hybrid composites made from basalt fiber and hemp hurd reinforced polypropylene.
Biocarbon Hybrid Composites for High-Temperature Automotive Applications
Automotive manufacturers have been increasing use of natural fiber composites to reduce vehicle weight and respond to consumer demand for environmentally friendly products. However, the low thermal stability of natural fibers can limit their use to low-processing-temperature polymers and low-temperature automotive environments. Pyrolysis of biomass results in the formation of a porous substance called biocarbon, which can improve composite thermal performance, eliminate odor, and reduce hydrophilicity. The objective of this study was to investigate the effects of biocarbon on the performance of biocarbon-glass fiber hybrid composites for use in under-the-hood automotive applications. This study evaluated the macroscopic (mechanical performance, density) and microscopic (SEM) characteristics of biocarbon-hybrid composites with varying loading level and biocarbon type. Biocarbon-hybrid composites were approximately 10-13% lighter than currently used fan-and-shroud materials and the addition of biocarbon content improved composite flexural strength & modulus.
Multi-Scale Modeling of the Replication of Submicron-Structures by Micro Injection Molding
The replication accuracy of submicron surface structures by micro injection molding control the replicated part functionalities, such as tissue engineering. In this work, we propose a multi-scale model for the replication quality of laser-induced periodic surface structures by micro injection molding of different bio-based polymers. The model decouples the macro cavity flow, investigated through a numerical simulation, from the micron-scale flow, that is modeled with a novel analytical approach. The macro model determines the boundary conditions for the filling of the sub-micron surface structures. An in-depth characterization of the mold topography of the polymer thermal, rheological, and wetting properties was carried out to feed the model. Injection molding tests were performed, varying the mold temperature to manufacture sub-micro textured parts for the model validation. The sensitivity of the replication accuracy to mold temperature and polymer selection was captured. The multi-scale model showed a maximum deviation of 8% from the experimental results.
Water Absorption Behavior of Recycled PP and PA6 Composites with Fiber Reinforcement
The recyclability of natural fiber and glass fiber reinforced polypropylene composites and glass fiber reinforced nylon composites have been studied through injection molding and mechanical grinding. Mechanical properties of virgin and recycled composites were assessed through flexural, tensile, and impact tests. No significant degradation in the mechanical properties of natural fiber composites was observed after subjecting the composites through several rounds of recycling and water absorption at ambient temperature in tap water. However, severe degradation in the mechanical properties was observed for glass fiber composites. For instance, after five cycles of recycling, only 59% of flexural strength and 64% of flexural modulus was retained for glass fiber reinforced nylon composite. This is mainly due to severe attrition in glass fibers caused by recycling as evidenced by studies on fiber length distribution. Water absorption tests conducted at room temperature and subsequent environmental conditionings such as freeze-thaw cycling and extended freeze cycling only affected nylon composites. At saturation point, water absorption for nylon composites was 7.7% by wt. after 45 days of immersion, which significantly affected the mechanical properties. The tensile strength of the nylon composites reduced from 88.4 MPa to 36.2 MPa, and modulus reduced from 5.6 GPa to 1.8 GPa after saturation.
Thermal and Mechanical Techniques for Troubleshooting Polylactic Acid Processing Issues
This paper describes the use of differential scanning calorimetry (DSC), modulated DSC, and dynamic mechanical analysis to characterize different regions of thermoformed beverage cups made from polylactic acid. These techniques demonstrated the differences in crystallinity and mechanical strength of the cup based on the location of the specimen. These techniques can guide the processor in resin selection and processing conditions.
The Study on Replacement of Steel Cord Reinforcements by Synthetic Fibers in Composite Materials
The emergence of new composite materials as replacements for metals has been demonstrated in many studies. Many products derived from steel-reinforced composite materials can potentially be modified by replacing the existing steel cord reinforcement with that of synthetic fibers such as carbon to overcome the problems involving dimension instability and the effect of creep which could pose problems in applications such as belts driving heavy machinery. In the present study, Carbon fiber reinforced in the TPU matrix was manufactured by compression molding and was tested for dynamic mechanical and tensile analysis. The results obtained with carbon/TPU are positive with respect to steel/TPU composites which proves that the carbon fibers can be a suitable replacement to the steel cords that are used in applications such as conveyor belts for providing the required tensile strength and creep resistance.
Method to Evaluate Shrink Film Material Properties
Understanding heat shrink film properties and behavior will help optimize shrink wrap formation in packaging applications. Two experiments were conducted to better understand shrink properties of PE film. The first experiment was to collect data on film shrink ratios. The second experiment was an attempt to compare film preshrunk and post-shrunk mechanical properties. For this, a fixture was developed to quantify film shrink under isothermal heating. The film submersion tool successfully yielded films that were shrunk at different temperatures and demonstrated a method applicable for analyzing properties of heat shrink film at various stages of the shrinking process. Further work is focused at developing correlations between preshrunk properties to post-shrunk properties.
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.
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