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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Simulation of Co-Rotating Fully Intermeshing Twin-Screw Compounding Extruders: Alternatives for Process Design
The co-rotating fully intermeshing twin-screw extruder is the primary production unit for compounding polymer based materials. It also has had a long term presence in processing material in the chemical and food industry and more recently in pharmaceuticals. The layout of a co-rotating twin-screw compounder for a specific processing task is primarily based on 1) the experience of the process development engineer and 2) tests run on a lab-scale unit. Additionally, scale-up to a much larger extruder is very often required as part of the development process. Traditionally this scale up has been based on experience and classical scale-up rules.
In addition to experience and lab tests, good simulation software can help guide the development engineer in the design of initial compounding extruder configuration as well as scale-up to a commercial unit. The overall objective being to minimize risk (cost). Know-how based on experience, trials in the laboratory, production and simulation software are the preferred combination for the layout of an extrusion process.
A New Evolution Equation for Polymer Coils with Non-Affine Rotation
When applied to shear flow, Maxwell-type constitutive models typically over-predict shear thinning. For many known models such as the Leonov model, the slope of the viscosity vs. shear rate plot in log-log scales converges to -1 at high shear rate. This is not realistic for polymer melts and concentrated solutions. In this work, rotational retardation is introduced to the evolution equation so that rotational ‘softening’ can be better controlled in rotational flow such as shear flow. The new evolution equation involves a new parameter n to control the affine advection of rotation so as to adjust the degree of shear thinning or thickening. In combination with finite stretch, a five-parameter nonlinear viscoelastic fluid model is proposed. The resulting constitutive model is suitable to describe the deformation of polymer coils and demonstrates excellent data fitting capability to realistic rheological data for both shear and extension.
Solid-State Foaming of Polylactic Acid-Hexagonal Boron Nitride Composites to Fabricate Thermally Conductive Foams
Micro-and-nano-electronic devices are prompting for new demands in light-weight and flexible multifunctional materials, including those for thermal management applications. In this context, this study presents a new industrial viable processing strategy to develop and fabricate light-weight thermally conductive polymer composites, through physical foaming, with reduced filler loadings. While foams are known for their good thermal insulating properties, experimental results revealed that foaming-induced filler reorientation would help to partially compensate the negative impact made by the voids on the composite’s effective thermal conductivity (keff). As a case example, thermally conductive PLA-hBN composite foams were fabricated by solid-state carbon dioxide foaming. With a filler loading of as little as 10 vol.%, the PLA-hBN composite foam’s keff was about 3.5 times higher than that of neat PLA.
Electrical Conductivity and Humidity Sensing Properties of PVA/CNT Nanocomposites
In this study, multi-walled carbon nanotubes (MWCNT)/polyvinyl alcohol (PVA) nanocomposite films were fabricated and characterized. The effect of MWCNT loadings in the insulating PVA matrix and the influence of relative humidity on the electrical conductivity of the nanocomposite were investigated. The results of different measuring techniques were also characterized and compared together. Experimental results of this research revealed that the electrical conductivity of 1 wt.% MWCNT/PVA nanocomposites increases up to six orders of magnitude by increasing the relative humidity from 0 to 80 percent. This characteristic demonstrates the potential of using MWCNT/PVA nanocomposite thin films in moisture sensing applications.
Accounting for Pressure Dependent and Elongational Viscosities to Improve Injection Pressure Predictions in Mold Filling Analysis
The increasing demand for shorter product development timelines and more robust plastic part designs has made injection-molding simulation a critical tool for plastic part and mold designers. One of the most common objectives of injection-molding simulation is determining the pressure requirement to manufacture the part for a given resin and set of process parameters. The reliability of injection-pressure prediction is dependent on many factors including accurately modeling the part and mold geometries, and predicting the material behavior during this dynamic process. While advancements have been made with regards to improving the ability to properly represent the mold and plastic part geometries, the ability to adequately model the molten polymer behavior remains a difficult task. Of particular importance is the ability to properly characterize the material viscosity during the injection molding process. The ability to account for the effects of pressure and elongation deformation on the material viscosity is critical for providing reliable injection pressure predictions. This paper will present the results of an experimental validation study in which the effect of accounting for the pressure dependence and elongation deformation on the material viscosity influences the injection pressure predictions.
Fast Prediction of Crystallinity in Injection Molding during the Packing Stage
Being able to predict products’ degrees of crystallinity, and thereby optimize their crystallization processes, is of great significance for producing high quality polymeric products in injection molding. Injection molding simulation software can simulate polymers’ density results during the packing stage, and these predicted density results can be used to calculate polymers’ crystallinity results. Based on this idea, a novel method was proposed to predict the degree of crystallinity for polymers during the packing stage. For this method, pressure and temperature results were first simulated using injection molding simulation software, and then the density results were calculated based on a pressure–volume–temperature (PVT) model. Next, the crystallinity results were solved according to the densities of the fully crystalline part and the purely amorphous part. Finally, a real part in production was conducted as a case study to verify the proposed crystallinity prediction method. Experimental results showed that the proposed method was both correct and effective.
Automotive Glazing – Polymeric Systems Providing Enhanced Design Freedom and Functionality
Automotive glazing using engineering thermoplastics (ETP) is an area of immense interest for the automotive industry as it provides unique opportunity to redefine the overall appearance and styling of the vehicle in addition to light weighting. Typical transparent parts seen on a car such as the side moving windows, rear windshield, rear quarter windows (RQWs), panoramic sunroof and the lift-gate (or tailgate) are traditionally made of tempered or laminated glass. Use of ETP materials that are transparent like polycarbonate (PC) can offer comparable functional performances at reduced system cost in addition to significant weight reduction. Such parts made of PC are virtually unbreakable, have good weatherability and scratch resistance imparted through proprietary surface coating technology. The advanced molding process used to manufacture such large transparent part is termed as 2-shot injection-compression colding (2K-ICM). This paper focuses on identifying the critical molding process variables and capturing their effect on the final part quality. The emphasis is on minimizing the combined part warpage and maintaining lower levels of residual stress in the part. By performing a simulation-based design-of-experiments (DOE) study, the relationship between the process parameters on the part warpage is elucidated. Finally, through a regression analysis, an estimate of the warpage is made using the mathematical model.
Study on Fabrication of CNT-Based Conductive Products via Melt Differential 3D Printer
Circuit and anti-electrostatic products via 3D printing technology exhibit unparalleled advantages over other manufacturing technologies, because it can precisely control the shape of the path and structure. The existing FDM device has a flexible buckling failure phenomenon, difficult to fabricate elastomers and other soft products. A new polymer melt differential 3D printing device was designed in this paper, and the experimental research of printing conductive products with polylacide (PLA)/ carbon nano tube (CNT) composites was made. The result showed that the conductivity of the composites can reach to 1.6 S/cm (10wt%CNT) and the composites also possesses excellent printing performance. Polymer melt differential 3D printer was used to fabricate the conductive circuits with the substrate of paper, the composite circuit has strong interface bonding force with the substrate. Then the anti-static shell of the designed pattern with multilayers were printed, the SEM images show that the shaping precision and bonding between the layers are to meet the practical requirements. The results show that the polymer melt differential 3D printer can be satisfied to printing conductive PLA/CNT composites products, which can provide the theoretical basis and technical guidance for the accurate printing of circuit and anti-electrostatic products.
Preliminary Study of Changeover Time in a Twin-Screw Extruder
Changeover times differ from ‘pulsed’ tracer residence time distributions in that the starting and ending materials may have different viscosities, densities, and processing properties. Changeover times for twin-screw extruders are relatively unstudied, yet have far-reaching impacts for transient operations in the polymer processing industry. In this work, we examine the changeover of polyethylene and polystyrene in a twin-screw extruder using an online Raman detector. The detected changeover times were generally longer than the residence times found for analogous ‘pulsed’ experiments. Viscosity ratio (between ending and starting materials) and throughput have a significant effect on changeover time, whereas screw speed does not.
Farmlands for Plastics, Textiles, Dyes or Food: Are Bio-Based Materials Really Sustainable?
This presentation aims to contribute to an honest dialog on sustainability of oil-based vs bio-based materials in a consumer context that often includes significant “greenwashing” based on misinformation. This consumer context has raised consumers’ expectations and has put undue burden on many industries and in particular on the plastic and textile industries. Textile companies have tried to find a niche or “green” appeal in this increasingly competitive market; therefore, some are using labels such as “Sustainable”, “Eco-friendly”, “Eco-fashions” etc. As a result of high competition and low margin of profit, some companies have adapted practices such as creative marking and creative reporting/labeling that makes the consumer feel good about a “sustainable” choice, while the carbon footprint, or overall environmental impact, of the products or their production processes on the environment is not significantly better, and in some cases is even worse, than the alternative. Therefore, consumers either have false assumptions about the products they purchase, or are receiving conflicting information and are confused. Consumers are not the only ones that are confused; some members of industry have a hard time sorting out information on sustainability and, in turn, making decisions about where to invest their resources to create more sustainable products. This presentation will attempt to shed some light on these issues and raise some serious questions.
Fire Survival Cable: Understanding of Lab Scale to Manufacturing Scale Cable Validation
In order to successfully develop fire survival cable products it is important to have a good understanding of the relationship between lab scale material development testing and production-scale cable capability. Research and development work on fire survival cables has been active for more than a decade and today many commercial products exist in the market for these applications. However each fire survival cable design, application type and testing protocol is designed to be different to meet specific regional standards and customer requirements. In this work, we have demonstrated lab scale understanding of ceramic formation in silicone compounds and translated to large scale IEC 60331- 21 fire survival cable test validation, while also meeting other electrical, mechanical and heat ageing requirements.
Investigation on Warpage and Sink Mark for Injection Moulded Parts Using Taguchi Method
Injection molding is a complex process for many production engineers as it involves selection of many process parameters to produce quality products to meet customer requirements. Determination of the optimal process parameters in injection moulding is an important design task as it influences part quality, production rate, and production cost and energy consumption. The purpose of this paper is to investigate the effect of selected process parameters in injection moulding on part quality. The paper applies Taguchi’s parametric design and analysis of variance (ANOVA) technique to study the effect of process settings of plastic injection molding on part quality. Experimental data are used to identify the relationship between the injection molding process parameters and product quality. Mold surface temperature, melt temperature, mold open time and ejection temperature are selected as the process control parameters. Warpage and sink mark depth are selected as the multi-product quality characteristics.
Using Infrared Temperature Sensors to Study Temperature Changes of PVC during Flow with the Incorporation of Melt Rotation Technology
Infrared temperature sensors were used to study the effect of mold rotation technology on the plastic melt temperature and shear-burning that commonly occurs with PVC. Inserts were designed and built so that areas of high shear could be introduced during flow through a runner, as well as provide for the incorporation of melt rotation technology. A DOE was used to investigate how factors such as melt temperature, residence time, injection rate, and packing rate affected the temperature at various points along the flow path. It was found that the use of melt rotation technology could allow more uniform temperatures after the point of rotation without causing a larger problem with shear-burning.
Interlaminar Fracture Toughness of Woven Glass Fiber-Epoxy Laminates with Carbon Nanotube Buckypapers
In this paper we present the potential of applying buckypapers (BP) films for the improvement of the interlaminar fracture toughness of laminated composites. We experimentally investigated the effect of interposing BP between plies on the interlaminar fracture behavior of glass fiber / epoxy woven fabric composite laminates. Crack propagation was examined during mode I - fracture testing using double cantilever beam (DCB) specimens prepared with different types of BP placed at the midplane.
While lower fracture toughness values were determined when using BP prepared with untreated carbon nanotubes (CNT) and graphene nanoplatelets (GNP) - CNT/GNP – (hybrid filler at a weight ratio CNT/GNP=80/20), a slight increase in toughness was observed employing BP prepared with oxidized CNT (CNT-ox). Morphological analysis of the fracture surfaces indicated that this increase in toughness was related to fracture phenomena that were enabled by the presence of BP film. Cohesive failure of the BP film and fiber bridging positively contributed to the increase in toughness observed in the case of composites reinforced with BP-CNT-ox.
The adhesive failure mode of BP-CNT/GNP was different from the cohesive mode characteristic of BPCNT- ox, indicating the importance of promoting cohesive failure of the BP, as it enables a more effective energy dissipation mechanism.
Thermoplastic Polyurethane Chitosan / Cellulose Nanocrystals Composites for Wound Healing Applications
This research is concerned with creating an antibacterial wound dressing material by introducing naturally-derived chitosan into thermoplastic polyurethane (TPU) matrix. Chitosan is a promising filler to improve the antibacterial properties of wound dressing materials including TPU. A combination of chitosan with cellulose nano-crystals (CNCs) can help meeting the mechanical design requirements of wound dressing applications. TPU nanocomposites modified with CNCs were prepared by using an optimized solution casting method. Morphological analysis carried out through scanning electron microscopy (SEM) showed that CNCs are well distributed within the matrix up to a filler amount of 2wt%. Thermal analyses indicated that the incorporation of nanofillers leads to significant changes in the glass transition temperature and melting behavior characteristic of the hard segments. Rheological analyses performed on molten TPU incorporating CNCs indicated that the presence of the filler favors shear-thinning behavior.
TPU films containing a combination of CNCs and chitosan were made through a solvent exchange method and solution casting. Current investigations are focused on the characterization of the mechanical properties, water absorption behavior and water-responsive mechanically adaptive properties of the hybrid TPU-CNC-chitosan composites.
Effect of Degradation Caused by Water Absorption on Mechanical Properties of Injection-Molded Glass Fiber Reinforced Polypropylene
Injection molded glass fiber reinforced polypropylene (GFPP) was immerged into hot water and its bending test was carried out to study about degradation of GFPP caused by water absorption. Although the water absorption of GFPP is low (about 0.2 wt%), it shows obvious decrease both in flexural modulus and flexural strength. Flexural strength decreases with the immersion time continuously, while flexural modulus shows rapid decrease during early period of immersion and then become constant. Another experiment in which the specimens were dried after immersion shows the flexural modulus after the early drop correlates with amount of water absorption and recovers by drying to the same level of immersed samples having the same amount of water absorption. That indicates there are different mechanisms while flexural strength decreases as a result of some irreversible degradation during water immersion, flexural modulus is just due to a reversible swelling by water absorption. And the rapid drop of modulus seems to be not caused by water absorption but by heat.
Improving PLA-based Material for FDM 3D-Printers Using Minerals (Principles and Method Development)
A method has been developed to study the performance and suitability of thermoplastic polymeric material for Additive Manufacturing (3D-printing) based on Fused Deposition Modeling (FDM). The method has been used to study the benefits of minerals for PLA-based material (filaments) that are commonly used in FDM 3D-printing. An optimized formulation has been presented that enhances the printing performance and print quality, reduces warpage and curling of the edges, and allows 3D-printed PLA objects to be annealed while maintaining their original shape and dimensions. The annealed PLA objects show significantly improved heat/temperature resistance and can withstand temperatures as high as 120ºC.
Development of Predictive and semi-gSEM Models of Backsheet Degradation under Multifactor Accelerated Weathering Exposure
Poly(ethylene terephthalate) (PET), with its high dielectric breakdown strength, is widely used in multilayer PV module backsheets as a core layer. However, it degrades due to ultraviolet light and humidity. Failures such as cracking and delamination in backsheets caused by weather-induced degradation may result not only in performance loss of the modules, but also loss of electrical insulation, which is a safety concern. Degradation of different grades of PET and two types of backsheets were studied and modeled under multi-factor accelerated weathering exposures. The formation of light absorbing chromophores, changes in the fundamental absorption edge of the polymers, and UV stabilizer bleaching were confirmed through UV-Vis optical spectroscopy. FTIR-ATR analysis showed that chain scission is the common mechanism under all exposure conditions. The degradation mechanisms determined from optical and chemical evaluations were then used to construct a set of degradation-pathway network models using semi-gSEM (semi-supervised generalized structural equation modeling) methodology using a
Soy Protein Isolate Films with Improved Mechanical Properties via Bio-Based Dialdehydecarboxymethyl Cellulose Crosslinking
Glycerol-plasticized soy protein isolate (SPI) films with dialdehyde carboxymethyl cellulose (DCMC) as crosslinking agent were solvent casted and tested for their mechanical properties. Results indicate that the addition of DCMC increased tensile strength (TS) up to 218%, suggesting effective crosslinking between SPI and DCMC. The significant improvements in the TS compared to other dialdehyde polysaccharide crosslinking agents such as the dialdehyde starch is due to higher compatibility of DCMC with SPI, which was confirmed by SEM imaging. Furthermore, based on stress-strain features, a hypothetical mechanism was proposed to illustrate the effect of the polymeric cross-linking agent.
Evaluation of Methodoligies Utilized to Determine the Pressure Drop throughout an Injection Mold
Two of the most common industry methods for evaluating the pressure drop through an injection mold during mold filling are investigated against an instrumented mold. The first is injection molding simulation and the second is the shop floor applied “Pressure Drop (Loss)” study method that is widely accepted as part of modern injection molding practices. The study finds that the shop floor method can significantly misrepresent the relative pressure developed through progressive regions of a mold. Injection molding simulation was found to provide a better agreement with the actual measured mold filling pressures.
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