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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Rotational Molding of Linear Low Density Polyethylene with Different Concentrations of Ground Tire Rubber
In this work, ground tire rubber (GTR) was dryblended with linear low density polyethylene (LLDPE) to produce thermoplastic elastomer parts by rotational molding. In particular, different GTR concentrations (0, 5, 10, 15, 20, 25, 30, 35, 40, 45 and 50% wt.) were incorporated to determine the effect of the rubber phase on the processability and overall properties of the parts. Each composition was characterized in terms of morphology and mechanical properties (tensile, flexural and impact). The results show that the addition of the rubber phase decreased the tensile and flexural moduli and strengths, but the tensile elongation at break was always above 100%. This good elasticity produced impact strengths higher than the neat matrix with an optimum GTR content around 20% wt.
Low Density Open Cell Flexible Foams with High Tortuosities and Mechanical Properties Highly Dependent on the Strain Rate
This paper describes the mechanical behavior in compression, at both low and high strain rates, of several low density open cell polyolefin cellular materials with different gas phase tortuosity of the cellular structure. Due to the high tortuosity of some of the polyolefin foams under study they have a mechanical behavior similar to that of open cell polyurethane foams at low strain rates (i.e. they could be used for comfort applications) and they have a similar mechanical behavior to that of closed cell polyolefin foams at high strain rates (i.e. they could be used in body protection applications). Therefore, these new materials with high tortuosities have an unique mechanical performance strongly influence by the strain rate.
Analyzing the Viscous Dissipation of a Two-Dimensional Flow of Non-Newtonian Fluids in Single Screw Extruders
For modeling the flow of non-Newtonian polymer melts in single screw extruders numerical methods are required in general. In this study the viscous dissipation and the conveying characteristics in the melt channel of single screw extruders are analyzed for a two-dimensional, fully developed flow of power law fluids. Therefore three different numerical methods are presented and the results are compared. Furthermore, a comprehensive parametric design study is shown, analyzing the viscous dissipation depending on three independent parameters: (i) pitch to diameter ratio, (ii) power law exponent, and (iii) dimensionless pressure gradient. The derived results for the viscous dissipation can be used to calculate the mean melt temperature profile more precisely.
In-Situ Visualization and Cell Growth Modeling in a Polymeric Foaming Process
In this paper, we consider a two-dimensional model of the foam nucleation process of CO2 in polystyrene (PS) matrix by random initiation of growing bubbles in time and space. The model was extended to account for the simultaneous cell nucleation, growth, and collapse processes of the foaming bubbles at two different viscosities of PS resins. By means of connection among neighboring bubbles, secondary nucleation behaviors emerged from a multi-bubble system were attempted in simulations. The resulting cell size distribution (CSD) of bubbles shows power law behaviors for both simulations and experiments. The cell size distribution and morphologies obtained from the numerical simulation agreed with the snapshot pictures of the experiments qualitatively and quantitatively. Finally, different nucleation and growing rates were investigated to understand the relationship between the bubble nucleation /growth and final morphology of the foam structure. Potential applications lie in the analysis of the resulting micro-/nano-cellular structures due to secondary nucleation and the foam stabilization.
The Adhesion of LSR Thermoplastic Composites after Storage Tests
The adhesion properties of liquid silicone rubber (LSR) and different thermoplastics (PC, PA, and PP) were examined in this investigation. In order to guarantee the adhesion of both components, an activation (silicatization) of the TP surface, which is a conventional method, was carried out. Furthermore, the long-term stability of the silicatization (storage of the activated surfaces) as well as the wetting behavior were investigated. Moreover, microscopic investigations were performed to analyze the activated thermoplastic surfaces. The test specimens were produced on a 2-component injection molding machine. In accordance with the guideline VDI 2019, the peeling resistance was determined and the results were compared.
Characterization of Developed Hybrid Moldings by Textile and Short Fiber Reinforced Composites
Advanced material is developed by using continuous fiber reinforcement to achieve higher strength than can be obtained with injected composite material. High forming performance has been achieved by using the cloth-like textile fabric material, made from combined filament yarn. By applying the developed textile composite, parts can be molded with deep drawing and complex shapes with ribs. Moreover, high weld strength has been achieved between the materials of compression molded textile composite and injection molded short fiber reinforced material in hybrid molding.
Effect of Die Design on Liquid-Liquid Mixing in Polymer Based Additive Manufacturing
Incorporating liquid fillers in additive manufacturing processes can produce liquid-filled solid parts with unique properties. To develop this, the behavior of immiscible droplets in a polymer matrix subject to different kinds of flows is explored. Castor oil droplets, with a range of capillary numbers much higher than the critical capillary number, were injected in a matrix of Silicone oil and subjected to flows within a converging channel. The rate of change of capillary number as the droplet moves down the channel was measured to illuminate the effect of the die design. The affine state was not reached when the droplets were deployed in the center but was achieved when injected in an offset position. This data is valuable to understand the effect of the die on the deformation induced on immiscible droplets and is one of the preliminary steps to incorporate liquids in additive manufacturing.
Utilizing Dynamic Hold Capability of Servo-Driven Ultrasonic Welders in Studying Cooling Phase of the Ultrasonic Welding Process
Ultrasonic welding of thermoplastics is widely used by many industries to fuse together two parts in a short time without introducing additional consumables such as fasteners, adhesives, or solvents. The recent development of servo-driven ultrasonic welders, as opposed to pneumatically driven welding machines, introduces unique levels of control throughout the welding cycle. This study focuses on the final phase of the welding process, i.e., the hold cycle, and the benefits that the servo-driven ultrasonic welders can provide to this final phase by controlling both hold distance and the velocity at which this final phase is accomplished.
Micropelletization of Virgin and Recycled Thermoplastic Materials
Traditional polymer powder and micropellet based processes, such as powder bed fusion and rotational molding, have been in increased demand in modern processing industries. These processes require polymer powders and micropellets with a small particle size, narrow size distribution and defined geometry for a variety of polymer resins. Therefore, micropelletization technologies, where particles in the size range of 50 to 1000 µm are generated, have been attracting growing attention over the past decade. A new technique, developed at the Polymer Engineering Center, yields micropellets with a controlled morphology and narrow particle size distribution. In this process, a polymer melt is extruded through a capillary and is subsequently stretched with a hot air stream until flow instabilities cause it to break up into particles. Small changes in process conditions result in different size distributions and particle shapes, such as lentil-like pellets, fibers and thread segments. This work shows how material properties and processing parameters influence the produced micropellets. Besides the processing of virgin thermoplastic material, recycled high density polyethylene flakes are used as feedstock for the micropelletization process in order to show the capability of this process to contribute to current polymer recycling efforts.
Effect of Pre-Cross-Linking on Mechanical and Rheological Properties of Solid Silicone Rubber and its Processability in Extrusion Blow Molding
The blow molding process offers the possibility of reproducible, fully automatic and therefore cost-efficient mass production of complex hollow bodies. Due to the poor mechanical properties of uncured rubber, it has not yet been used for the manufacturing of elastomeric hollow parts. In this contribution, it is shown that with a defined pre-cross-linking of solid silicone rubber the blow molding of the material is possible. With pre-cross-linking the mechanical material properties can be adjusted precisely. This allows parison extrusion without strong drawdown. During the forming, it provides the necessary elasticity while maintaining the weldability and formability of the material. But pre-crosslinking also influences the materials rheological properties. Preliminary investigations showed pre-crosslinking has to take place in the blowing head bevor the material leaves the die. Therefore, changes in rheological material behavior are investigated and considered for the flow channel design. It is shown that the pre-cross-linking allows the blow molding of elastomeric hollow bodies with a surface stretch ratio of 3.6 to 1. However, precross- linking can also lead to flow instabilities such as wall slippage and melt fracture.
Influences on the Flow Behaviour of Phenolic Molding Com-Pounds Measured in Continuous Kneaders
Due to their complex flow and curing behavior the quality of parts made from thermosetting molding compounds depends to a high degree on the reactive and viscous characteristics during their processing. In the presented studies a continuous kneader was used to investigate how those characteristics depend on the filler content of the fluid molding compound, the grain size distribution and the present material humidity. Therefore, the grain size of different batches of three thermosetting molding com-pounds was examined, they were purposefully impinged with high air moisture and their flow resistance was measured using various kneader temperatures. The results display a strong dependence of the flow resistance on the filler content, the respective composition of the molding compound and the water content within the material. They will be discussed and interpreted according to their influences within the injection molding process.
Determination of Pressure Correlation Factors to Improve the Quality of Injection Molding Simulations
Injection molding simulation is taking an increasingly important part in the development of new plastic components and in tool and mold making. However, in particular, the results of the filling pressure simulation frequently deviate from the filling pressures occurring in the injection molding process, so that injection molding tools are often oversized and too large injection molding machines are used for serial production in order to ensure the complete filling of the component cavity. The aim of this paper is therefore to define a correction factor which can be used to infer the pressure losses of an injection molding simulation to the real pressure loss that occurs in the injection molding process, the under- or over-dimensioning of injection molding tools and the use of injection molding machines which are too large or too small to avoid. For this purpose, a correction factor has been defined which consists of three individual correction factors, each taking account of the influence of the material used, the influence of the injection molding machine used and the influence of the component geometry to be produced. In addition, an addendum has been defined which maps the pressure loss of the screw of the injection molding machine used. The tests were carried out with five plastics: polypropylene (PP), acrylonitrile-butadiene-styrene (ABS), a blend of acrylonitrile-butadiene-styrene and polycarbonate (PC/ABS), polycarbonate (PC) and polyamide 66 (PA 66). Four factors from the control variables were defined and their influence on the injection molding process was systematically investigated using the means of statistical experimental planning. These factors are the melt temperature of the plastic, the coolant temperature, the injection speed, and the residual cooling time. Factor levels have been defined in order to examine the effects in a defined process window.
Cell Nucleation in High-Pressure Foam Injection Molding of Semicrystalline Polymers
We investigated the solidification behavior and foaming behavior of a grade polypropylene in high-pressure foam injection molding process by means of an in-situ mold visualization technique. We observed that the solidification behavior of polypropylene had a clear influence on the cell nucleation and on the final cellular morphology of the foam injection molded parts. By adjusting the processing condition, we could control the sequence of the cell nucleation and melt solidification such that either would occur earlier, influencing the final cell morphology and structure.
Preventing Failures in Elastomeric Resistance Bands
The failure of an elastomeric resistance band used in performing physical exercises can often result in human injury. This paper investigates the cause(s) of failure and attempts to identify designs, materials, and manufacturing methods that can prevent failures in elastomeric resistance bands. This paper discusses three separate failure analysis case studies involving elastomeric resistance bands to identify failure modes. It also provides evaluation of six different elastomeric resistance bands to identify design, manufacturing, and material characteristics that are important in prevention of elastomeric resistance band failures.
Effect of MnO2 Nanowire on Rheological and Dielectric Properties of PVDF/CNT Hybrid Nanocomposites
Poly (vinylidene fluoride) (PVDF) matrix hybrid nanocomposites incorporating MnO2 nanowire (MnO2NW) and Carbon nanotubes (CNT), were fabricated by melt mixing in a batch mixer followed by hot pressing. Dielectric properties of fabricated nanocomposites were studied in X-band frequency (8.2-12.4GHz). The conductive CNT increased the dielectric permittivity of the PVDF by serving as a nanocapacitor. Increasing CNT loading enhanced dielectric loss due to the formation of a conductive network. Adding MnO2NW increased the dielectric permittivity while decreasing dielectric loss. Rheology coupled with dielectric properties and electrical conductivity measurements of the nanocomposites showed the effect of MnO2NW, as secondary nanofillers, on the CNT percolative network. We attribute the superior dielectric properties of the hybrid nanocomposites to the role of MnO2NW on improving the dispersion state of CNT (confirmed by rheology) and also its barrier role on hindering the CNT network formation.
Confinement Effects on Molecular Orientation in Multilayer Films of Low Molecular Weight Polypropylene
Attributed to the confinement effect and unique properties, multilayer nanostructures have attracted extensive attention. Coarse-grained molecular dynamics simulations were carried out to understand the interfacial microstructure and mechanical properties of multilayer low molecular weight polypropylene (PP) films by comparison with those of the corresponding bulk material. The molecular order parameter, radius of gyration and end-to-end distance of the chains were calculated. Out of surprise, in the multilayer PP films, the confinement effects make the polymer chains at the interfaces keep being highly ordered, extended and perpendicular to the normal of the interfaces, and those in the layer keep unordered and shrunk, with little interlayer interpenetration. However, for their bulk material, all polymer chains are in the state of being highly extended, ordered, and crystallized. These results are distinct from those of general flexible linear polymers. We found that the dependence of the tensile strength of the multilayer PP film on the degree of interfacial integration between the layers is weak. The distinction of the microstructure between the multilayer films and its bulk material is a critical factor that influences the fracture behavior of material. These findings would give rise to better understandings about the mechanical properties and crystalline behaviors of the multilayer polymer films.
Enhancement of Flame Retardancy of Unsaturated Polyester Resin Based on DOPO Derivatives and Aluminum Hypophosphite
The main aim of this work was to investigate the enhancement of flame retardancy of unsaturated polyester resin (UPR) based on DOPO derivatives-DHP and aluminum hypophosphite (AHP). The UPR/DHP/AHP composites were characterized by UL-94 vertical combustion tests, limiting oxygen index (LOI), microscale combustion calorimetry (MCC), and thermogravimetric analysis/infrared spectrometry (TG-IR) tests. These results reveal that the flame retardancy of UPR/DHP/AHP composites is significantly enhanced, such as passed UL-94 V-0 classification, decreased peak heat release rate (PHRR) maximally by 40.3% and total heat release (THR) maximally by 18.5%. TG-IR results demonstrate that the incorporation of DHP and AHP in the composites could reduce flammable gas amounts and capture free radicals in gas phase. SEM images show that a dense and compact char layer is formed during the combustion.
Improving Mechanical Properties of Immiscible Polymer Blends
A process for obtaining improved mechanical properties for immiscible polymer blends was proposed and proved valid for the system of polypropylene (PP) and polystyrene (PS). By minimizing the jet stretch applied to the fiber precursor and implementing a standalone hot drawing stage, the Young’s modulus and tensile strength of the processed fiber were shown to be greatly improved. The mechanisms responsible for improved modulus and tensile strength, achieved via low jet stretch and subsequent hot drawing, are quantitatively explored and explained. A model with logarithmic strain relaxation is provided to explain the radical distribution of the area of PS phases. Empirical models for predicting Young’s modulus were also used and compared with experimental data to identify the best fitting model.
Effects of Processing Parameters on the Surface Structure of Injection Molded Parts: Application of Image Analysis for the Investigation of 2D Cavern Structures with Respect to Electroplating Quality Requirements
For the production of injection molded parts with a subsequent electroplated coating, technical polymers like acrylonitrile butadiene styrene or polycarbonate/ acrylonitrile butadiene styrene blends are used. The quality of these parts is affected by both the electroplating parameters and the properties of the surface and subsurface structures of the injection molded part. Processing parameters influence these structures during injection molding and hence are responsible for the adhesion of the polymer and the metal ,. The effects on the resulting caverns in polymer surfaces (after etching) caused by changing injection molding parameters are investigated. For this purpose, relevant processing parameters affecting the surface structure are examined. Furthermore, image analysis is applied as an objective evaluation method to quantify the two-dimensional shape of caverns. This analysis is based on electron microscope (SEM) images of chemical etched polymer part surfaces (ABS, PC/ABS). Meaningful key figures, such as roundness, degree of orientation, caverns/µm², and area of caverns, are emerged to quantify the surface structure. An ABS and PC/ABS material is tested and compared, and coherences between the shape of the caverns, processing parameters, material properties, and geometry influences are elaborated.
Influence of High-Speed Extrusion on Structure and Properties of Bioplastics Blends
This work describes a novel, high-speed twin-screw extrusion process applied to blends of bioplastics. The blends were chosen for their ability to combine synergistic polymers to produce more robust bioplastics with diverse properties. The influence of interfacial reaction was also studied, both from the perspective of morphology development and final properties improvements. Immiscible PLA/PA11 blends were successfully compatibilized by in-situ reactive twin-screw extrusion. During processing, the molecular weight of PLA sharply decreased due to chain scission. Mechanical property improvement was realized through processing parameter optimization and addition of a chain extender.
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