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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.
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.
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.
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.
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.
Short glass fibers are widely employed in reinforcement of nylon compounds to significantly improve mechanical properties. These properties are dictated by fiber length and orientation distributions in the compounds. Fiber breakage takes place during the compounding process. When the fibers break into sub-critical length, the reinforcement of the compound is limited. This paper used a full factorial design investigating the effects of nylon’s viscosity and twin screw extruder’s screw configuration on glass fiber length retention and mechanical properties of the final compounds.
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.
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.
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.
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.
This research studied the morphologies of layer-bylayer (LBL) assemblies, comprising clay and alternative polyelectrolyte layers of polyethyleneimine (PEI) and sulfonated polyethyleneterephthalate (PETi). The samples prepared with such coatings on polystyrene, showed very low permeability values against gases, like oxygen, that can be considered as the lowest recorded value for this polymer. Transmission electron microscopy and x-ray diffractometry pointed to the increased level of intercalation and orientation of LBL assemblies, below a certain range of montmorillonite (MMT) concentration in deionized water, above which LBL assemblies’ gas barrier improvement leveled out. These results may be connected to the possible decreased level of MMT dispersion in its suspension and its increased viscosity. Comparing the LBL assemblies formed from two alternative polyelectrolytes used, the ones comprising PEI showed better orientation and regularity levels. It may conjecture that PEI makes more significant interactions than PETi, with clay platelets surfaces.
Grooved-bore, single-screw extruders are commonly used in Europe, and they are used to a lesser extent in North America. In North America, they are often used as the extruders for blown film, blow molding, and pipe processes where the discharge temperatures need to be relatively low and the rates high. Screw designers for grooved-bore machines are very good at providing screws that discharge at low temperatures and high rates, but they typically are not focused on providing a gel-free extrudate. This paper will discuss methods to mitigate gels for grooved-bore machines running polyethylene (PE) resins.
Fused filament fabrication (FFF) has the potential to enter industrial application due to the possibility of producing complex designs in limited series. However, currently only a limited number of materials is commercially available for use in this process. This study aims at expanding the material range for FFF towards polypropylene (PP) by modifying it with 30 vol.-% of glass spheres and a compatiblizer. Furthermore, the difference between hollow borosilicate and solid inorganic soda lime glass spheres of the same mean filler diameter was examined. In this paper the shrinkage upon solidification, the thermal behavior of the compounds, the mechanical properties of the filaments, and the viscosity of the molten materials were analyzed, as these properties are decisive parameters for a successful printing process. Additionally, the adhesion between the filament and various printing surfaces is addressed and all results are compared to PLA, a well-established FFF filament material. It was observed that the addition of spherical glass fillers leads to a reduction in shrinkage and an increase in the crystallization temperature, while the degree of crystallinity remains unaltered. The efficiency of the compatibilizer depends distinctly on the used glass type. Well-compatibilized compounds reveal yield stresses similar to unfilled PP and lead to a decrease in the overall viscosity. The PP-based compounds investigated do not adhere to the standard printing bed (mirror). However, they exhibit a tendency to stick to surfaces with similar polarity, such as PP-films.
In the Particle-foam Composite Injection Molding (PCIM) process a compact material is injection molded onto foam. PCIM parts combine the positive properties of both material types, compact materials and particle foam in one part. This means it is possible to manufacture parts with thermal insulation properties, force absorbing properties, a high degree of stiffness and attached elements like snap-fits and screw fittings for example. The University of Applied Sciences Osnabrueck examines the adhesion properties between these components. This results in a mechanical characterization of PCIM parts, which will allow dimensioning of these composites in the development phase of PCIM products. The project is supported by the Federal Ministry of Education and Research (BMBF) and the companies Arburg, Krallmann and Ruch Novaplast are project partners.
Previous attempts to accurately measure the real polymer melt temperature in the screw chamber have failed due to the challenging metrological boundary conditions (high pressure, high temperature, rotational and axial screw movement) in the plasticizing unit. We developed a novel ultrasound system - based on reflection measurements - for the online determination of these important process parameter. The system is compared to an infra-red- (IR-) camera system, which measures the melt temperature during an air shot in front of the nozzle. The recorded data of the measurement systems are used to study the influence of process parameter variations on the melt temperature profile in the screw chamber of a reciprocating single screw plasticizing unit.
The poly (lactic acid) (PLA) crystallization behavior was investigated during an extrusion process via visualization techniques. Effects of various processing parameters, such as extruder barrel temperature profiles, the system pressure, the flow rate, and the blowing agent content, on formation of PLA crystallites in the melt flow were discussed. Various observations and results are reported. First, the PLA crystallites were visualized by decreasing the barrel temperature at a low flow rate. Then, it was visualized and quantified that a sudden increase in the flow rate, under the identical cooling protocol, enhanced the PLA crystallization dramatically. Moreover, by introduction of CO2 into the system, the PLA crystallites formed at a lower temperature profile. Finally, it was revealed that the induced crystallites improved the foaming behavior of extruded foams through minimizing the cell coalescence.
Filling ratio is an important process parameter related to the residence time distribution and thermal history of resin in a twin-screw extruder. This study presents a theoretical method of filling ratio distribution calculated by our newly developed 2.5 D Hele–Shaw flow model and finite element method. The calculated filling ratio distribution of a full-flight screw was validated by on-line measurement of resin volume with the laser light section method. The calculation and measurement results were in good agreement.
Ballistic clay is used as a backing material for standards-based ballistic resistance tests for the purposes of providing a measure of the energy transferred to the body when a threat is defeated. However, this material exhibits complex thermomechanical behavior under actual usage conditions. In this work, we characterize rheological properties of the standard backing clay material, Roma Plastilina No. 1, used for body armor testing, using a rubber process analyzer. Test methods employed include oscillatory strain sweep, frequency sweep, and oscillatory strain ramp. The results show that the material is highly nonlinear, thermorheologically complex, and thixotropic. The modulus decreases under dynamic deformation and partially recovers when the deformation is discontinued. Experimental protocols developed in this study can be applied for the characterization of other synthetic clay systems.
Most plastics products are made from a base polymer mixed with complex blends of materials known collectively as additives, to ensure that the physical, mechanical and surface properties of the final product is optimised in all aspects. This will include safer, cleaner product possessing optimal colour and properties. Fine additives such as fillers or coloured pigments are most widely used and the improved technique for dispersing particles into polymer is highly demanding in industrial practice. A USV (ultra-sonication and vibration) assisted process during twin screw extrusion system was implemented and the dispersion results tested in our labs and the technology transferred to our industrial partner’s manufacturing facility. Particle additives such as clay, organic and inorganic pigments were compounded and tested using USV assisted twin screw extrusion.
Cyclic olefin copolymers (COC) offer many benefits for packaging films, including stiffness, strength, transparency, gloss, heat resistance, improved thermoforming, moisture, and alcohol barrier to name a few. Using full factorial experimental design, COC glass transition temperature, COC modification and blow-up ratio were studied to show how COC influences performance of several key blown film properties. Three-layer packaging films can be engineered with modified COC to provide higher than expected toughness, strength, and stiffness. By splitting COC into at least two layers in five layer structures, further significant property enhancements are possible without changing COC content.
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