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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Compounding Challenges for Vinyl Flooring
Luxury Vinyl Tiles (LVT) are the largest growing product group in vinyl flooring. The high-quality appearance combined with the ease of installation and maintenance results in a steadily growing demand. As more and more companies are entering the market, a broad variety of processing options evolved. The compounding processes are required to deal with higher line speeds on one side and higher expectations concerning process flexibility and higher economical pressure on the other side. In the last years, more and more Continuous Kneaders are applied in this application. The unique principle of operation is used for all the different layers of the LVT. In the course of this talk we will investigate different options (with a focus on pelletizing and calendering processes) to deal with the demands of the market. New developments concerning the addition of fillers into the compounding process applying Continuous Kneaders are investigated and compared to standard solutions. A significant increase of the line productivity can be achieved applying the newly developed intake system while keeping the screw speed of the Kneader screw at a very low level.
Low Density HMS Polypropylene Foam: Controlling Foam Density and Cell Morphology
Linear isotactic polypropylene (PP) is used in a vast array of applications because it provides mechanical strength, chemical resistance, and thermal stability. However, semi-crystalline linear PP has limited use in low-density foam applications, which are dominated by amorphous polymers, such as polystyrene. This paper discusses technical challenges that have limited the use of PP in low-density, extruded foams. Specifically, the challenge of controlling foam density along with closed cell percent and cell count is addressed. The rheological properties have been evaluated in terms of viscosity, elasticity and melt strength which show good foaming potential. Interactions between the HMSPP polymer, linear PP blend polymers, blowing agent type, additive formulation, and process variables are investigated here for a new, developmental HMSPP grade. Braskem has developed a proprietary technology to produce High Melt Strength Polypropylene (HMSPP), branded as the Amppleo family, with a specific long chain branching configuration that helps overcome the limitations of linear PP when foaming to low densities of 150-50kg/m3.
Advanced Data Acquisition and Analysis for Injection Molders
The subject of this publication is the detection of optimization potential and the avoidance of faults and errors in the injection molding process using process data analysis. In modern injection molding machines, in addition to the produced plastic moldings, high amounts of process and machine data are available – in very high quality. Injection molding machines are equipped with high-resolution measuring devices that are connected to the bus system of the machine, which reaches out to all the components from the plasticizing barrel, frequency converters for drives, mold cavities, etc. To date, however, these data have not been fully exploited and have not been accessible in a convenient way. Through the further development of bus-based data interfaces, it is now possible to obtain all signals and sensor data, and use these data for external analysis purposes. The decisive factor is central recording of the relevant signals with a uniform time base. Corresponding recording in real-time facilitates complete documentation and utilization of the relevant process and machine data. Subsequently, these raw data must be processed appropriately so that they can be used for analysis purposes in order to extract the information from process and production, and generate corresponding benefits for the users and operators. Firstly, strategies and methods are shown on how (raw) data from a machine control (PLC) can be extracted and made available to the operator. For a diagnostically conclusive analysis, the complexity and the size of the data must be significantly reduced – here, machine and process-specific key figures are generated. Key figures are combined with one another and further compacted so that additional information can be obtained more easily.
Effects of Extruder Temperature and Screw Speed on Thermal Properties of Glass Fiber Reinforced Polyamide 6 Composites throughout the Direct Long-Fiber Reinforced Thermoplastics Process
This study investigates the effects of extruder temperature and screw speed on the thermal properties of glass fiber reinforced polyamide 6 (PA6) composites throughout the direct long-fiber reinforced thermoplastic (D-LFT) process. Thermogravimetric analyses (TGA) and differential scanning calorimetry (DSC) analyses were performed on samples taken from different locations along the D-LFT process. TGA results showed that the low screw speed of the extruders increased apparent activation energy of the final product. Non-isothermal DSC crystallization analysis revealed no substantial changes to the material’s degree of crystallinity with the variations in extruder temperature and screw speed; however, isothermal DSC crystallization analysis showed that the low screw speed of the extruders increased crystallization half-time of the final product.
Injection Molding of Glass Fiber Reinforced Polypropylene Composite Foams with Laminate Skins
Sandwich panels which consist of discontinuous glass fiber reinforced polypropylene composite foam core and continuous glass-fiber reinforced polypropylene laminate skins were manufactured using industry-scale equipment in a streamlined manner. The process included the two stages: (1) continuous glass-fiber reinforced polypropylene laminates as the face skins were produced using an automated tape layup machine and a hydraulic press and (2) discontinuous glass-fiber reinforced polypropylene composite as the core was foam injection-molded onto the face laminates (i.e., overmolding) with a physical blowing agent, nitrogen. The results suggested that the addition of the laminate skins and foaming by the core-back (or mold opening) technique can greatly reduce weight of material needed to have the same bending stiffness and maximum bending force.
Nanocomposites of SEBS/CNT for Electromagnetic Shielding: Effect of Processing Method and Maleic Anhydride
In this work, poly (styrene-b-ethylene-ran-butyleneb- styrene) (SEBS) and SEBS grafted maleic anhydride (SEBS-MA) and carbon nanotube (CNT) nanocomposites (SEBS/CNT and SEBS-MA/CNT) were prepared for electromagnetic shielding applications. Two different melt compounding methods were used, mixing followed by extrusion, and mixing followed by compression molding. In order to assess the morphologies and properties, the different nanocomposites were characterized through rheology, AC electrical conductivity measurements, and electromagnetic shielding analysis. Three different nanocomposites prepared in this work presented the requirements necessary to be used commercially for electromagnetic shielding applications. The higher electrical conductivity, around 6.0E-4 S.cm-1, and the higher electromagnetic shielding effectiveness, 31.67 dB, were achieved by the nanocomposite of SEBS/CNT with 5 wt% of CNT prepared by melt mixing followed by compression molding. This nanocomposite presented an attenuation of 99.93 % of the incident electromagnetic radiation.
Lightweight Design with Long Fiber Reinforced Thermoplastics - Mechanistic Direct Fiber Simulation for Prediction of Long Fiber Effects during Compression Molding
During the processing of long fiber reinforced plastics, both with thermoset and thermoplastic resins, the fibers inside the melt undergo complex movements which can cause a drastic decrease of the component’s mechanical properties. The most significant effect is observed in changes of the fiber orientation during processing, but furthermore extensive fiber breakage and deviations in fiber content in complex part regions can occur with the use of longer fibers. These effects could cause design problems and part failures, if not accounted for. With traditional process simulation tools focusing on the prediction of short fiber reinforced polymers, these long fiber effects are not displayed accurately. A novel simulation tool, the Direct Fiber Simulation using a mechanistic model, is applied where traditional process simulation tools show deficiencies. Hereby, the fibers inside the polymer flow are simulated as beam elements in a micro-mechanistic model with multi-scalar interactions. In this paper, the application of the micro-mechanistic model is examined for the use with long fiber reinforced plastics in compression molding. In the simulations, a ribbed plate geometry is examined in a wide range of fiber properties and simulation settings. The results show that the Direct Fiber Simulation is suitable to display the stated long fiber effects during compression molding and will be applied for further research.
An Approach to Improve the Prediction of Injection Pressure in Simulation Technology
Injection molding process simulation is a complex phenomenon wherein a thermoplastic material in melt state is injected into a cavity. The polymer melt replicates the details from the cavity and retains it as it solidifies and subsequently is ejected out of the mold. The Computer Aided Engineering (CAE) tools used for process simulation should be able to estimate the flow pattern, temperature distribution, shrinkage arising from material compressibility, viscous heating, pressure distribution, solidification, crystallization, fiber orientation, clamp force, etc. Despite many complexities arising from both material and molding process behavior, the CAE tools have evolved and matured to be reliable, accurate and useful in providing insightful details that can be used during product and process development. In some situations these tools still lack accuracy and overall reliability while analyzing some of the complex molding processes like thin wall molding, gas-assisted molding, etc. and needs to be studied to reduce these gaps and increase manufacturing predictability. In this report a systematic approach and detailed steps to further improve the overall accuracy of CAE prediction is described. This covers critical aspects like measurement of mold surface temperature, melt temperature and reduce their uncertainty while using them as inputs in CAE. Through a detailed in-mold rheological study the influence of injection speed on pressure to mold the part is studied leading to derivation of molding window. The pressure loss that occurs in the machine screw barrel can be significant and is captured through an air-shot study. All these studies provide insights about the process and forms the basis for setting up the model in CAE, which is more representative of the actual process consisting of the part, material, the flow channels, initial temperature conditions of melt and mold. Using this approach and with the inclusion of improved characterization of resin’s viscosity in the CAE material model, we are able to predict the peak pressure in this representative tool within 10% of actual value for LEXAN™ LS1.
Experimental Set up for Radiation Based in-Mold-Coating for Optical Components
The in-mold-coating (IMC) as a mass production process offers potential to generate low-cost, high precision surface qualities on polymeric composite materials for optical applications. The combination of the IMC process and photo-curable coating systems provides several advantages, especially reduced process complexity and short curing durations. This work presents the development and realization of an experimental set-up to apply high precision ultra-violet (UV-) curable coatings on polymeric substrates in an in-mold-coating process. Key aspect is the selection of a UV-transparent mold insert material, which was examined by UV-vis-spectroscopy, pull-off adhesion tests and contact angle measurement. Based on the results, a plasma-polymeric anti-adhesive coating applied on PMMA was used to verify the applicability of the experimental set up. A mold accuracy of more than 90 % of the generated photo-coatings to the used mold insert surface and a noticeable roughness improvement between the uncoated and coated specimen was achieved, which sets the basis for further investigations.
Simulation-Based Investigation of the Temperature Influence during Laser Transmission Welding of Thermoplastics
Because of several advantages, e.g. an exact and high energy input, laser transmission welding has become more and more important in the last few years. Due to the contactless energy input, a sufficient process control is a challenge. In industrial production, the process parameters for a good weld seam are qualified by the energy input, which describes the process parameters laser power, laser velocity and irradiation time. These process parameters lead to the welding temperature, which influence the weld seam quality. The question remaining is whether the energy input describes the weld strength sufficiently or whether the welding temperature has a higher influence on the weld quality. In this study the influence of the energy input on the weld quality is determined for an industrial material combination (PBT ASA-GF20 and PC) in experimental examinations for quasi-simultaneous welding. The welding temperature for every design point is calculated and the influence of the temperature on the weld strength is analyzed in an FEM model. In order to compare the influences of the two factors, welding temperature and energy input, a correlation analysis is performed. The correlation analysis shows a higher influence of the welding temperature on the weld strength compared to the energy input. But the energy input is also able to describe the weld strength.
Increasing Surface Properties by Using an Integrated Screw-Based Additive and Subtractive Manufacturing Process
Additive manufacturing is a promising way of producing function-integrated multi-component parts in addition to the machining of semi-finished parts, welding and injection molding. Additive manufacturing offers a high potential especially regarding individualization, geometrical complexity and functional integration. However, additive manufactured parts have disadvantages in terms of dimensional accuracy, surface quality and functional integration by using inserts. Moreover, the industrial variety is very limited in today’s additive manufacturing processes. So the overall goal of customized production can only be achieved by using the optimum manufacturing process that is most suitable to the customer's requirements. For that purpose, the IKV developed the hybrid manufacturing technology to combine advantages and reduce disadvantages of each involved manufacturing process. In this study it is shown that a subsequent subtractive manufacturing process enables the production of high-gloss plastic components. Additionally the subtractive manufacturing process offers the potential to increase the dimensional accuracy. The shown hybrid concept enables the integration of different extruders as well as the integration of different machining or handling tools for inserts operations. The used extruders base on a screw extruder technology. For this reason it is possible to process standard thermoplastic materials. In order to calibrate CAM interfaces the extruder throughput should be calculated in advanced. For that different throughput models were used and validated with the existing systems engineering.
Comparison of the Processing Properties of Thermoplastic Elastomers and Thermoplastics Using Gas Assisted Injection Molding
The process of gas assisted injection molding (GAIM) with thermoplastic materials has been investigated comprehensively in recent years. This has been done using both experimental and numerical (mostly finite-element-method) studies. In the study presented in this paper the possibilities of using thermoplastic elastomers (TPE) within this process are shown and compared to typical thermoplastic polymers. The results include the obtained residual wall thicknesses and measurements of gas front velocities. The minimal wall thicknesses obtained with TPE materials and thermoplastics at high gas pressures within this study are of similar level. The values for lower pressure levels however are significantly influenced by the rheological properties of the particular materials. The distinctive shear thinning of the TPE materials and the Newtonian flow behavior of the thermoplastics used in this study have major influence on the melt displacement velocity and the residual wall thickness.
Ultrathin Nanolayer Films for High Energy Density, High Temperature Capacitors
Fabrication of multilayer dielectric films to improve the dielectric properties was demonstrated by combining two or more polymers as a layered structure via coextrusion process. Recently, process innovations in film production scale-up of thin nanolayered films was demonstrated at PolymerPlus. Using conventionally used film metallization and capacitor winding capabilities nanolayer film capacitor prototypes were also created. Use of high temperature and high energy density films was demonstrated in capacitor applications. Recent results on effect of multilayer film thickness and number of layers on the dielectric performance is discussed in this paper.
Nonwoven Filters via a Novel, Continuous Melt Coextrusion Process
A novel melt co-extrusion process with two-dimensional multiplication technology created a fiber-film mat with polymer layer dimensions comparable with conventional fibers. When the layers were exfoliated using a high pressure water jet delamination technique a fibrous filter media were fabricated. The filter media made from polypropylene (PP) / polyamide 6 (PA6) system exhibited microscale fibers with uniform fiber distribution and superior mechanical properties. Previously, improved filter surface area and porosity, and decreased the mean pore size was demonstrated with increasing film draw ratio prior to delamination. In current work, applications of this filter for water removal in fuel filters are demonstrated. In addition, PolymerPlus has also demonstrated fabrication of continuous large filter media sheets demonstrating scalability. This melt process based, flexible technology can be extended to other melt-processable polymers for various liquid or gas filtration applications.
Effect of Acrylic Core-Shell Impact Modifier on Processing and Thermo-Mechanical Properties of Stereocomplex Poly(lactic acid)
Injection molding grade PLLA/PDLA compounds have been developed by melt blending. The article reports in particular about influence of acrylic core-shell impact modifier on crystallization behavior, thermo-mechanical properties of the compounds and injection molding cycle time. DSC results have shown formation of stereocomplex crystalline structure in compounds. Addition of impact modifier displays no influence on melting point or enthalpy of crystalline structure. Plasticization of compounds resulted in decrease of tensile properties, however impact strength has increased. Additionally a peak of maximum loading with additive was observed. Plasticizing effect due to addition of core-shell entities was confirmed by sharp increase of elongation at break. Only marginal effect on heat distortion temperature of the compounds was found. Increasing content of the toughening agent caused lowering of materials’ flowability. Influence of impact modifier on resulting injection molding cycle time was insignificant.
Rapid Photo-Oxidation of UV-Stabilized Polypropylene Fiber Due to an External Antagonist
Polypropylene fiber in an outdoor carpet exhibited unusual photo-oxidation behavior that occurred in some cases in as little as 3 months. Degradation rate and severity were shown to be dependent on exposure to materials the carpet came into contact with after manufacturing. Other causes of increased UV sensitivity were also identified. Since the failure manifested as a consistent change in color, colorimetry was used as a simple diagnostic tool. Mechanisms for accelerated degradation are discussed whereby the effectiveness of hindered amine light stabilizers (HALS) is disrupted by external antagonists.
Effects of Supercritical Carbon Dioxide Processing on the Crystallization of Polyvinylidene Fluoride
Polyvinylidene fluoride (PVDF) is an environmentally friendly, durable and low-cost alternative to traditional piezoelectric materials in sensors and actuators. PVDF is a semi-crystalline polymer with different crystal phases. Among them, the polar ß-phase is the crystalline structure that is responsible for its piezoelectric property. Conventional technology for promoting ß-phase crystals in PVDF is mechanical stretching. In this paper, processing of PVDF with supercritical carbon dioxide (ScCO2) was investigated to examine its effect on PVDF’s crystallization behavior. In the long-run, elucidation of potential strategies to tailor PVDF’s crystal structures would help to identify feasible route to tailor PVDF’s crystalline structure for emerging applications including sensing and energy harvesting. The foam morphology of PVDF was analyzed by scanning electronic microscopy while its crystallization behavior was studied by differential scanning calorimetry and Fourier transform infrared spectroscopy. Experimental results reveal that PVDF samples foamed at 120°C and 160°C under 2000 psi showed the highest crystallinity (54%) and volume expansion ratio (15.4 times), respectively. The crystallinity increase in ScCO2 processed PVDF represents a 16% increase over that of its compression-molded samples.
Study of Fiber Length and Modeling of Partially Compacted, Commingled Polypropylene Glass Fiber Fleece Composites
In this work we investigated the influence of glass fiber content, number of layers and initial length on the residual fiber length and the properties of partially compacted composites made of commingled polypropylene and glass fibers. Furthermore, we wanted to develop a model to predict the properties of such composites. We found, that despite of a significant degradation of fiber length due to the processing, increasing glass fiber content and initial fiber length leads to higher portions of longer fibers and mechanical properties are improved, but only when the porosity remains among certain levels. Porosity is therefore the critical factor influencing this type of composites. The modeling of the elastic modulus was found satisfactory for composites with porosity volume content under 0.5.
Mechanical, Thermal and Electrical Property Enhancement of Graphene-Polymer Nanocomposites
In this work, NanoXplore’s proprietary graphene nanoplatelets, heXo-G V20, are melt-extruded into thermoplastics LLDPE, HDPE and TPU. Graphene is shown to effectively increase the stiffness and the strength of a matrix TPU. The flexural and tensile moduli increase with loading levels of graphene whereas the tensile strength increases at low loading levels, but does not further increase at higher graphene concentrations. A ten fold increase in thermal conductivity was achieved by adding heXo-G V20 graphene to LLDPE matrix. The thermal conductivity percolation threshold was reached at 10% loading. At 1% loading of graphene the onset of the decomposition temperature and maximum weight loss temperatures were shifted by about 50°C, significantly improving the thermal stability of the PE matrix. Fourteen orders of magnitude increase in electrical conductivity of HDPE was obtained at 30% loading of graphene. Excellent EMI shielding of 40 dB was achieved with 20 wt% addition of graphene in a TPU matrix.
Influence of Glass Transition Temperature on Mechanical and Self-Healing Behavior of Polymers Bearing Hindered Urea Bonds
Considerable interest has been placed on polymers which can intrinsically self-heal. Numerous studies have shown that polymer networks bearing dynamic covalent bonds exhibit the ability to self-repair. The focus of this paper is to describe the synthesis and characterization of polymer networks of varying rigidity bearing hindered urea bonds (HUB) based on 1-(tert-butyl)-1-ethylurea (TBEU). Results indicate that the partial substitution of Hexamethylene Diisocyanate (HMDI) with an aromatic diisocyanate (m-Xylylene Diisocyanate, XDI) results in a predictable increase in Tg and a corresponding increase in both modulus and tensile strength at break. Furthermore, polymers containing up to 50mol% XDI were shown to self-heal, though the efficacy decreases with increasing XDI content at constant healing conditions (60°C/12 hours).
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