SPE Library
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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Conference Proceedings
Layer-Multiplying Co-Extrusion of High Viscoelasticity Ratio Polymers
Traditionally, viscosities of co-extruded polymers are required to match to obtain decent multilayer structures, which severely narrows the processing window. In this study, we introduce a way to improve the non-uniform multilayered structure in rheologically mismatched polymers during layer-multiplying co-extrusion. Both high viscosity ratio (PS/PMMA) and high elasticity ratio (TPUs) polymers were used in this paper. The solution to this problem was broken into Engineering and Material approaches. In the Engineering solution a 9-layer feedblock and a new design of multiplier die are combined to start layering with more (and more uniform) layers and lower the pressure drop. In the Material approach, external lubricants are applied to provide the system with maximum wall-slip effect, thus reducing second normal stress difference (N2) responsible for the development of elastic instabilities. Finally, finite element method simulation (FEM) via ANSYS POLYFLOW® is used as a comparison tool to validate the accuracy of predicting the formation and development of flow instabilities.
Thermal Ageing of Polyamide 12 Used for Polymer Laser Sintering – Influence on Part Quality Characteristics
Polymer laser sintering is one of the most important additive manufacturing technologies for the tool-less production of three-dimensional prototypes and end-use parts. In this process, parts are manufactured layerwise out of a polymer powder by laser exposure. After the building process, these parts are located within a loose bulk powder cake. Due to long process times and high process temperatures, this powder ages thermally, which reduces the recyclability of the material. As a result, mixtures of used and virgin powder (“refreshed” powder) with a mixture ratio of approximately 50% are commonly used in the industry. The goal of this work is to determine the exact influence of different powder ages on resulting part quality characteristics, especially the mechanical behavior and the surface quality. Therefore, refreshed powder with different qualities adjusted by the melt volume rate (MVR) was processed along a defined process quality chain. To analyze the part qualities, mechanical tensile and profilometer tests were performed. The focus is on an application-oriented test set-up to ensure the usability of the results in the industry. The material used is polyamide 12 (PA 2200) processed on an EOSINT P395 laser sintering system from EOS GmbH, Krailling, Germany.
Wear Behavior of Polyaryletherketones (PAEK) under Multidirectional Sliding and Fretting Conditions
Fretting is said to occur when mutually loaded contacts move relative to one another with nominally small displacements. The resulting stick slip between asperities causes cracks to nucleate at the surface and may eventually lead to catastrophic part failure. Furthermore, prediction of how a material might respond to such a scenario is challenging due the overall complexity of the process. The polyaryletherketone (PAEK) family of thermoplastics has been increasingly used in such fretting environments, but few studies exist regarding their fretting behavior. In this study, a custom built multi-axis tribometer has been shown to replicate fretting of PAEK in a pin on flat configuration. The experimentation and analysis has provided new insights into this phenomenon.
Experimental and Numerical Analysis of Material Properties of Unidirectional Composites Manufactured by Tailored Fiber Placement
Working with fiber-reinforced plastics, not only the materials influence the resulting component properties but also the fabrication techniques. The Tailored Fiber Placement (TFP) technology is a textile manufacturing technique, where the reinforcing fiber thread (roving) is placed along almost arbitrary programmable curves in a 2-D plane and fixated by the stitching yarn on a textile base material. Hence the highly anisotropic material characteristics of reinforcing fibers can be fully exploited for lightweight construction if a dominating load case is known. This can lead to a dramatically increasing stiffness or strength per mass compared to conventional quasi-isotropic design. However, the TFP technology also leads to a small waviness of the reinforcing fibers in-plane and out-of-plane, decreasing the resulting mechanical properties of the component slightly. For high performance lightweight construction it is important to know about these effects qualitatively and predict the reduction of material properties compared to ideally placed fibers quantitatively. The goal of this work is to gain a first overview of the geometry of the waviness and to estimate the amount of its effects on the properties of a part produced by TFP. We start by measuring and characterizing the effects of different parameters, which can be set at the TFP machine, on the geometry of the fiber waviness. The data is analyzed statistically and by means of Fourier analysis. The findings were put into finite element (FE) analysis models of a single cell to predict the reduction of the resulting tensile stiffness. Experimental tensile stiffness measurements verify the simulated results.
Advancements in Lasermarkable Engineering Resins
Laser marking on plastics is growing in use. Bar codes and product lot data can currently be marked with lasers some commodity resins. However, of specific interest is the use of lasers to mark functional or decorative information on engineering resins. Because of their inert surface characteristics, these resins can be difficult to mark via printing using ink. This paper focuses on the development of specialty grades of engineering resins that yield excellent sharp, clear images when laser marked. Grades have been developed for laser marking white characters on black, dark characters on white and other effects.
Poly(Lactic Acid) with Improved Melt Strength and Gardner Impact Strength
Poly(lactic acid) or PLA is a commercial biopolymer made from lactic acid derived from sugar fermentation. “Greenbased” [1] PLA is desired as a biodegradable film, sheet and food packaging alternative to oil-based polymers. PLA has a Tm melting point range of 150-162°C [2]. Unfortunately, PLA has poor melt strength and impact strength. High melt strength and impact strength are important properties when manufacturing sheet, film, fibers and molded goods. In this paper we explored several ideas to improve the performance of PLA while maintaining its “green” characteristics. We found that an acrylic based core-shell polymer used at a low concentration significantly increased the Gardner impact strength of 15mil extruded sheet. Also, a high molecular weight acrylic copolymer used at low levels doubled the PLA melt strength. Lastly, reacting PLA with organic peroxides increased the shear modulus, molecular weight and melt strength based on rheometer, multi-angle light scattering and Rheotens analysis.
Characterization of Carbon Fiber Laminates: Determining Ply Orientation and Ply Type via Ultrasonic A-Scan and C-Scan Techniques
As companies search for strong, lightweight materials to incorporate into their product line, several are turning to fiber reinforced composites. While this material is lighter than traditional metals, its properties are dependent upon the manufacturing process and the orientation of the fibers within the part. For example, in a carbon fiber reinforced laminate the orientation of each ply directly affects the properties of the total stack and ultimately the final processed part. Employing a destructive testing method to determine material properties will render the part unsuitable for its intended application. Thus, a nondestructive testing method must be applied to determine the part’s material properties. The current study applies ultrasonic A-scan and C-scan techniques to characterize the final as-manufactured part. The as-manufactured part is not always the same as the as-designed part. Thus, a non-destructive testing technique that can validate manufacturing at the individual ply level is of critical importance. In this method, the C-scan measurements are analyzed using a custom Matlab program, and the results are displayed to the user in the form of a video. The video begins with an image of the top surface of the laminate, and each subsequent frame steps further into the thickness of the laminate. The uniqueness of this system lies in its ability to capture the carbon fiber tows within a given ply thus allowing the ply type and orientation to be determined for each lamina in the bulk laminate. While the initial results of this study are promising, surface features, which are a common artifact of the manufacturing process, have affected the analysis of the C-scan data. This study focuses on the effects of these surface features and discusses potential solutions.
Extensional Flow Blending of Immiscible Polymers with Nanoparticle Stabilization
In this work, blends of high-viscosity polyethylene dispersed in polystyrene (viscosity ratio > 4) were employed to study the effects of extensional flow mixing on morphology. Coarse blends, prepared in an internal mixer, were subjected to extensional flow by forcing them through converging flow dies, which resulted in decrease in the volume-average diameter of the drops. To inhibit coalescence, nanosilica was incorporated into the blend. This was found to decrease both the initial coarse blend dispersed phase size and the drop size after extensional flow. However, addition of nanosilica had only a small effect on blends subjected to extensional flow.
Ratio Function of Dynamic Moduli and its Application in Consistency Check
A new type of functions – a ratio of linear combination of dynamic moduli at different frequencies – and their bounding properties were studied. It was shown that these functions have an important feature, that is, if f represents a given ratio function for a Maxwell model whereas F represents the same function for a generalized Maxwell model, then f and F have exactly the same bounds. So the bounding properties of F can be known by analyzing simple function f only. The study showed that all four ratio functions proposed are bounded for a linear system, which means the dynamic moduli at different frequencies are not independent. Given any dynamic data, one can check the data by calculating the value of ratio function and comparing it with the bounds. If the value breaks the bounds and the violation cannot be attributed to normal experimental errors, then the data must be inconsistent. If the violation exists in the shifted data but not the original ones, then the shifted data might contain artificial errors. The method worked well as it was used to check the real G’, G” data reported in the literature.
Effect of Fountain Flow on Fiber Orientation and Distribution in Fiber Filled Polymers during Mold Filling
The mold filling process of fiber reinforced parts manufactured by injection or compression molding plays a significant role on the quality of the finished product. For instance, during the injection molding process, the fountain flow dominates the mold filling stage, having a strong effect on fiber orientation at different locations within the molded part. In this work, the effect of fountain flow on fiber orientation is studied via simulation as well as experimentation. The fiber motion is simulated using a mechanistic approach where fibers are modeled as interconnected elements subjected to hydrodynamic and contact forces (fiber-fiber interactions). The simulation results show a good match with experiments performed in a device that allows visualization of the fountain flow region during injection molding.
Mechanistic Model to Determine Fiber Orientation Simulation Material Parameters
A joint Natural Fiber Composite (NFC) research project [1] aims for an integrated mechanical/crash simulation of natural fiber reinforced plastics. This paper presents results from one of the NFC tasks, namely, an alternative way to find fiber orientation material parameters for commercial simulation software by using a mechanistic fiber motion model. During processing of fiber reinforced plastic parts, anisotropy is introduced due to fiber alignment caused by the deformation of the flowing polymer melt. Different models are available to model the development of fiber orientation during processing. These orientation models include material dependent parameters, which are obtained using cumbersome reengineering techniques. These techniques involve measuring the fiber orientation within the finished parts, and fitting the material dependent parameters until the model’s fiber orientation distributions match the actual fiber orientation. For glass fibers, the models and the parameters have been well investigated. However, data for modeling the orientation distribution development during processing natural fiber filled resins, is basically non-existent. Furthermore, actual measurements of fiber orientation distributions within natural fiber filled composites are challenging to obtain. In this work, an alternative method has been developed to find the fiber-fiber interaction coefficient Ci from the Folgar-Tucker model, by coupling the model with a mechanistic fiber model. In this technique, Ci is iteratively optimized until the fiber orientation distribution computed using the Folgar-Tucker model fits the fiber orientation fields predicted by the mechanistic model. With this virtual method, the costly measurement of actual fiber orientation fields within a finished part, and the subsequent re-engineering approach can be avoided. Furthermore, the mechanistic model can be used to determine any material dependent parameters needed for other fiber orientation predictive model
Flow-Induced Fractionation of Bimodal Metallocene Polyethylene in Capillary Extrusion
We studied the melt fracture and wall slip behaviors during the capillary extrusion of metallocene-catalyzed bimodal polyethylene resins. The bimodal resin comprising a higher content of low molecular weight component showed more wall slip and unusual melt fracture behavior. GPC measurement done on the surface section of the extruded pipe of the bimodal resin showed the wall had enriched low MW component relative to the bulk. The distinct separation of the two modes and the high content of small chains of the bimodal resin promote the flow-induced fractionation leading to the small chains being more concentrated near the die walls, which in turn result in significant wall slip and unusual melt fracture behaviors observed.
Effect of Drying and Processing on the Performance of Eastman Tritan™ Copolyesters
Proper processing of polymeric materials is often the key to achieving desirable properties, and good aesthetics in molded parts and extruded film or sheet. Proper drying of resin is particularly important for condensation polymers, which are often prone to molecular weight loss through hydrolysis. Tritan™ Copolyesters are transparent engineering thermoplastics used in medical, durable, and packaging applications. This paper discusses drying and processing conditions for Tritan Copolyesters, and its effects on mechanical properties, chemical resistance, and molded/extruded color.
The Effects of Matrix Type and P Roperties upon the Tensile Properties and Notch Sensitivity of Recycled Jute Mat Reinforced Polymerica Matrix Composites
The main objective of this research is to study the effects of matrix type and properties on the tensile properties and notch sensitivity of recycled jute mat reinforced polymeric matrix composites. A single recycled jute fiber mat was used as a natural fiber reinforcement system for three kinds of composites made from three types of resins. The three thermoset resins which were used as matrix for these composites are vinyl ester and two types of unsaturated polyester, low and high tensile strength resins. Three types of jute composites having the same fiber weight content were fabricated by the modified hand lay-up method with pre-impregnation stage in vacuum; we developed this method to solve the problem of the poor impregnation in the thick fiber mats using the normal hand lay-up method. This modification showed in this research as well as our previous research a better impregnation of resin throughout the jute mats and lower voids contents in the composites. Tensile tests have been performed on smooth specimens to evaluate the effect of matrix type and properties on the mechanical properties for the all considered composites. Also, tensile tests have been carried out on notched specimens with different center-hole diameters and having similarly geometrical diameter/width ratio to evaluate the notch sensitivity for each composite. All considered jute mat composites exhibited a higher tensile modulus than that of their neat resins. Although the higher tensile strength of the neat unsaturated polyester resin than that of the neat vinyl ester resin, the jute composites with vinyl ester matrix showed a higher tensile strength by 74% and 55% than that of both composites with unsaturated polyester matrix. In comparison with jute composites with high strength unsaturated polyester matrix, the jute composites with vinyl ester matrix showed a higher tensile modulus and strength by 13% and 55%, respectively. The two jute composites with unsaturated polyester matrix showed
Characterization of Recycled Carpet Samples by TG-FTIR, TG-MS, and TG-GC-MS
Limitations in landfill capacity and the environmental impact of disposing of carpet waste in landfills have made recovering nylon from carpet waste an increasingly important enterprise. Since carpet compositions vary and can contain nylon-6 and/or nylon-6,6, along with variety of other materials, characterizing waste carpet composition and its thermal decomposition profile is essential for the recycling process. In this study, material recovered from carpet waste was analyzed by TG-FTIR, TG-MS, and TG-GC-MS. TG-GC-MS proved to be the most informative method of analysis because of its identification of organic decomposition productions characteristic of nylon-6 and nylon-6,6.
Die-Drawn HDPE Pipes: Crystalline and Lamellae Orientation
It is well known that the mechanical properties of isotropic polymers, such as tensile modulus and tensile strength, can be considerably improved by orientation of the molecular chains. This can be achieved by deforming the polymer in the solid state by die-drawing process It is also possible to orient a semi-crystalline polymer in two directions rather than one, resulting in polymer pipe, sheet or film with increased strength and toughness. Crystallite orientation has been studied in a series of HDPE pipes prepared via the die-drawing process. Combined results from small angle X-ray scattering and wide-angle diffraction reveal a change in the texture of the initially unoriented billets towards a uniplanar orientation with predominant orientation of the c*-axis (i.e. polymer chain axis) along the axial direction.
Flame Retardant Polypropylene Copolymer and EVA Blends Filled with Micro- and Nanoparticles of Magnesium Hydroxide
Magnesium hydroxide (MDH) is an inexpensive inorganic flame retardant agent that has been increasingly used to replace conventional halogen-containing flame retardants in polymers. In this work, the effects of combination of micro-sized MDH particles (mMDH) with different morphologies and nano-sized MDH particles (nMDH) on flame retardant and mechanical properties of random polypropylene copolymer /EVA blends were studied. The results demonstrated that the morphology of mMDH particles also plays an important role on flame retardant properties mechanisms of the polymer. Issues concerning with the initial endothermic decomposition stage of the mMDH particles are crucial in the final flame retardant property of the composites.
Impact Modified PBT-PC Blends with Improved Ageing Characteristics
Molded in color weatherable Xenoy™ PBT-PC blends have been widely used in automotive, transportation, and leisure vehicles exteriors applications because these products offer a good balance of mechanical properties as well as weatherability. SABIC recently commercialized a Xenoy™ grade with improved property retention after heat and hydro ageing. While the initial impact strength of the new grade was similar to other existing weatherable Xenoy™ grades the property retention after heat and hydro ageing showed a significant improvement. Color retention under the SAE J1960 protocol of weathering was comparable to other existing grades in chromatic colors. Some of these blend properties shall be discussed in the paper.
Spectrophotometric Assessment: The Challenges of 0/45-45/0 in a D8 World
Determining the acceptability of automotive interior has typically been accomplished through visual consensus and spectrophotometric analysis. As many have experienced in this all too subjective pursuit, not only can three or more separate sets of eyes discern three or more totally diverse variations in color acceptability, our benchmark instruments of choice can offer distinctly different opinions also. Diversity in devices, innumerable surface-variation characteristics of the sample and inherent human imperfection in the repeatability of the manual “reading” process are all contributing factors to spurious spectrophotometric results. We will discuss what instrumental options we have available in order to have our electronic results correlate with what we see.
Crystallization Characterization of Injection Molded Parts Using Ultrasonic Technology
A method based on ultrasonic technology to study the crystallization characteristics of injection molded parts has been proposed. A new method for calculating the ultrasonic velocity and attenuation is presented. The ultrasonic velocity and attenuation signals, together with differential scanning calorimetry (DSC) measurements, were used to characterize injection molded polylactic acid (PLA) speci-mens annealed at 80 °C for different periods of time. Experimental results show that the ultrasonic velocity and the ultrasonic attenuation increased with the degree of crystallinity in the annealed specimens. This suggests that the non-destructive ultrasonic technology could be an effective tool in characterizing or monitoring the crystallization of injection molded parts during or after injection molding.
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