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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Experimental Investigation of Combined Electrical and Mechanical Joints for Thermoplastic Composites
Textile-reinforced thermoplastics including embedded sensor networks allow for the production of competitive lightweight structures with integrated functionalities. With regard to assembly processes, material- and function-adapted techniques are needed to join such components efficiently. A combined joining technique based on blind riveting is investigated in the present paper, which enables both the transmission of mechanical loads and electrical signals. Therefor, specimen plates made of glass-fiber-reinforced polypropylene (GF/PP) with embedded conductors were joined by blind riveting. Different joint configurations were analyzed regarding their electrical performance. Also, the characteristics of the rivet joint under mechanical loading were investigated revealing a stable electric connection until the ultimate failure of the joint.
A Parametric Study of the Crack Growth Behavior of High Density Polyethylene Based on Crack Layer Theory
Due to unique characteristics of the crack growth behavior of polymers, conventional fracture mechanics approaches on the crack growth have not been very successful. Crack Layer theory (CL) can be a good theoretical approach to model the sophisticated crack growth behavior of polymers. According to CL theory, polymers have different size and shape of process zone (PZ), and, especially, in the case of high density polyethylene (HDPE), a crack commonly propagates in a discontinuous manner under fatigue and creep loading conditions. In this paper, a parametric study was performed by a computer program based on CL theory for HDPE with two general types of test specimens, i.e. single edge notched tension (SENT) specimen and compact tension (CT) specimen. The effects of key parameters, i.e. the stress ratio (R-ratio) which is defined as the ratio of minimum and maximum stress of loading, specific fracture energy, and draw stress, on the crack growth behavior of HDPE were studied.
Electrospun Protein and Polysaccharide Nanostructures to Improve Barrier Properties of Multilayer Systems Based on Polyhydroxyalcanoates and Biopolyesters
This work studies de effect of incorporating high barrier se lf-adhesive nanostructured interlayers of zein, pullulan and whey protein isolate between of polyhydroxyalkanoate (PHA) materials. Oxygen and water vapour barrier properties were greatly influenced by the morphology, thickness and inherent barrier of the electrospun interlayer materials. Thus, zein (in agreement with previous works) and pullulan formed fibrillar structures which significantly contributed to improve barrier properties of the multilayer systems. On the other hand, electrospun WPI formed bead microstructures and did not improve oxygen and water barrier properties of these multilayer systems. While the oxygen barrier properties was significantly improved by the presence of a zein nanostructured interlayer, the water vapour permeability of this multilayer system was seem to vary among materials since the zein interlayer was only efficient as a barrier element in the PHA materials as compared to polylactic acid (PLA).
The Influence of Process Parameters on the Mechanical Properties of Textile-Reinforced Thermoplastic Composite Structures and the Functional Capability of Integrated Sensor Elements
Within the Collaborative Research Centre 639 “Textile-reinforced composite components for function-integrating multi-material design in complex lightweight applications” novel processes for the manufacturing of structures are developed. In this context the process chain from the filament to the part is considered [1, 2]. One focus is on the production of biaxial reinforced multi-layer fabrics (MKF) out of hybrid yarn textile thermoplastics (HYTT) and their processing to complex structures using novel mold- and manufacturing technologies. Based on preliminary tests it is known that process parameters like temperature, applied pressure and holding time have an influence on the mechanical properties of the analyzed material combination glass fiber and polypropylene (PP). Hence, the correlation of these parameters was analyzed using a statistical design of experiments method to set and achieve high mechanical properties of the samples. Furthermore, to exploit possible application and function integration, the capability of this applied material combination can be utilized by embedding sensor elements. In this context, the integration of sensors was investigated in some random tests. Here, different exemplary chosen production processes were compared concerning the functional capability of the sensors.
Influence of Interfaces/ Weld Lines on Fracture Behavior of Polypropylene Specimens Related to Material Properties
In this study the correlations between inner properties and fracture behavior were investigated on the “cold” interface that occurs during a multi-shot injection molding process and “hot” interface or well known as weld line, which represents two melt streams meeting. By using Nanoindentation, inner properties, like Young’s modulus, were measured through the cross section and had shown similarities to break surfaces. With reference to in-situ SEM tensile test the fracture behavior becomes clearer. Imbalances of mold design, caused by core mechanisms, which are required for multi-shot injections, are reasons for deviation of properties. As basis for complex components, these results provide fundamental approaches.
On the Microstructure and Mechanical Performance of Friction Spot Joining with Additional Film Interlayer
Friction Spot Joining (FSpJ) is a new technology for joining polymer-metal hybrid structures. The technique is environment-friendly and involves very short joining cycles. The feasibility of FSpJ to produce composite to metal structures has already been demonstrated. The intention of the current work is to investigate the FSpJ of aluminum AA2024-T3 / CF-PPS with additional polymer film interlayer. The joints showed similar bonding mechanisms to other composite-metal FSp joints, i.e. mechanical interlocking and adhesion forces. Sound joints with promising mechanical strength (up to about 2000 N) were produced. The temperatures involved during the joining process were also studied (peak temperatures between 350 to about 400°C). The strength of the FSp joints with interlayer proved to be affected largely by the tool plunge depth in the selected range.
Abrasive Wear Behavior of Different Fillers in PP Measured by Means of a Novel Injection Molding Wear Apparatus
The aim of this work was to investigate the abrasive wear of test platelets inserted in a novel injection molding wear apparatus with a capillary slit die in regard to the filler amount, type and geometry in the polymer melt processed through the slit. Furthermore the arrangement of the filler material along the slit was considered. We found, that the geometry of the filler has a high influence on the abrasive wear. From all tested filler materials, the long glass fibers induce the highest damage to the surface.
Optimization of Pack and Hold times for Hot Runner and Valve Gated Systems in Injection Molding
For cold runner molds, the pack and hold times are optimized by conducting a gate freeze study (or gate seal study) where the part weight is recorded as a function of the pack and hold times. When the gate freezes the part weight remains constant with increasing pack and hold times. A second or so is added to the lowest value of time where the part weight stays constant and this number is taken as the total time for the setting of the pack and hold times. However, in hot runner systems or in valve gated systems the gate area always has molten plastic and therefore the above method does not produce acceptable results. A method for optimizing this value in hot runner systems or valve gated systems is proposed based on the Cosmetic and Dimensional Process Window concept that was introduced by the author in an earlier paper. This was followed up with experimental results.
Test Method Development for Outdoor Exposure and Accelerated Weathering of Vinyl Siding Specimens
This paper provides an overview of extensive research conducted by the Vinyl Siding Institute (VSI) on the development of new test methods for exterior plastic building products. The purpose of the VSI study was to develop an accelerated testing protocol for use in certifying materials. This paper describes the development of an outdoor certification test program and subsequent efforts to create an accelerated weathering test method that could be used to predict the results of the outdoor protocol with a high degree of accuracy. Outdoor weathering tests were conducted in Florida, Arizona and Northern temperate locations to obtain baseline data for comparison. This part of the research led to the development and subsequent publication of ASTM D6864. Accelerated laboratory tests were performed in Fluorescent UV/Condensation test apparatus and Xenon Arc test chambers. The process involved the examination of multiple types of equipment, multiple cycles, and multiple conditions, and comparing the various results to the outdoor exposures. Testing suggested that for this particular material, one method was more suitable than the other. The proposed method was verified with repeat testing and rugged statistical analysis. Round robin testing was conducted to determine repeatability and reproducibility. Although the proposed accelerated method was not adopted into the VSI’s certification program, its results demonstrated high rank order correlation with outdoor test results, giving the user much greater confidence that materials passing the accelerated test will pass the outdoor test. The accelerated method, therefore, is useful during research and development because it provides a fast and reliable method for evaluating small formula changes. It is useful for selecting formulations to include in a 2 year certification test.
Formation of Morphology as a Function of Process Control by Foam Injection Molding of a Functionally Graded Component
A special mold technology enables the production of foam injection molded components with locally differing foaming ratios. Thus, components with functionally graded foam structures can be produced in one processing step. The method (pull and foam method) is based on the idea of creating components with thin-walled areas with a high surface quality and partially foamed, thick-walled areas (e.g. with the function of integrated structural elements) in a controlled foaming process. This paper describes the characteristics of the structure and density in the differentially foamed areas in correlation with the essential processing parameters.
Investigation of Melt Modulation Control and its Effect on Cold-Runner Injection Molding Packing Parameters and Final Product Quality
This paper describes current efforts to investigate and expand melt modulation capabilities in controlling the packing parameters of cold-runner based injection molding processes. Packing parameters, including packing pressure and packing time, have significant impact on the internal molecular orientations, mechanical properties and optical performance of injection molded polymeric products. This investigation focuses on manipulating and controlling packing parameters using melt modulation in order to produce molded parts with different optical and physical properties in each injection molding cycle. Numerical simulations of common thermoplastic optical polymers, such as PMMA, PC, and PS are also demonstrated herein.
Improved Processability and Productivity of Thermoset Compounds Using Sp Scorch Protected Peroxides
Peroxides are used to vulcanize a wide variety of elastomers and plastics including saturated polymers that are not curable by other means. The cure rate obtained varies depending on the stability of the peroxide. Some peroxides provide relatively fast cures but could suffer from premature crosslinking which is also known as scorch. This may result in higher scrap rates and clogged processing equipment. Other peroxides cure more slowly and are less prone to scorch but require longer cycle times. To address this predicament, Arkema has developed a series of scorch protected peroxides1 which are capable of providing protection against premature crosslinking while not affecting the overall cure time. This allows the use of faster curing peroxides to reduce cycle times without concern about scorch. It also allows for more rigorous mixing and processing conditions to increase output without sacrificing efficiency.
Sb2O3 Free FR PBT Product Development
Antimony trioxide (Sb2O3, ATO) is widely used as a flame retardant in combination with halogenated materials. The combination of the halides and the antimony is the key to the flame-retardant action for polymers, helping to form less flammable chars. The Objective of this work is to develop ATO free FR PBT products with equal robust FR properties. Many candidates were screened to replace ATO as the flame retardant synergist. Among them all, one FR combination package with no ATO was tried in a glass filled PBT system. Experimental results demonstrated that this ATO free FR PBT product shows good flame properties and passes UL 94 V0 rating @ 0.71 mm thickness. Meanwhile, the physical properties, mechanical properties, and processability were all well maintained. In addition, the ATO free FR PBT formulation is very robust against both extreme extrusion conditions and abusive molding conditions even when recycle materials are incorporated. The same ATO free FR package has the potential to work in other unfilled and filled PBT resins or blends too.
Tuning the Compatibility of Polyolefins with Polypropylene-Based Olefin Block Copolymers – Stiff, Tough, and Clear
Polyolefin materials requiring high clarity and low haze are still challenged to achieve the material property balance of stiffness and toughness required for durable storage containers and food containers especially at low temperatures. The selection of polypropylene polymers having a combination of high clarity and impact resistance is limited to random copolymers (RCP), impact copolymers (ICP) or those impact modified with elastomers that are either miscible with the polypropylene (PP) or have similar refractive indices. Impact efficiency of an elastomeric modifier is directly related to its crystallinity and dispersion of the individual elastomer domains into a PP matrix. Conventionally, dispersion of an elastomer into polypropylene is challenged by the melt-mixing process and compatibility with the polypropylene. The recently announced INTUNE™ polypropylene-based olefin block copolymer comprising iPP hard blocks and ethylene-propylene soft blocks can minimize the compatibility differences (between the polypropylene and an ethylene-based elastomer) by containing intra-chain segments that are compatible with polyethylene and polypropylene, respectively (1). This new polyolefin compatibilization approach is effective in combination with ethylene-based elastomers for improved dispersion and morphology stabilization, leading to modifier solutions that have high impact toughness and clarity in polypropylene.
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”  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 . 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.
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