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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Energy Transfer Single-Screw Extruder Design For Peroxide-Containing Polyolefin Compositions
Peroxide-containing ethylenic polymers are used in many power cable applications. The processes involve extrusion of the polymer compositions to form one or more layers on a conductor, followed by crosslinking in a continuous vulcanization step. To extrude the composition, it is critical to maintain a low discharge temperature so that the peroxide does not decompose significantly during the extrusion process, so as to prevent premature crosslinking. However, with a low discharge temperature, the rate is usually reduced; for some formulations, the rate reduction is dramatic. This paper describes an energy transfer (ET) screw design that enables high rates at acceptably low melt discharge temperatures, or alternatively, yields significantly lower melt discharge temperatures at a given rate than a conventional Maddock mixing screw. The design simulations of the new ET screw were validated experimentally.
Engineering Impact Modification of Polypropylene for Low-temp/High-strain rate Loading Conditions
This communication presents a systematic investigation of polypropylene (PP) formulations modified using SEBS (Styrene-ethylene/butylene-styrene) and POE (Polyolefinic elastomer) block copolymers for impact modification. Impact performance of PP formulations containing POE, SEBS+POE and SEBS is compared under extreme conditions (high strain rate at -15°C and -30°C) and during quasi-static fracture tests at 25°C. Present work also discusses the effect of talc reinforcement on the fracture toughness of these formulations. The focus of the present work is to investigate the failure mechanisms of these formulations and understand how it correlates with the size, shape and other morphological features of the phase-separated SEBS and/or POE domains. The results show that the formation of crazes is the major energy absorbing mechanism at subzero temperatures. The 1 um domain sizes for SEBS modified PP leads to the stabilized craze formation and the highest fracture energy absorption amongst all the formulations investigated. It is shown that the effective stiffness of the dispersed phase and optimum particle size controls the damage density and energy absorption for polypropylene under extreme conditions.
Enhanced Filling of Injection Molds By Microstructured Cavity Surfaces
The main objective of this paper is to evaluate the influence of microstructured injection mold cavity walls on cavity filling. Thermoplastic material has been tested with a variety of micro structured molds. The area density of the structures has been varied and the flow length of the plastic melt using constant filling pressure has been measured. Microstructures applied on one side of the injection mold significantly extend the flow length of the molten plastic. In addition, depending on the processing viscosity, there is an optimum structure area density for the longest possible flow paths. This knowledge is therefore valuable in production to realize longer flow paths with the same machine technology.
Enhancement of Binding Matrix Stiffness In Composite Filament Co-Extrusion Additive Manufacturing
The Flexural modulus and strength are an intrinsic aspect of parts produced via dual matrix composite filament co-extrusion (CFC) based additive manufacturing. In this research work, the main objective is to optimize thermoplastic’s (TP) flexural properties by reinforcing it with particulate fillers for CFC printed parts. Accordingly, an effort has been made in this respect and neat Polyamide-6 (PA6) and its composite (PA6.CF) was chosen as a binding matrix for CFC flexural specimens. The PA6 binding matrix is reinforced with particulate carbon fibers (PCF). To improve the compatibility between the PCF and matrix, stearyl titanate coupling agent (1.5 wt. %) was utilized. Constraints such as defects and porosity are of critical attributes and play a vital role in defining the mechanical performance of the 3D printed parts. Herein, the printed specimens were subjected to a non-destructive testing method: micro-computed thermography (µ-CT). PA6 and reinforced PA6 specimen revealed similar porosity and defect volume. Furthermore, the three-point bending test results of 3D printed CFC composite with PA6.CF as a binding matrix showed approx. 46% increase in flexural stiffness and 27% increase in flexural strength when compared to CFC specimens printed with neat PA6 as a binding matrix. In addition, the cryo-fractured fractography of carbon composite filament, an epoxy-based thermo-cured continuous carbon fiber, revealed even distribution of carbon fibers with no visible voids.
Erucamide Slip Analysis in Polyethylene by GC using a Nitrogen Chemiluminescence Detector
Additives are commonly used in polyethylene applications to provide processing and long-term stability as well as to enhance or modify polymer performance for specific physical properties. Slip agents are one type of modifier used to alter the coefficient of friction in polyethylene films. Fatty amide based slip agents function by migrating to the surface of the film to provide a lubricating layer which enables the film surfaces to slide more easily across one another and when in contact with blown film extrusion and conversion equipment to facilitate processing. A combination of direct (e.g. XRF) and indirect (e.g. HPLC) analytical methodologies are used to measure the additive types and levels used for polyethylene applications. For slip agent analysis, the fatty amide is typically separated from the polymer matrix using an extraction technique (e.g. Soxhlet, Microwave, ASE) or by use of total polymer dissolution followed by polymer precipitation. The extract is then filtered and analyzed by a chromatographic technique, typically, HPLC-UV, GC-FID, or GC-MS. In some instances, polymer matrix signals from oligomers or other additives can interfere with the analysis. Furthermore, the slip agents from various suppliers are a mixture of fatty amides so analysis of the erucamide peak requires inherent knowledge of the specific amide distribution for the supplied slip agent. In this paper, a new and novel use of a gas chromatograph with a nitrogen chemiluminescence detector will be presented which illustrates a universal calibration of erucamide slip agents that compensates for the various amide distribution profiles from three different suppliers. This approach can also be extended to other slip agents such as behenamide and oleamide.
Experimental vs. Numerical Buckling/Post-Buckling Response of Cantilever Orthotropic Web Beams Under Tip Force
A combined numerical and experimental study of lateral torsional buckling of orthotropic rectangular section beam is presented. Pre and post-buckling analysis of beams is studied using Abaqus Riks analysis and compared with experimental results. Timoshenko’s solution with replacement stiffnesses is adopted to calculate the lateral torsional buckling load of six orthotropic beams. Four laminated composite beams with 0 degree layups and two beams with 90 degree layups are prepared in lab. Beams had different length-to-height (l/h) ratios ranging from 6.67 to 20 to study its effect on the critical load. All beams are assumed cantilever and tested under a concentrated load at the free end. Two laser pointers mounted horizontally at the free end are used to measure twisting rotation of beam section (β) for every load increment. Load vs. β plots are generated and compared with numerical and analytical results. The proposed experimental technique could be adopted to study lateral-torsional buckling response of laminated beams with arbitrary fiber orientations (generally anisotropic) under different load and support conditions. The technique also helps to generate load vs. lateral and vertical deflection simultaneously while measuring the section twisting rotation angle (β).
Experimental Wear Data Acquisition for Condition Monitoring in Injection Molding Machines
Condition Monitoring and Predictive Maintenance are big fields of research in the context of Industry 4.0. The ability of determining the state and predicting the lifetime of specific components can have a big economic impact. As datasets from production containing wear data are rare, it makes sense to generate this data in laboratory experiments. In this paper we present methods for implementing condition monitoring of injection molding screws and non-return valves. After developing key indicators, wear datasets are generated in laboratory experiments and the results are compared to the theoretical considerations.
Extension of the Rivlin Polynominal for the simulation of the non-linear material behaviour of TPE
The non-linear material behaviour of thermoplastic elastomers (TPE) show a considerably higher stiffness compared to pure elastomers due to the presence of the thermoplastic phase. The approximation of non-linear material behaviour via generally known hyperelastic material models illustrate some deficits regarding the initial stiffness and the course at higher deformation. In order to ensure a precise dimensioning of TPE parts via the finite element analysis (FEA), current hyperelastic material models have to be extended by user-defined formulations. For this purpose, the existing Rivlin polynomial is extended by an additional material parameter as exponent. This extension leads to a more accurate prediction of the non-linear material behaviour. Even the simple extended Neo-Hooke material model shows a good accuracy regarding the determined material behaviour and the initial stiffness of the used practical part.
Fabrication of Multifunctional PVDF/MWCNT Nanofibrous Membrane via Electrospinning for Membrane Bioreactors
Nanofibrous membranes in membrane technology applications for water and wastewater treatment have gained interests among researchers because of their high mechanical and chemical resistances. In this study, Polyvinylidene fluoride (PVDF) nanofibrous membranes were prepared by electrospinning method with 20 wt% PVDF solution. The effects of processing parameters including flow rate, applied voltage, tip-to-collector distance and presence of multiwalled carbon nanotube (MWCNT) on fibers morphology were observed using scanning electron microscopy. The changes of fiber diameters, pore size, and membrane porosity were investigated to investigate the characteristics of nanofibers as a function of processing parameters. The modified membranes with MWCNT were characterized with contact angle analyses and water filtration tests to evaluate the performance of the membranes.
Failure Analysis of an Outdoor Instrument Housing
Cracking occurred within the housing for a piece of weather monitoring instrumentation being used as part of field service trial. The cracking was observed within the bosses used to secure the housing section to the mounting hardware. The focus of this investigation was the determination of the nature and cause of the failure. The results obtained during the evaluation of the failed housing indicated that the cracking occurred through three separate mechanisms. Significant factors in the failure included aspects of design, manufacturing, and the service conditions. This paper will review the testing performed to characterize the failure modes and identify the causes of the cracking, while demonstrating the analytical procedures used in the investigation.
Failure Analysis of Polymer Coating Systems
Failure analysis of polymer coating systems can be challenging due to the fact that coating systems typically involve multiple and generally very thin layered components. The root-cause for the failure of a polymer coating can be attributed to many factors. Thus, it cannot be easily determined by inspection or observations, and significant amount of testing is often required to determine the root cause for the failure. Typically, failures can be caused by selection of improper coating system, or it can be caused by insufficient surface preparation, or it can be caused by application related issues. This paper attempts to provide a guide to performing failure analyses of polymer coatings by discussing two separate coating systems that utilized a polyvinylidene fluoride (PVDF) top coat and evaluates the fundamental root causes of failure. The importance of reviewing background information, performing site-inspections, conducting relevant laboratory and field testing, and utilizing published literature to reach a root-cause for the failure is high-lighted. In both cases, laboratory examinations revealed that while high performance coatings were utilized, their compatibility within the system and their susceptibility to hazards within their respective applications, were not accounted for, leading to poorly designed coating systems that eventually failed.
Fatigue Resistance of Structural Adhesives
Adhesive selection in high dynamic load environments relies heavily on mechanical adhesive properties, including shear, peel and compressive strength. Over time and in the life a part, fatigue can occur to metals, plastics and adhesives. Fatigue weakens the overall strength of these components and can lead to premature failure. In the case of adhesives, shear strength values may depreciate an order of magnitude, from thousands to hundreds of psi due to a life of wear and dynamic movement, which can lead to failure. When selecting an adhesive for bonding a joint, the likely first choice is the adhesive with the highest shear strength with the assumption that the higher the shear strength the longer the part will last. However, upon testing, higher shear strength does not directly correlate to a longer part life. In the case of hybrid adhesives (Loctite® HY4090GY™ and HY4070™) compared to epoxies (Loctite® E-20HP™), the epoxy greatly outperformed the hybrids in shear strength, but the hybrids greatly outperformed the epoxy in limit of endurance. Overall, the methyl methacrylate (MMA) adhesive (Loctite® H8003™) proved to be the most fatigue resistant adhesive tested.
Fibrillated and Highly Interconnected Porous PCL Scaffolds by Supercritical Foaming and Leaching
Highly porous and interconnected 3D structures are crucial elements for tissue engineering scaffolds since they can support the mass transport of cell nutrients and waste. Supercritical foaming technology is an environmentally-friendly and solvent-free way of manufacturing porous scaffolds. In this research, highly porous, interconnected poly(ɛ-caprolactone) (PCL) scaffolds combined with supercritical carbon dioxide (SCCO2) foaming and a polymer leaching process were fabricated by blending PCL with water-soluble poly (ethylene oxide) (PEO) as a sacrificial material. The effects of phase morphology of PCL/PEO blend on foaming behavior and pore morphology were investigated. The incorporation of PEO not only facilitated the foaming of PCL by increasing its viscosity, but also improved the porosity and interconnectivity of the post-leached PCL scaffolds. The fibrillated porous scaffolds with open-pore content up to 91% were obtained after the leaching process because of two different cell-opening mechanisms. Cell-opening on surface of scaffolds is difficult in preparing porous materials. In the end, a novel method for improving surface porosity and producing the so-called outer and inner porous PCL scaffolds is described. The information gathered in this study may provide a theoretical basis for research into porous tissue engineering scaffolds.
Finite Element Modeling on Barrel Mar Behavior of Amorphous Polymers
Mar damage on polymer surfaces has become a significant concern over a wide range of engineering applications. To gain insight into the strategies for improving mar damage resistance of polymers, it is necessary to learn about why and how mar damage is formed and how it is related to constitutive parameters such as Young’s modulus and yield stress, etc. In this study, three model amorphous polymers, i.e., PMMA, PC, and PS, were investigated using a well-established ASTM/ISO scratch testing in combination with the finite element method (FEM) parametric study to gain the fundamental structure-property relationships to furtherly understand mar damage. It is found that the total plastic energy dissipation during mar process correlates well with mar damage formation and can possibly be chosen as the criterion for mar damage formation. Three-dimensional FEM parametric study was further performed based on the verified mar damage criterion.
Flow Simulation of A Microcapillary Cast Film Die
A relatively wide (610 mm) lab-scale microcapillary cast film die was fabricated to aid in the development of this unique film processing technology. Due to the approach used to create microcapillary channels, standard die design techniques for maintaining uniform film gauge (e.g. die lip adjusters) are not applicable. A series of modifications were made to the original die design to improve film gauge. One such modification was the use of computational fluid mechanics (CFD) to improve flow uniformity across the die. Due to the multitude of air pins located near the die outlet, it is impractical to perform direct CFD simulations based on the actual flow geometry. Instead, the flow geometry associated with the comb-like structure of the air pin region is replaced by a porous medium with an equivalent viscous resistance. The primary focus of this paper is a description of the porous medium CFD technique used in the design of the 610 mm wide die.
Foam Sheet Extrusion with Blowing Agent Mixtures and Correlation Analysis With Dimensionless Numbers
In foam extrusion, the blowing agent has a significant influence on the process parameters and the resulting foam properties. Low-density polystyrene foam sheets are usually produced with aliphatic hydrocarbons or alkanes as physical blowing agent. Due to the necessary safety precautions and the environmental impact, there is great interest in using alternative blowing agents such as carbon dioxide (CO2). The sole use of CO2 often leads to corrugation, open cells or surface defects on the foam sheet and therefore requires modifications to the process technology. The aim of this work is to investigate the effect of blowing agent mixtures of CO2 and organic solvents on the production of foam sheets. In particular, the interactions between the blowing agent formulation, the process parameters and the foam sheet properties are analyzed. The knowledge of the interactions can allow a systematic influencing of the foaming behavior without modifying the polymer itself. For a systematic evaluation, an existing process model for describing the melt flow in the extrusion die is extended and applied to an annular gap die. Based on the model, dimensionless numbers can be calculated to describe the foaming behavior. The characteristic numbers enable the direct comparison of different recipes, process settings and die geometries.
Foaming of PVC Using Ultra High Molecular Weight Acrylic Processing Aids
Polyvinyl Chloride (PVC) foaming was studied as a function of high molecular weight acrylic processing aids. It was demonstrated that an ultra-high molecular weight processing aid is 25-30% more efficient than relatively lower, but still high, molecular weight acrylic processing aids. The higher Mw processing aid provided similar foaming performance at lower loading levels. Foaming reduced the density of PVC compounds to 0.32-0.34 g/cc. More than 1000% expansion was achieved in the melt extrusion process using a chemical blowing agent. Fusion characteristics were also studied. Fusion times for initial fusion peaks were in the range of 42-44 seconds while the fusion times of the second fusion peaks were in the range of 74-94 seconds. The higher molecular weight processing aid maintained fusion characteristics of PVC compounds, warranting no significant changes in extrusion process.
Functional Alkane Solvent Systems
An oligomeric hydrocarbon, Poly(α-olefins) (PAOs), were previously reported as a potential greener solvent to replace conventional alkanes solvent due to its lower toxicity, flammability and volatility. However, its poor solubility toward most organic substrate may limit its applications as solvent. This work demonstrated three strategies to introduce polarity in PAOs and recycle polar additives simultaneously: polymerization of polar monomers onto a PAO anchor, host-and-guest interaction and end-group modification of a PAO anchor, vinyl-terminated polyisobutylene (PIB). In the first method, RAFT polymerization gave a better control of polar polymers onto PIB in order to maintain hydrocarbon solubility over other two polymerizations (hydroboration/O2 initiation, ATRP polymerization). Secondly, the polar polymer, poly(isopropylacrylamide) (PNIPAM) could be successfully brought into and recover back out an alkane phase by treating with chemicals via a hydrogen bond network. The reversible solubilization of PNIPAM were used in recyclable Rhodium catalyzed hydrogenation. Lastly, a hydrophilic moiety (Hexamethylphosphoramide, HMPA) was successfully incorporated onto PIB. The hydrocarbon soluble Lewis base catalyst can be used in allylation of benzaldehyde in PAOs. Other ongoing studies are exploring this molecular recognition based solubilization with other solubilizing agents, other precipitation agents and exploring the use of this chemically responsive solubility both as a tool to prepare new solvent systems and new sorts of recyclable catalysts.
Glass Reinforced PA 66 Compound with Improved Flowability for Thin Wall Applications
Glass reinforced polyamide compounds are widely used in various applications. Many of these applications require a material with high flowability to allow the molders to properly manufacture parts with thin walls and complex geometries. In this study, a flow enhancing additive is used to improve the flowability of a glass reinforced polyamide 66 compound. Flow characteristics of the new formulation were studied using various characterization methods. Test results showed that physical and mechanical properties were maintained very well while flowability of the modified formulation was enhanced significantly compared to the control material.
Hot Runner Molding of Bioplastics and Recyclates
The interest for molding of bioplastics and recyclates is continuously increasing, not only with increased awareness of sustainability issues but also in response to regulatory mandates to reduce environmental impact. Bioplastics and biopolymers have been successfully derived from renewable resources, however their commercial adoption remains hindered by the lack of processing experience. Degradation issues are a potential concern for manufacturers, especially for hot runner injection molding. In this work, the performance and thermal stability of three commercial biopolymers and a recycled resin were characterized and compared to a reference synthetic polypropylene. The results indicate that bioplastics can be readily processed by hot runner injection molding by following design and processing rules similar to those conventionally implemented for synthetic resins. Minor degradation and quality issues are solved by routine optimization of processing parameters.
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