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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A Practical Example of Film Extrusion Process Troubleshooting and Fine Tuning
This case study is a practical example showing the importance of process and material characterization when designing high performance extrusion dies. In this study, we show the approach to troubleshoot a film extrusion process as the initial extrusion performance is not meeting the theoretical behavior.
Warpage Control of Thin-Walled Parts Using Local Mold Temperature Setting in Injection Molding
Computer, communication, and consumer electronics products are currently required to be lightweight, portable, and convenient. Injection molding is among the most used techniques for mass production in plastic processing industries; however, producing thinner parts that do not warp is challenging. Causes of warpage in thin-walled molding are numerous such as material properties, product geometry, mold design, and processing conditions. For example, inconsistent thickness in component geometry, poor sprue-runner-gate or cooling design in the injection mold, and improper molding condition settings may cause plastic parts to warp excessively. Warpage causes unpredictable component shapes, which may cause poor assembly quality. Although mold cooling achieved by adjusting mold temperatures improves warpage, the conventional single mold temperature setting for each male or female mold plate limits the cooling capability. Consequently, this study employs an asymmetric cover for handheld communication devices as a research carrier, and proposes a local mold temperature setting to adjust the deformation of injection molded parts. Particularly, a neutral axis theory for analyzing the temperature distribution at the cross section of the thickness and then predicting the trend of warpage is used. Through CAE simulation and experiment, the feasibility of employing an ideal cooling design featured with local mold temperature setting to reduce warpage has been verified.
Evaluation of Shelf Life of Resin
Resin samples were aged under accelerated conditions and post aging Material characterization was performed using analytical techniques such as Gel Permeation Chromatography (GPC), Oxidation Induction Time (OIT) and Differential Scanning Calorimetry (DSC).
Each technique provided specific polymer evaluation. GPC was used to provide molecular weight information. Molecular weight of polymer is one of the key characteristics since it is related to mechanical properties such as stiffness, tensile strength and flexibility of the material. Molecular weight of polymer is directly related to overall performance of material.
DSC was used to provide thermal properties such as melting and glass transition temperature of polymer. These thermal properties are mainly used in establishing processing conditions (molding and extrusion) of polymers. Any drastic change in the melting point affects process settings and can be related to material degradation via change in the melt viscosity.
The primary source of degradation during shelf life exposure is thermal oxidation. Resistance to oxidation is manifested by a higher OIT. As a result, Samples are placed into DSC testing equipment with continuous exposure to oxygen for set amount of time and temperature. Output is recorded as time (minutes) it takes to observe oxidative exotherm.
In summary, key material properties such as molecular weight , oxidation resistance and thermal property (melting point) were unchanged when exposed to accelerated aging conditions simulating ten years (in case of ABS, Nylon, PEBAX, TPU and PVOH resin will be five years) of shelf life.
Novel Saturated Slip Additive with Superior Oxidative Stability
Since the 1950?s primary fatty acid amides have been used as additives in polyolefins and other polymers to reduce the coefficient of friction of films, enable easy mould release, enable easy assembly of moulded components and reduce tendency of polymer articles to scratch. Unsaturated amides such as oleamide and erucamide have been recognised the best performing additives in this area giving low friction by rapid migration to the polymer surface to form a coherent lubricating layer or layers. It is also well known that the elimination of the double from oleamide or erucamide offers considerable advantages in oxidative stability over the unsaturates but at the expense of slip performance.
This work illustrates that by manipulation of the alkyl chain it is possible to produce a fully saturated slip additive with excellent stability whilst retaining good friction reducing performance comparable with unsaturated slip agents. Comparison of this new slip additive with conventional slip agents in LDPE film, PP film, PP and bottle closures is reported showing the additive to be largely equivalent to erucamide.
Colour and retention of slip properties after exposure to an oxidising environment is also demonstrated along with good anti-scratch and low visible bloom in a black PP automotive formulation.
High Strain Rate Testing of Glass Fiber Reinforced PEEK
Fiber reinforced polymers are used in a wide range of applications involving impact, including automobile and aerospace components, consumer products, and industrial products. These materials, however, are difficult to characterize under high strain rate conditions, particularly at strain rates exceeding 1000 1/second. This difficulty occurs due to numerous factors, including specimen design and size factors, absence of appropriate test equipment for high strain rate characterization, and interpretation of measurement data. This presentation presents high strain rate testing experience on short fiber injection molded thermoplastics. We present stress/strain behavior at different strain rates, and discuss the effect of specimen design and different methods to evaluate high strain rate response and failure
Benefits of Conformal Cooling in improving Blow Molded Container Performance
Mold cooling efficiency often affects container performance in many ways. The change in dimensions after molding and the gradual relaxation stresses can cause performance issues. For example, carbonated soft drink containers can exhibit a lower level of stress crack performance or excessive gate area relaxation can cause containers to rocker and tip over. The higher production speeds associated with newest machinery, result in lower blow mold residence time. This is justification to take a fresh look at how to improve the package performance via more effective mold cooling. This study looks at improving mold cooling methodologies via virtual modeling. This is done by analyzing different preform and mold temperatures to determine optimum cooling channel design. Several case studies for petaloid and champagne style-base for carbonated soft drink containers are presented in this paper.
Using ZeMac? Copolymers To Reduce Costs in Nylon Compounds While Meeting Exacting Customer Performance Specifications
Nylon is widely used in many applications. At the 2013 ANTEC in Cincinnati, our paper covered the results obtained with compounding primarily recycled nylon with the addition of small quantities of alternating ethylene and maleic anhydride ZeMac? copolymers and specific property improvements for applications in injection molded compounds. The resulting compounds have performance that can match or exceed prime virgin nylon at 30-50% cost savings. At the 2014 ANTEC in Las Vegas, our paper covered the performance enhancements to provide several advantages for upgrading virgin nylon such as increasing relative viscosity for improved melt strength and the unique improvements obtained in impact-modified nylon-6 and nylon-6,6 by reducing the negative impact of traditional impact modifiers by offering synergistic set of properties. This current paper will cover how using the unique chemistry of these copolymer products can reduce costs in nylon compounds and still meet performance specifications.
PET/Organoclay Nanocomposites Synthesized by Solvent Blending with Sonication
Preparation and analysis of PET nanocomposites with 5wt% organoclay via solution blending using sonication technique. Degree of dispersion of organoclay in PET nanocomposites was observed by using SEM technique. SEM images of plasma treatment etching to show degree of clay distribution in the composite and distance between clay particles was studied and reported. SEM results exhibit the significance of sonication on the separation and distribution of clay particles and layers in the PET nanocomposites. Thermal analysis results using DSC technique revealed that the existence of solvent residue in the cast virgin PET samples and cast PET/clay nanocomposites samples resulted in a decrease of the glass transition temperature and cooling-crystallization temperature but an increase in the rate of crystallization, the heating-crystallization temperature, and crystallinity content.
Analysis of the Rheological Behavior of EPDM Rubber with Blowing Agent
An experimental investigation is made to study the rheological behavior of an Ethylene Propylene Diene Terpolymer rubber (EPDM) compound for extrusion containing blowing agent. The variation of the viscosity with time has been determined using a plate-plate rheometer at constant frequency. The obtained data is modeled using the Castro-Macosko model and the methodology to develop it uses a nonlinear least-squares regression method following the protocol proposed by Hernandez-Ortiz and Osswald. A good agreement between the data and the theoretical values is found and the values of constant viscosity are superposed in the TTT diagram to determine the operational window for the compound. The effect of the vulcanization and the temperature of processing on the rheological properties have also been studied.
Novel Integration Concepts for Automotive Sensors in Composite Structures
An approach to compensate additional costs by using carbon fiber reinforced polymer (CFRP) structures for automotive lightweight components is functionalized lightweight design. The latter is addressed by the publicly funded project ARENA2036-LeiFu, ?Lightweight Design by Functional Integration? at the University of Stuttgart (Germany). As one of the participants the Robert Bosch Company is focusing on the integration of state of the art automotive sensors in CFRP structural parts. The research approach is based on the functional characterization of integrated automotive sensors and their behavior being surrounded by the new carrier material is analyzed. This paper provides an initial functional assessment of the sensor?s characteristics as it is integrated in the new carrier structure. Also a novel preparation towards the integration of the sensor's subsystem inside the laminate is demonstrated.
Parameterization and Validation of Discrete Element Simulations regarding the Pressure Propagation in Plastic Pellets Bulk
The Discrete Element Method (DEM) is a powerful instrument when simulating the behavior of bulk solids such as pellets or powders. However, the quality of the simulation results is directly related to the simulation and material parameters used. The goal of this contribution is to describe a method of parameterization to be used in simulating the compression of plastic goods in form of bulk solids. Particular attention is paid to the coefficient of restitution (COR), as well as to the yield strength of the materials. The parameters under investigation have been determined such that identical pressure-deformation curves could be obtained for the comparison between the simulation and the experimental results. The parameters thus determined can, under certain circumstances, also be used later in simulations of conveyance processes with pressure buildup. Such simulations are important to better understand the buildup of pressure in high-speed single-screw extruders.
Thermal History Effect of PTFE
Failure analysis is often thought of as a technical support service for the sole purpose of fixing underperforming materials, components, systems, or processes which typically result from unforeseen, unexpected, or underestimated conditions or changes. In most cases, identifying the root cause of the issue at hand and providing a mitigation strategy are the primary functions of failure analysis, however more value can be extracted from these efforts. While it is imperative that a root cause and mitigation strategy are identified in the most efficient and effective manner, having the mindset that each effort presents an opportunity for improvement and innovation can drive an even greater impact from these investigations.
One case study will be discussed where during the process of identifying root cause and mitigation strategies of a polytetrafluoroethylene (PTFE) tube failure, additional materials characterization methods and understanding were developed that could have impact on both current and future materials characterization techniques and technology innovations. Specifically thermomechanical analysis techniques were developed to accurately identify the maximum temperature exposure of PTFE tube segments. These techniques were made possible by discovering that PTFE has an inherent thermomechanical memory behavior that effectively records the most prominent temperature excursions while under mechanical stress or applied strain.
Progress in Assessing Fiber Orientation and Flexibility with Increased Fiber Lengths
The mechanical performance of a fiber reinforced injection molded composite is determined by the fiber length and orientation within the part. During processing, significant fiber length attrition can occur which will result in a broad distribution of fiber lengths. In this work, we investigate three fiber length distributions created from the same base formulation in order to gain an understanding of fiber orientation dynamics and shear stress during the startup of simple shear flow. Results show that the rate of fiber orientation and the extent of fiber alignment will decrease with increases in fiber length. Differences in the fiber length appear to be more pronounced in measurements of shear stress in simple shear flow than direct measurements of fiber orientation. A semi-flexible orientation model is used to compare the bending contribution to stress based on measured values of fiber orientation. Trends in predicted bending stress seem to coincide with the experimental values.
A New DSC Thermopile Sensor for combined Heat Flux and Power Compensated Measurements
Claus Linseis, Linseis GmbH, Vielitzer Str. 43, 95100 Selb, Germany
The Differential Scanning Calorimetry (DSC) is the most popular analytical method used in thermal analysis for polymers. The DSC technique is applied to measure the specific heat capacity, phase transitions, curing, kinetics etc.
The performance of a DSC instrument depends on its resolution and sensitivity. However up to now it was not possible to optimize both performance parameters at the same time. There are two basic concepts of DSC instruments- the Power Compensated DSC which has a high resolution and low sensitivity and the Heat Flux DSC with an opposite characteristics.
A new DSC thermopile sensor was designed which can be operated in both modes, heat flux and power compensate. For samples with weak phase transitions or for smallest sample quantities the heat flux mode is used to achieve the highest sensitivity. For applications with several peaks within a narrow temperature range, the sensor can be switched to the power compensated mode with highest resolution.
Non-linear Rheology in Shear and Extensional Flows of Maleated PP-Clay Nanocomposites
The strain dependence of large amplitude dynamic shear moduli and the transient extensional viscosity were investigated for model polymer nanocomposites with organoclays. A linear maleic anhydride grafted polypropylene copolymer was compounded with 5 wt% each of two different organically modified clays that had different onium ion surfactants and different aspect ratios. The non-linear storage modulus for the compound with the higher aspect ratio particles showed a two stage drop with increasing strain which highlights the breakup of two structures at different rates?an entanglement network of particle attached chains with free chains and another entanglement network of free chains alone. The same nanocomposite melt also displayed a greater extent of strain hardening in uniaxial extensional flow. Both effects may be attributed to a stronger polymer mediated entanglement network in this nanocomposite.
Dispersion Effect of Extensional Flow for PP/CNT Nano-Comosite with Blister Disk of Twin Screw Extruder
Extensional flow has been shown to be more efficient solution for improving the dispersion of nano-composites as compared to shear flow. One of the production processes of nano-composites is melt extrusion with co-rotating twin screw extruder (TSE) which is superior in terms of productivity and mixing performance. Our objective is the optimization of Blister Disk geometry which has many holes for improving the dispersion of nano-composites. The holes were drilled through the Blister Disk seal ring segments to create extensional flow in TSE.
However, it was difficult to evaluate the mixing effect of Blister Disk because the flow patterns are complex in TSE, and there is some possibility of no flow through the holes of Blister Disk. To evaluate the dispersion effect of only holes, fundamental evaluation equipment was developed.
Firstly, the stress magnitude was investigated for each elongational flow and shear flow by changing the geometries (e.g., hole numbers, hole diameter and hole width) with 3D numerical simulation. Then, the dispersibility variation of polypropylene (PP) and Carbon Nano Tube (CNT) nano-composite was investigated by using various geometries of Blister Disk with fundamental evaluation equipment.
Transversal Molecular Orientation of Isotactic Polypropylene at Conventional Processing
Structure and properties of an extruded sheet and an injection-molded plate composed of isotactic polypropylene (PP) containing a small amount of N,N?-dicyclohexyl-2,6-naphthalenedicarboxamide as a ?-form nucleating agent have been studied. The nucleating agents exist as needle-shape crystals in the molten state of PP. They orient to the flow direction at processing. Moreover, PP chains crystallize on the surface, in which chain-axis of PP molecules orient perpendicular to the long axis of the nucleating agent. Consequently, PP chains orient perpendicular to the flow direction in the extruded sheet, because the needle crystals orient to the flow direction by the hydrodynamic force. Furthermore, in the case of injection-molded products, the direction of molecular orientation in the skin layer is parallel to the flow direction owing to the flow-induced crystallization. In contrast, PP chains orient perpendicular to the flow direction in the core layer because of the crystallization from the nucleating agents. The anomalous molecular orientation is responsible for the reduced anisotropy in thermal expansion
Nonlinear Structural Analysis of Short Fiber Filled Injection Molded Parts
Short fiber filled injection molded plastic parts are widely used in industrial applications due to their enhanced stiffness-to-weight and strength-to-weight ratios compared to homogeneous plastics and metals. Injection molding simulation software packages can be used to predict the distribution of fiber orientation throughout a part, in addition to the warped shape of the ejected, room-temperature part. In order to facilitate subsequent nonlinear (progressive failure) structural simulation of the short fiber filled part, Autodesk has developed new software to seamlessly link the results of injection molding simulation with nonlinear structural response simulation that features a multiscale progressive failure model for short fiber filled plastics. This paper describes the theoretical foundations and capabilities of the new software.
Preparation and Tube Shortening Effects of Multi-walled Carbon Nanotubes on Electrical and Mechanical properties of Polycarbonate/MWCNT Composites
The effect of nanotube preparation method (freeze drying (FD) vs. oven drying (OD) during synthesis) and length of three multi-walled carbon nanotubes (MWCNTs) on the dispersion and further on the percolation and mechanical behavior of polycarbonate (PC)/MWCNTs composites was investigated. Nanocomposites were melt mixed in a twin-screw micro-compounder at concentration of 0.1-3.0 wt% MWCNTs. Tensile strength was independent of MWCNT concentration while the Young?s modulus slightly increases and strain at break appreciable decreases when compare with pure PC. Scanning electron microscopy (SEM) and light microscopy (LM) micrographs revealed that at sub-micron scale shorter MWCNTs were found to be better dispersed than longer tubes, while at the macro scale the dispersion of long and short MWCNTs was comparable. Also, MWCNTs prepared by oven drying methods were found to be better dispersed at the sub-micron scale. Nanotubes with longer lengths (or aspect ratio (AR)) exhibited higher percolation thresholds (pcS) irrespective of differences in dispersion.
Chemorheological Behaviors of a Reactive Epoxy-Amine System during Isothermal Curing
For a typical reactive epoxy-amine system, the initial (Tg0) and ultimate glass transition temperatures (Tgì) prior to curing and after full cure were measured, respectively, by nonisothermal differential scanning calorimetry (DSC). The chemo-rheological behaviors during isothermal curing of the system were investigated at various temperatures below, near and above the ultimate Tgì by means of dynamic rheometry. According to the characteristics of the time-evolving viscoelastic material functions of the curing system, physical transformations, such as gelation and vitrification, occurring during isothermal curing are identified and analyzed. The dependences of such transformations are then presented in terms of a cure temperature-time-transformation (TTT) diagram, which is of critical importance to providing a practical guidance for the relevant process development in manufacturing a medical device.
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