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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When Standards Get In the Way of Innovation
Standardization is a cornerstone of modern civilization. The weathering testing industry of today exists because of the work of standards writers around the world. However, there can be too much of a good thing. Test standards in weathering sometimes get in the way of innovation. For example, the most common cycle for testing polymeric materials in xenon arc test chambers is the 102/18 cycle. That is, the test is run for 102 minutes with light only, followed by 18 minutes of light plus water spray. Users of weathering standards assume the prevalence of this test cycle must mean that it has been carefully validated for a wide variety of materials over the decades. They may also assume that this cycle was developed to provide good correlation to natural outdoor weathering, with extensive scientific research and statistical analysis to support its broad application. They assume incorrectly. The origin of this cycle dates back to the Victorian era when the first carbon arc weathering test chambers were developed. Rotating racks completed one revolution in two hours, and specimens were sprayed with water for 18 minutes as they moved past the fixed spray nozzles in the chamber. In other words, the 102/18 cycle was set in stone a century ago and has rarely been questioned since then.
Standards have also hindered innovation by overstepping their boundaries. For decades automotive OEMs bemoaned the lack of correlation between their laboratory tests and real outdoor test results. Through the development of SAE J1960 and similar standards, OEMs wrote their testing requirements around specific pieces of hardware rather than test conditions designed to simulate and accelerate natural weathering conditions. Flaws and limitations in the old technology thus became standardized, precluding any improvements to the test methods. A few of the OEMs decided to do something about it, and this was the origin of ASTM D7869, which is a true state of the art weathering test standard fo
Selecting the Best Remediation Option for Failing CPVC Piping Systems
Chlorinated polyvinylchloride (CPVC) is widely used for many piping systems including potable water, hydronic heating/cooling, corrosive liquid drains, and fire suppression systems. CPVC is popular because of its ease of installation and corrosion resistance. However, as with all plumbing products, occasionally pipes or fittings may fail. Our goal as forensic scientists is to determine the root cause of failure of the CPVC piping and to provide the client with data that will help them select the most appropriate remediation option for their building. This paper presents four unique case studies, the forensic tools we used to evaluate the CPVC piping systems, and the logic behind the remediation option selected by the client.
Impact Modeling of Single-Ply TPO Roofing Systems
A finite element model was developed to simulate dynamic stress distributions in thermoplastic polyolefin (TPO) roofing systems subjected to severe impact events, e.g., hail and hard object strikes. In order to build an integrated TPO layered composite roofing system model, separate sub-models are developed that include: the TPO membrane, polyester reinforcement scrim, low modulus closed-cell foam and fiber-glass stiffened facer sheets. A hyperelastic Mooney-Rivlin model of the TPO membrane is utilized to simulate the membrane’s large-deformation mechanical response during simple impact tests. Straightforward force-contact measurements on the TPO membrane material and low modulus foam backing, using spherical indenters, are shown to provide sufficient material properties for the impact model of interest. It is demonstrated that the local failure modes for the layered composite roofing system can be adequately characterized by using relatively simple failure criterion for each of the individual component layers in this type of roofing system. Both high-speed indentation and ice ball impact experimental tests have been performed to evaluate and verify the predicted performance of a single ply TPO roofing system. Excellent correlation is obtained between model predictions and experimental dynamic indentation tests.
Troubleshooting Extrusion Using chillWARE Computer Simulation for Sagging and Collapsing of Pipe Ends
The Extrusion process is a complex process in which a good product quality can only be achieved when all the parameters of influence (e.g. design of machinery, throughput, temperature set up, cooling situation, vacuum level, etc.) are set correctly. In everyday production on only one extrusion lines several products have to be produced (often more than 100 different products on 1 line). Following, process parameters have to be changed quite often to adjust the machine for the demands of the new product. During such a product change procedure, very often product quality problems occur.
Frequent problems like sagging, roughness on surfaces, geometric problems, deformations or a bad mechanical strengths are caused very often by the cooling situation and can often easily be reduced, if correct process parameters would be used. In this paper the use of a computational system is presented to analyze the reasons and possible solutions for such problems during extrusion. The computational system is based on finite difference method and finite element method and shows the capability to calculate the cooling process, the crystallization time and the residual stress distribution in the product.
Improved Troubleshooting and Appropriate Maintenance in Injection Molding Using Adequate Measuring Technique
Injection molding is a sensitive process. After implementing a stable process to achieve the required product quality, there are many potential external disturbances that might lead to downtimes or off-quality production. Machine manufacturers do a lot of research to adjust the process and react on external disturbances, e.g. varying residual moisture of the resin . Disturbances coming from the central cooling unit, air compressors or the nitrogen generator can also lead to low product quality or high production costs, but have not been studied sufficiently as of today.
Simulation Based Determination of the Crystallinity Distribution in Polymer Pipes
The crystallinity and density of extruded semi crystalline polymer products has an intensive influence on the mechanical, geometrical and optical properties. Basically, the final polymer morphology depends on the overall production process. For semi crystalline polymers, the crystallization process can be separated into three sequential stochastic processes: 1. Nucleation: Arising of spherulite origins 2. Growth: filling the space, starting from the origins 3. Secondary Crystallization: compilation of the final crystalline structures Thus, the overall production process has an impact on the degree and type of crystallinity. The crystallization process is very complex and is influenced by the thermal and structure-mechanical history during the production process. A unified modeling of the different phenomena is hard to realize.
The simulation system chillWARE® is utilized to calculate the degree of crystallinity in dependency of the cooling process (thermal history) for polymer pipes. It is shown, how the distribution of the degree of crystallinity and density can be influenced by using alternative cooling technologies like internal pipe air cooling.
The Melt Temperature Variation in the Barrel of Injection Molding Machine
Experimental observations on the melt temperature variation in the barrel of injection molding machine are reported in this article. To examine the temperature variation in depth, the accuracy of temperature sensor should be much higher than the sheathed thermocouple used widely in the field. A novel temperature sensor with a less heat capacity than the usual sheathed type sensors was developed in this study. The effects of some process conditions on the variation were examined. The experimental results showed that the melt temperature in the barrel was affected by the process conditions such as the screw rotation speed and the heater temperatures as well as the injection rate. Also additional conditions such as the shot volume, the dwell time after plasticizing and the length of feeding section were examined.
Investigation of Fiber Breakage Phenomena for Different Fiber Types in Injection Molding
The lightweight technologies become the driving force for people in automotives and other developments in recent years. Among those technologies, using short and long fiber-reinforced thermoplastics (FRT) to replace some metal components can reduce the weight of an automotive significantly. However, the microstructures of fiber inside plastic matrix are too complicated to manage and control during the injection molding through the screw, the runner, the gate, and then into the cavity. In this study, we have integrated the screw plastification, to injection molding for fiber microstructures investigation. Specifically, we have paid our attention on fiber breakage prediction during screw plastification. Results show that fiber breakage is strongly dependent on screw design and operation. When the screw geometry changes, the fiber breakage can be higher even if the compression ratio is lower. Moreover, the fiber breakage phenomena for two types of fibers (glass fiber and carbon fiber) are also investigated. It shows that carbon fiber is easier to be broken. Also the carbon fiber length distribution has higher peak at the exit of the screw.
Tannic Acid: A Bio-based Intumescent Char-forming Additive for Nylon 6
Intumescent and char forming additives are typically blended into certain types of commercial plastics to impart resistance to fire propagation. Intumescent compounds such as ammonium polyphosphate/ melamine/ pentaerythritol, silica gel/potassium carbonate are already used as flame retardant (FR) additives. In this work, a naturally occurring polyphenol, namely tannic acid, is explored as an intumescent and char forming additive for polyamide - Nylon 6. The tannic acid was meltblended into Nylon 6 and the compounded plastic was evaluated for thermal stability, total heat release (THR) and heat release capacity (HRC). It was found that HRC and THR of nylon blended with tannic acid decreased by 50% and 20% respectively.
Scratch Resistance of Thin polymeric Films: Effect of Orientation and Polyethylene Content
Thin films are extensively used in many industrial applications such as automotive, electronics and packaging industries. However, their properties are significantly affected by several mechanical damages like scratch. Little has been done to understand the scratch behavior of polymeric thin films. Here, we consider investigating the impact of orientation and ethylene addition on the scratch resistance of PP thin films using an ASTM/ISO standard. Experimental results show that scratch resistance has improved with higher film orientation and lower ethylene content. A comparison between machine direction and transverse direction shows that scratch performance is much better in MD. Also, an FEM simulation has been performed to support the experimental findings. It is believed that this study is beneficial to design polymeric films with better scratch resistance.
Fundamental Factors for Opacity and Tint Generated with Titanium Dioxide
Titanium dioxide is a common pigment used in plastic applications to provide opacity. The opacity derived from a particular grade of titanium dioxide results from the optimization of several factors such as refractive index differentials, particle size distribution, levels of impurities, surface coatings and crystal phase. This paper describes the relationship of these factors with the pigment volume concentrations relevant to many plastic end uses and provides a general scale of which factor provides the most opacity impact. The paper highlights the areas of opportunity to tune opacity based on scattering for titanium dioxide particles due to particle size distribution and the expected boost in opacity. The matrices employed for the evaluation of optimization are tinted systems which demonstrate the relationship of pigment volume concentration with various particle size distributions. The results compare particle size distribution of various rutile products with elevation of the L* values at constant TiO2 loadings.
Clean Enough? The Importance of a Clean Surface to Attaining Adhesion
The cleanliness of plastic surfaces has a significant impact on adhesion - the largest factor in paint, coating, ink and adhesives failures. This article examines the use of atmospheric plasma to remove organic contaminants from plastic surfaces. We examine the importance of cleanliness to adhesion, and the results of plasma cleaning from a number of applications. We also review two common direct methods for measuring surface contamination: contact angle and optically stimulated electron emission. Taken together, atmospheric plasma cleaning along with an appropriate method for monitoring the cleaning process provide a significant safeguard for avoiding adhesion related failures in plastic part manufacturing.
Fabrication and Characterization of a Honeycomb Structure Piezoelectric Foam Based on Cyclic Olefin Copolymer
This paper discussed the fabrication and characterization of a COC based pseudopiezoelectric material. A multi-layer honeycomb structure was fabricated using supercritical CO2 bonding to maintain the original structure. The disklike shape of bubble is ideal for the piezoelectric foam. The results shows that the quasi-static piezoelectric coefficient can reach up to 7000 pC/N. And thermally stimulated discharge shows that sample has a working temperature higher than 150°C. The hysteresis loop test illustrated the charge build up process inside the artificial void. The charging threshold breakdown voltage is about 5000V. Such material have applications on sensing, actuating and energy harvesting and many other fields.
Design Optimization of the Layout of the Heating/Cooling Pipes in Rapid Heat Cycle Molding of a LED TV Shell
Compared to conventional injection molding, the rapid heat cycle molding (RHCM) mold design must meet higher requirements. Taking the average temperature, the quadratic sum of the temperature deviation, the average stress, the average maximum stress, and the average life as test indexes, the orthogonal test was done. Employing the math optimizing analysis software, 1stOpt, response surface models and regression equations of different indexes were obtained by analyzing the results of the orthogonal test. The optimization model of the heating/cooling pipe layout for a LED TV shell RHCM mold was established. Finally, the optimization design of the heating/cooling pipe layout was realized by employing nonlinear programming. The heating/cooling efficiency and lifetime of the optimized RHCM mold was ensured, and the molding cycle could be done in 62 seconds.
The Ultimate Thermal Transitions and Isothermal Curing Behaviors of a Two-Part Epoxy-Amine Adhesive System: Effects of Different Mixers
Various raw mixture samples of a two-part epoxy adhesive system were prepared using different mixers, including a series of commercially-available static mixers and a dual asymmetric centrifugal mixer. The total reaction enthalpies and ultimate glass transitions of the mixtures were measured using nonisothermal differential scanning calorimetry (DSC). The isothermal cure behaviors of the mixtures at selected temperatures were kinetically monitored as the time-resolved viscoelastic material functions by means of small-amplitude oscillatory shear rheometry (SAOS) and then, the characteristic physical transformation events including gelation and vitrification were determined. Based on these DSC and SAOS studies, it has been found that the ultimate glass transition temperatures and the occurrences of physical transitions during isothermal curing for different adhesive mixture samples may exhibit strong correlations to mixing tools. Hence, to attain optimum material properties at the cured states, it is important to choose and use a proper mixer for a two-part epoxy-amine adhesive system.
Determination of Stress Concentrations in Orthotropic Composites Using Mapping Collocation Techniques
This paper demonstrates the ability to determine the individual components of stresses by processing isopharic stress (sum of the normal stresses, sometimes it is called stress invariant or the trace of the stress tensor) with a series representation of the Airy stress function in complex analysis for orthotropic materials. The present case of a loaded plate containing an elliptical hole uses simulated experimental input from exact solution. The method presented here, which is based on equilibrium and compatibility, used complex-variable formulation involving conformal mappings, analytic continuation and numerical techniques. The technique utilized complex variables and mapping, and satisfies the traction-free condition analytically at the hole. The method is applicable for both isotropic and orthotropic materials.
Environmental Stress Cracking of Medical Thermoplastics: Assessing Lifetime of High Performance Amorphous Resins in Presence of Hospital Cleaners
There is a critical need to quantify and predict the likelihood of Environmental Stress Cracking (ESC) in medical devices, due to the expanding use of medical cleaners in hospitals to prevent infection as well as increased FDA documentation requirements. This paper performs constant flexural strain ESC experiments on two high performance resins, Noryl 20%gf and Ultem 20%gf, using three common hospital cleaners (bleach, quaternary amine with isopropanol, and hydrogen peroxide). ESC testing was performed using a 7-day soak followed by tensile testing to assess residual stress-strain performance.
From strain-at-break results for this 7-day soak method, ratings were obtained for each resin-cleaner combination. These results can be fed into mechanical models of components to quantify likely failure locations and safety factors.
Using time-to-crack datasets, an initial estimate of the n exponent for the ESC dependence on stress was obtained. Also, it was found that the use of Hansen Solubility Parameters could, with reasonably accuracy, predict trends in ESC damage.
Cavity Effect on Core Penetration in Co-Injection Multi-Cavity Molding
Co-injection molding is commonly used in daily accessories, car parts, and structural-reinforcement product. However, there are too many combinations of designs, materials, core/skin ration, and process condition, how to have suitable control of co-injection is very challenge. Furthermore, co-injection with multi-cavity system is also utilized in some forks structure products. Due to the complicated nature, the inside mechanism of the multi-cavity co-injection system is still not fully understood yet. In this study, we have proposed three kinds of multi-cavity systems to investigate cavity design influence on the core material penetration behavior. In Model 1, it is a three separated cavities system. Although the flow rate can influence core penetration during early history through the runners, the separated cavity structure will restrict the core development in Cavity 1. Then it ends up with a non-uniform skin/core distribution in presence of different flow rates influence. Moreover, when it has a different thickness of connection between cavities in Model 2 (with 3.5 mm thick connector) and Model 3 (with 1.75 mm thick connector), during the early filling age (less than 90% of total volume filled), it is Branch 2 dominant in Model 3; while in Model 2 it has no preference for Branch 1 and 2. The flow rate conditions have no significant effects for core penetration in this period. However, as more melt keeps flowing into cavities till the end of filling, the core penetration behavior is dramatically different at low flow rate (say 10 cm3/s). These results show that in the presence of different thickness of connector, the penetration history and final shapes of core layer are significant different to that of separated cavity system (Model 1). Obviously, cavity design can alter the preference of core penetration from one side to the other. The results can help people for the management of skin/core distribution in co-injection molding.
Characterizing the Rheological Behavior of Liquid Silicone Rubber Using a High Pressure Capillary Rheometer
The injection molding process of liquid silicone rubber (LSR) imposes high demands on the injection molding machines and the tools due to the low viscosity of silicone rubber. There is very little data which describes the rheo-logical behavior of LSR and its influencing factors across a range of shear rates.
In this study, the rheological behaviors of different types of LSR were characterized using a high pressure capillary rheometer with an apparent shear rate that ranged from 350 to 4000 1/s. In order to identify the temperature-dependent behavior, the test temperatures were varied between 27 and 42 °C. The behavior of the material at a high pressure was evaluated by analyzing the pressure profile of each measurement.
All types of LSR displays a low level of viscosity from approx. 150 to 30 Pa s. As the shear rate and temperature rise, the viscosity of LSR decreases by at least 25 %. Ad-ditionally, we discover that the viscosity of LSR-materials with the same shore hardness differ strongly depending on which producers had made the materials. It was able to be shown that LSR displays homogenous material behavior across a wide range of shear rates.
The low viscosity of LSR makes it well-suited for applica-tions with complex structures, which require long flow paths in the injection molding process. If the viscosity sinks too low, the requirements for the tool construction increase, and, consequently, also the costs.
Using Ultrasonic Technology to Prepare Well-Dispersed Polycarbonate/Carbon Nanotubes Composites at High Flow Rate
Polycarbonate (PC)/carbon nanotubes (CNTs) composites were prepared using ultrasonic twin screw extruder at two different flow rates. During the extrusion of PC/CNTs composites, both the shearing and ultrasonic treatment helped dispersing CNTs into the polymer matrix. At low flow rate and longer residence time, CNTs can be well dispersed, but this may induce more degradation of polymer and low production throughput, which is not good for industrial production. At high flow rate, the dispersion of CNTs is worse than that in low flow rate and thus worse properties. Regarding to this problem, ultrasonic technology stands out and shows superior capability in improving the dispersion of CNTs and increase the throughput at the same time, which is especially beneficial for industrial production of polymer/nanofiller composites. The electrical, morphological, rheological and mechanical properties of the untreated and ultrasonically treated samples were investigated. The results supported the conclusion that ultrasonic technology is exceptionally efficient on improving the dispersion of CNTs and preparing welldispersed polymer composites at high flow rate.
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