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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The combined effect of two major causes of polymer failure, photo-oxidative degradation and environment stress cracking (ESC), have been investigated in this paper. Polycarbonate (PC) injection molded specimens were aged for 168 hours at 50 °C in an ultraviolet (UV) weatherable chamber. Then the stress relaxation and tensile tests were carried out in the ethanol environment to examine ESC behavior of PC. The results show that the tensile yield stress and stress relaxation resistance of PC improve slightly due to photo-oxidative degradation, while the ethanol will accelerate the failure of undegraded PC. When the previous degraded specimens were tested under the presence of ethanol, the stress relaxation rate increases significantly and the surface cracks appear to be more intensive in comparison with other ones. This indicates that there is a synergistic effect between photooxidative degradation and environmental stress cracking for PC injection molded parts.
Run Hong, Jian Han, Qing Zhang, Zhixiang Cui, Hongzhou Zhang, Chenguang Yan, Xiaodong Wang, May 2014
Biodegradable poly(lactic acid) (PLA) blend with other materials is widely demanded as an effective approach for preparation of porous materials. In the present wok, two phases blends of PLA and polystyrene (PS) were prepared by twin-screw extruder and Torque Rheometer. For the latter blending method, the effects of various conditions such as blends mass and the temperature of mixing chamber on phase morphology were explored. A bimodal distribution of porous structure was presented after extracting the PS phase from the samples prepared by two different blending methods. Different with Torque Rheometer, the blends of twinscrew extruder rarely appears reunion phenomenon; therefore, a better phase morphology can be expected. It further found that the phase morphology of blends was apparently optimized under proper post annealing conditions.
Malvika Bihari, Jon Malinoski, Hans de Brouwer, May 2014
High-flow polycarbonate (PC) copolymer derived from bisphenol-A (BPA) and a specific biosourced monomer derived from castor bean oil for medical applications available in two melt flow ranges is reported. This copolymer belongs to the class of Lexan™ HFD resins known for their improved melt flow and ductility balance compared to standard polycarbonate yet with similar high optical clarity and light transmission properties. These high-flow HFD copolymers for the healthcare industry are designed to have all attributes of the Lexan™ HFD resins such as lower temperature processing capability, longer injection molding flow lengths and improved low temperature ductility versus a standard polycarbonate and ISO10993 biocompatibility. The superior flow enables molding of thinner parts with similar practical impact to standard healthcare PC.
As medical infusion treatments become increasingly more common in the United States and across the globe, the need for better and faster fluid delivery is greater than ever. The use of advancements in polymer and polymer composites structures will provide for medical products that have increased fluid flow while maintaining required outer dimensional sizing, adequate tubing stiffness, and tubing burst resistance characteristics compared to the currently used medical tubing materials. Tubing structures of current medical tubing proprietary polyurethane structure with glass bead filler of 4% by weight (structure A), with carbon nano tube filler of 1% by weight (structure B) and a polyurethane structure with 10% increased shore durometer without fillers (structure C) were tested per ISO 10555-1 for tubing d tensile strength, stiffness, flexural fatigue resistance, vacuum lumen collapse resistance and hydraulic burst resistance. With variations of each structure having outer wall thickness of 0.010”, 0.015” and 0.020”. Structure C tubing with increased shore hardness with wall thickness of 0.020” passed all minimum requirements per ISO 10555-1. Structure C exhibited a tensile strength 13.4% less than the control group however was 52.7% stiffer and did not sustain any noticeable wear or defects during flexural fatigue testing. Structure C demonstrated tensile strengths on average 14.8% less that the control group at post flex fatigue tensile testing but showed no failures at 150 psi burst testing when applied to it for 5 seconds. Structure C with the 0.020” wall thickness is estimated to have a 43% higher flow rate capacity than the current material. Thus providing for a significantly higher rate of infusion treatment.
Atakan Alt?nkaynak, Mahesh Gupta, Mark A. Spalding, Sam L. Crabtree, May 2014
For an ABS resin, a three-dimensional finite element simulation of melting and flow in the melting and metering sections of a single-screw extruder was performed using barrel rotation boundary conditions. In the simulations, the flow domain was modeled as a full three-dimensional helical channel with flight clearance. The simulation results were then compared with the corresponding results from the screw-freezing experiment. Maddock melting mechanism was observed both in experimental results and numerical predictions. However, some discrepancies existed between the numerical predictions and experimental results, which are further discussed in the paper. These discrepancies may be clarified with simulations using screw rotation boundary conditions.
Qi Li, John P. Coulter, John P. Beaumont, Alicyn M. Rhoades, May 2014
For some time now the effects of runner-based shear imbalances on melt flows during polymer molding processes have been studied and found to be problematic, even in cases where mold cavities are naturally balanced as traditionally defined. In such instances, melt rotation technology has been applied on many occasions to accommodate resulting cavity filling imbalances as well as shrinkage and warpage issues. In the present study, this approach was taken a step further with the goal of exploring affiliated product quality variations that exist as an extension of the imbalanced polymer melt flow problem. Molding trials were conducted with and without melt rotation using several types of polymers, and the resultant effects on final product physical, thermal and mechanical properties were explored. When this was done, it was found that important product quality parameters such as crystallinity and tensile modulus can vary significantly throughout conventionally molded products and be dramatically altered by the implementation of melt rotation technology. Specimens taken from product regions associated with higher melt flow shear levels exhibited higher crystallinity levels as well as higher tensile moduli. This supports the concept of melt rotation adoption for a broader range of problems extending far beyond cavity fill balancing alone.
Anshuman Shrivastava, Rachel Kamish, Bruce Carpenter, Mark Scheel, Julie Strama, May 2014
Plastics consumption into various products has substantially grown over the years. Increasing resin prices and escalating environmental legislatives towards landfills are encouraging recycling of plastics. Recyclability of thermoplastic materials facilitates innovative application established on their residual contents. The plastic scrap thus is classified into predominant categories as postindustrial resin (PIR) and postconsumer resin (PCR). Postconsumer resin (PCR) is recovered from recycled products such as disposable packaging containers, bottles, and commodities in landfills. Discarded carpets are becoming a compelling source of PCR- Nylon resins. This paper evaluates the use of PCR-PA6 resin for automotive component application. The lifetime performance of these formulations was estimated through prolonged heat aging and testing at various intervals.
Three commercial jacketed ignition cables were obtained and the inner and jacket insulation materials identified by FTIR analysis. The cables were found to be made of silicone, chlorinated polyethylene, and PVC with both the inner and jacket made from the same polymer base. Flynn-Wall analysis was performed using TGA to calculate activation energies for 10% mass loss. These values, in conjunction with actual TGA measurements of the time for 10% mass loss at 300 and 400°C, enabled estimation of cable service lifetimes at 100 and 170°C service temperatures.
John W. Rodgers, Meghan E. Casey, Zachary R. Miller, Sabrina S. Jedlicka, John P. Coulter, May 2014
Microfeatured petri dish inserts containing consistent microtopography were manufactured for the intentional control of stem cell shape and function. Polyolefin plates were micro-injection molded through utilization of an actively heated assembly containing a negatively featured silicon inlay. Surface properties were characterized through microscopy and water contact angle (WCA) analysis. Human Mesenchymal Stem Cells (hMSCs) were grown on microfeatured and flat substrates. Microtopography dramatically altered surface hydrophobicity and hMSC morphology. Micro-injection molding offers unique industrially relevant manufacturing possibilities for use in the biomedical field.
Ehsan Moghbelli, Hung-Jue Sue, Reid Banyay, May 2014
Effects of moisture exposure on scratch performance of polymethylmathacrylate (PMMA) and polypropylene (PP) were investigated. Three different grades of PMMA and PP with varying levels of polarity and molecular weight were chosen and their scratch resistance compared in both dry and moist conditions. Linear increasing load scratch tests were performed according to ASTM D7027/ISO 19252 standards. Results indicate a drop in scratch resistance with initial exposure to moisture in all three PMMA systems. In the two highly polar PMMA systems, the scratch resistance recovers to that of the dry condition after exposure to moisture while PP scratch resistance remains unchanged. It is proposed that the moisture absorbed initially acts as a plasticizer causing weakening of the surface for PMMA. In the case of more polar systems this moisture absorption continues until saturation where water molecules cluster and impart a degree of lubrication and consequently improve scratch resistance.
Xiaofei Sun, Hrishikesh Kharbas, Jun Peng, Lih-Sheng Turng, May 2014
A novel method of improving the ductility of injection molded plastic parts has been developed. By applying either gas-laden pellet technology or microcellular injection molding to polymer blends or composites of proper material formulations, the ductility and toughness of the molded foam parts can be significantly improved compared to those of solid parts. The key is to achieve a microcellular structure with a sub-micro scale immiscible secondary phase. Upon tensile loading, cavitation of the secondary phase facilitates the interconnection of microcellular voids to form channels such that the stretched component becomes a bundle of fibrils. This change in structure turns the fracture mechanism from crack propagation across the matrix into shear yielding of a bundle of fibrils in the loading direction. Compared with other toughening methods, this method achieved a more significant improvement in ductility and toughness with reduced material consumption and lighter part weights.
Ian P. Query, Emily McBride, William Arendt, May 2014
High solvating plasticizers have recently been of interest in industry in regards to PVC melt compounding. Dibenzoate plasticizers comprise a family of high solvating plasticizers that have been known for the beneficial effects they impart to vinyl. In the pursuit of improving dry blend characteristics and conserving manufacturing energy usage, a study was conducted to determine the effects of dibenzoate plasticizers both alone and in blends with general purpose plasticizers. The dry blends were analyzed using a torque rheometer under both isothermal and constant heat ramp conditions. Experiments with plasticizers on a PVC resin have shown dibenzoates to improve processing time over the use of general purpose plasticizers alone, and plasticizer blend experiments have given insight into the utility of incremental benzoate usage. Further experimentation indicated that pressure application to dry blends gives further insight into the level of plasticizer incorporation.
Cuntao Wang, Kazuhisa To, Yuqiu Yang, Hiroaki Ichikawa, Hiroyuki Inoya, Hiroyuki Hamada, May 2014
In order to reduce the energy consumption in processing and improve the productivity, Direct Fiber Feeding Injection Molding (DFFIM) technology is developed and established. In this study, the carbon fiber (CF) from four different companies and polycarbonate (PC) resins were used to mold the CF/PC dumbbell specimens. Nano Indentation technique with cycle load test method was adopted to evaluate the interfacial property of CF/PC composites and Kelly-Tyson Model was used to calculate the interfacial shear strength based on tensile test and the fiber length distribution. Scanning electron microscope (SEM) observation on the interface after tensile test was applied to relate the change in mechanical properties with the interfacial fracture mechanisms. It is found that Nano Indentation test with cycle load method is an effective method to estimate the interfacial property and the results reveal good agreement to Kelly-Tyson model. Due to the different interfacial property, these four kinds composite have significant different mechanical properties.
James Wirwille, Stephen Johnston, Vito Galati, William Rousseau, May 2014
A major design consideration and benchmark for a high quality injection molding hot runner system is color change performance. The focus of this project was to evaluate the effect of temperature uniformity and surface finish on color change performance and frozen layer formation. Trials were conducted using two hot-sprues, with different surface finishes and configurable heating elements, representative of typical configurations. The thermal profile of each sprue was mapped at steady state conditions prior to processing. Sprue pulls were then performed to study the efficiency of each color change and results. It was determined that temperature uniformity greatly altered a system’s color change performance. Cool regions in the sprue formed frozen layers of the original material that would re-melt over subsequent cycles negatively impacting the color change performance. The effect of surface finish on color change performance was less definitive and dependent upon frozen layer formation.
Patrick J. Harris, Sidney Carson, Jesse L. Gadley, Joao M. Maia, May 2014
This research work presents the first developed multilayer co-extrusion system for high viscosity elastomer materials. Three unvulcanized rubber materials were chosen; two butyl rubbers and a polyisoprene. The elastomers were characterized under oscillatory shear conditions and placed into either a rheologically ‘matched’ or a ‘mismatched’ category. Multilayer co-extrusion was achieved at a total of 8 layers then 32 layers; with two different extrusion rates. Results show good layering performance for both systems; however, interestingly, the rheologically mismatched systems showed a better layer quality as well as a more stable variation coefficient with an increasing amount of layers.
Understanding polymerization kinetics during reactive extrusion maintains the potential to improve processing efficiency. This study focused on understanding the kinetics and mechanical development of aromatic thermoplastic polyurethanes (TPU). The results indicate that rheology coupled with spectroscopy techniques provides a means to capture chemical and physical property development. Information on the development of materials during controlled reactions may then be applied to scenarios in extrusion of reactive systems. This study noted a significant change in both reaction rate and storage modulus as the hard segment content of the system increased from 26.4% to 55.6%.
Some trends in failure are due to errors of design or bad judgment (plastics) or unwise life conditions (human biopolymers). An encouraging trend for human biopolymers is synthetic polymers designed as replacements for damaged biopolymers (electrical polymers for nerves, and targeted drug delivery). Environmental, recycling and health effects on failure are a strong recent trend in polymer failure. Examples are bisphenol A (BPA) and phthalate plasticizers, both limited by bans for health reasons. PVC is also attacked for health reasons. Even if a plastic is very worthy, inexpensive and was accepted for years, it may be considered for banning (PE thin bags).
Liezl Wee Sit, Carol Barry, John Shearer, Joey Mead, Mayur Kumbhani, Josue Acevedo, May 2014
A novel additive manufacturing approach was investigated for fabrication of steel tooling with microstructured surfaces. Varying processing parameters (printing pressure and speed) as well as material viscosity provided better control of microfeature height and width. Viscosity significantly affected feature uniformity, with higher viscosity materials producing narrow lines and more uniform feature heights. This tooling was unchanged after 5000 injection molding cycles, and so, has great potential as microstructured tooling for microfluidic devices.
Austin Coffey, Aimee Dunne, Niall Murphy, Philip Walsh, Rachel Walsh, Seán Lyons, May 2014
Models of human blood vessels have many potential applications as aids in continuing research on new medical devices. The work detailed herein describes the development of a hydrogel material to mimic the mechanical and biological response of a range of human arteries. The developed hydrogels were characterized via swelling studies, differential calorimetry and spectroscopic techniques, while viscoelastic property measurement was investigated primarily using rheological testing methods. A range HEMA/NVP hydrogel materials were successfully developed with properties comparable to a range of arteries, namely, the thoracic and abdominal aorta with storage moduli (G’) varying from 43kPa to 64kPa depending on the formulation. This paper also describes the construction of a mathematical model for the viscoelastic properties of these materials, representing the time-dependent behaviour of the simulated areterial material when subjected to loading and unloading phenomena.
In this study, for the first time, we developed microcellular PLA bead foams with double crystal melting peak structure followed by steam-chest molding of the foamed beads. The generated high melting temperature crystals during the saturation significantly affected the expansion ratio and cell density of the PLA bead foams by enhancing the PLA’s melt strength and promoting heterogeneous cell nucleation around the crystals. The tensile mechanical properties of the molded EPLA bead foams showed that EPLA bead foams with double melting peak structure can be a promising substitute not only for EPS products but also for expanded polypropylene (EPP) products.
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