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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Flow and Weld Lines when Using Aluminum Pigments
Injection molded parts normally have flow and weld lines arising from part design and injection point. These flow and weld lines are accentuated when molded with aluminum pigments. This flow and weld line study first examines what can be optimized in injection molding conditions to improve part appearance when using aluminum pigments. Having optimized conditions, color formulation changes are then made to further improve part appearance. The most important new piece of information gained is that weld lines can improve with increasing aluminum pigment concentration, whereas flow lines become worse. This makes finding a solution for flow and weld lines in the same part particularly difficult. The weld line at low aluminum pigment concentration is dark and wide, in relation to the surrounding area. The effect is described as an enhancement of weld line visibility, due to the absence of pigmentation. Flow lines, on the other hand, become more noticeable with increased flake concentration. Flow lines are caused by changes in the flake orientation or direction of fill. Thus, flow and weld lines should be regarded as separate phenomena with different causes.
A Comparison of Different Material Models for Thermoplastics
The mechanical behavior of thermoplastics in monotonic loading is characterized by an initial linear elastic response, followed by distributed yielding, large-scale plastic flow, and gradual strain stiffening until failure is initiated. In this study we have experimentally and theoretically studied the deformation behavior of ultra high molecular weight polyethylene (UHMWPE). The goal of the study was to compare the predictive capabilities of a new constitutive theory for thermoplastics with predictions from traditional models such as J2- plasticity and linear viscoelasticity. The results from the study indicate that the new constitutive model outperforms the traditional and commonly used models, demonstrating that with an appropriate choice of material model it is possible to perform accurate finite element simulations of thermoplastic components.
Soft Thermoplastic Vulcanizates for Long Term Elastic Recovery Applications
Soft Thermoplastic Vulcanizates (soft-TPVs) have been developed for soft touch and elastic recovery applications. These low durometer, 15~30 Shore A materials were compared with soft non-crosslinked styrenic thermoplastic elastomers (TPEs). The mechanical properties, compression set, solvent resistance, rheological properties and dynamic mechanical properties were investigated. It was observed that these soft TPVs have excellent elastic recovery properties at 70°C and 100°C when compared to comparable TPEs. Specifically, long term compression set at 70°C for 1400 hours showed soft-TPVs to be 50% lower than that of similar TPEs. The tensile properties were lower for these soft-TPVs relative to the non-crosslinked TPEs. These “Soft Thermoplastic Vulcanizates” are ideal for applications in which lower compression set, higher elasticity and softness are required.
The Effect of Addition of PCL on the Mechanical Properties and Thermal Transitions of PLA
Biodegradation of polymers is becoming an increasingly important consideration for packaging and biomedical applications. The availability of biodegradable materials would allow the invention and continuation of many polymer applications without any hazardous effects on the environment. Material scientists are focusing more intently on making environmentally-friendly polymers by developing biodegradable polymeric materials. Polylactic acid (PLA) and polycaprolactone (PCL) are two systems of application of this interest.Polylactic acid (PLA) is a frequently investigated, readily biodegradable polymer made from renewable agricultural products. It’s mechanical properties, and biocompatibility allow PLA to be used in a wide range of applications, such as biomedical implants and food packaging. However, despite it’s good tensile strength and high melting point, PLA is too brittle to be used in many of these applications. Polycaprolactone (PCL), on the other hand, is a very flexible and biodegradable polymer. In general the degradation of a polymer depends on various factors such as molecular weight, amorphous phase content, moisture level, temperature and pH. The main disadvantage of PCL is that the overall tensile strength of PCL is low. In addition, the low melting point of approximately 60 °C limits its use in many applications. We investigated the benefits of blending these systems and optimized one blend composition. Nanocomposites of this blended system are studied in detail.
Anisotropic Shrinkage in Injection Molding of Various Polyesters
A novel approach to predict anisotropic shrinkage in injection moldings of various polyesters was proposed using the flow-induced crystallization, frozen-in molecular orientation, elastic recovery and PVT equation of state. The frozen-in orientation function was calculated from the amorphous contribution based on the frozen-in and intrinsic amorphous birefringence and crystalline contribution based on the crystalline orientation function determined from the elastic recovery and intrinsic crystalline birefringence. To model the elastic recovery and frozen-in stresses related to birefringence during molding, a non-linear viscoelastic constitutive equation was used. The flow-induced crystallization was introduced through the elevation of melting temperature affected by entropy production during flow of the viscoelastic melt. The measured and predicted thickness, length and width shrinkages for numerous molding runs were found to be in a fair agreement.
Analysis of EBeam Irradiated Polyporpylene
Polypropylene (PP) was irradiated with an E Beam with doses of 2.5 Mega Rads (MR), 5 MR, 10 MR, 15 MR, and 20 MR. The un-irradiated and the irradiated material was analyzed using a parallel plate rheometer, capillary rheometer and gel permeation chromatograph (GPC). The objective of this effort was to probe the structural changes in the polymer using aforementioned analytical techniques and determine the utility of the E Beam technique for rheology control. Of interest was the ability to narrow the molecular weight distribution of the material to achieve better process-ability and repeatability. The scope is limited to the results from the previously mentioned analytical techniques. Behavior of the material in actual processes such as injection molding and extrusion is beyond the scope of this study.
Biomimetic Polymer Composites for Orthopedic Implants
The development of biomimetic femoral stems based on composite materials is presented. They are composed of an internal low density core, a carbon fiber-reinforced polymer composite molded into a hollow conical-shaped stem formed by inflatable bladder compression molding, an intermediate bioactive compound and finally a plasma-sprayed bone-like hydroxyapatite coating. Results concerning the physico-chemical and mechanical characteristics of the biomimetic THP stem will be presented, including strength, bone-matching rigidity and fatigue. The manufacturing of the stem itself, including the optimal molding conditions will be described as well as preliminary testing regarding biocompatibility and finite element validation.
Accelerated Aging Study of Gamma and E-Beam Irradiated Poly(Ether-Block-Amide) (PEBA)
Medical polymers require sterilization and must be able to maintain material properties for a specified shelf life. Sterilization can be achieved by using gamma or e-beam exposure. Shelf-life estimates of irradiated polymers are typically determined using data from accelerated aging in an oven and by using a simple degradation model assuming Arrhenius behavior.In this study, preliminary accelerated aging tests of two poly(ether-block-amides) (PEBA) copolymer samples is presented. PEBA copolymer samples with different polyether content that result in Shore hardness of 25D and 40D respectively, were sterilized using gamma or e-beam radiation followed by accelerated aging between 40°C and 80°C. The objective was to find the best sterilization method for extending shelf life.
The Glass Transition Temperature Versus the Fictive Temperature
It is well known that both the glass transition temperature (Tg) and the limiting fictive temperature (Tf') depend on the cooling rate. However, a comparison of the values of Tg and Tf' as a function of cooling rate has not previously been performed. In this work we have performed this comparison for a polystyrene sample using both capillary dilatometry and differential scanning calorimetry. The results from both techniques indicate that both Tg and Tf' have almost the same dependence on the cooling rate. However, Tf' is systematically lower than Tg presumably due to relaxation that occurs on heating.
Enthalpy Recovery: Do Materials Reach the Equilibrium Line?
Glasses are inherently non-equilibrium materials, and consequently, their properties evolve toward equilibrium in a process known as structural recovery or physical aging. Recently, several authors have suggested that the equilibrium liquid line is not reached even when properties have ceased to evolve. In this work, we present measurements of the enthalpy recovery of polystyrene at temperatures ranging from the vicinity of glass transition temperature to 10°C below Tg (90°C), for aging times up to 200 days. The results are analyzed in the context of the TNM model of structural recovery. In addition, we analyze data in the literature to determine whether enthalpy recovery ceases prior to the material reaching the equilibrium liquid line obtained by extrapolation of the liquid line above Tg. The results suggest that, in fact, the liquid enthalpy line is reached at temperatures below Tg when equilibrium is reached, i.e., when properties cease to evolve.
The Challenge of Teaching Blow Molding in a University Setting
Teaching blow molding at the university level can be quite a challenge. Most universities with a plastics program focus on injection molding, as it represents the vast majority of the plastics industry. When blow molding is taught, it is usually buried within a course on other non-injection molding processes. The challenge is to bring together trained faculty, modern equipment (machines), challenging blow molding courses, a variety of training supplies (resin, molds, auxiliary equipment, …), and industrial support. Only then will there will be highly skilled students with blow molding knowledge and internship experience that are ready to make a positive impact in their field.
Morphology and Thermal Properties of In-Situ Composites
Melt blending of polypropylene (PP) and poly (ethylene terephthalate) (PET) was carried out in a single screw extruder. The extruded blend was continuously drawn using an on line stretching equipment at different stretch ratios .The stretched blend was injection moulded to obtain an in-situ composite where PET microfibrils are randomly distributed in an isotropic PP matrix. The morphology of the blend was studied at the different stages of the composite preparation at different stretch ratios. It was found that the fibril diameter decreased as the stretch ratio increases. The thermal characterization of the stretched blend indicated that the PET phase act as nucleating agent for the crystallization of PP.
The Development of a New Generation of Novel High Performance Olefin Elastomers: From Molecular Design to Market Development
The polyolefins industry has had a long history of new product introductions brought about through technological developments, and the pace of these developments has accelerated in the last 20 years. This has been a period of breakthrough discoveries, from advanced Ziegler-Natta catalyst technology, through metallocene catalysis in the 1990’s, and more recently with the development of post-metallocene technology. With each of these new technology developments, more control of the polymer structures were achieved by the product designers allowing new, high value products to be produced. For example, in the 1990’s, metallocene technology allowed the control of polymer composition distributions and long chain branching.Today, at The Dow Chemical Company, a new generation of post-metallocene technology has been developed. This technology has allowed a more precise control of the polymer microstructure and has resulted in the making of novel, high performance olefin elastomers. This new capability allows the product designer to use molecular architecture approaches to further refine new products for its customers to rapidly capture market development needs. In this paper, the authors will discuss an on-going research effort at The Dow Chemical Company in using molecular architecture approaches to advance polyolefins product development and the use of the Speed Based1 market development approaches to provide new products for Dow’s customers to capture new markets.
The Physical Property Advantages Gained when Alloying/Blending of Polycarbonate with Polymethyl Methacrylate
Blends of Polymethyl Methacrylate and Polycarbonate (20/80 & 50/50) were made. This was accomplished using a Dual TekFlow Processor which has already demonstrated its ability not only to blend and intimately alloy polymers, but also offers the advantage to reduce the viscosity of the new blend by disentanglement. The result is usually a new blend, with properties closer to a theoretical mix, i.e. with a more predictable performance level than what has been possible by more conventional methods of blend preparation. Rheological and thermal testing shows that the blends have very little degradation and about 40% disentanglement, meaning an improved fluidity by 40% when compared to the compounded contribution of the individual components. The 20/80 PC/PMMA blends look white, extremely well dispersed, and could be mistaken, at first glance, with Polypropylene. Injection molded specimens were made for the blends and both virgin resins, which allowed for investigation of their comparative tensile, flexural, impact and thermal properties. Mechanical test results indicate that the properties of the 20/80 PC/PMMA blend are slightly better than the Virgin PMMA, whereas the 50/50 PC/PMMA blend has intermediary properties compared to both resins.
α- and β-Polypropylenes: The Effects of Processing on Final Properties
The study directs attention towards different effects of mould temperature and holding pressure on the tensile properties of injection-moulded neat and ?-nucleated polypropylenes. A commercial-grade of polypropylene was modified with a ?-nucleator. From both the original and ?- nucleated materials, tensile test specimens were injection-moulded. Stress-strain measurements performed at room temperature revealed that the effects on the tensile characteristics of both materials are more pronounced within mould temperature changes, compared with those of holding pressure.
New Long Rayon Fiber Reinforced Thermoplastics Utilizing the LFT-D Process
PowerPoint Presentation at ACCE 2005.
Long-Fiber Reinforced Thermoplastics Tailored for Structural Performance
PowerPoint Presentation at ACCE 2005.
Thermoplastic Pressure Vessels for Automotive Applications
PowerPoint Presentation at ACCE 2005.
Thermoplastic Film Adhesives
PowerPoint Presentation at ACCE 2005.
Aerospace Composites Processing Methods for Light Weight Automotive Body Panels
PowerPoint Presentation at ACCE 2005.
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