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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Impact of Titanium Dioxide Surface Characteristics on Extrusion Processing
Interfacial interactions between the titanium dioxide pigment surface and the polymeric matrix have a significant impact on the energy requirements for incorporation and the rheology of the resulting compound. This study investigated the effect of screw geometry and operating conditions on dispersion performance and torque loading during twin-screw compounding of three different grades of titanium dioxide pigments with different surface treatments into highly loaded polyethylene masterbatches. It was found that the screw design and operating conditions where the pigments performed best were quite different for the three grades. It was found that low intensity mixing sections and cooler barrel temperature settings seemed to favor the pigment with a compatibilizing hydrophobic surface treatment and high intensity mixing sections and hotter barrel temperature settings favored the pigments that did not have such a surface treatment. It was also found that by optimizing screw designs, much higher throughputs and better dispersion could be achieved.
Twin Screw Extrusion of the Reactive Blends of Thermoplastic Polyurethanes and Poly(Vinyl Chloride)
The reactive blending of Poly (Vinyl Chloride) (PVC) and Thermoplastic Polyurethanes (TPU) was performed by using a counter-rotating, intermeshing twin-screw extruder. The blending technique consists of two sequential stages of mixing and reaction respectively. In the first stage, the PVC is pre-blended with monomers of the TPU (soft segment and chain extender). In the second stage, the polymerization of the TPU in-situ with the PVC takes place upon the addition of the third monomer of the TPU (diisocyanate). In this study, the novel in-situ reactive extrusion technique and the procedure for producing PVC/TPU blends are discussed.
Single Site Catalysts and Dual Reactor Technology Create More Freedom in Pe Rotomolding Resin and Product Designs
While polyethylene continues to be the resin of choice for rotational molding, advancements in material design are still required. From a structure-property perspective, a thinner lamellar thickness of a polyethylene resin may lead to a higher tie chain formation probability. It is also believed that longer polymer chains with proper comonomer incorporation enhance this probability. Single site catalysts and octene comonomer usage enable the design of rotomolding resins with superior properties compared with conventional Ziegler-Natta resins. This paper combines our fundamental understanding of this topic with experimental data.
Characterization of Reactive Blends of Thermoplastic Polyurethanes and Poly(Vinyl Chloride)
In this study, a novel reactive blending technique was used to produce PVC/thermoplastic polyurethane (TPU) blends. The blending technique consists of two sequential stages of mixing and reaction. In the first stage, the PVC is pre-blended with two monomers of the TPU (soft segment and chain extender). In the second stage, the in-situ polymerization of the TPU with the PVC takes place upon the addition of the third monomer of the TPU (diisocyanate). TPU monomers were changed in order to determine the effect of chemical structure and isomers on the miscibility with the PVC and the tensile properties of the resultant blends.
Nanotribology of Protein- Modified Surfaces
Nanoprobe technology has emerged as an important tool for the study of thin films and biological materials. Atomic force microscopy (AFM) is widely employed to determine surface features at the nano- to microscale, and is increasingly used for evaluation of friction and wear performance at small scales. Hydrophobins are a unique class of amphipathic fungal proteins that exhibit remarkable capability to modify surfaces, both natural and synthetic. Novel rigid rod polymers with high strength to weight ratios are of interest for a wide range of engineering and biomedical applications. The nanotribological properties of spin coated rigid rod polymer and hydrophobin-modified polymer surfaces are reported. Surface roughness analysis is reported for uncoated as well as hydrophobin-coated rigid rod polymer samples.
Material Properties of Thermal Conductive Thermoplastics for Mold Design and Processing Strategies
The use of highly filled thermal-conductive thermoplastics is an innovative approach to directly adjust the thermal conductivity of plastic parts for heating and cooling systems. Compared to standard resins thermal conductive thermoplastics show a higher thermal conductivity in the range of 2 – 20 W/mK. The filler-content and the high thermal conductivity affect directly the flow- and cooling-conditions during injection molding. Therefore, the manufacture of injection-molded parts requires adjusted processing strategies. In this paper properties of thermal conductive thermoplastics relevant to the design of injection-molded parts as well as the effect to relevant processing parameters are introduced.
Retardation of Shrinkage in Phthalosyanine Blue Pigmented Polypropylene Using Nanoclay as Filler
A common problem with crystalline polymers that occurs when an organic pigment is added to the melt matrix is non-uniform or anisotropic shrinkage. A nanoclay has been compounded into polypropylene. An organic pigment masterbatch was made and then added to the nanoclay/polyproplyene (PP) compound. Percent crystallinity was then tested using Differential Scanning Calorimeter (DSC). Percent elongation also was tested using a standard tensile testing machine. Shrinkage differences between colorant with and without nanoclay were measured using the ASTM flame-bar and mold and a two inch disk and mold.
Bioactive Composites for Tissue Regeneration
A wide variety of bioactive composites for bone regeneration have been developed and investigated over the last decades. In order to promote bioactivity, certain types of glasses, ceramics and minerals are incorporated into biodegradable or biostable polymers. In this study, several established and novel fillers such as calcium phosphates, silicates and glasses were screened for bioactivity. Promising candidates were then incorporated into two different grades of poly-?-caprolactone by solution mixing, and testing was conducted in a simulated body fluid to determine in vitro bioactivity. At different time periods the exposed samples were characterized by SEM, EDX and FTIR microscopy in order to investigate the formation of the apatite layer needed for bone ingrowth. The screening results of this work produced suitable polymer/filler combinations for further in vitro and in vivo testing in different types of tissue engineering applications.
Development of Plastic Recycling Companies in the Czech Republic: An Analysis Using Economic Value Added
Extensive use of plastic products in a country like the Czech Republic make the recycling of plastic unavoidable. This also is influenced by a host of factors such as increasing price of raw materials (oil and other semi processed products), growing concern for ecology and environment, etc. However, recycling is not only the technology alone, but it also includes issues such as legislation, both social and most importantly economics. The present study attempts to describe the economic conditions that influence the performance of plastic recycling companies. The paper analyses the conditions of development of plastic recycling companies in the Czech Republic using Economic Value Added (EVA) indicator.
Nucleation and Reinforcement of Carbon Nanofibers on Polystyrene Nancomposite Foam
As the demand for highly functional polymeric materials grows, nanocomposite foams are likely to play a vital role in the future foam industry. In this research work, carbon nanofibers (CNFs) were used as both nucleants and reinforcements for polystyrene (PS) foams. It was found that a microcellular foam structure could be achieved with low fiber loading. Moreover, the nano-scaled dimension of CNFs made them desirable elements to reinforce the cell walls, leading to an enhanced tensile modulus. Intensive shear force exerted by the twin- screw extruder broke the fibers in length and deteriorated their nucleation efficiencies.
Synthesis and Reinforcement of Nylon 6 Copolymers with Phenolics
Block copolymers of nylon 6 with 10, 15 and 20% of poly(ether-esteramide) as elastomeric phase were synthesized by reactive extrusion. These materials are the result of the anionic polymerization of ?-caprolactam in the presence of a linear prepolymer of poly(ether-esteramide) with a Grignard reagent (1). Reinforced copolymers were prepared by melt mixing copolymers containing 15% of elastomeric phase with 3, 5 and 7 phr of phenolic resin in a single extruder; and also copolymers with 10 and 20% of elastomer and 5 phr of phenolic resin. On the other hand, reinforced copolymer with 15% of elastomer phase and 3 phr of resin was also synthesized “in situ” by reactive extrusion.
Biodegradable Hollow Nanospheres for Drug Delivery
Diabetes is one of most common and widespread diseases. As high as 6% of the world population suffers from diabetes, which, including its complications, is the fourth most important cause of mortality and the main cause of permanent blindness. In the United States alone, 16 million people, nearly one in 17 people, have diabetes. More than 2,000 new cases are diagnosed every day. Most patients require three to four injections of insulin a day. In addition to patient compliance problems, chronic subcutaneous injection may cause side effects, such as lipoatrophy or lipohypertrophy. Oral delivery of insulin has been elusive due to acidic and enzymatic degradation of insulin in the gastrointestinal tract.Oral delivery of insulin is more preferable to subcutaneous injections, because it may provide a better glucose homeostasis and decrease the chances of peripheral hyperinsulinaemia, which is linked to neuropathy and retinoendopathy. Successful oral delivery has not been achieved due to various challenges regarding the sustainability of peptides in the gastrointestinal tract. Typical oral bioavailability of proteins is generally less than 1-2 % because of the numerous physiological barriers in the digestive tract. Ingested proteins become subjected to acidic degradation in the stomach, luminal degradation by enzymes in the intestine, and intracellular degradation. Since proteins are built with peptide linkages, they are susceptible to acidic degradation. It has been shown that some proteins do have some bioavailability when administered directly into the intestine, bypassing the acidic milieu of the stomach.  Various polymer matrices have been designed for enteric coatings with adequate pH-response to protect insulin in the stomach. Polyacrylates Eudragit RS1 and RS2 showed bioavailabilities of 9.3-12.7 % due to their ability to release insulin further down in the gastrointestinal tract at pH 7.5-8.0. Polymer nanospheres have been studied for oral delivery. Accordin
A New Absorption Based Model for Sheet Reheat in Thermoforming
Thermoforming is the process of manufacturing plastic parts by preheating a sheet and then draping it onto a mould. At present, the heater temperature set points for sheet preheat are typically chosen by trial and error. Very little work has been published regarding the control of the sheet surface temperature. Such a control system will improve the quality of the product, reduce scrap and allow for temperature zoning. However, before a suitable control can be successfully designed, an accurate model of the process is required. In this paper, we present such a model of the sheet reheat process which includes the effect of radiation absorption inside the sheet. The inclusion of the radiation absorption effect corrects errors which were found in some previously published controllers. The model presented here is a nonlinear, temperature-dependent multivariable representation of the temperature variation through the sheet thickness.
Advanced Technologies for High Contrast & Color Laser Marking of Plastics
The newest generation of laser material science and hardware/software is driving strong industry demand for indelible, high speed laser marking processes to replace conventional ink printing. This paper presents a “total solutions” methodology for achieving unprecedented marking contrast quality and color laser marking of plastics via concomitant engineering of: 1) laser additive material science, 2) primary molding operations, 3) laser/software technology, and 4) systems integration. The first of its kind laser pigment to receive U.S. Food and Drug Administration (FDA) approval for use in laser processes is introduced as well as techniques to achieve high speed vector marking of alphanumeric text, graphics and product security codes.
The Role of Surfaces on the Impact Response of Polymers
We have evaluated the effect of three decoration methods on the impact response of polymers: automotive paint systems, flexible color films, and molded-in-color pigments. The resulting surface composition and mechanical behavior can differ significantly and was found to affect the impact response of the decorated polymer. Painted surfaces induced fracture on otherwise flexible substrates, while color films could increase, decrease, or have no effect on the dynamic flexural modulus of a decorated polymer. The dynamic flexural modulus and strength of injection-molded polymers varied as a function of thermal aging, due to re-crystallization and oxidation of the molded surface. The trends observed intensified at higher deformation speeds (2.2 m/s) and lower temperatures (-20 to -30 °C).
Can the Nanoindentor Become a Rheological Tool?
The Nanoindentor is a modern version of the hardness tester designed for metals and ceramics. Recently, it has been proposed as a technique to measure rheological properties of soft time-dependant polymeric materials. This technique offers the promise of micron scale spatially resolved rheological information. Additionally, the theoretical foundation and historical development of the working equations for nanoindentation and traditional rheological instrumentation will be presented and discussed. The major difference between nanoindentation and the more classical rheological instrumentation is in the treatment of the instrument-sample interface. To illustrate how the treatment of the instrument-sample interface affects the data a series of measurements was preformed on poly(methyl methacrylate), (PMMA), and poly(dimethyl siloxane) (PDMS) samples.
Constancy of Properties Resulting from Foam Injection-Molding Techniques
Modified injection-molding techniques for foam molding show technical benefits over conventional injection molding, e.g. reduced part warpage and improved dimensional accuracy. However, the density reduction leads to a change in mechanical properties that might even cause premature failure. As long as the specific values for stiffness and strength of the foamed product exhibit small variations - comparable to those in conventional injection molding - one might account for the absolute property change during the design procedure. Accordingly, high property constancy is a technical pre-requisite for load-bearing components and would even allow foam molding of safety relevant parts. The effect of foam molding on the constancy of mechanical properties was investigated and compared to the characteristic performance of conventional injection molding with respect to processing repeatability.
Enzymatic Degradation of Polyurethane-Based Coatings
In order to develop a potentially environmentally safe alternative to conventional paint removal methods we are investigating the enzymatic degradation of liquid polyurethane-based coatings and their films. A simple protocol for degradation has been developed using aqueous buffer solutions at 37 °C and an optimum pH. Two enzymes were selected, namely am esterase from Bacillus sp. and a protease (papain) that could potentially attack ester and urethane linkages. The extent of degradation was characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and weight loss. Results indicate higher activity for the papain enzyme depending on the type of paint, enzyme concentration and conditions of application.
Eliminating Surface Melt Fracture Using PPA: The Role of Shear Rate
The efficiency of fluoropolymer processing aids (PPA) in the elimination of surface melt fracture (sharkskin) is determined by several factors, including the PPA domain size, the throughput, and PPA/Polyethylene viscosity ratio. The development of techniques such as frustrated total internal reflectance has allowed for a better understanding of the mechanism of the PPA coating. In this work, the role of shear rate in the elimination of surface melt fracture was investigated. The parameters monitored were die entrance pressure, PPA coating thickness and extrudate appearance. We found that the steady state pressure reduction scaled with increasing shear rate while the final PPA coating thickness was only proportional to droplet size. This is consistent with previously observed polyethylene flow curves.
Extrusion of Microcellular PVC
A novel process for continuous production of microcellular plastics has been developed and applied to make microcellular PVC profiles. The first novel aspect of the process consists of the way in which the blowing agent, or gas, is delivered to the extruder. We pre-saturate the solid PVC pellets with carbon dioxide prior to their delivery into the extruder’s hopper. The second novel aspect of the process is the application of nucleation in solid state to continuous extrusion. When the polymer is saturated with a high-pressure gas, a large number of microvoids get 'charged' with the gas, and act as sites where bubbles will nucleate later when the polymer is heated. As the pellets are crushed and heated in the extruder, a large number of bubbles nucleate as the temperature reaches the Tg of the CO2 plasticized PVC. The melt thus is full of nucleated bubbles that are not able to grow in size due to the pressure that develops in the barrel. When the melt exits at the die, where the pressure is atmospheric, the bubbles have a chance to grow larger and create foam. The process employs effective cooling strategies at the die exit, including lower melt temperatures, to keep the bubbles small.
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