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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Extrusion Foaming Behavior of PBT Resins
An investigation of the foaming behavior of polybutylene terephthalate (PBT) resins in extrusion was performed. Commercial grades of PBT with different molecular weights and rheological characteristics were chosen. PBT’s with a high temperature chemical blowing agent were extruded under different material and operational conditions (e.g. amount of blowing agent, set temperature at the die, screw rpm, etc.) to allow the understanding of the effects of those conditions on product characteristics. The foamed extrudates were analyzed for density, morphology, and crystallinity. It is shown that the foaming behavior and the foam quality of PBT are functions of the characteristic properties of the resins including rheological and crystallization behavior.
Growth in the Medical Polymers Industry
The healthcare industry is poised to experience both unparalleled challenges and growth as the Baby Boom generation ages. The steadily increasing volume of persons needing advanced care, new developments in diagnosis and treatment, and the increased lifespan resulting from these developments all combine to produce new opportunities in the area of medical plastics: new materials, processing and product design will make possible the next generation of medical products. During the 1980s 60 patents were issued in the area of medical plastics. That number jumped to 209 in the 1990s. During the first 4 years of the 2000s 218 patents were issued in this field. The growth of the medical plastics industry will only continue. The areas seeing the strongest growth will be discussed in this paper, as will likely future trends.
Polyolefin Nanocomposites with Improved Performance
The preparation of nanoclay-reinforced polyolefin nanocomposites by means of melt processing was investigated. Different types of compatibilizers based on glycidyl-methacrylate-grafted polypropylene (PP) have been developed for the formation of PP nanocomposites. Different formulations and processing conditions were used to optimize the chemical interaction between the organic and inorganic phases (i.e. the polymer matrix and the clay) in order to maximize the clay dispersion and the clay-matrix interface. Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used to study the chemical interactions between the polymer and the organoclay as well as the dispersion of the organoclays and the nanocomposite morphology. Various properties of the resulting nanocomposites, such as the physicochemical properties, the mechanical properties (including fracture toughness from essential work of fracture), and the thermal stability, were also evaluated. The relationship between formulation, structure, and performance is discussed.
An Investigation into the Reuse of Painted TPO Regrind
Thermoplastic olefin (TPO) is currently the material of choice for automotive bumpers and fascias. The part is generally painted with thermoset paint after molding. Unless removed, this paint layer creates problems during recycling of rejected parts. It causes a change in the processing characteristics and properties. The techniques used for removing the paint layer from the TPO create additional steps in the process and adds extra costs. The concept studied is the possible reuse of painted regrind by reducing the paint particle size in an injection molding process; possibly eliminating the need for paint removal in some recycling applications.A modified progressive double row grater screw was used to reduce the particle size of the paint flakes. The physical properties of these material blends are compared to similar blends obtained using a general-purpose screw. It is shown that reducing the paint flake size has a marginal effect on mechanical properties. However, the surface finish is greatly enhanced when the paint flake size is reduced.
Amorphous Phase Study in Propylene-Ethylene Copolymers: Positron Annihilation and Gas Transport Properties
The average free volume hole size
Influence of the Synthesis Thermal History on the Structure of Acrylate Based Hydro Geles
Acrylate based hydro gels synthesized at very high controlled conditions exhibit structures at three different length scales (10-6, 10-4 and 10-2 m) as well as an unusual combination of surface properties, morphology, mechanical properties and swelling capacity. These properties depend strongly on the thermal history during the synthesis and on the cross-linking agent concentration. Mechanical properties, swelling capacity and structures at different length scales of these hydro gels show transitions at a critical concentration of cross-linking agent and a critical temperature of synthesis.
The Effect of the Processing Parameters on the Mechanical Properties of PMMA Microcellular Foams
Microcellular closed-cell PMMA foams are prepared using a two stage batch process method. The foam structure is controlled by altering the foaming temperature, foaming time and saturation pressure. The effects of processing parameters on the mechanical properties of the foamed material are characterized under different foaming conditions. Elastic modulus, tensile strength and elongation at break were studied as functions of the different foaming parameters. The mechanical properties are found to be greatly affected by the foaming parameters and vary with cell morphologies. The experimental results are compared with existing analytical and numerical models to evaluate them and predict the mechanical properties of microcellular polymeric foams. The results of this work help to optimize the foam processing parameters and achieve desired mechanical properties and material density.
Examining Blow Molding Pinch-Off at Different Parison Temperatures
This study is designed to observe the effects of temperature on the pinch-off strength of extrusion blow molded bottles. Pinch-off design is a crucial component because it welds the sides of the parison as the mold closes. The strength of this weld is important because a weak weld will result in part failure.This experiment examines the effects of processing. To assure a uniform parison wall thickness, the die and mandrel were adjusted for each combination. Special attention was placed on accurate wall thickness. The thicknesses were confirmed by measuring the parison. This study was performed by changing melt temperatures for the HDPE bottles.
Rheology of Heat-Induced Gelation of Chitosan Solutions
Heat-induced gelation was observed above 80°C on a chitosan solution neutralized with a weak base, ? - glycerophosphate. Urea, a hydrogen bonding decomposing agent, was also used in some of these solutions to investigate the presence of hydrogen bonds in the resulting gels. The solution behaviour and gelation process were investigated using linear viscoelasticity.In solution state, the addition of urea decreased the rheological properties due to the reduction of hydrogen bonding interactions. During the gelation tests, the evolution of the storage and loss moduli was monitored as a function of temperature. Heating resulted in sol-gel transition at a critical temperature, the so-called gelation temperature Tgel. It was found that adding urea decreased the resulting gel strength and increased Tgel, corresponding to the retardation of the gelation process. These results indicate that hydrogen bonding is an important parameter in the chitosan physical gels formed, even at high temperature, which is not the usual belief. In parallel, pH and conductivity measurements revealed that gelation was also caused by polymer-polymer hydrophobic associations enhanced at high temperature, due to increased ionic strength.
Melt Grafting of End-Functionalized Poly(Tert-Butyl Acrylate) to Silicon Substrates
This work is part of a study aimed at creating surface grafted polymer layers. After deposition of amineterminated monolayers, poly(tert-butyl acrylate) (PtBA) was grafted ‘from the melt’ to silicon wafer substrates as a function of reaction temperature. The polymer layer of interest in this study was PtBA because it is relatively easy to subsequently substitute the tert-butyl ester groups with other functional groups to create a chemically tailored layer. The thickness of the monolayer and grafted polymer layer were monitored using ellipsometry and static contact angle was used to characterize the surface energy.
Fracture Behavior of Natural Fiber Composites
The fracture behavior of two natural fiber composites was investigated. Tensile and fracture tests were performed on sisal reinforced HIPS and sisal/starch based composites. An increasing trend of stiffness with fiber content was found in both cases, whereas tensile strength decreased for sisal/HIPS composites. A maximum in sisal/HIPS composites quasi-static fracture toughness with fiber loading was observed, while they exhibited lower impact toughness values than HIPS. For the biodegradable composites, fracture toughness increased with fiber content and it depends on fiber orientation. In puncture tests, these composites exhibited higher values of fracture energy than neat matrix and fiber orientation affected the damage zone.
Homocomposites of Poly(Ethylene Terephthalate)
While the advantages of homocomposites over heterogeneous composites are obvious, the fabrication of homocomposites for fast crystallizing polymers is challenging because the melting temperatures of the fiber and the matrix are very close. In the present study, an approach of using poly(ethylene terephthalate) (PET), a slowly crystallizing polymer, to form homocomposites was investigated. Because PET experiences slow crystallization during typical polymer processing, distinct physical forms with a large difference in crystallinity and thus in melting temperature can be readily obtained. In the experiment, highly crystalline PET fibers laid between two amorphous PET films were compressed between heated platens at 180°C, a much lower temperature than the melting temperature of the fiber, and rapidly cooled after a holding stage of 90 seconds. The resulting homocomposites have a tensile strength about twice higher than the non-reinforced PET processed under the same condition.
Morphology Development in Blends of Nanoclay, Polyamide 6, and Polypropylene Processed in a Chaotic Mixer
In this paper, we studied the effect of organically modified montmorillonite clay (OMMT) on morphology development in the mixing of polyamide 6 (PA6) and polypropylene (PP). The clay particles were initially present in the PP-phase. All morphological forms, e.g. lamella, fibrils, and droplets were seen as in blends without clay. Much finer PP-phase droplets were observed during breakup of the fibrils into droplets. The thread breakup studies revealed that the changed interfacial tension due to presence of clay was responsible for finer morphology. In addition, the clay particles in the PP-phase disrupted the break pattern of fibers and expedited fibril-droplet transition.
A Description of the Fluoroelastomer Coating Evolution as a Polymer Processing Aid
For decades, fluoroelastomers have been used as polymer processing aids (PPA). Previous works have measured the thickness of the PPA coating, its effects on the polymer/die interface, and proposed several mechanisms of PPA coating. In this work, the coating process of a fluoroelastomer was visualized during the extrusion of a PPA/Polyethylene blend. The apparatus consisted of a capillary rheometer fitted with a sapphire die and a high resolution imaging system. The images obtained show a coating evolution from the adhesion of scarce PPA particles, to the massive wave flow of PPA, and finally the formation of streaks on the die wall. These sequences of images are correlated with the measurements of the die entrance pressure and the appearance of the extrudate.
Higher Performance Polyethylene Powders
Over 800MM lbs/yr of polyethylene (PE) powders are used in a very broad array of applications in North America. These PE powders range in size from coarse, 1200 micron (16 mesh) powders, down to extremely fine powders well under 5 micron in size. The various applications for these powders include wood plastic composite lumber, battery separators/membranes, architectural paints/coatings, cosmetics/beauty care, to name just a few.This paper will provide an overview of the PE powder market in North America. The characterization of the various types of PE powders will be presented, as well as the different manufacturing processes utilized to produce these powders. Performance requirements for various PE powder applications will be detailed, and examples presented where PE powder product design provides performance enhancement in selected applications.
Study of the Interface Deformation when Gas Is Injected into Polymer Melt Flow Field
Much work has been reported about the deformation of a dispersed single droplet under the flow field of another continuous phase. This investigation has a great significance upon the dispersion or mixing of the multiphase polymer blends. Similar to this, the deformation of a single gas bubble under polymer melt flow field is also well worth studying since its importance upon the dispersion or breakup of bubbles. To obtain the rules of bubble deformation when gas is injected into polymer melt flow field, a series of experiments were made through changing the gas injection pressures. It was found that bubble shapes for the different time periods were changed greatly since its dilatation and the effects of the flow fields. Moreover, the deformation of bubble was severely affected by its volume. Therefore, several different bubble deformation processes were characterized.
High Scanning Rate DSC for the Characterization of Proteins
Protein and protein based formulations present some interesting difficulties when studied by traditional Differential Scanning Calorimetry techniques. Compared to synthetic polymers, proteins tend to have weak transitions and are more sensitive to thermal effects. Modulated temperature techniques have show some utility in the analysis of these materials, but some issues with kinetic effects, weak transitions, and the time required for screening samples remain. A series of protein-based formulations were studied using high scanning rate DSC. Application of high scanning rate DSC to proteins was found to have some significant advantages in both increasing throughput and in enhancing weak transitions. Not only can throughput be increased dramatically, but very weak transitions like the glass transition of a pure protein could be measured directly.
New Developments in Micro-Compounding of Polymeric Materials
This paper presents the most recent development in microscale compounding technology in material science. The equipment consists of a 6-inch conical twin-screw extruder co- and counter-rotating and housed in a vertical clamp shell barrel, which can be operated in batch and continuous modes. The design and versatility of this equipment allows the evaluation of a myriad of materials ranging from polymer blends to filled systems and Nano-composites with 5 to 15 grams of sample. It is also possible to monitor changes in the rheological properties of the materials during processing allowing a better assessment of mechanisms such as polymer degradation and stability, reactive extrusion and crosslinking. Comparative analysis with other processing equipment such as mixing bowl and twin screw extruders on model systems and in terms of extent of dispersion and mixing is achieved.
Lifetime Prediction for Slow Crack Growth on Polyethylene Pipes for Gas Distribution
The required performance of polyethylene pipes for gas distribution is firstly described. As an evaluation method for slow crack growth, the relation between crack growth length and time under test was obtained to investigate the stress crack resistance of polyethylene pipes for gas distribution after conducting three-point bending tests at 23 degrees C for fifteen years as the maximum test period. The incubation period leading to crack initiation was much longer and the crack growth was slower for domestic resins. The relation between the stress intensity factor and the crack growth rate of several pipes are also discussed. The full-notch tensile creep test is specified by JIS K6774, which is now under consideration for adoption by ISO as a standard. The data on and the results of the full-notch tensile creep tests have been accumulated for several years to decide whether to introduce new resins or modified resins, and to evaluate the lot-to-lot variation of resin production for the quality control of polyethylene pipes. The full-notch tensile creep test is also applied to the evaluation of fusion joints, especially electrofusion joints, as well as the substrate of pipes. The test results have also been accumulated to determine suitable fusion conditions and to evaluate fusion integrity between different grades of pipes or joints.
Probing the Amorphous Structure of Semicrystalline PET by Positron Annihilation Life Time Spectroscopy
Rigid amorphous fraction (RAF) in semicrystalline poly(ethylene terephthalate) is associated with very thin (20- 40Å) amorphous layers confined between the crystalline lamellas in the regions of lamella stacks. In comparison with mobile (regular) amorphous fraction (MAF), it is constrained and vitrifies at much higher than regular Tg temperature, presumably at crystallization temperature, Tc. The structure of semicrystalline PET was probed by positron annihilation lifetime spectroscopy (PALS). Systematic divergences in the o-PS annihilation lifetimes and intensities were observed, as a function of crystallinity. The results indicate that the fractional free volume of RAF as measured by the product of the hole number density and the average hole volume indeed showed a direct correlation with crystallization temperature.
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