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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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.
Numerical Simulation of the Flow Behavior and Breakthrough Phenomenon in Co-Injection Molding
In this work, a three-dimensional finite element flow analysis code is used to study the flow behavior during sequential co-injection molding. Non-Newtonian, non-isothermal flow solutions are obtained by solving the momentum, mass and energy equations. Two additional transport equations are solved for tracking polymer/air and skin/core polymers interfaces. In this paper solutions will be presented for the filling of a spiral-flow mold for which experimental data is available. The numerical approach is shown to predict the experimentally observed core advance stage on which the core flow front catches up on the skin flow front and the core expansion phase during which the flow fronts of core and skin materials advance together without breakthrough. The breakthrough phenomenon is also predicted. The numerical solution is in good agreement with the experiment and predicts correctly the beginning of the core expansion phase and the occurrence of core breakthrough.
Recycling of Butyl Rubber by Ultrasonic Devulcanization
The recycling of butyl rubber based tire-curing bladder was carried out by means of a grooved barrel ultrasonic extruder. Die pressure and ultrasonic power consumption were measured as a function of flow rate and ultrasonic amplitude. Gel fraction and crosslink density of the ultrasonically devulcanized rubber were substantially reduced. The latter caused some reduction in gel fraction and crosslink density in the revulcanized rubber. The mechanical properties of the revulcanized rubber, dependent on processing conditions during devulcanization, were compared with that of the virgin vulcanizate. Good mechanical properties of revulcanized rubber was achieved with 86% and 71% reduction of the tensile strength and the elongation at break respectively, and with modulus increased by 44%. The devulcanized rubber was found to contain tiny gel particles of a wide size distribution with a predominant size of less than 4µm.
Effect of the Compatibilization on the Fluidity of Post Consumer Blends
The blends studied are compound from materials of soft drink and milk post consumer bottles. The materials used were HDPE, PET and two compatibilizers, which are triblock copolymers. The melt flow index test serves to distinguish the qualities of the blends and corroborate the molecular weight effects on density and viscosity. It was obtained viscosity versus blend composition behavior; as PET concentration increases, viscosity decreases. Also were obtained mixing energy curves, and was observed the compatibilizer effect.
Development of Novel Barrier Films using Chaotic Advection ‘Smart Blending’ Device
A Smart Blending Device (SBD) enabled by chaotic advection was used to blend linear low density polyethylene (LLDPE) with 20% and 30% by volume ethylene vinyl alcohol co-polymer (EVOH). Films were extruded to study the relationships of morphology to processing conditions and composition. Morphologies other than droplet, i.e. multilayer, platelet, ribbons and fibers were obtained for each composition. Oxygen barrier, water vapor barrier and mechanical properties were measured. Optimal oxygen barrier and break elongation were obtained with mechanically interlocked single phase continuous laminar-platelet morphology. This blend morphology also eliminated the need for a tie layer. Oxygen ermeation was reduced by 238 and 355 times corresponding to 20% and 30% EVOH. Water vapor permeation was not significantly affected. Tensile strength and ultimate elongation for this morphology were at close to the maximum observed for all blends.
Morphology and Fracture Behavior of Nanoclay-Filled Polypropylene
Polymer nanocomposites are of interest due to improvement in certain material properties relative to virgin polymer or conventional composite materials. For example, compared to conventional materials, Nylon 6/Montmorillonite nanocomposites demonstrate improvements including high strength, high modulus and high heat distortion temperature. Generally speaking, optimal composite properties have been achieved with polar polymer matrixes, which readily disperse polar fillers. A plausible hypothesis proposes that similar improvements could be achieved with non-polar polypropylene (PP)/clay nanocomposites, thus expanding their use in automotive and packaging applications. As a result, both academic and industrials labs have extensively investigated these PP nanocomposites. Consistent with most filler-polymer composite systems, this one demonstrates increased stiffness; however, this improvement is often accompanied by a decrease in toughness. This work examines key factors, which influence the stiffness-toughness balance of PP nanocomposites.
The CIE L*C*h Scan-Color Atlas a Novel Tool for Finding the Right Color
As reported earlier, a preliminary, computer assisted 3D-chromographic representation of all 16.7 million possible RGB colors in the standard CIE L*a*b* (or L*C*h) color space reveals important deviations from well established theoretical concepts. Taking into consideration that the newly defined standard color space appears to have the shape of an anisometric, strongly distorted, RGB cube, we have developed, by binary programming, a complete tridimentional color atlas which, within that space, encompasses all possible colors around a white-to-black lightness axis. The longitudinal distribution of the atlas’ 360 “hue pages” and the latitudinal stacking of its 101 individual “lightness strata” allows the user to pinpoint any one specific color of the thousants that compose the particular CIE h page or CIE L* stratum selected by the user and have it isolated and displayed on screen. A simple mouse click on the chosen color makes a larger sample of that same color appear on screen, accompanied by its correct colorimetric values in all imaginable color spaces and systems. Comparisons between complex 3D-chromographic spectra - which can be fingerprints of anything that shines, glows and spakles in plastics, paints and coatings - become much easier when individual colors composing such spectra can be matched with colors readily identifiable with the novel atlas.
Verification of Blow Molded FEA and Extrusion Blow Molded Bottles
Greater blow molded products can be produced in a shorter time if the promises of finite element analysis programs are true. Reliable and accurate simulation software will allow product designers to make better-informed decisions. Currently in the blow molding industry simulation software is rarely used, because its reliability is unknown.Extrusion blow molded bottles were produced for testing. The bottles were then measured and thicknesses applied to the simulation model. The bottles were tested and compared to results from simulation software. Finite Element Analysis (FEA) was run to simulate loading of the top surface and side loading.
Development of Lubricious Compound for Biomedical Applications Using Hydrophilic Polymers
An attempt was made to develop blends having self-lubricating properties. The approach was to melt blend various base polymers used in the medical industry with hydrophilic polymers known to impart lubricity when applied on the surface as coatings.Different base polymers used were nylon based elastomers and nylons. Hydrophilic polymers used were polyethyl oxazoline and polyvinyl pyrrolidone.These polymers were melt-blended at concentrations of 25% and 50% using a twin-screw extruder. Rheology, coefficient of friction and mechanical properties were studied.
Study of Distributive Mixing Using Polymeric Reactive Tracers in a Co-Rotating Twin Screw Extruder
The distributive mixing profiles were studied during melt-melt blending of two polypropylene melts in a corotating twin screw extruder using the interfacial reaction between two functionalized macromolecular tracers, which were separately blended into each of the polymer melts. The mixing performance is directly related to the conversion of this interfacial reaction. We studied the effect of operating conditions and kneading disk configurations with various combinations of staggering angles (forward 30°, neutral 90°, and reverse 30°) and thicknesses (thick and thin) on distributive mixing.
Comparison of X-Ray Fluorescence Spectrometry to Traditional Analytical Methods for Elemental Determination in Polymeric Materials
The ability to quantitatively identify specific restricted or “hazardous” elements (lead, cadmium, etc.) in polymer matrices is an analytical challenge. Many companies, particularly those in the electrical and electronic manufacturing industry supply chains, are attempting to obtain the necessary data to comply with a variety of customer-driven and/or legislative restricted substance requirements. Two analysis testing approaches being employed are traditional elemental analysis procedures, and x-ray fluorescence spectrometry (XRF).The purpose of this work was to empirically evaluate the effectiveness of XRF quantitative elemental analysis in polymeric matrices and compare this approach to traditional acid digestion – inductively coupled plasma (ICP) measurement techniques. While others are included in this evaluation, the primary elements of interest are lead, cadmium, mercury, and chromium.XRF and Acid Digestion - ICP measurements were conducted on twenty-two polymeric materials, including PVC and polyolefin materials. The polymeric specimens included certified reference materials, custom compounded materials, and others. The data includes measurements performed by four different XRF instrument manufacturers as well as Underwriters Laboratories (UL). Both fundamental parameter and simple “standards” calibration XRF data was collected. The majority of the Acid Digestion - ICP measurements were performed by UL.Although correlation between XRF and Acid Digestion – ICP methods varied widely in some instances, this study’s results suggest promise for the use of XRF as a qualitative screening tool for the material types investigated. Additional work needs to be done, however, to realize the full capability of the XRF analysis approach, particularly using a fundamental parameter or simple calibration approach.
Optimization of the Injection Molding Process Using Design Sensitivity Analysis
Getting the proper combination of different process parameters such as injection speed, melt temperature and mold temperature is important in getting a part that minimizes warpage and has the desired mechanical properties. Very often a successful design in injection molding comes at the end of a long trial and error process. Design Sensitivity Analysis (DSA) can help the processors improve the design and can produce substantial investment savings in both time and money. This paper investigates the ability of the sensitivity analysis to drive an optimization tool in order to improve the quality of the injected part. The paper presents the solution of the filling stage of the injection molding process by a 3D finite element solution algorithm. The sensitivity of the solution with respect to different process parameters is computed by using the continuous sensitivity equation method. Solutions are shown for the non-isothermal filling of a rectangular plate with a polymer melt behaving as a non-Newtonian fluid. Sensitivity of the solution is used to build the surface response of the injection pressure with respect to a given design parameter (the injection speed in the present case). This is then used to determine the conditions corresponding to the minimum injection pressure.
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.
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