SPE Library

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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Conference Proceedings

Thermomechanical Modelling, Microstructure Development and Part Performance in Stretch Blow Moulding

D. Laroche, R. DiRaddo, J. Brace, May 2001

Blow moulding simulation can be used as a predictive tool for determining the bottle performance as a function of the stretch blow moulding operating conditions. Modelling the successive processing steps is necessary in order to obtain the final bottle geometry and the distribution of polymer microstructure. The container properties are then used to estimate top load resistance. The objective of this work is to integrate microstructure models in process simulation in order to better estimate part performance in service. The models are evaluated for the prediction of top load resistance of PET containers. Experimental validations of the integrated process and performance models were conducted for the one-stage injection stretch blow moulding process.

Dispersion of Nanoparticles in High Performance Polymers Using Thermosetting Resins

Sadhan C. Jana, Sachin Jain, May 2001

A low molecular weight epoxy was used as dispersant of fumed silica in polyether sulphone (PES), a high performance polymer with typical processing temperatures of ~340-380°C. Small amounts of low molecular weight epoxy reduced the processing temperatures of PES by as much as 100°C and, due to polar nature, helped disperse fumed silica particles, which contained active silanol groups. Epoxy molecules were later crosslinked using suitable curing agents. An order of magnitude reduction in the size of dispersed fumed silica particles and significant improvement in HDT were observed.

On the Effects of Migration of Filler Particles on Conductivity and Mechanical Properties

Sadhan C. Jana, Sashishekhar Doni, May 2001

Shear-induced migration of filler particles during molding and extrusion of filled polymer compounds of polypropylene and glass beads and conductive carbon particles was investigated. The high-shear flow conditions were generated in capillary rheometers with length to diameter ratio of 20 and 30 and in injection molding machine. Reduction of both surface and volume conductivities of injection molded samples was observed, especially in the cases of conductive compounds with conductive particle composition in the range of percolation volume fraction. Significant migration of glass beads was observed from the surface to the interior in blends with PP. Maleic anhydride grafted polypropylene (PP-g-MAH), used to promote binding with filler particles, reduced the extent of migration of glass beads, but improvement in conductivity of injection molded samples was not observed.

Are Fundamental Mechanistic Studies Useful? A Novel Study in the Thermal Degradation of PET during its Manufacture and Processing Will Be Discussed to Illustrate the Importance of Mechanistic Studies

Kishan C. Khemani, May 2001

PET polyesters for food packaging comprise one of the fastest growing polymer markets in the world. One of the biggest challenges in the PET industrial R&D sector for the past twenty years has been to find the means to reduce the amount of acetaldehyde (a PET polyester's degradation by-product) generated during PET production and processing. A novel approach for studying the mechanism of thermal degradation of PET polyesters and copolyesters is described in this study, which also suggests precisely the ways to significantly reduce the acetaldehyde content in these polyesters. In this study, the amount of acetaldehyde evolved was measured over time at an elevated constant temperature. We found that there was a gradual decrease in the amount of acetaldehyde generated with time, and that this decline eventually approached a near asymptotic value. A degradation mechanism was proposed which showed that acetaldehyde was generated by three different routes involving, first, the hydroxyl end-groups, second, the vinyl end-groups and finally, the mid-polymer chain-scission. It was further suggested that of these, the hydroxyl and the vinyl end-group based acetaldehyde generation routes depleted with time leaving behind the last, but inexhaustible, chain-scission route. From the data in this study, it was also possible to estimate the rate of acetaldehyde generation by this mid-polymer chain-scission route. This information was then applied together with the (a) amount of residual acetaldehyde in the resin, (b) HO-end group concentration and (c) vinyl- end group concentration, to calculate the amount of acetaldehyde generation possible over a given period of time. This calculated [acetaldehyde] compared very well with the actual observed [acetaldehyde] over the same period of time, thereby validating the proposed mechanisms. In agreement with the thermodynamic principles, a near doubling of the chain-scission acetaldehyde generation rate was also observed when the temperature

Surface Modification of Polymer via Surface-Induced Migration of Copolymer Additives

Hojun Lee, Lynden A. Archer, May 2001

Surface-induced migration of low surface tension block copolymer additives, polystyrene-b-polydimethylsiloxane (PS-b-PDMS) and high surface energy copolymer additives, polystyrene-b-polymethylmethacrylate (PS-b-PMMA) in a polystyrene (PS) host was investigated using a series of matrix PS molecular weight (Mw). Dynamic Contact Angle analysis and Attenuated Total Reflection Fourier Transform Infrared spectroscopy measurements were used to characterize surface properties of polymer/additive blends created by solvent casting, precipitation, and melt annealing processes. For all matrix Mw, selective DMS enrichment of the air/polymer interface was observed due to the strong surface energy difference between additives and matrix. The surface excess concentration of DMS group, ??DMS was also found to depend on host polymer Mw and annealing conditions: ??DMS ~ Mw,PS?, where the scaling exponent a is a function annealing conditions. Whereas entropic-driven surface migrations were observed in PS-b-PMMA/ PS blends. The diffusion of PS-b-PMMA in PS matrix was found to depend on matrix molecular weight even though much high Mw, which is not consistent with reptation theory in molecularly homogeneous linear blends. And also for high molecular weight PS, thermodynamic driving force is revealed to compete with diffusion rate of additives. These findings could be discussed in terms of the matrix Mw dependence of diffusivity, surface tension and configurational entropy of host polymer.

Kinematics of Quasistatic Inflation of a Catheter Balloon Made of Elastomeric Material: Simulation and Experiment

Xiaoping Guo, Michael Bednarek, May 2001

Based upon a nonlinear membrane theory, a theoretical model is proposed for simulating a quasistatic deformation process of a catheter balloon made of an elastomeric material and inflated by the internal pressure acting across the membrane of the balloon. A Lagrangian approach is utilized to describe a material particle's motion during inflation. The deformation field and the system of governing equations are determined in terms of the principal stretches and the Cauchy stresses. With ~, incorporation of the constitutive laws of hyperelasticity and a set of proper boundary conditions, the numerical scheme for calculating the deformation-loading relationship of the balloon under quasistatic equilibrium condition is developed. The inflation experiments are conducted under the assumed quasistatic condition for various angiographic catheter balloons of different designs. Intermediate inflated geometries and inflating pressures at various inflating volumes are measured and compared with the predictions. It is found that the theoretical model can reliably predict the short-term kinematic behavior of balloon inflation. In addition, the effects of various balloon design parameters on the kinematics of inflation are evaluated.

High Performance Decoration with Polyamide Films

Joerg Lohmar, Michael Beyer, May 2001

Over the last decades a large number of new surface decoration and protection processes have been developed using polymer films instead of coatings. Films of polyamide 12 and polyamide 12 elastomers offer the best combination of transparency, mechanical properties, and chemical resistance. Highest quality diffusion printing techniques are applied to create brilliant decorations on i. e. sports articles like snowboards, skis, tennis rackets, or for demanding automotive applications. Most recently two-layered so called lacquer films with brilliant metallic or other effect fillers were introduced into the market to replace conventional multi-step coatings. In the paper we will present mono- and multi-layer structures of decorative and protective polyamide films. Printing and processing techniques will be discussed showing various applications.

Structure of Propylene/1-Pentene Random Copolymers

L. Halász, K. Belina, O. Vorster, I. Tincul, May 2001

Propylene/1-pentene copolymers were prepared, characterized and reported previously. [1-6]. This new family of copolymers form ?-modification during isothermal crystallization. Upon deformation significant changes take place in the crystalline structure of the material. Two extensional deformation methods, (thermoforming and cold stretching) were used and the thermal and crystalline properties of both the deformed and undeformed samples were determined by DSC and WAXD. Thermoforming has no effect on the thermal and crystalline properties of the material. On the other hand, cold stretching changes the crystalline structure of the material. Upon extension, the degree of ?-modification decreased with a corresponding increase in the degree of ?-modification.

In Situ Observation of Fracturing Behavior of Polyethylenes by Transmission Electron Microscopy

Tatsuya Kasahara, Noboru Yamaguchi, May 2001

In situ observation of deformation and fracturing process of polyethylenes was carried out using a transmission electron microscope (TEM). It was found that there are three kinds of fracturing behavior concerning polyethylenes. In case of linear polyethylenes, two kinds of fracturing behavior caused by Crazing" and "Elongation" were observed. On the other hand low-density polyethylenes (LDPEs) having long-chain branches (LCBs) were fractured dominantly by "Interfacial splitting" of spherulites. These results show that the molecular structure of polyethylenes effects the deformation and fracturing behavior."

The Effect of Wall Slip on the Performance of Flat Extrusion Dies

W.A. Gifford, May 2001

Flat extrusion dies are commonly used in a wide variety of film, sheet and coating applications. Although flat dies can be designed to produce an exit flow distribution that is very uniform across most of the width, there will usually be a region along each side where it drops gradually to zero. This often requires trimming the edges of the film or sheet downstream in order to meet product specifications. It is commonly believed that treating the land area of the die with coatings that promote a small amount wall slip will reduce the size of this edge effect and therefore improve die performance. This analysis shows that slip over the entire land region of the die will adversely affect die performance. Better performance is possible but only if the sides of the land are treated.

FFT - An Efficient Process Analytical Tool for Plastics Film and Sheet Processes

Tan Srinivasan, May 2001

Every Plastics Film and Sheet Processor, whether using Calendering, Extrusion or Coating process, strives to manufacture the best quality product with minimal variations. The total variations in a product comprise of Cross Direction (CD) and Machine Direction (MD) variations. The Machine Direction variations can be further broken down into controllable Long-Term drift and uncontrolled Short-Term high frequency variations. Gauging Systems have been available in the Marketplace for quite a few years, which efficiently control the Profile (CD) and Long Term Machine Direction (LTMD) variations. This paper illustrates the capability of Gauging Systems that incorporate Fast Fourier Transform (FFT) feature to provide the plastics film & sheet processors with a timely and detailed analysis of the uncontrolled high frequency variations (Short Term Machine Direction (STMD) and the causes thereof. This efficient process analytical tool enables the processor to take timely action to reduce STMD, thus improving the overall product quality. The economic benefits to the plastics film & sheet processors derived from down-gauging, while meeting the specifications for end-use applications of the product can be substantial. This paper presents a case study of FFT application to a vinyl calendering process.

Optical Haze Properties of Polyethylene Blown Films: Part 1-Surface Versus Bulk Structural Considerations

Garth L. Wilkes, Matthew B. Johnson, Ashish M. Sukhadia, David C. Rohlfing, May 2001

In this paper we report on some recent findings regarding the factors affecting the optical (haze) properties of polyethylene (PE) blown films. The large majority of the contribution to the total haze in these blown films was a result of the surface roughness of the films, with the bulk (internal) contribution being relatively minor. Using several characterization techniques, we found, rather unexpectedly, that the surface roughness in some of these films was a result of the development of distinct spherulitic-like" superstructures formed during the blown film processing. Analysis of the rheological and molecular characteristics led us to conclude that in blown films of LLDPE-type resins the optical haze properties are adversely affected due to enhanced surface roughness caused by the formation of "spherulitic-like" superstructures in polymer melts that possess fast relaxing and low melt elasticity rheological characteristics."

Optical Haze Properties of Polyethylene Blown Films: Part 2-The Origins of Various Surface Roughness Mechanisms

Ashish M. Sukhadia, David C. Rohlfing, Matthew B. Johnson, Garth L. Wilkes, May 2001

In continuation of our associated report here (see Part 1, ANTEC 2001), we have now found that high haze in PE blown films can be caused by very different surface roughness mechanisms having unique origins. The total haze % exhibits a complex parabolic relationship with the logarithm of the recoverable shear strain parameter, ??. At low ??, spherulitic superstructures are formed. As ?? increases, an oriented, row-nucleated stacked lamella texture is developed. However, at even higher ??, fine-scale surface roughness due to high melt elastic instabilities is induced. We believe that this is the first time that both very low and very high melt elasticity have been shown as primary causative factors in yielding high haze in PE blown films, albeit for fundamentally very different reasons.

Recovery of Post-Consumer Plastic Waste via Solid State Mechanochemistry

Klementina Khait, Erin G. Riddick, John M. Torkelson, May 2001

A new solid-state mechanochemical technology is being developed to create value-added materials from post-consumer plastic waste. The process, called solid state shear pulverization (S3P), can recycle various mixtures of ordinarily incompatible plastics, including post-consumer film waste, by subjecting the polymers to high shearing forces in the solid state. This produces uniform, light-colored powders of variable fineness suitable for processing by all conventional plastic fabrication techniques. The resulting materials consistently exhibit high elongation and impact strength. Northwestern University and Material Sciences Corporation are transitioning S3P from the laboratory to the commercial scale.

Confocal Laser Scanning Microscopy of Pigmented Polypropylene Systems for Dispersion Evaluation

Erik C. Nielsen, May 2001

Determining the level of dispersion of pigments in polyolefins is a critical quality control issue in the production of color concentrate masterbatches. Confocal laser scanning microscopy (CLSM) can be used to identify the presence of agglomerates in the pellet form rather than diluting the material and blowing a film. This technique requires minimal sample preparation and is non-destructive in nature. Micrographic images can be correlated with traditional dispersion tests to develop a repeatable protocol. Four commonly used high performance pigments are investigated in a polypropylene carrier.

VOCs Emissions and Structural Changes of Polypropylene during Multiple Melt Processing

Q. Xiang, M. Xanthos, S. Mitra, S.H. Patel, May 2001

Polypropylene, as a commodity recyclable thermoplastic, is studied in this research to evaluate the potential environmental impact resulting from volatile organic compounds (VOCs) emitted during multiple reprocessing. Unstabilized commercial polypropylene (PP) grade was processed several times by injection molding. Samples were examined after each cycle for total VOCs emissions with a flame ionization detector (FID) and cumulative VOCs emissions were obtained after each processing step. Corresponding structural changes were investigated with Fourier Transform Infrared (FTIR) Spectroscopy and results were correlated with rheological data that showed decreasing viscosity particularly after the 7th processing cycle.

Extrusion Foaming of PET/PP Blends

C. Wan, M. Xanthos, S. Dey, Q. Zhang, May 2001

In order to develop new applications for recyclable commingled resin streams, blends containing PET and PP resins with different rheological characteristics were dry blended or compounded at different ratios and subsequently foamed by using PBAs and CBAs. Properties of the foamed blends were compared with those of similar products obtained by foaming the individual PET and PP components in the absence of compatibilizers/rheology modifiers. Foamed polymer blends with fine cell size and low density could be produced in the presence of suitable compatibilizer systems consisting of functionalized polyolefins or their combinations with reactive coagents

Compression Molding Tooling for Thermoplastic Composites

Harold F. Giles, Jr., May 2001

Tooling requirements for compression molding continuous glass mat, long fiber glass, or other types of reinforced thermoplastic composite products is presented along with critical tooling aspects. Emphasis is placed on the general tooling concepts associated with cooling lines, shear edges, guidance systems, ejectors and stop blocks. Basic product design issues that can lead to poor part performance i.e. weld lines, tabs and mounting holes, ribs and bosses, sink marks, multiple cavity molding, and venting are discussed. The relationship of prototype tooling and the requirements to go from design to production is discussed briefly.

A Physical-Mathematical Model for the Description of the Process Behavior of Mixing Elements

H. Potente, K. Kretschmer, J. Flecke, May 2001

Tightly intermeshing, co-rotating twin screw extruders are commonly used for tasks requiring good mixing. The modular constitution of both barrel and screw makes it possible to optimize the extruder configuration for a given task. Physical-mathematical models enable the process engineer to predict the process behavior of a chosen extruder configuration and to optimize existing compounding processes. We will present physical-mathematical models for the prediction of the pressure-throughput relationship of grooved conveying and grooved reconveying elements. The models are based on an analytical approach for the description of the flow patterns within the investigated screw elements. Experimental investigations were performed with varying geometry, material and process parameters. Finally the developed model was compared to the experimental results.

Extrusion/Compression of Long Fiber Thermoplastic Composites

Klaus Gleich, May 2001

It is becoming common for long fiber-reinforced thermo-plastics (LFT) to replace existing GMT-type applications as well as to capture new applications. This is especially true in the European automotive industry, where the market for parts made from LFT is experiencing tremendous growth. The following paper discusses the available materials, the mechanical and physical properties, machine techniques and processing details of the LFT process. It will also discuss potential applications for LFT. The paper will cover different process techniques such as direct processing and make comparisons with other processes. An explanation on the effects that LFT has on properties and economics will be made. It will show how the economics can be improved by adding recycled material to the process. This paper will provide a better understanding of the LFT-process and how you could get benefits from this process.