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

Polymer Layered Silicate Nanocomposites Prepared by a Two-Stage Method
Changchun Zeng, L. James Lee, May 2001

Polymethylmethacrylate (PMMA) and polystyrene (PS) clay nanocomposites were prepared via in-situ bulk polymerization. The effects of initiators and clay surface chemical modification on the nanocomposite structures were studied. Exfoliated PMMA and PS clay nanocomposites were synthesized. A two-stage method was then used to prepare PS clay nanocomposites. The masterbatch nanocomposites with a high clay concentration and good dispersion were first prepared via in-situ polymerization. The masterbatch was then blended with a pure polymer using a compounder to lower the clay concentration to the desired level. The thermal stability of the nanocomposites was investigated.

On the Correlations between Thermodynamic and Dynamic Fragility of Polymers
Dinghai Huang, Gregory B. McKenna, May 2001

The correlation between the thermodynamic measure of fragility Cpl/Cpg(or Cpl/Cpc) and the dynamic fragility index m (1) , are presented for small molecule organic, polymeric and inorganic glass forming liquids. The results are consistent with three classes of behavior: 1) a decrease in m with increasing Cpl/Cpg for the polymeric glass formers; 2) a nearly constant value of m independent of Cpl/Cpc for small molecule organics and hydrogen bonding small molecules; 3) an increasing value of m with increasing Cpl/Cpc for inorganic glass formers as originally considered by Angell. (1)

Isobaric and Isochoric Fragility of Polymers
Gregory B. McKenna, Dinghai Huang, May 2001

Data taken from the published literature were used to determine the dynamic fragilities for several polymers in both isobaric and isochoric conditions. We find that the path dependence of fragility varies widely for different polymers. For PVAc and PEA, The fragility is independent of the pressure and specific volume, the isochoric fragility and isobaric fragility are almost the same. But for PVC and PMA, the fragility is sensitive to the change of pressure and volume, and the isobaric liquid is more fragile than the isochoric one. Both the pressure dependence of the isobaric fragility, dm/dP, and the specific volume dependence of isochoric fragility, dm/dV, were determined from the data.

TTT Diagram Development of a High Performance Epoxy Resin and Prepreg
Walter X. Zukas, Linda L. Ghiorse, May 2001

Hexcel Corporation's 8552 resin is a thermoplastic-toughened high-performance epoxy and is being used in the construction of the Army's prototype Comanche helicopter. Understanding the cure behavior of a thermosetting system is essential in the development and optimization of composite fabrication processes. A time-temperature- transformation (TTT) diagram was constructed, which characterizes the relationships between the degree of cure, temperature, time, and material processes of the 8552 resin. Torsional braid analysis (TBA) and differential scanning calorimetry (DSC) were used to develop this diagram. By using the TTT diagram, development of a solid-state cure cycle was begun. This will then be used to prepare composites for comparison to those prepared with the manufacturer's recommended cure cycle.

A Range of Processing Methodologies for Designing Adequate Tissue Engineering Scaffolds Based on Natural Origin Degradable Polymers
R.L. Reis, M.E. Gomes, J.S. Godinho, D. Tchalamov, A.M. Cunha, May 2001

An ideal tissue engineering scaffold must be designed from a polymer with an appropriate degradation rate, and the processing technique must allow the preparation of 3-D scaffolds with controlled porosity and adequate pore sizes, as well as tissue matching mechanical properties. This communication revises recent work that has been developed in our laboratories with the aim of producing porous polymeric structures (from starch based blends) with adequate properties to be used as scaffolds for bone tissue engineering applications. The developed methods include a range of melt processing technologies (based on injection molding and extrusion using blowing agents and in some cases surfactants) and other innovative combined techniques, such as, solvent casting-particulate leaching and compression molding + particulate leaching. The samples produced by the different methods were characterized with respect to the morphology of the porous structures and their mechanical and degradation behavior.

A New Model for Interpreting Nanocomposite Behavior
G.W. Beall, May 2001

A new model has been developed to help in understanding nanocomposite behavior. This model employs the concept of a constrained polymer region around the nano-particles. The constrained polymer region characteristics are dependent upon a number of factors that involve both the type of nano-particle but also the characteristics of the polymer. The intermolecular bonding energies of a given polymer profoundly affect the size and stability of the constrained polymer region. The model will be discussed in some detail as well as the application of the model to interpret nanocomposite data. The model has shown utility in interpreting both physical as well as permeability behavior in a variety of composites.

The Role of Fabrication Technology Inventions in the Introduction of LLDPE
Stuart J. Kurtz, May 2001

Innovation and invention were key to meeting the challenges of overcoming fabrication process limitations of Linear Low Density Polyethylene (LLDPE). In the late 1970’s as Union Carbide sought to commercialize LLDPE from a gas phase reactor, we found that the “as polymerized” resin product, targeted for the blown film market, had significantly better physical properties than LDPE but poorer processibility, at least in the common equipment in use. UCC met this challenge by assigning product development and fabrication process experts to develop and implement appropriate technologies. The problems we investigated covered many of the classical polymer processing issues including melt fracture, draw resonance and film blowing instabilities. Although only solutions that were projected to be economically acceptable were pursued to completion, all of our studies helped to develop a better understanding of these classical problems. In this presentation, I will discuss some of the important scientific and technological understandings and solutions that were found or rediscovered and how they were applied to compounding and fabrication extrusion lines. A number of examples that illustrate the technical advances in supporting LLDPE commercialization will be given both from our own experience and from other researchers. We will also use these examples to show the synergistic interaction among laboratory experiments, scientific theory and production economics as a feedback loop driving innovation.

Structure and Thermodynamic Behavior of Polymeric Gels
Ferenc Horkay, Gregory B. McKenna, Erik Geissler, May 2001

During the last decades the macroscopic mechanical and osmotic properties of hydrogel systems have been extensively studied. Less attention has been paid to the organization of the polymer chains in the network. Cross-links generate local elastic constraints which induce density fluctuations having spatial extension in the nanometer range. The small angle neutron or X-ray scattering response of gels depends sensitively on their microscopic structure. Since thermodynamic fluctuations are governed by osmotic forces, comparing the results of scattering with macroscopic osmotic observations provides insight into the origin of molecular interactions that control the thermodynamic properties of swollen polymer networks.

Injection Molding of Metal - Updating a New Market for Mold Builders
Frederick T. Gerson, May 2001

After briefly reviewing the process of metal injection molding, its rapid adoption and more recent developments , the focus of this paper shifts to the implications for mold design and mold making. Some new markets created by injection molding of magnesium, zinc and aluminum alloys are described, and so are the principal characteristics and technical requirements of the process. It is commonly referred to as thixomolding - TXM for short. Mold building and design for TXM calls for special attention. Here semi-solid metals rather than plastics are processed. Therefore, molds must sustain significantly higher operating temperatures, pressures, erosion and corrosive attack. Parting line integrity is critical, especially for parts that feature very thin sections - as low as 0.45mm (0.018). Mold alloy selection will become even more important when injection molding of aluminum reaches commercial production status in the months ahead. Typical end uses and a rationale for further strong growth of TXM will be illustrated by specific product examples."

Ethylene Styrene Propylene Terpolymers: Structure/Property Relationships
Martin J. Guest, Y. Wilson Cheung, Teresa P. Karjala, James M. Ruiz, Brian W.S. Kolthammer, May 2001

The terpolymerization of ethylene(E), styrene(S) and propylene(P) has been enabled by INSITE* Technology. ESP terpolymers differing in monomer composition ratio have been produced and characterized by solid-state dynamic mechanical spectroscopy and differential scanning calorimetry. Crystallinity and thermal transitions are correlated with the comonomer composition of the ESP terpolymers. Melt rheology and stress/strain behavior of selected ESP terpolymers are described and compared to ES and EP copolymers. Models developed to interpolate the characteristics of the terpolymers further help to develop structure/property relationships of these novel polymeric materials.

Effect of Filler Size on Cell Nucleation during Foaming Process
Lee Chen, Rich Straff, Xiang Wang, May 2001

This work concerns the effects of filler size on cell nucleation during the foaming process. The cell density of foams with fillers of two different sizes has been investigated using the foaming process simulator developed previously. It was found that the cell density is strongly affected by the filler size. Foams with a fine filler show a higher cell density at a high saturation pressure but give a lower cell density at a low saturation pressure. At a certain value of the saturation pressure, cell density becomes similar with both fillers. This transition pressure changes with the foaming condition. It goes down with a higher pressure drop rate. The experimental results have been explained with an analysis of filler particle size distribution. The analysis also recommended a way to select filler size if a high cell density is desired in the foaming process.

Comparison of a Polyester Blend of PET and PETI-40 with a Random Copolyester of the Same Composition
Robert J. Schiavone, May 2001

Ethylene isophthalate/ethylene terephthalate copolymers (PETI) have been evaluated for higher gas barrier and low temperature preform molding. However, as more ethylene isophthalate is incorporated into the copolyester, the rate of crystallization and the ability of the copolymer to crystallize are significantly reduced. To improve the crystallization behavior of higher ethylene isophthalate copolyesters, a copolyester was prepared by melt blending PET with PETI-40 which contains 40 mole percent ethylene isophthalate in a weight ratio of 3 to 1 to give ten mole percent ethylene isophthalate. The differences in the polyester blend versus random copolymer are compared.

Exploiting Refractometry to Calculate the Density of Polyethylene: The Lorentz-Lorenz Approach Re-Visited
Rajendra K. Krishnaswamy, Jay Janzen, May 2001

The Lorentz-Lorenz equation is a fundamentally sound theoritical equation that relates refractive index and density. In this study, refractive index measurements were used in combination with the Lorentz-Lorenz equation to determine the density of various polyethylene specimens. Excellent agreement was observed between the specimen density calculated from the Lorentz-Lorenz equation and as measured using a density gradient column. Further, calculating polyethylene density from refractometry experiments using a Metricon Prism Coupling device was noted to be more accurate, more reproducible, simpler and consumes far less time compared to the traditional density gradient column technique.

Rheo-Optical Studies of the Effect of Shear Flow on the Structure of Elastomer Blends
Tao Xu, Montgomery T. Shaw, R.A. Weiss, May 2001

The effect of shear flow on the structure of near critical composition blend of 50/50 (w/w) blend of poly(styrene-co-ran-butadiene) (SBR) and polybutadiene (PBD) was studied using two different custom-built rheo-optical instruments that combined polymer melt flow and small angle light scattering (SALS). One instrument (Rheo-SALS) was based on a commercial parallel plate rheometer that was modified with an optical path for laser light scattering. For the second instrument (Extrusion-SALS), a commercial normal-stress extruder was redesigned to allow light to be directed down the rotor shaft and to include an optical window in the header for SALS. Turbidity measurements indicated that SBR/PBD blends exhibited upper critical solution temperature(UCST) phase behavior. At relatively low shear rates, the characteristic length of the phase separation in the flow direction increased exponentially with shear strain while the characteristic length perpendicular to the flow direction remained constant. No evidence of a phase transition induced by flow was observed for any shear rate.

Process Monitoring at the National Institute of Standards and Technology: Celebrating 100 Years of Measurement Excellence
Anthony J. Bur, Kalman Migler, Steven C. Roth, May 2001

Two events that coincide in the year 2001 are the NIST centennial year anniversary and the inauguration of the SPE Special Interest Group on Process Monitoring and Control. To celebrate these two events, this paper will highlight polymer process monitoring activities at NIST describing the full range of measurement and sensor developments for real-time monitoring of resin temperature, rheology, morphology, molecular orientation, and dielectric properties of polymers, filled polymers and polymer blends.

In-Line Dielectric Monitoring during Extrusion of Filled Polymers
Michael McBrearty, Anthony Bur, Steven Roth, May 2001

Dielectric measurements were made on clay filled polyethylene-ethyl vinyl acetate (EVA) copolymer nanocomposites during processing by extrusion. The results show that, at processing temperatures, composites containing chemically treated clays display significant dielectric dispersions. The addition of natural clay to the EVA copolymer increased the dielectric constant (relative permittivity) above that of the EVA copolymer but did not increase the conductivity or cause any dispersion. The chemically treated clays, which are known to exfoliate when compounded with EVA copolymer, gave substantially higher relative permitivity and conductivity having distinct variations with frequency consistent with dielectric relaxations at frequencies below 3000 Hz. One clay treatment gave a larger dielectric dispersion than the other.

The Use of Ethylene/Styrene Interpolymers in Crosslinked Foams for the Footwear Industry
Robert Dubois, Seema Karande, David P. Wright, Felipe Martinez, May 2001

Ethylene/Styrene Interpolymers (ESI) currently under development by The Dow Chemical Company can be effectively crosslinked using current commercial equipment to produce extruded sheets, bun foams, and injection molded foams (IMF) for footwear parts providing properties that enhance and/or outperform current foams of crosslinked ethylene vinyl acetate copolymers (EVA). Crosslinked EVA foams with density ranging from 0.12 to 0.35 g/cc are becoming increasingly popular in many athletic, ladies high heel, and casual shoes, for the fabrication of insoles, midsoles, and unisoles where light weight, comfort, aesthetics, low cost, and performance are the key. ESIs can be blended with EVA or used pure to give light weight, softer foams with better compression set while maintaining or improving on resiliency, heat shrinkage, and split tear.

Plasma Polymerized Films for Optoelectronic Applications
Jennifer Conley, Rachel Gahn, May 2001

Photovoltaic devices and light emitting diodes are now being developed from thin films of conjugated polymers and other organic systems. The potential to create lightweight, flexible, and inexpensive structures are the main advantages of using conjugated polymers over the conventional inorganic systems. However, the challenge is to create organic devices that are more efficient than inorganic devices already in existence. Currently, we are conducting research at the University of Cincinnati using plasma polymerization to produce optical quality thin films of Benzene, Furan, and other polymers for photovoltaic devices and light emitting diodes (LEDs).

Environmental Lining Systems - Raising the Standards
Ian D. Froment, May 2001

Annually, the United Kingdom deposits around 20 million tonnes(1) and the United States around 2 billion tonnes(2) of waste into landfill. To protect the environment from the harmful effects of leachate from the waste, landfill sites are protected using a system of thermoplastic liners, typically made from polyethylene. Due to manufacturing limitations on the size of the lining sheets, welding is employed to join adjacent sheets at the landfill site. This paper reviews current welding practices, the industry approach to quality, and discusses the moves towards certification of welding personnel in order to raise standards across the industry.

Improved Part Quality Using Cavity Pressure Switchover
Birju Sheth, Carol M.F. Barry, Nick R. Schott, Richard D. Higdon, Brady Davison, May 2001

This study examined the improvements in injection molded part quality using cavity pressure to initiate switchover from injection pressure to holding pressure. Cavity pressure produced more controllable and uniform part dimensions than the time and position switchover typically employed in older, point controlled injection molding machines. The controller was relatively easily incorporated into an older machine. When the cavity pressure set point was determined from the position switchover conditions, the pressure may not have been optimized, but provided better parts than the other transfer techniques. Direct determination of the cavity pressure set point is still being evaluated.

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