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.
Binary blends of polyester ionomers with polar polymers have been prepared by both solution and melt-mixed methods to determine the effect of melt-processing on blend compatibility. The effect of metal-sulfonate groups and counterion type was evaluated by blending sulfonated and non-sulfonated forms of an amorphous polyester ionomer with both nylon 6,6 and poly(ethylene terephthalate). The thermal properties and phase behavior of the blends were determined by DSC and ESEM analysis, respectively. A comparison of the degree of compatibility for melt and solution blends suggests that polyester ionomers can interact with polyamides by strong specific interactions between the metal counterions and the amide functionalities. In contrast, polyester ionomers may become compatible with other polyesters by melt-phase transesterification (i.e., in situ copolymer formation). In blends of PBT with Nylon 6,6, sulfonated PET ionomers may be used as minor component additives for blend compatibilization. These compatibilized blends show synergistic improvements in mechanical properties with a significant decrease in minor phase domain size.
In this paper, the effects of operating conditions in a polystyrene microcellular foaming process, such as CO2 content, die pressure and die temperature, are explored. Experiments were performed on a two-stage single screw extruder. Below the solubility limit, the higher the CO2 concentration, the smaller the cell size and the greater the cell density. With an increase of die pressure, the cell size decreases and the cell density increases. The experimental results indicate die temperature plays a strong role in determining the cell size, cell density and cell structure.
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.
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)
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.
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.
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 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.
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.
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.
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."
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.
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.
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.
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.
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.
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.
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.
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).
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.
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Brown, H. L. and Jones, D. H. 2016, May.
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ANTEC 2016 - Indianapolis, Indiana, USA May 23-25, 2016. [On-line].
Society of Plastics Engineers
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