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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A 'Bleed' on Line Rheometer for Polymer Melts
A process-driven on line rheometer has been designed and used to obtain at-process assessment of variation in polymer melt shear viscosity, in conjunction with statistical and dynamics studies of the extrusion process. No gear pumps are involved in this device: melt flow through a chosen die/dies is driven by the melt pressure in ,the extruder. The bleed rheometer mounts via a standard Dynisco pressure transducer fitting. Results for an LDPE and an LLDPE are presented, for differing die geometries and extrusion screw speeds. These compare well with on-line rheometry studies in our laboratory. The effects of extruder conditions on the results obtained from the bleed rheometer are discussed. It is clear that such a simple device could be used for process quality assessment.
Statistical Process Control Applied to the Extrusion Process
Statistical Process Control (SPC) is a powerful tool that can be extremely useful in assessing the performance of the extrusion process, provided it is applied properly. Histograms, normal probability plots and control charts have been used in this work to assess the operation of the extrusion process, as part of a fuller statistical and dynamic study of the extrusion process. It was observed that the extrusion process changed its behaviour with time in a way that affected statistical measures (mean and standard deviation) of key extrusion variables (melt pressure, screw speed, motor current, extrudate diameter). Such observed behaviour of the extrusion variables is categorised as statistically unstable" in classical SPC and control charts cannot be applied to the extrusion process variables directly. A treatment (a transform) is suggested for use with the extrusion variables which might show a stable behaviour allowing control charts to be used."
Processing and Morphology of Hyperbranched Polyester Polyol/Polystyrene Blends
Recent work has shown that hyperbranched polymers have promise for use as processing aids for polyolefins and as toughening agents for thermosetting resins. This promise stems from the high reactivity and unique rheological properties of hyperbranched polymers, which are attributable for the unusual molecular structure. However, there are difficulties associated with the blending of these small, branched molecules into high molecular weight polymers, and processing can be challenging. In this study, we investigate the blending of hyperbranched polyester polyols (HBP) and high molecular weight polystyrene using batch and continuous processing techniques. The overall size, or generation, of the individual hyperbranched polyols is varied, as is the reactivity of the thermoplastic matrix toward to the polyol. Large reductions in system viscosity resulted from the addition of the hyperbranched polymers to the polystyrene. High energy processing and reactive compatibilization were effective in producing finely dispersed morphology in the blends. The processing characteristics, compatibility, and morphology of the blends are reported as a function of HBP generation, reactivity, type of processing, and shear rate.
Recycling of 100% Cross-Linked Rubber Powder by High-Temperature High-Pressure Sintering
Studies estimate there are two billion scrap tires in U.S. landfills with over 270 million tires added yearly. An overview of a simple technique for recycling thermosets will be discussed. In short, it is possible to recycle rubber powders made from scrap tires with the application of only heat and pressure and achieve good mechanical properties. An investigation of the mechanical properties of typical consolidated rubber powders as a function of the molding variables is be shown. To date every type of cross-linked elastomer investigated could be sintered, including silicone rubbers, natural rubbers, ethylene-propylene-diene rubbers, styrene-butadiene rubbers and fluoroleastomers.
Bridging the Modulus Gap between LLDPE and HDPE
Developing blown film resins for the production of films that exhibit the toughness properties of LLDPE with the stiffness and tensile characteristics of HDPE has historically been difficult to achieve for both resin producers and film converters. Resin producers have attempted to push the density higher for LLDPE film resins and lower for HDPE film resins. Separately, film producers are continuously searching for the same hybrid film through blending low, linear low, medium and high-density polyethylenes. Producing successful film blends for heavy-duty applications with densities over 0.918 g/cc usually results in a high performance LLDPE film resin blended with low levels of a MDPE or HDPE. As the level of MDPE or HDPE increases, loss of critical toughness properties such as machine direction tear (MD tear) and dart impact strength is observed. There now exists a novel method of producing films that possess a full density range between 0.918 g/cc and 0.938 g/cc. This approach is based on the utilization of a new family of lower density, high molecular weight medium density (HMW-MDPE) film resins. Blending a HMW-HDPE with a resin density of 0.938 g/cc with high performance LLDPE film resins, films can be fabricated over a wide range of densities without the loss of tear and impact properties. These blends can be produced at thin or thick gauge on either high stalk or conventional blown film equipment.
Bonding of Vulcanized Rubber to Polyester Fibers with Modified RFL Adhesives
Resorcinol-Formaldehyde-Latex (RFL) adhesive and its modification were used to bond rubber to polyethylene terephthalate (PET) cord. The modification of RFL was done by adding the activating materials such as a chlorophenol condensate (DK) and chlororesorcinol condensate (CRA). The effect of heat treatment time, test temperature, aging, and cure conditions on adhesion were studied. Overcure conditions were used to simulate long service time. It was shown that adhesive strength decreases with increasing test temperature and deteriorates with overcure. Bond strength increases with increasing heat treatment time. In addition, adhesion increases with increasing ratio of DK or CR to RFL.
The Effect of Cavity Pressure Transducer Location on Process Robustness
This paper presents the results of a study on the effect of cavity pressure transducer location on process consistency, when the transducer is used for control of the velocity to pressure transfer during the injection phase of the injection molding process. Specifically, a three-stage molding process, where a velocity phase is used to pack the part out slowly, was studied. This study looks at the weight and dimensional stability, when the process is subjected to material variation and check ring wear, of parts molded with the transducer near the gate versus near the last place to fill. It is found that, in some instances, the consistency of the parts can be improved by placing the controlling pressure transducer at the last place to fill in the mold cavity.
Polyester Ionomers in Binary and Compatibilized Blends with Poly(Ethylene Terephthalate), Poly(Butylene Terephthalate) and Nylon 6,6
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.
Polymer Layered Silicate Nanocomposites Prepared by a Two-Stage Method
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.
Isobaric and Isochoric Fragility of Polymers
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
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
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
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
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
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
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
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
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
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
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.
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