56 results on '"Montgomery, T."'
Search Results
2. Effect of hydroxyapatite concentration on high‐modulus composite for biodegradable bone‐fixation devices
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Kevin Grassie, Bryant Heimbach, James R. Olson, Mei Wei, and Montgomery T. Shaw
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Toughness ,Materials science ,Polyesters ,Biomedical Engineering ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,Biomaterials ,Flexural strength ,Elastic Modulus ,Absorbable Implants ,Ultimate tensile strength ,Fracture fixation ,medicine ,Composite material ,Elastic modulus ,Nanotubes ,Flexural modulus ,Stress shielding ,021001 nanoscience & nanotechnology ,Orthopedic Fixation Devices ,0104 chemical sciences ,Durapatite ,medicine.anatomical_structure ,Cortical bone ,0210 nano-technology - Abstract
There are over 3 million bone fractures in the United States annually; over 30% of which require internal mechanical fixation devices to aid in the healing process. The current standard material used is a metal plate that is implanted onto the bone. However, metal fixation devices have many disadvantages, namely stress shielding and metal ion leaching. This study aims to fix these problems of metal implants by making a completely biodegradable material that will have a high modulus and exhibit great toughness. To accomplish this, long-fiber poly-l-lactic acid (PLLA) was utilized in combination with a matrix composed of polycaprolactone (PCL) and hydroxyapatite (HA) nano-rods. Through single fibril tensile tests, it was found that the PLLA fibers have a Young's modulus of 8.09 GPa. Synthesized HA nanorods have dimensions in the nanometer range with an aspect ratio over 6. By dip coating PLLA fibers in a suspension of PCL and HA and hot pressing the resulting coated fibers, dense fiber-reinforced samples were made having a flexural modulus up to 9.2 GPa and a flexural strength up to 187 MPa. The flexural modulus of cortical bone ranges from 7 to 25 GPa, so the modulus of the composite material falls into the range of bone. The typical flextural strength of bone is 130 MPa, and the samples here greatly exceed that with a strength of 187 MPa. After mechanical testing to failure the samples retained their shape, showing toughness with no catastrophic failure, indicating the possibility for use as a fixation material. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1963-1971, 2017. more...
- Published
- 2016
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Catalog
3. A modified pultrusion process for preparing composites reinforced with continuous fibers and aligned hydroxyapatite nano needles
- Author
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Mei Wei, James R. Olson, Shih-Po Sun, and Montgomery T. Shaw
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business.product_category ,Materials science ,Polymers and Plastics ,Composite number ,General Chemistry ,Bioabsorbable polymer ,chemistry.chemical_compound ,chemistry ,Pultrusion ,Nano ,Polycaprolactone ,Materials Chemistry ,Ceramics and Composites ,Die (manufacturing) ,Fiber ,Composite material ,business ,Suspension (vehicle) - Abstract
Of importance to orthopedic procedures are repair materials that can carry significant loads without excessive deformation. In addition, these materials need to be biocompatible, bioabsorbable, and conducive to the replacement of the repair material with native bone. To meet these requirements, we have designed composites using two biocompatible/bioabsorbable polymers, poly(l-lactic acid) (PLLA) in fiber form and polycaprolactone (PCL) filled in a carefully designed fashion with nano needles of hydroxyapatite (HA). Discussed in this article is a modified pultrusion process that proved useful for producing suitable composites. In this process, the feed to the pultrusion die is a stabilized suspension of the HA needles in a PCL/MEK solution, whereas the fiber “bundle” is a single yarn containing 360 PLLA fibers. The small scale is needed to maximize the content of HA in the final composite and assure uniformity. Process variables studied include the ratio of HA to PCL in the suspension, the solids content of the suspension and various geometrical variables in the die design that influence the shear-rate profile along the fiber path. The goal of the pultrusion step is to fill all interstices between the fibers with a PCL matrix that is reinforced with highly aligned HA needles. POLYM. COMPOS., 36:931–938, 2015. © 2014 Society of Plastics Engineers more...
- Published
- 2014
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4. Fabrication and Characterization of Conductive Nanofiber-Based Composite Membranes
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Chitrabala Subramanian, Robert Weiss, and Montgomery T. Shaw
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chemistry.chemical_classification ,Materials science ,Fabrication ,General Chemical Engineering ,technology, industry, and agriculture ,Physics::Optics ,General Chemistry ,Polymer ,Conductivity ,Industrial and Manufacturing Engineering ,Characterization (materials science) ,Condensed Matter::Soft Condensed Matter ,chemistry.chemical_compound ,chemistry ,Nanofiber ,Polymer chemistry ,Polystyrene ,Composite membrane ,Composite material ,Electrical conductor - Abstract
Cross-linked electrospun fiber mats of highly sulfonated polystyrene were combined with a polymer matrix to fabricate nanofiber-based composite membranes and characterized. In-plane conductivity of... more...
- Published
- 2013
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5. Laboratory Testing, Field Installation, and Monitoring of a Silicone Foam Sealant for Bridge Expansion Joints
- Author
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Brian J. Swanson, Ramesh B. Malla, and Montgomery T. Shaw
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Materials science ,Sealant ,Polymer concrete ,Building and Construction ,Expansion joint ,chemistry.chemical_compound ,Compressive strength ,Silicone foam ,Silicone ,chemistry ,Asphalt ,Ultimate tensile strength ,Composite material ,Civil and Structural Engineering - Abstract
Bridge expansion joint sealants are used to deter water and corrosive materials from leaking through the joint and damaging the bridge structure. However, problems with leakage from failing joint sealants have been observed. In response to this situation, a silicone foam sealant designed for small-movement bridge expansion joints was developed. The foam sealant proved to be easy to use and economical. In previously reported studies, various laboratory tests were conducted to evaluate the foam sealant’s tensile strength, compressive strength, reaction to various temperatures, stress relaxation, creep behavior, and bonding capabilities to various substrate materials, such as steel, asphalt, concrete, and polymer concrete. In the current study, further laboratory tests were conducted on the sealant. These tests included ponding and freeze-thaw resistance. The subject study included the development and use of an application procedure to install the silicone foam sealant into bridge expansion joints. After being applied to expansion joints on four bridges in the Northeast (Connecticut, New Hampshire, Rhode Island, and New York), continuous monitoring of the temperature, precipitation, and physical condition of the sealant was conducted for over 1 year. Based on these tests, it can be concluded that the silicone foam sealant is as easy to install and as durable as conventional solid sealants. more...
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- 2013
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6. Self-reinforced composites of hydroxyapatite-coated PLLA fibers: Fabrication and mechanical characterization
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James R. Olson, Lyndon F. Charles, Montgomery T. Shaw, Erica Kramer, and Mei Wei
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chemistry.chemical_classification ,Minerals ,Materials science ,Polymers ,Flexural modulus ,Polyesters ,Simulated body fluid ,Composite number ,Biomedical Engineering ,Compaction ,Modulus ,Polymer ,Biomaterials ,Polyester ,Durapatite ,Coated Materials, Biocompatible ,Flexural strength ,chemistry ,Biomimetics ,Mechanics of Materials ,Materials Testing ,Lactic Acid ,Composite material ,Mechanical Phenomena - Abstract
Self-reinforced composites (SRCs) are materials where both the matrix and fiber-reinforcing phase are made up of the same polymer. Improved bonding can be achieved with self-reinforced composites compared to traditional dual-polymer, fiber-reinforced composites owing to the identical chemistry of the components in SRCs. Bonding between the fiber and matrix phase is an important factor in applications where mechanical stability is required, such as in the field of bone repair. In this study, we prepared bioabsorbable poly(L-lactic acid)/hydroxyapatite (PLLA/HA) self-reinforced composites via a three-step process that includes surface etching of the fiber, the deposition of the HA coating onto the PLLA fibers through immersion in simulated body fluid (SBF), and hot compaction molding. Although coated with a layer of HA, self-reinforced composites were successfully generated by hot compaction. The effects of compaction time (15 and 30 min), compaction temperature (140, 150, 155, 160, 165, and 170 °C), and HA wt% (0, 5, 10, and 15 wt%) on flexural mechanical properties were studied. Mechanical test results indicated that in unfilled (no HA) PLLA SRCs, compaction time and temperature increased the flexural modulus of the composites tested. Based on the results obtained for unfilled composites, a single compaction time and temperature condition of 15 min and 170 °C were selected to study the effect of HA loading on the composite mechanical properties. HA was successfully loaded onto the fibers at 0, 5, 10, and 15 wt% before hot compaction and was found to significantly increase flexural modulus (P=0.0001). Modulus values ranged from 8.3 GPa±0.5 (0 wt% HA) to 9.7 GPa±0.6 (15 wt% HA). Microscopy results suggest that the HA in these composites forms a nodular-like structure along the fibers, which allows polymer-polymer contact yet prevents longitudinal shear. The procedure used successfully generated composites with flexural moduli near the lower range of bone that may have a possible clinical use for load-bearing bone-fixation devices. more...
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- 2013
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7. Biodegradable composites with aligned hydroxyapatite nanoneedles
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Shih-Po Sun, Montgomery T. Shaw, Mei Wei, and James R. Olson
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Materials science ,Polymers ,Polyesters ,Composite number ,Biomedical Engineering ,Modulus ,Biodegradable composites ,Nanocomposites ,Biomaterials ,Durapatite ,X-Ray Diffraction ,Nanocrystal ,Pultrusion ,Natural bone ,Absorbable Implants ,Bone Substitutes ,Lactic Acid ,Composite material ,Anisotropy - Abstract
We prepared an anisotropic bone graft composite to mimic the hierarchical structure of the natural bone in which aligned hydroxyapatite (HA) nanocrystals deposit along collagen fibers. To approach the modulus and strength of the bone, we incorporated synthesized HA nanoneedles and melt drawn poly(L-lactic acid) fibers in our composite as reinforcing components. Their preferred orientation was induced via a modified pultrusion process. The HA orientation distribution was examined using wide angle X-ray diffraction. Micromechanical Halpin–Tsai model predictions considering the amount, shape, and orientation distribution of HA were compared, favorably, with the experimental observations. © 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2012. more...
- Published
- 2012
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8. Laboratory evaluation of a silicone foam sealant bonded to various header materials used in bridge expansion joints
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Montgomery T. Shaw, Brian J. Swanson, and Ramesh B. Malla
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Materials science ,Sealant ,technology, industry, and agriculture ,Modulus ,Polymer concrete ,Building and Construction ,Expansion joint ,chemistry.chemical_compound ,Silicone foam ,Silicone ,chemistry ,Asphalt ,General Materials Science ,Composite material ,Civil and Structural Engineering ,Tensile testing - Abstract
A silicone foam sealant was developed to provide an easy-to-use and economical joint sealant for small-movement bridge expansion joints. In studies reported previously, various laboratory tests were conducted to evaluate the performance of the sealant using concrete as the bonding substrate. In the present study, laboratory tests on the sealant were conducted using other substrates found in practice, including steel, asphalt, and polymer concrete. Some of the tests conducted included a tension test, repair test, oven-aged bonding test, salt water immersion test, and a cure (modulus over time) test that evaluated the mechanical properties of the sealant as it developed its final state of cure. Through the laboratory tests, it has been observed that the silicone foam has the ability to bond to various substrate materials and can easily accommodate deformation typical of small-movement expansion joints in bridges. more...
- Published
- 2011
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9. Hydroxyapatite Needle-Shaped Particles/Poly(<scp>l</scp>-lactic acid) Electrospun Scaffolds with Perfect Particle-along-Nanofiber Orientation and Significantly Enhanced Mechanical Properties
- Author
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Mei Wei, Fei Peng, James R. Olson, and Montgomery T. Shaw
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Scaffold ,Toughness ,Materials science ,Modulus ,Young's modulus ,engineering.material ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Shear (sheet metal) ,symbols.namesake ,General Energy ,Nanofiber ,symbols ,engineering ,Particle ,Biopolymer ,Physical and Theoretical Chemistry ,Composite material - Abstract
Electrospun hydroxyapatite (HA)/biopolymer fibrous composites have attracted much interest in the field of hard-tissue engineering. Unfortunately, poor mechanical property is a continuing problem and limits their usefulness in many applications. In this study, we attempted to improve the mechanical strength, modulus, and toughness of the HA/poly(l-lactic acid) (PLLA) electrospun scaffold by aligning the needle-shaped HA particles within the PLLA nanofibers. Three types of HA particles with different aspect ratios and sizes were incorporated into PLLA nanofibrous scaffolds with a random or aligned fibrous assembly. It was the first time that the needle-shaped HA particles with high aspect ratios were perfectly oriented along the long axes of the nanofibers. All HA particles significantly enhanced the tensile modulus, strength, and toughness of the corresponding scaffold, but to different extents. The dramatic reinforcement effects for different morphologies were rationalized using the Halpin–Tsai and shear... more...
- Published
- 2011
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10. Temperature Aging, Compression Recovery, Creep, and Weathering of a Foam Silicone Sealant for Bridge Expansion Joints
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Smita Brijmohan, Matu R. Shrestha, Montgomery T. Shaw, and Ramesh B. Malla
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Materials science ,Sealant ,Modulus ,Building and Construction ,Temperature cycling ,Silicone foam ,Creep ,Mechanics of Materials ,Ultimate tensile strength ,Hardening (metallurgy) ,General Materials Science ,Elongation ,Composite material ,Civil and Structural Engineering - Abstract
Silicone foam was investigated as a sealant for small movement expansion joints in bridge decks. This paper presents results from the laboratory assessment of a model foam sealant subjected to thermal aging (exposure to high and low temperatures and temperature cycling), fatigue conditions, and outdoor weathering. Parallel tests were performed on a commercial solid-silicone bridge-joint sealant. Test results showed that the solid sealant recovered faster than the foam sealant after being subjected to prolonged compression at elevated temperature. When subjected to a constant tensile force, both the foam and solid sealants exhibited high initial creep rates (rate of elongation), but appeared to reach an equilibrium level of elongation at longer times. The foam sealant creeps at a slower rate and takes more time to get to the equilibrium elongation, whereas the solid sealant creeps much faster initially and reaches equilibrium faster. Thermal aging was found to have significant effects on the sealant modulus (increases with temperature); however, the effects on ultimate stress and strain were not apparent for both types of sealants. Temperature cycling between 24 and -29°C was observed to diminish the ultimate stress and strain of both the sealants by roughly 25%; however, no significant changes in modulus were found. Results from the tests on a limited number of outdoor-weathered sealant specimens showed that weathering appeared to produce an increase in sealant tensile and shear moduli (i.e., hardening effects because of weathering) and a decrease in ultimate strain. The weathered samples show tension loading-unloading behavior similar to the unaged samples. The tensile stress relaxation rate of the outdoor-weathered sealants could not be distinguished from those laboratory-cured (unweathered) counterparts. more...
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- 2011
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11. Rheological behavior of needle-like hydroxyapatite nano-particle suspensions
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Mei Wei, Montgomery T. Shaw, James R. Olson, and Shih-Po Sun
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Materials science ,Nanocomposite ,Nanoparticle ,engineering.material ,Condensed Matter Physics ,Viscoelasticity ,chemistry.chemical_compound ,chemistry ,Rheology ,Coating ,Pultrusion ,Polycaprolactone ,Polymer chemistry ,engineering ,General Materials Science ,Extrusion ,Composite material - Abstract
We describe here the preparation and rheological behavior of stable suspensions of needle-like hydroxyapatite nanoparticles dispersed in organic media, including methylethylketone (MEK), polycaprolactone (PCL) solutions in MEK, and PCL melt. These suspensions are the main ingredients in preparing certain biodegradable orthopedic materials that have some advantages over traditional implants. Rheological properties were experimentally determined at shear rates approaching those used in the processing methods such as roll coating, extrusion, and pultrusion. Analysis of the flow behavior suggests possible shear alignment at high Pe number (Pe ≈ 6,000). The linear viscoelastic properties and the paste-like behavior suggest the formation of a network as the particle content increases. These results are critical in designing a process for making composite materials containing highly oriented anisotropic particles. more...
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- 2010
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12. Electrospinning and characterization of highly sulfonated polystyrene fibers
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Robert Weiss, Chitrabala Subramanian, and Montgomery T. Shaw
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Materials science ,Morphology (linguistics) ,Polymers and Plastics ,Organic Chemistry ,Electrospinning ,Polyelectrolyte ,Viscosity ,chemistry.chemical_compound ,chemistry ,Nanofiber ,Electrode ,Materials Chemistry ,Polystyrene ,Fiber ,Composite material - Abstract
Nanofibers of highly sulfonated (IEC ∼4.5 meq/g) polystyrene (SPS) were successfully electrospun. To accomplish this, the process of electrospinning this difficult-to-spin material was studied in detail. Fiber quality was optimized by manipulating the process and solution variables to fabricate continuous bead-free fibers. Bead-free fibers (average diameter 260 nm) were electrospun from 25 wt% SPS (500 kDa) in DMF at an electrode separation of 10 cm, an applied voltage of 16.5 kV and a flow rate of 0.3 mL/h. With increasing solution concentration, and thereby the solution viscosity, the morphology changed from beads to bead-on-string fibers to continuous cylindrical fibers. Beaded fibers and continuous bead-free fibers of SPS (500 kDa) could be spun at ∼2 C e and 3.5 C e , respectively, where C e is the entanglement concentration determined from solution-viscosity measurements. The onset of formation of beaded fibers coincided with a sharp transition in the scaling of the storage modulus-concentration relationship. more...
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- 2010
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13. Alkali Etching of a Poly(lactide) Fiber
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Mei Wei, James R. Olson, Montgomery T. Shaw, and Shih-Po Sun
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Time Factors ,Materials science ,Surface Properties ,Polyesters ,Biocompatible Materials ,macromolecular substances ,symbols.namesake ,chemistry.chemical_compound ,Crystallinity ,Etching (microfabrication) ,Materials Testing ,Sodium Hydroxide ,General Materials Science ,Fiber ,Composite material ,Thermal analysis ,Arrhenius equation ,Models, Statistical ,Hydrolysis ,fungi ,Temperature ,technology, industry, and agriculture ,Alkali metal ,Microstructure ,Kinetics ,chemistry ,Chemical engineering ,Sodium hydroxide ,Microscopy, Electron, Scanning ,symbols ,Crystallization - Abstract
Alkali etching of a poly(l-lactic acid) fiber was studied by exposing the fiber surface to sodium hydroxide solutions. The factors examined included the etching time (0-1.5 h), alkali concentration (0.25-3 mol/L), and etching temperature (25-80 degrees C). The extent of etching was determined gravimetrically. Both weight loss and mechanical testing results suggest that alkali etching is strictly a surface hydrolysis reaction, as opposed to a bulk reaction, and thus the weight loss rate decreases with a shrinking fiber radius. A slight increase in the fiber crystallinity observed from thermal analysis was interpreted as a result of surface-limited etching on a sheath-core fiber microstructure. The dependence of the rate on the alkali concentration is nonlinear, suggesting that the fiber weight loss rate is subject to both chemical hydrolysis and transport limitations. The dependence of the rate on the temperature follows the Arrhenius equation. The fiber weight after etching can thus be predicted by an overall expression combining all factors: time, temperature, concentration, and fiber diameter. more...
- Published
- 2009
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14. Influence of pretreatment on the surface characteristics of PLLA fibers and subsequent hydroxyapatite coating
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F. Peng, James R. Olson, Montgomery T. Shaw, and Mei Wei
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Materials science ,Polymers ,Surface Properties ,Polyesters ,Biomedical Engineering ,macromolecular substances ,Surface finish ,engineering.material ,Biomaterials ,Hydrolysis ,chemistry.chemical_compound ,stomatognathic system ,Coating ,Biomimetics ,Etching (microfabrication) ,Apatites ,Materials Testing ,Humans ,Sodium Hydroxide ,Lactic Acid ,Fiber ,Composite material ,Probability ,fungi ,Temperature ,technology, industry, and agriculture ,Water ,Oxygen ,Polyester ,Durapatite ,chemistry ,Sodium hydroxide ,Sodium hypochlorite ,Bone Substitutes ,engineering - Abstract
A fibrous precursor for bone repair composites was made by coating poly(L-lactide) (PLLA) fibers with hydroxyapatite (HA) using a biomimetic method. To enhance the bonding between the HA coating and the PLLA fiber, PLLA fibers were etched with either sodium hydroxide or sodium hypochlorite to generate carboxyl groups on fiber surfaces. The experiments were designed to determine the influence of etching on the fiber surface morphology and chemistry as well as the subsequent HA coating on the etched fiber surfaces. It was found that the etching pretreatment increased the roughness as well as the hydrophilicity of fibers, indicating that hydrolysis of PLLA chains had taken place on fiber surfaces. The etching pretreatment also promoted HA coating formation by introducing thicker coating on the surface of fibers with a longer etching time, a higher etching concentration, or with NaOCl as the etching agent. A mechanism of surface hydrolysis and oxidation of PLLA was proposed. more...
- Published
- 2009
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15. Reversible thermal gelation of soft semi-crystalline polyethylene microparticles with surface interactions in squalane
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Montgomery T. Shaw and Gerald H. Ling
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Materials science ,Polymers and Plastics ,Rheometry ,Concentration effect ,General Chemistry ,Polyethylene ,Suspension (chemistry) ,chemistry.chemical_compound ,Viscosity ,chemistry ,Squalane ,Materials Chemistry ,medicine ,Composite material ,Microparticle ,Swelling ,medicine.symptom - Abstract
The effect of temperature on the steady-shear viscosity of a soft semi-crystalline crosslinked-polyethylene microparticle suspension in squalane was studied using rotational rheometry. The results show a sharp increase in the viscosity of the system occurring at about 86°C. The magnitude of this spike is dependent on the concentration of the suspension and is reproducible over multiple heating and cooling cycles. This phenomenon has been attributed to the melting of the crystalline regions within the particles, causing them to swell by soaking up squalane. The Mooney equation was used to model the viscosity data based on swelling data obtained from separate experiments. The results showed that the model is inadequate for describing the observed phenomenon, suggesting the possibility of additional interactions existing among the particles. POLYM. ENG. SCI., 2008. © 2007 Society of Plastics Engineers more...
- Published
- 2008
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16. Development and Laboratory Analysis of Silicone Foam Sealant for Bridge Expansion Joints
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Ramesh B. Malla, Matu R. Shrestha, Montgomery T. Shaw, and Smita Brijmohan
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Materials science ,Sealant ,Stiffness ,Building and Construction ,Expansion joint ,Elastomer ,Extensibility ,Silicone foam ,Stress relaxation ,medicine ,Composite material ,medicine.symptom ,Curing (chemistry) ,Civil and Structural Engineering - Abstract
Sealing of bridge expansion joint systems is important to protect the structural components below the joint. An elastomeric foam-type joint sealant has been developed for sealing small-movement bridge expansion joints. Laboratory tests including tension, compression, shear, bonding, stress relaxation, cure rate, tack-free time, and water tightness were performed on this sealant. In addition, loading-unloading behavior in tension and compression and effects of immersion in saturated saltwater solution on its engineering properties were investigated. The silicone foam sealant showed an increase in volume of ~70% on curing and attained approximately 80% of the 21-day curing strength in the first 7 days. Tack-free time for the foam sealant was below 1.5 h and comparable to that for the solid sealant. The mechanical test results indicated lower stiffness, greater extensibility, and better bonding associated with the foam sealant compared to the solid (unfoamed) sealant. The foam sealant exhibited smaller loss in extensibility at failure due to saltwater immersion compared to the solid sealant. While in tension both sealants exhibited similar rates of stress decay, in compression the foam sealant was found to relax faster than the solid. Neither sealants exhibited any water leakage during a 96-h test period. more...
- Published
- 2007
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17. Investigation of basalt fiber composite aging behavior for applications in transportation
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Qiang Liu, Richard S. Parnas, Anne-Marie McDonnell, and Montgomery T. Shaw
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Basalt ,Materials science ,Polymers and Plastics ,Moisture ,Composite number ,Modulus ,General Chemistry ,Durability ,Basalt fiber ,Ultimate tensile strength ,Materials Chemistry ,Ceramics and Composites ,Composite material ,Elastic modulus - Abstract
New materials such as basalt fiber offer the promise of innovative applications in transportation because of documented strengths (V. Ramakrishnan, N.S. Tolmare, and V. Brik, “NCHRP-IDEA Program Project Final Report, ” Transportation Research Board, Washington, DC, (1998)). Previously, we found that mechanical properties of basalt twill fabric-reinforced polymer composites were comparable to composites reinforced with glass fabrics of similar structures [Q. Liu, M.T. Shaw, R.S. Parnas, and A.M. McDonnell, Polymer Composites, 27(1), 41 (2006)]. Use in transportation also requires knowledge of environmental durability. This study reports the tolerance of basalt-fiber-reinforced polymer composites to salt water immersion, moisture absorption, temperature, and moisture cycling. Parallel tests were conducted for the corresponding glass-reinforced polymer composites. Aging for 240 days in salt water or water decreased the Young's modulus and tensile strength of basalt composites slightly but significantly (p < 0.05). Freeze-thaw cycling up to 199 cycles did not change the shear strength significantly, but aging in hot (40°C) salt water or water did decrease the shear strength of basalt composites (p < 0.05). The aging results indicate that the interfacial region in basalt composites may be more vulnerable to damage than that in glass composites. POLYM. COMPOS., 27:475–483, 2006. © 2006 Society of Plastics Engineers more...
- Published
- 2006
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18. Effect of Operation Conditions on HA Synthesized by the Hydrothermal Method
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Mei Wei, Chandrasekhar R. Kothapalli, and Montgomery T. Shaw
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Materials science ,Morphology (linguistics) ,Mechanical Engineering ,Calcium nitrate ,Hydrothermal circulation ,Autoclave ,law.invention ,chemistry.chemical_compound ,Flexural strength ,chemistry ,Chemical engineering ,Mechanics of Materials ,law ,Particle-size distribution ,Particle ,General Materials Science ,Calcination ,Composite material - Abstract
This paper reports the influence of aging time and reaction temperature on the surface morphology and mechanical properties of hydroxyapatite (HA) synthesized by a hydrothermal method. Calcium nitrate and ammonium orthophosphate solutions were premixed and fed to an autoclave and reacted to temperatures varying between 25-250°C for 2-10 h. Results indicate the strong positive influence of reaction temperature on the HA particle aspect ratio. The density of the discs pressed from these samples reached 85-90% of the theoretical density after calcination at 1200°C for 1 h. Sintered density and flexural strength were found to increase with increasing aging time and reaction temperature. A maximum flexural strength of 78 MPa was observed for the sample synthesized at 170°C for 5 h with the predicted average at these conditions being 65 MPa. more...
- Published
- 2005
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19. Investigation of basalt fiber composite mechanical properties for applications in transportation
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Richard S. Parnas, Anne-Marie McDonnell, Montgomery T. Shaw, and Qiang Liu
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Materials science ,Polymers and Plastics ,Composite number ,Modulus ,General Chemistry ,Epoxy ,Compressive strength ,visual_art ,Basalt fiber ,Void (composites) ,Ultimate tensile strength ,Materials Chemistry ,Ceramics and Composites ,visual_art.visual_art_medium ,Shear strength ,Composite material - Abstract
New materials offer the promise of innovative applications in transportation. One such new material is basalt fiber, which is used in other industries because of documented strengths [Ramakrishnan et al., “Performance Evaluation of 3-D Basalt Fiber Reinforced Concrete and Basalt Rod Reinforced Concrete,” NCHRP-IDEA Program Project Final Report, Transportation Research Board, Washington, DC, 1998]. Use in transportation, however, requires a better knowledge of many properties. This article discusses initial work with basalt-reinforced polymer composites. Polymer composites reinforced by basalt fabric and glass fabrics were produced for these tests. Void content below 3% were measured for all the composites produced for the testing program. No significant differences in Young's modulus, tensile strength, flexure strength, shear strength, and compression strength were found between basalt composites and glass composites. Environmental durability testing of basalt composites is ongoing. POLYM. COMPOS. 27:41–48, 2006. © 2005 Society of Plastics Engineers more...
- Published
- 2005
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20. Actuating properties of soft gels with ordered iron particles: basis for a shear actuator
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Montgomery T. Shaw and Yuxian An
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Materials science ,Rheometry ,Modulus ,Condensed Matter Physics ,Atomic and Molecular Physics, and Optics ,Magnetic field ,Condensed Matter::Soft Condensed Matter ,Shear (sheet metal) ,chemistry.chemical_compound ,Silicone ,chemistry ,Mechanics of Materials ,Electric field ,Signal Processing ,Shear stress ,Particle ,General Materials Science ,Electrical and Electronic Engineering ,Composite material ,Civil and Structural Engineering - Abstract
Soft electrorheological (ER) gels were prepared by arranging iron particles in silicone prepolymers within magnetic fields and crosslinking the obtained structure. The gap between the particles, and consequently the conductivity, was controlled by swelling the crosslinked material with additional silicone prepolymer. Iron-particle chains were made with as little as 0.5% particles and at angles from 0° to 60° to the normal of the sample surface. The ER, transducing and actuating properties of these materials were explored using rheometry and dielectrometry. In general, the dynamic shear moduli of the aligned ER gels increased quadratically with the electric field intensity. With only 1 vol% particles, the modulus doubled to an electrical field of around 2 kV mm−1. Transducer and actuator properties were noted. With particle chain alignment of 30°, shear stresses of around 150 Pa were measured with a special sandwich-type shear fixture. The influence of tilt angle on the shear stress was found to be qualitatively consistent with the calculation based on the point-dipole approximation. more...
- Published
- 2003
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21. Electrorheology of filled silicone elastomers
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Bo Liu and Montgomery T. Shaw
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Permittivity ,Materials science ,Mechanical Engineering ,Condensed Matter Physics ,Silicone rubber ,Elastomer ,Silicone Elastomers ,chemistry.chemical_compound ,Surface conductivity ,Silicone ,chemistry ,Mechanics of Materials ,General Materials Science ,Composite material ,Polarization (electrochemistry) ,Prepolymer - Abstract
Electrorheological (ER) silicone elastomers containing particles based on silica (SiO2) and titania minerals (BaTiO3, Ba2Ti9O20, and BaTiO3/CaZrO3) were prepared and characterized. An electrical field was applied to align the particles during the cure of the silicone prepolymer. For the silicone/silica compositions, a prominent Maxwell–Wagner dispersion in the dielectric response suggested that surface conductivity of the silica particles dominated the polarization. Alignment of the particles increased the overall dielectric permittivity as well as the magnitude of the Maxwell–Wagner dispersion. Their ER response exhibited a negative deviation from a quadratic dependence on field intensity at high fields, and was accompanied by nonlinear conductivity. A highly nonlinear enhancement of the ER effect with increasing particle concentration was observed. For the silicone/titania elastomers as a class, the ER response increased with the particle’s permittivity. In the case of the silicone/BaTiO3 elastomer, the... more...
- Published
- 2001
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22. Electrorheological Effects of ER Gels Containing Iron Particles
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Montgomery T. Shaw and Bo Liu
- Subjects
010302 applied physics ,Materials science ,Mechanical Engineering ,Composite number ,02 engineering and technology ,Conductivity ,021001 nanoscience & nanotechnology ,01 natural sciences ,Magnetic field ,Shear (sheet metal) ,chemistry.chemical_compound ,Silicone ,Volume (thermodynamics) ,chemistry ,Electric field ,0103 physical sciences ,General Materials Science ,Composite material ,0210 nano-technology ,Order of magnitude - Abstract
Electrorheological (ER) gels were prepared by aligning 5-mm iron particles in liquid-like silicone RTV prepolymers in magnetic fields while the silicone cured. The pre-cured composite was then swollen with oil to reduce the conductivity. The iron content was held at 3% by volume, while the oil content ranged up to 20% by weight. In general, the dynamic shear moduli of the aligned ER gels increased quadratically with the electric field intensity, following the empirical equation G = G0 [1 + (E/E0)α], with α≈ 2. Observed values of G/G0 ranged up to 2.5. When the iron-particle chains were tilted with respect to the electrical field direction, the electrorheological effect decreased. While the rate of decrease was in approximate accord with the prediction of the point-dipole assumption, the magnitudes of the ER effect were under predicted by two orders of magnitude. more...
- Published
- 2001
- Full Text
- View/download PDF
23. Efforts to find stick-slip flow in the land of a die under sharkskin melt fracture conditions: polybutadiene
- Author
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Liangshi Wang, Yong Woo Inn, and Montgomery T. Shaw
- Subjects
business.product_category ,Materials science ,Polybutadiene ,Polymers and Plastics ,Organic Chemistry ,Slip flow ,Materials Chemistry ,Fracture (geology) ,Die (manufacturing) ,Sharkskin ,Composite material ,Condensed Matter Physics ,business - Published
- 2000
- Full Text
- View/download PDF
24. Structure evolution and phase behavior of polymer blends under the influence of shear
- Author
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Z. Hong, Robert Weiss, and Montgomery T. Shaw
- Subjects
Spinodal ,Materials science ,Polymers and Plastics ,Scattering ,Organic Chemistry ,Materials Chemistry ,Shear stress ,Viscometer ,Polymer blend ,Composite material ,Shear flow ,Lower critical solution temperature ,Light scattering - Abstract
The effect of shear flow on the phase behavior, structure formation and morphology of a near-critical composition blend of poly(styrene- co -acrylonitrile)/poly(methyl methacrylate) (SAN/PMMA) and an off-critical composition blend of SAN/poly(e-caprolactone) (SAN/PCL) were investigated. Both blends exhibited lower critical solution temperature (LCST) behavior. Rheo-SALS (small angle light scattering) was used to characterize the time-dependent structure evolution during flows with shear rates from 0.01 to 0.05 s −1 and stresses from 8 to 60 kPa. Two types of transient “dark-streak” scattering patterns were observed. One featured a dark streak that diverged with increasing scattering vector, q , which corresponded to a chevron-like structure in the morphology of the blend. The other type of dark streak converged with increasing q , and may be due to a spinodal structure that was stretched in the flow direction. A capillary viscometer was used to achieve shear stresses as high as 400 kPa for the SAN/PCL blends, and microscopy analysis of microtomed extrudates revealed a dispersed phase morphology of cylindrical PCL-rich domains highly oriented in the flow direction. No shear-induced phase transitions were observed for either blend for the range of shear stress studied. more...
- Published
- 2000
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25. Separation, size reduction, and processing of XLPE from electrical transmission and distribution cable
- Author
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J. Wagenblast, Montgomery T. Shaw, and C. C. White
- Subjects
Power transmission ,Materials science ,Electric power transmission ,Polymers and Plastics ,Size reduction ,Ultimate tensile strength ,Materials Chemistry ,Compression molding ,Extrusion ,General Chemistry ,Molding (process) ,Composite material ,Injection pressure - Abstract
The recycling of power transmission cable insulated with crosslinked PE (XLPE) was investigated by using different methods of separation and reprocessing. Separation was attempted by thermo-chemical, thermo-mechanical and microwave-mechanical means, the latter being the most successful. A mechanism encompassing all of these was formulated. Compression molding, extrusion, and injection molding with and without preheating of the material were also investigated. It was found that by preheating the XLPE and injection molding under high injection pressure, the neat XLPE could be formed into shapes with tensile strengths equal to that of the original insulation. In view of available observations, possible mechanisms for the flow and reconsolidation of XLPE crumb are proposed and discussed. more...
- Published
- 2000
- Full Text
- View/download PDF
26. Mechanical properties of blends of HDPE and recycled urea-formaldehyde resin
- Author
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Chris C. White, Montgomery T. Shaw, and Evelin D. Bliznakov
- Subjects
Filler (packaging) ,Materials science ,Polymers and Plastics ,Urea-formaldehyde ,Thermosetting polymer ,General Chemistry ,Polyethylene ,Surfaces, Coatings and Films ,chemistry.chemical_compound ,chemistry ,Ultimate tensile strength ,Materials Chemistry ,Polymer blend ,High-density polyethylene ,Composite material ,Ionomer - Abstract
The mechanical properties of blends of high-density polyethylene (HDPE) with a recycled thermosetting filler, urea-formaldehyde grit (UFG), were evaluated in the range of 0 -23% of filler by volume. Ethylene-acrylic acid (EAA) copolymers and an ionomer based on EAA were evaluated as compatibilizers. The observed tensile mod- ulus of the ionomer-treated blends was raised to three times the modulus of virgin polyethylene, whereas the modulus of the untreated blends reached double that of polyethylene. The ionomer-treated blends also showed a higher tensile strength than the blends without filler treatment. The improvement in the properties was assigned to an increased interaction between the filler and the polymer matrix. © 2000 John Wiley & more...
- Published
- 2000
- Full Text
- View/download PDF
27. Visual observation of development of sharkskin melt fracture in polybutadiene extrusion
- Author
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Robert J. Fischer, Montgomery T. Shaw, and Yong Woo Inn
- Subjects
Extrusion moulding ,business.product_category ,Materials science ,Sharkskin ,engineering.material ,Condensed Matter Physics ,Linear low-density polyethylene ,Polybutadiene ,Coating ,Fracture (geology) ,engineering ,Die (manufacturing) ,General Materials Science ,Extrusion ,Composite material ,business - Abstract
We studied the sharkskin melt fracture phenomena of polybutadiene (PBD), which exhibits similar flow properties and instabilities to linear low density polyethylene (LLDPE). The advantages of using PBD are that it exhibits larger distortions and slower development due to its high viscosity. By using a video camera with close-up lenses focused at the die exit, we observed the development of sharkskin in profile. It was shown that the sharkskin melt fracture develops with the cohesive failure at the die exit due to a peeling of surface layers as described by Howell and Benbow (1962). Oddly enough, this mechanism is similar to that proposed by Ovaici et al. (1998) for the extrusion of chocolate. A soap solution coating around the die exit to induce a slippery interface eliminated the sharkskin fracture, similar in the effect of fluoro-elastomer coating with LLDPE. Based on our visual observations, we qualitatively modeled the sharkskin fracture by modifying Cogswell‘s (1977) idea on exit stretching at the die exit and the force balance of Ovaici et al. on the ring formation of the chocolate extrusion. more...
- Published
- 1998
- Full Text
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28. Effect of Shear Flow on the Morphology and Phase Behavior of a Near-Critical SAN/PMMA Blend
- Author
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Zhengyu Hong, Montgomery T. Shaw, and Robert Weiss
- Subjects
Materials science ,Polymers and Plastics ,Organic Chemistry ,Mineralogy ,Lower critical solution temperature ,Miscibility ,Light scattering ,Inorganic Chemistry ,Drag ,Phase (matter) ,Microscopy ,Materials Chemistry ,Polymer blend ,Composite material ,Shear flow - Abstract
An ongoing debate concerns whether experimental observations of flow-induced miscibility of polymer blends actually result from a "true" shift of the critical temperature. To elucidate the origin of the phenomenon more clearly, we have investigated the structural changes of phase domains of a number of polymer blends under the influence of flow. The most recent study used a near-critical blend of poly(styrene-co-acrylonitrile)/poly(methyl methacrylate), which exhibits LCST type phase behavior. Rheo-SALS (small angle light scattering) was used to probe the time-dependent structure evolution during shear flow. Quenched samples were examined with TEM and phase contrast light microscopy, and the Fourier transforms of digitized micrographs were compared with two-dimensional light scattering measurements of the same samples. The blends were also subjected to pressure-driven flows and drag flows at very high stresses, and their morphology was similarly studied. The structure evolution due to flow could be explained by hydrodynamic effects consistent with droplet breakup theory. more...
- Published
- 1998
- Full Text
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29. Sedimentation-resistant electrorheological fluids based on PVAL-coated microballoons
- Author
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Mancun Qi and Montgomery T. Shaw
- Subjects
Coacervate ,Polymers and Plastics ,Chemistry ,Sedimentation (water treatment) ,General Chemistry ,Surfaces, Coatings and Films ,Electrorheological fluid ,Simple shear ,Glass microsphere ,Shear rate ,Breakage ,Materials Chemistry ,Shear stress ,Composite material - Abstract
Sedimentation is often a problem in electrorheological (ER) fluids featuring solid particles suspended in a low-density hydrocarbon oil. This problem was addressed by synthesizing particles comprising silica microballoons coated with PVAL using a salt-induced coacervation process. The ER performance of the fluids based on these particles was equivalent to prototypical commercial fluids, both with respect to current leakage and shear stress under steady simple shear flow. For comparing diverse fluids as to these practical characteristics, a dimensionless ER effectiveness number, Er, was proposed: Er = σγ/EJ where σ is the shear stress, γ is the shear rate, E is the electric field, and is the current. The resulting uniform coatings were also found to impart a degree of resistance to breakage. more...
- Published
- 1997
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30. Phase Structure Changes in a Sheared Blend of High Molecular Weight Polybutadiene and Polyisoprene Elastomers
- Author
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Nikolais G. Remediakis, Robert Weiss, and Montgomery T. Shaw
- Subjects
Shearing (physics) ,Spinodal ,Materials science ,Polymers and Plastics ,Microstructure ,Elastomer ,Polybutadiene ,Natural rubber ,Phase (matter) ,visual_art ,Polymer chemistry ,Materials Chemistry ,visual_art.visual_art_medium ,Composite material ,Phase diagram - Abstract
The flow-induced phase behavior of polyisoprene—polybutadiene elastomer blends is of concern to the rubber industry because of the wide practical applications of these blends. We have been investigating examples of these blends using a Rheo-SALS instrument in conjunction with light microscopy. The subject of this work was a high molecular weight, near-critical blend (35/65 ratio) comprising polybutadiene (Mn=413, 000) and polyisoprene (Mn=177, 000) (Blend II). The results were contrasted with those for a previously studied blend (Blend I) comprising polybutadiene (Mn=164, 000) and polyisoprene (Mn=125, 000), also near the critical composition at a 40/60 ratio. Both featured the same microstructure. Each was examined under quiescence and flow conditions. For Blend I at a 24 °C quench depth, the scattering pattern was the expected spinodal ring; which, upon shearing, changed to an H-shaped pattern and then to a bright streak in the vorticity direction. Direct observation showed that these patterns corresponded to a fibrillar structure aligned in the flow direction. Similar light scattering patterns were obtained after a temperature jump (24 °C) under steady-state shearing. With Blend II at a 40 °C quench depth, the scattering pattern was again a spinodal ring, but this changed on shearing to an anisotropic pattern having the shape of an “8” or a “butterfly.” The shape of this pattern depended on shear rate, and its origin was hypothesized to be phase domains following helical paths with axes aligned in the vorticity direction. The corresponding micrographs are consistent with this supposition, as is an instability phenomena observed in the parallel-plate rheometer at higher shear rates. These purely hydrodynamic phenomena should be kept in mind when interpreting observations of “flow-induced mixing” at lower quench depths. more...
- Published
- 1997
- Full Text
- View/download PDF
31. Evaluating Applications of Field Spectroscopy Devices to Fingerprint Commonly Used Construction Materials
- Author
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Iliya Yut, James Mahoney, Adam Zofka, Maria Chrysochoou, Michael Donahue, Montgomery T. Shaw, Chad P. Johnston, Shih-Po Sun, and Stuart Farquharson
- Subjects
Materials science ,Analytical chemistry ,X-ray fluorescence ,Infrared spectroscopy ,Epoxy ,law.invention ,Portland cement ,law ,Asphalt ,visual_art ,Attenuated total reflection ,visual_art.visual_art_medium ,Adhesive ,Composite material ,Curing (chemistry) - Abstract
This report documents the results of the evaluation of practical portable spectroscopic equipment for in-situ analysis of a wide range of commonly used construction materials. The initial range of spectroscopic techniques evaluated by the project Team included Fourier-Transform Infrared (FT-IR) Spectroscopy, Size-Exclusion Chromatography (SEC), Nuclear Magnetic Resonance (NMR), X-Ray Fluorescence (XRF), and X-Ray Diffraction (XRD). The aforementioned techniques were applied to the following construction material categories: epoxy coating and adhesives, traffic paints, Portland cement concrete with chemical admixtures and curing membranes, asphalt binders, emulsions, and mixes with polymer additives. A series of laboratory and in-situ tests showed that the compact FT-IR spectrometer in the Attenuated Total Reflectance (ATR) mode, hand-held XRF instrument, and RTA’s Raman analyzer were successful in fingerprinting epoxy coatings and adhesives, curing compounds, and waterborne traffic paints. The ATR method also positively identified chemical admixtures in fresh mix samples and verified polymer presence in asphalt binders and emulsions. An electronic library of signature spectra of the materials tested in this project was created and submitted to SHRP 2 administration. Among other deliverables of this project are proposed AASHTO standards of practice for the analysis of titanium content in traffic paints by XRF, and identification of chemical admixtures by ATR. more...
- Published
- 2013
- Full Text
- View/download PDF
32. Rheo-Optical behavior of binary polymer blends: The effect of simple shear flow on phase behavior
- Author
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Z. J. Chen, Robert Weiss, R. J. Wu, M.L. Fernandez, Julia S. Higgins, and Montgomery T. Shaw
- Subjects
Shearing (physics) ,Simple shear ,Shear rate ,Materials science ,Polymers and Plastics ,Upper critical solution temperature ,Rheometer ,Materials Chemistry ,General Chemistry ,Polymer blend ,Composite material ,Shear flow ,Lower critical solution temperature - Abstract
The phase behavior of polymer blends under simple shear flow has been studied using a custom-designed rheo-optical system consisting of a two-dimensional small-angle light scattering (SALS) device incorporated into a conventional rheometer. Two-dimensional SALS images were gathered for model polymer blend systems with different quiescent phase behavior: polystyrene/polyisobutylene (PS/PIB) that exhibits upper critical solution temperature phase behavior and polystyrene/poly(vinyl methyl ether) (PS/PAGE) that shows lower critical solution temperature phase behavior. For the PS/PIB blend, shear-induced phase mixing occurred at a critical shear rate. Below that critical shear rate, the dispersed phase was highly elongated parallel to the flow direction. For PS/PAGE blends, a streak scattering pattern was observed even though the sample became optically clear after shearing. We observed, apparently for the first time, the development of a bright-stress pattern from a transient dark-stress pattern for a polymer blend system under shear. Rheo-microscopy studies revealed an intriguing wave pattern that developed coincident with the observation of a stress pattern by SALS. The relationship between the two phenomena has not yet been established more...
- Published
- 1995
- Full Text
- View/download PDF
33. Influence of surface treatment and biomimetic hydroxyapatite coating on the mechanical properties of hydroxyapatite/poly(L-lactic acid) fibers
- Author
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Mei Wei, James R. Olson, Montgomery T. Shaw, and Fei Peng
- Subjects
Poly l lactic acid ,Materials science ,Tissue Engineering ,Polymers ,Surface Properties ,Polyesters ,Biomedical Engineering ,Biomimetic coating ,engineering.material ,Biomechanical Phenomena ,Biomaterials ,Durapatite ,Coating ,Coated Materials, Biocompatible ,Biomimetic Materials ,Tensile Strength ,Bone Substitutes ,Materials Testing ,engineering ,Hydroxyapatite coating ,Microscopy, Electron, Scanning ,Lactic Acid ,Composite material - Abstract
Poly(L-lactic acid) (PLLA) micro-fibers have been coated with hydroxyapatite (HA) using a quick biomimetic method to form a precursor for bone repair composites. To increase the coating content within a coating time as short as 1–2.5 h, PLLA fibers have been treated by soaking in NaOH or NaOCl solutions at mild conditions. Although different surface hydrolysis and coating methods have been used to prepare bioceramic/polymer composites, it is for the first time that the influences of the surface treatment and HA coating process on the mechanical properties of the polymer and HA/polymer composite fibers were investigated systemically. more...
- Published
- 2012
34. Normal Stresses-Ordinary Behavior for Polymeric Fluids
- Author
-
Montgomery T. Shaw
- Subjects
chemistry.chemical_classification ,Simple shear ,Materials science ,chemistry ,Polymer ,Composite material - Published
- 2012
- Full Text
- View/download PDF
35. Laboratory Evaluation of a Silicone Foam Sealant for Field Application on Bridge Expansion Joints
- Author
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Ramesh B. Malla, Brian J. Swanson, and Montgomery T. Shaw
- Subjects
Substrate (building) ,Silicone foam ,Materials science ,Tension (physics) ,Asphalt ,Sealant ,Expansion joint ,Composite material ,Compression (physics) ,Joint (geology) - Abstract
A silicone foam sealant was developed to provide an alternative small-bridge joint sealant that was effective, easy-to-use, and economical. In the previous study various laboratory tests including tension, bonding, compression, shear, stress relaxation, and other were conducted to determine the engineering characteristics of the sealant. All these tests were limited to the concrete as the substrate to which the sealant was bonded to. In the present study, laboratory tests on the sealant were conducted using other substrates found in practice, including steel, asphalt and polymeric concrete. Some of the tests conducted included tension (pull to failure) test, oven-aged bonding test, salt water immersion test, and a performance-during-curing test that evaluated the strength and strain of the sealant.. Through the laboratory tests, it has been observed that the silicone foam can exhibits good bonding to various substrate materials and can easily accommodate small movement bridge expansion joints. In addition to these tests in small specimen, a procedure to produce larger quantity of sealant and apply it to an actual bridge expansion joint was developed using a simulated joint built in the laboratory. Through the development of this procedure and the eventual application of the sealant into various bridge expansion joints, it can be determined that the silicone foam presents an alternative sealant that is east-to-use and allows for quick installation. more...
- Published
- 2011
- Full Text
- View/download PDF
36. The linear elastic properties of microcellular foams
- Author
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Montgomery T. Shaw, J.H. Aubert, and Catheryn L. Jackson
- Subjects
Materials science ,Polymers and Plastics ,Organic Chemistry ,Linear elasticity ,Polyacrylonitrile ,Modulus ,Young's modulus ,Dynamic Tension ,symbols.namesake ,chemistry.chemical_compound ,chemistry ,Materials Chemistry ,symbols ,Polystyrene ,Composite material ,Elasticity (economics) - Abstract
The mechanical behaviour of a new type of open-cell foam made by a thermally induced phase separation (TIPS) process was investigated. Foams made by the TIPS process are characterized by cell sizes which are 10–100 times smaller than conventional foam materials. In this work, the linear elastic modulus of these foams in dynamic tension/compression was measured. A comparison was made with the theoretical predictions and experimental data for conventional large-cell foams. Foams studied include polystyrene, poly(4-methyl-1-pentene), polyacrylonitrile and poly(γ-benzyl- l -glutamate) in the density range 0.04–0.13 g cm −3 . more...
- Published
- 1991
- Full Text
- View/download PDF
37. Thermo-Gelation of Surface-Modified Polyethylene Microgels from Fragmentation and Immiscible Blends
- Author
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Gerald H. Ling, Montgomery T. Shaw, Albert Co, Gary L. Leal, Ralph H. Colby, and A. Jeffrey Giacomin
- Subjects
chemistry.chemical_compound ,Materials science ,Rheology ,chemistry ,Viscoplasticity ,Squalane ,Thermal ,technology, industry, and agriculture ,Polymer blend ,Polystyrene ,Polyethylene ,Composite material ,Grinding - Abstract
Polyethylene microgels were created by swollen‐state grinding and ultrasonic fragmentation of bulk crosslinked polyethylene (XLPE) suspended in squalane, and by the extraction of crosslinked‐polyethylene micro‐domains from an immiscible blend of polyethylene (PE) and polystyrene (PS). Crosslinking of the polyethylene micro‐domains in the blend was achieved by exposure to an electron beam. Suspensions of both microgels in squalane exhibit thermal gelation upon cooling where both G′ and G″ increase by up to five‐orders in magnitude when probed using small‐angle oscillatory shear. We propose that this phenomenon is attributed to weak short‐range interactions among the particles whereby surface terminal chains on the microgels can co‐crystallize forming inter‐particle bonds. However, these interactions are mild enough that the systems may be reverted to its original state by applying higher shear stresses at elevated temperatures. more...
- Published
- 2008
- Full Text
- View/download PDF
38. Study of a thermotropic liquid-crystalline polyester at elevated pressures
- Author
-
Montgomery T. Shaw, Edward T. Samulski, and Benjamin S. Hsiao
- Subjects
Hydroxybenzoic acid ,Materials science ,Polymers and Plastics ,Mesophase ,Condensed Matter Physics ,Copolyester ,Thermotropic crystal ,Crystallinity ,Differential scanning calorimetry ,Differential thermal analysis ,Materials Chemistry ,Physical and Theoretical Chemistry ,Composite material ,Bar (unit) - Abstract
A thermotropic liquid-crystalline copolyester of 20% hydroxybenzoic acid, 40% isophthalic acid, and 40% hydroquinone polymer was studied at elevated pressures. The characterization techniques at elevated pressures (0–1000 bar) included high-pressure differential thermal analysis and dilatometry; at atmospheric pressure, differential scanning calorimetry, thermal optical analysis, and x-ray analysis were employed. The mechanical properties of the solid specimens prepared at different pressures were studied by compression and dynamic rotation mechanical testing techniques. High-pressure induced a new crystal habit in the solid state and a new mesophase in the melt. These transitions are summarized in a proposed phase diagram. Mechanical tests on the material produced at elevated pressure indicate the possibility of improved properties, implying that the pressure-dependent morphological changes in thermotropic copolyesters could be of practical significance. The finding of a pressure-induced mesophase also confirmed the possibility of extending the range of polymers which might exhibit liquid crystallinity via the application of pressure. more...
- Published
- 1990
- Full Text
- View/download PDF
39. Fabrication of novel calcium phosphate/poly(lactic acid) fiber composites
- Author
-
Montgomery T. Shaw, James R. Olson, Mei Wei, and Chandrasekhar R. Kothapalli
- Subjects
Calcium Phosphates ,Materials science ,Scanning electron microscope ,Polymers ,Polyesters ,Biomedical Engineering ,Nucleation ,Biomaterials ,chemistry.chemical_compound ,Flexural strength ,Polylactic acid ,Coated Materials, Biocompatible ,Fiber ,Lactic Acid ,Composite material ,Precipitation (chemistry) ,Compomers ,technology, industry, and agriculture ,Saponins ,Polyester ,chemistry ,Models, Chemical ,Microscopy, Electron, Scanning ,Stress, Mechanical ,Caprolactone ,Algorithms - Abstract
Composites using high-modulus polylactic acid (PLA) fibers coated with calcium phosphate (CaP) were prepared using a cyclic precipitation technique. Scanning electron microscopy revealed that small nuclei of CaP formed after the first soaking cycle, while large quantities of CaP particles were observed after the sixth cycle. The amount of CaP deposited on the PLA yarn increased with deposition time in Ca(2+) and PO(4) (3-) solutions and number of cycles, and decreased with stirring rate during washing cycles. It was observed that around 35 wt % of CaP was deposited on the yarn surface after six cycles of cyclic-soaking. Based on the results, a heterogeneous nucleation and growth mechanism was proposed for the CaP deposition on the surface of hydrolyzed polyester. Composites comprising the coated fibers in a poly(caprolactone) matrix exhibited flexural moduli within the range of that of the cortical bone. more...
- Published
- 2007
40. Dielectric and NMR Methods
- Author
-
Montgomery T. Shaw and William J. MacKnight
- Subjects
Chemistry ,Analytical chemistry ,Interfacial polarization ,Dielectric ,Composite material ,Viscoelasticity - Published
- 2005
- Full Text
- View/download PDF
41. Biodegradable HA-PLA 3-D porous scaffolds: effect of nano-sized filler content on scaffold properties
- Author
-
Montgomery T. Shaw, Chandrasekhar R. Kothapalli, and Mei Wei
- Subjects
Scaffold ,Materials science ,Polymers ,Polyesters ,Biomedical Engineering ,Molecular Conformation ,Modulus ,Biocompatible Materials ,Biochemistry ,Hydrothermal circulation ,Absorption ,Biomaterials ,chemistry.chemical_compound ,Average size ,Absorbable Implants ,Materials Testing ,Transition Temperature ,Lactic Acid ,Composite material ,Particle Size ,Nano sized ,Molecular Biology ,technology, industry, and agriculture ,Temperature ,Water ,General Medicine ,Porous scaffold ,Lactic acid ,Nanostructures ,Molecular Weight ,Durapatite ,chemistry ,Leaching (metallurgy) ,Porosity ,Biotechnology - Abstract
Scaffolds comprising poly(lactic acid) and nano-hydroxyapatite (HA) were prepared using the solvent-casting/salt-leaching technique. NaCl was used as the leaching agent. Nano-sized HA was synthesized by a hydrothermal method at 170 °C and autogenous pressure. High-resolution TEM imaging revealed that the HA particles were ellipsoidal-shaped with needle-like morphologies. The particles had an average size of approximately 25 nm in width and 150 nm in length with aspect ratios ranging from 6 to 8. As the HA content increased in the scaffold from 0 to 50 wt%, the compression modulus of the scaffolds increased from 4.72 ± 1.2 to 9.87 ± 1.8 MPa, while the yield strength from 0.29 ± 0.03 to 0.44 ± 0.01 MPa. Such polymeric scaffolds should be suitable materials for non-load sharing tissue-engineering applications. more...
- Published
- 2005
42. Development of a phase diagram to control composite manufacturing using Raman spectroscopy
- Author
-
Victor Khitrov, Montgomery T. Shaw, Jessica Carignan, Antonio E. Senador, and Stuart Farquharson
- Subjects
Materials science ,Epoxy ,Autoclave ,symbols.namesake ,Isothermal transformation diagram ,Rheology ,visual_art ,visual_art.visual_art_medium ,symbols ,Process control ,Vitrification ,Composite material ,Raman spectroscopy ,Phase diagram - Abstract
Fiber reinforced epoxy resins manufactured in autoclaves are expected to continue to dominate the composites market through 2010. However, the ability to obtain consistent mechanical properties from product-to-product remains difficult. This is largely due to the inability to monitor and control epoxy cure, loosely defined as the process of chain extension and cross-linking. Current autoclave process control employs a heat schedule based on a time-temperature-transformation (TTT) phase diagram that is determined by dynamic mechanical rheology. The phase diagram defines epoxy cure in terms of gelation and vitrification. We have been using an FT-Raman spectrometer to develop correlations between molecular (chain extension and cross-linking) and macroscopic (gelation and vitrification) data. The basis of a TTT phase diagram using Raman kinetic data for process control will be presented for several reactions. more...
- Published
- 2004
- Full Text
- View/download PDF
43. SOFT GELS WITH ORDERED IRON PARTICLES: FABRICATION AND ELECTRORHEOLOGICAL RESPONSE
- Author
-
Yuxian An, Bo Liu, and Montgomery T. Shaw
- Subjects
Fabrication ,Materials science ,Rheometry ,Statistical and Nonlinear Physics ,Condensed Matter Physics ,Elastomer ,Magnetic field ,chemistry.chemical_compound ,Silicone ,chemistry ,medicine ,Particle ,Composite material ,Swelling ,medicine.symptom ,Prepolymer - Abstract
For a number of years we and others have investigated electrorheological (ER) gel systems comprising low-modulus elastomers mixed with various particles. Unlike ER fluids, the particles in gels do not change relative positions, thus creating model systems that can be used to check equilibrium theories of ER response. To make such materials, a magnetic field was used to align iron particles during the cure of a liquid silicone prepolymer in a sheet mold. Particle chains were made with as little as 0.5% particles, and aligned at angles from 0 to 45° to the normal. The gap between the particles was controlled by swelling the crosslinked material with additional prepolymer. The dependence of the ER effect on particle structuring in these materials was investigated experimentally using rheometry and dielectrometry. Also investigated were the properties of these materials as transducers and actuators. more...
- Published
- 2002
- Full Text
- View/download PDF
44. Electrospinning of Polymeric Nanofibers: Analysis of Jet Formation
- Author
-
Patrick T. Mather, Antonio E. Senador, and Montgomery T. Shaw
- Subjects
chemistry.chemical_classification ,Jet (fluid) ,Nanocomposite ,Structural material ,Materials science ,chemistry ,Capillary action ,Nanofiber ,Polymer ,Fiber ,Composite material ,Electrospinning - Abstract
Producing nanofiber-diameter polymeric fibers presents an attractive and robust approach toward the processing of nanocomposites, with applications ranging from clear optical components to toughened structural materials. In this work, we are examining the electrospinning process for the production of nanometer-diameter polymer fibers, giving particular attention to the following key features: jet-initiation, fiber architecture, and fiber distribution. A wide range of polymer systems and polymer-solvent combinations were studied in order to broaden the applicability of our conclusions to other systems. Specifically, a dimensional analysis was applied to jet-formation data obtained by quantifying the conditions required for the expulsion of fibers from a charged capillary to a grounded collection plate. The relationships between various dimensionless groups were compared with the expressions for the critical voltage that have been proposed for electrospinning of polymer solutions. more...
- Published
- 2000
- Full Text
- View/download PDF
45. Characterization of polymer composites by fiber optic Fourier transform Raman spectroscopy
- Author
-
Jennifer Rose, Montgomery T. Shaw, Richard Osbaldiston, Wayne W. Smith, Sanmitra A. Bhat, Marie B. DiTaranto, Yongming Liu, and Stuart Farquharson
- Subjects
chemistry.chemical_classification ,Materials science ,Optical fiber ,Infrared spectroscopy ,Polymer ,Epoxy ,law.invention ,symbols.namesake ,chemistry ,law ,visual_art ,visual_art.visual_art_medium ,symbols ,Composite material ,Raman spectroscopy ,Spectroscopy ,Curing (chemistry) ,Polyimide - Abstract
The in-use performance of polymer composites is highly dependent on the polymeric structure (e.g. chain length and cross-linking), which in turn, is highly dependent on the processing conditions. We have been developing a Fourier transformRaman system capable of high temperature measurements within curing devices (autoclaves and reaction injection moldingdevices, etc.) through the use of fiber optic probes. The goal is to use real-time spectral data to control heat schedules andultimately, composite properties. This presentation will describe the development of cure models based on reactionmechanisms for an epoxy resin and a polyimide using infrared and Raman spectroscopy. It will also describe correlationsbetween molecular structure and mechanical properties obtained by simultaneous Raman and rheology measurements. Inaddition, new spectral methods to determine cure kinetics will be presented.Keywords: polymer kinetics, epoxy resin, polyimide, composite cure, Raman spectroscopy, real-time monitoring more...
- Published
- 1999
- Full Text
- View/download PDF
46. A Close Look at the 'Sharkskin' Melt Fracture of Polybutadiene
- Author
-
Montgomery T. Shaw, Matthew G. Daly, Yong Woo Inn, and Robert J. Fisher
- Subjects
Flow curve ,Materials science ,Polybutadiene ,Soap solution ,Shear stress ,Sharkskin ,Extrusion ,Slip (materials science) ,Composite material - Abstract
Sharkskin melt fracture (SSF) refers to a fine surface distortion found on extradates of certain polymers at shear stress levels around 0.1 MPa. SSF can limit the productivity of extrusion lines. Two schools of thought concerning the mechanism of SSF have developed: one assigns the initiation of fracture to slip in the die land [e. g., Ramamurthy (1986)] whereas the other attributes the fracture to excessive stress at the exit as the flow profile redistributes [e. g., Howells and Benbow (1962), Kurtz (1984)]. Both may contribute to the problem. The former is supported strongly by the seeming invariant shear stress required for SSF and by the reported kink in the flow curve at this stress. more...
- Published
- 1998
- Full Text
- View/download PDF
47. Effects of DC and AC Electric Fields on the Response of Electrorheological Fluids Comprising Cylindrical PBZT Particles
- Author
-
Montgomery T. Shaw and Rex C. Kanu
- Subjects
Shear rate ,Materials science ,Polarizability ,Static dielectric constant ,Electric field ,Dynamic modulus ,medicine ,Stiffness ,Composite material ,medicine.symptom ,Electrorheological fluid ,Shock (mechanics) - Abstract
Electrorheological fluids (ERF’s) are suspensions consisting of micron-sized polarizable particles dispersed in non-conducting suspending media. ERF’s undergo liquid-to-solid transitions on the application of an electric field. These reversible transitions are on the order of milliseconds and are accompanied by orders-of-magnitude increase in yield stress and dynamic modulus (stiffness). This phenomenon is known as electrorheology (ER), and it is important because it permits the direct use of electricity without intermediate transformations. Therefore, devices based on ERF’s can be more economical and energy efficient than mechanical devices.1 ERF-based applications include shock absorbers2–4, clutches5–7, valves7–9, engine mounts2,11–13, brakes6,14, biomedical devices15 and control of high-speed machines.16 Shul’man et al.,17 have listed several ERF-based devices. However, in spite of its vast potential, relatively few ERF-based devices are in use. more...
- Published
- 1995
- Full Text
- View/download PDF
48. Using creeping squeeze flow to obtain low-frequency linear viscoelastic properties: Low-shear rate measurements on polydimethylsiloxane
- Author
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Edwin C. Cua and Montgomery T. Shaw
- Subjects
Materials science ,Polydimethylsiloxane ,Rheometry ,Mechanical Engineering ,Stokes flow ,Condensed Matter Physics ,Viscoelasticity ,Shear rate ,chemistry.chemical_compound ,Wavelength ,chemistry ,Creep ,Mechanics of Materials ,General Materials Science ,Composite material ,Melt flow index - Abstract
The problem of measuring the linear viscoelastic (LVE) properties of polymers at low frequencies is a long-standing one, especially for fractional melt index polyolefins with broad molecular weight distributions and small time–temperature shift factors. A squeeze–flow apparatus utilizing Newton’s interference rings was devised that could measure minute displacements less than 14 the wavelength of the light used. Maximum transient stresses achieved with the prototype ranged from 0.3 to 70.3 kPa. Its simplicity allows several samples to be run simultaneously under vacuum, minimizing degradation and cost, both critical considerations for long experiments. This paper covers the design of the prototype and results for polydimethylsiloxane at room temperature. more...
- Published
- 2002
- Full Text
- View/download PDF
49. Processing and commercial application of polymer blends
- Author
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Montgomery T. Shaw
- Subjects
chemistry.chemical_classification ,Materials science ,Polymers and Plastics ,chemistry ,Polymer science ,Materials Chemistry ,General Chemistry ,Polymer blend ,Polymer ,Composite material ,Preference - Abstract
The number of commercial blends has skyrocketed in the past several years and the trend toward blending—in preference to the creation of new polymer structures—has been firmly established. This paper analyzes the reasons for this growth; the types of commercial products, their manufacturer, and their applications; the patent situation; and possible future directions of the industry. more...
- Published
- 1982
- Full Text
- View/download PDF
50. Simulation of extrusion coating by tape drawing
- Author
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John Clark Miller and Montgomery T. Shaw
- Subjects
business.product_category ,Materials science ,Polymers and Plastics ,Extrusion coating ,General Chemistry ,Pure shear ,Shear (sheet metal) ,Stress (mechanics) ,Transverse plane ,Materials Chemistry ,Drawdown (economics) ,Die (manufacturing) ,Extrusion ,Composite material ,business - Abstract
Neck-in and maximum stress were studied in a tape-drawing experiment using a 3.5 MI low density polyethylene at 300°C. The conditions of the experiment were designed to reproduce closely those found in extrusion coating lines. The maximum stress was found to increase roughly with the 1.6 power of the drawdown ratio and the 1.0 power of the extrusion speed over a stress range of 4 × 103 to 5 × 105 Pa produced by drawdown ratios ranging from 2 to 22 and extrusion speeds of 2.3 to 6.1 cm s−1. The neck-in decreased weakly with drawdown ratio at low extrusion speed and with extrusion speed at constant drawdown ratio. After carefully characterizing the test resin in shear and extension, the similarities between predicted pure-shear (planar extension) transients and the tape experiments were studied. It was found that the trends, but not the magnitude of the experimental maximum stress were quite similar to the calculated longitudinal stress in pure shear. The behavior of the transverse to longitudinal stress ratio in pure shear was similar in behavior to the neck-in results, but considerable improvement was achieved by adding in a decayed stress from a simple-shear transient to simulate the conditions produced by the extrusion die. The philosophy of purposefully studying similarities between transient, pure or simple deformations and steady, complex processes is discussed. more...
- Published
- 1979
- Full Text
- View/download PDF
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