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Influence of Molecular Weight on the Mechanical Performance of a Thermoplastic Glassy Polyimide
Author: National Aeronautics and Space Administration (NASA)
Publisher: Createspace Independent Publishing Platform
Published: 2018-06
Total Pages: 34
ISBN-13: 9781720581222
DOWNLOAD EBOOK →Mechanical Testing of an advanced thermoplastic polyimide (LaRC-TM-SI) with known variations in molecular weight was performed over a range of temperatures below the glass transition temperature. The physical characterization, elastic properties and notched tensile strength were all determined as a function of molecular weight and test temperature. It was shown that notched tensile strength is a strong function of both temperature and molecular weight, whereas stiffness is only a strong function of temperature. A critical molecular weight (Mc) was observed to occur at a weight-average molecular weight (Mw) of approx. 22000 g/mol below which, the notched tensile strength decreases rapidly. This critical molecular weight transition is temperature-independent. Furthermore, inelastic analysis showed that low molecular weight materials tended to fail in a brittle manner, whereas high molecular weight materials exhibited ductile failure. The microstructural images supported these findings.Nicholson, Lee M. and Whitley, Karen S. and Gates, Thomas S. and Hinkley, Jeffrey A.Langley Research CenterMOLECULAR WEIGHT; MECHANICAL PROPERTIES; POLYIMIDES; ELASTIC PROPERTIES; THERMOPLASTICITY; TENSILE STRENGTH; DUCTILE-BRITTLE TRANSITION; TEMPERATURE DEPENDENCE; FRACTOGRAPHY; GLASS TRANSITION TEMPERATURE; STRESS-STRAIN DIAGRAMS; MODULUS OF ELASTICITY; MICROSTRUCTURE; POLYMER MATRIX COMPOSITES; NOTCHES; TENSILE TESTS
Influence of Molecular Weight on the Mechanical Performance of a Thermoplastic Glassy Polyimide
The Combined Influence of Molecular Weight and Temperature on the Aging and Viscoelastic Response of a Glassy Thermoplastic Polyimide
Author: Lee M. Nicholson
Publisher:
Published: 2000
Total Pages: 44
ISBN-13:
DOWNLOAD EBOOK →The effect of molecular weight on the viscoelastic performance of an advanced polymer (LaRC-SI) was investigated through the use of creep compliance tests. Testing consisted of short-term isothermal creep and recovery with the creep segments performed under constant load. The tests were conducted at three temperatures below the glass transition temperature of five materials of different molecular weight. Through the use of time-aging-time superposition procedures, the material constants, material master curves and aging-related parameters were evaluated at each temperature for a given molecular weight. The time-temperature superposition technique helped to describe the effect of temperature on the timescale of the viscoelastic response of each molecular weight. It was shown that the low molecular weight materials have higher creep compliance and creep rate, and are more sensitive to temperature than the high molecular weight materials. Furthermore, a critical molecular weight transition was observed to occur at a weight-average molecular weight of ~2500 g/mol below which, the temperature sensitivity of the time-temperature superposition shift factor increases rapidly. The short-term creep compliance data were used in association with Struik's effective time theory to predict the long-term creep compliance behavior for the different molecular weights. At long timescales, physical aging serves to significantly decrease the creep compliance and creep rate of all the materials tested.
The Role of Molecular Weight and Temperature on the Elastic and Viscoelastic Properties of a Glassy Thermoplastic Polyimide
Author: Lee M. Nicholson
Publisher:
Published: 2001
Total Pages: 26
ISBN-13:
DOWNLOAD EBOOK →Mechanical testing of the elastic and viscoelastic response of an advanced thermoplastic polyimide (LaRC-SI) with known variations in molecular weight was performed over a range of temperatures below the glass transition temperature. The notched tensile strenght was shown to be a strong function of both molecular weight and temperature, whereas stiffness was only a strong function of temperature. A critical molecular weight was observed to occur at a weight-average molecular weight of ~22,000 g/mol below which, the notched tensile strength decreases rapidly. This critical molecular weight transition is temperature-independent. Low molecular weight materials tended to fail in a brittle manner, whereas high molecular weight materials exhibited ductile failure.
The Combined Influence of Molecular Weight and Temperature on the Aging and Viscoelastic Response of a Glassy Thermoplastic Polyimide
Author: National Aeronautics and Space Adm Nasa
Publisher: Independently Published
Published: 2018-09-17
Total Pages: 34
ISBN-13: 9781723766961
DOWNLOAD EBOOK →The effect of molecular weight on the viscoelastic performance of an advanced polymer (LaRC-SI) was investigated through the use of creep compliance tests. Testing consisted of short-term isothermal creep and recovery with the creep segments performed under constant load. The tests were conducted at three temperatures below the glass transition temperature of five materials of different molecular weight. Through the use of time-aging-time superposition procedures, the material constants, material master curves and aging-related parameters were evaluated at each temperature for a given molecular weight. The time-temperature superposition technique helped to describe the effect of temperature on the timescale of the viscoelastic response of each molecular weight. It was shown that the low molecular weight materials have higher creep compliance and creep rate, and are more sensitive to temperature than the high molecular weight materials. Furthermore, a critical molecular weight transition was observed to occur at a weight-average molecular weight of M (bar) (sub w) 25000 g/mol below which, the temperature sensitivity of the time-temperature superposition shift factor increases rapidly. The short-term creep compliance data were used in association with Struik's effective time theory to predict the long-term creep compliance behavior for the different molecular weights. At long timescales, physical aging serves to significantly decrease the creep compliance and creep rate of all the materials tested.Nicholson, Lee M. and Whitley, Karen S. and Gates, Thomas S.Langley Research CenterAGING (MATERIALS); GLASS; MOLECULAR WEIGHT; TEMPERATURE EFFECTS; THERMOPLASTICITY; VISCOELASTICITY; POLYIMIDES; CREEP TESTS; ERROR ANALYSIS; TIME TEMPERATURE PARAMETER; GLASS TRANSITION TEMPERATURE; DURABILITY
The Role of Molecular Weight and Temperaturee on the Elastic and Viscoelastic Properties of a Glassy Thermoplastic Polyimide
The Combined Influence of Molecular Weight and Temperaturee on the Aging and Viscoelastic Response of a Glassy Thermoplastic Polyimide
Chemistry and Properties of Crosslinked Polymers
Author: Labana
Publisher: Elsevier
Published: 2012-12-02
Total Pages: 596
ISBN-13: 032313937X
DOWNLOAD EBOOK →Chemistry and Properties of Crosslinked Polymers provides a description of the structure property relationship, chemistry, and methods of characterization of crosslinked polymers. The book presents papers that discuss experimental techniques to study polymer network structure; deduction of information on network structure from theoretical considerations; interpenetrating polymer networks; crosslinked polymers for high temperature applications; a novel class of polyurethanes; crosslinking agents; and the influence of crosslinking agents on thermal and mechanical properties. The text will be of value to materials scientists and engineers, chemists, and researchers in the field of polymer science.
The Effect of Molecular Orientation on the Mechanical Properties of Polystyrene
Author: T. T. Jones
Publisher: Elsevier
Published: 2013-10-22
Total Pages: 21
ISBN-13: 1483139298
DOWNLOAD EBOOK →The Effect of Molecular Orientation on the Mechanical Properties of Polystyrene presents the results of a study that investigated the effect of molecular orientation on the mechanical properties of polystyrene. Oriented sheets of two commercial homopolystyrenes (PSA and PSB) differing in molecular weight, rheological and glass transition temperature properties were prepared by sheet extrusion and drawing. The properties of the resulting sheets were examined at seven different laboratories in Europe. The study focused on length reversion ratio, birefringence, orientation stress, shrinkage stress, and various mechanical properties such as rupture stress and strain, the specific energy of rupture, and sonic modulus and relaxation modulus. Impact behavior and environmental stress cracking behavior were also evaluated. One of the findings was that oriented polymers subjected to lateral strains can develop catastrophic crack growth when immersed in an active liquid. The onset of the cracks depends on the lateral strain imposed as well as the degree of orientation. PSB was more resistant than PSA. This monograph should be a useful resource for chemists.
