Some aspects of the molecular structure of stretched rubbers
Some aspects of the molecular structure of stretched rubbers
Three aspects of the molecular structure of stretched rubbers were studied: 1. Linear low density polyethylene was crosslinked and then stretched in the melt phase. Infra-red dichroism was used to characterise the orientation in the stretched polyethylene rubber as functions of crosslink density and stretch ratio. The same orientation analysis was performed on similarly crosslinked material which had been solvent extracted. X-ray diffraction confirmed the existence of molecular orientation in a stretched, crosslinked polyethylene melt. It was concluded that the amount of orientation developed in a stretched polyethylene rubber is measurable but small. If such a system is in some ways analogous to a flowing melt then it suggests that the amount of molecular chain extension in the melt is very small. It offers an explanation of why molecular orientation in flowing melts has not yet been observed by X-ray diffraction, infra-red or Raman spectroscopy. 2. A study was made of the same crosslinked polyethylene rubbers, stretched in the melt phase and then cooled below the melting temperature while held in the stretched position. Again, the molecular orientation was characterised by infra-red dichroism and confirmed by X-ray diffraction. It was concluded that highly oriented crystallites in the direction of stretch can be produced from a very small amount of orientation in the stretched polyethylene rubber pre-cursor. If the same analogy is drawn between the stretched polyethylene rubber and a flowing polymer melt, then the results suggest that a very small amount of molecular chain extension in a flowing melt can give rise to highly oriented products when cooled. Evidence was also found for some strain induced crystallisation. 3. A study was made of highly stretched, crosslinked natural rubber by Fourier transform infra-red spectroscopy, X-ray diffraction and the new technique of Fourier transform Raman spectroscopy. Changes which occur upon stretching, the effect of strain induced crystallisation and the effect of temperature on the strain induced crystallisation were studied. The results obtained led to the conclusion that a significant amount of strain induced crystallisation occurs when the rubber is highly stretched (greater than 550% extension). On heating, observed changes in the infra-red spectrum and X-ray diffraction pattern suggest a progressive melting of the strain induced crystallites and not a sharp melting endotherm. Upon stretching, consistent changes were observed in the Raman spectra, which may be attributed to orientation of strain induced crystallisation.
University of Southampton
1988
Stevenson, Timothy Hugh
(1988)
Some aspects of the molecular structure of stretched rubbers.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
Three aspects of the molecular structure of stretched rubbers were studied: 1. Linear low density polyethylene was crosslinked and then stretched in the melt phase. Infra-red dichroism was used to characterise the orientation in the stretched polyethylene rubber as functions of crosslink density and stretch ratio. The same orientation analysis was performed on similarly crosslinked material which had been solvent extracted. X-ray diffraction confirmed the existence of molecular orientation in a stretched, crosslinked polyethylene melt. It was concluded that the amount of orientation developed in a stretched polyethylene rubber is measurable but small. If such a system is in some ways analogous to a flowing melt then it suggests that the amount of molecular chain extension in the melt is very small. It offers an explanation of why molecular orientation in flowing melts has not yet been observed by X-ray diffraction, infra-red or Raman spectroscopy. 2. A study was made of the same crosslinked polyethylene rubbers, stretched in the melt phase and then cooled below the melting temperature while held in the stretched position. Again, the molecular orientation was characterised by infra-red dichroism and confirmed by X-ray diffraction. It was concluded that highly oriented crystallites in the direction of stretch can be produced from a very small amount of orientation in the stretched polyethylene rubber pre-cursor. If the same analogy is drawn between the stretched polyethylene rubber and a flowing polymer melt, then the results suggest that a very small amount of molecular chain extension in a flowing melt can give rise to highly oriented products when cooled. Evidence was also found for some strain induced crystallisation. 3. A study was made of highly stretched, crosslinked natural rubber by Fourier transform infra-red spectroscopy, X-ray diffraction and the new technique of Fourier transform Raman spectroscopy. Changes which occur upon stretching, the effect of strain induced crystallisation and the effect of temperature on the strain induced crystallisation were studied. The results obtained led to the conclusion that a significant amount of strain induced crystallisation occurs when the rubber is highly stretched (greater than 550% extension). On heating, observed changes in the infra-red spectrum and X-ray diffraction pattern suggest a progressive melting of the strain induced crystallites and not a sharp melting endotherm. Upon stretching, consistent changes were observed in the Raman spectra, which may be attributed to orientation of strain induced crystallisation.
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Published date: 1988
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Local EPrints ID: 461863
URI: http://eprints.soton.ac.uk/id/eprint/461863
PURE UUID: b4e6208c-0fcf-48e1-b837-31cdd0dd249f
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Date deposited: 04 Jul 2022 18:57
Last modified: 04 Jul 2022 18:57
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Author:
Timothy Hugh Stevenson
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