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Tensile strength and young's modulus of polyisoprene/single-wall carbon nanotube composites increased by high pressure cross-linking
Umeå University, Faculty of Science and Technology, Department of Physics.
Umeå University, Faculty of Science and Technology, Department of Physics.
Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
Umeå University, Faculty of Science and Technology, Department of Physics.
2010 (English)In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 43, no 18, 7680-7688 p.Article in journal (Refereed) Published
Abstract [en]

High-viscosity liquid cis-1,4 polyisoprene (PI), with up to 20 wt % single-wall carbon nanotubes (SWCNTs), has been cross-linked by high pressure and high temperature (HP&HT) treatment at 513 K and pressures in the range 0.5 to 1.5 GPa to yield densified network polymer composites. A composite with 5 wt % SWCNTs showed 2.2 times higher tensile strength σUTSUTS = 17 MPa), 2.3 times higher Young’s modulus E (E = 220 MPa) and longer extension at break than pure PI. The improvement is attributed to SWCNT reinforcement and improved SWCNT−PI interfacial contact as a result of the HP&HT cross-linking process, and reduced brittleness despite a higher measured cross-link density than that of pure PI. The latter may originate from an effect similar to crazing, i.e., bridging of microcracks by polymer fibrils. We surmise that the higher cross-link densities of the composites are due mainly to physical cross-links/constraints caused by the SWCNT−PI interaction, which also reflects the improved interfacial contact, and that the CNTs promote material flow by disrupting an otherwise chemically cross-linked network. We also deduce that the PI density increase at HP&HT cross-linking is augmented by the presence of CNTs.

Place, publisher, year, edition, pages
American Chemical Society , 2010. Vol. 43, no 18, 7680-7688 p.
Identifiers
URN: urn:nbn:se:umu:diva-38842DOI: 10.1021/ma101484eISI: 000281883000035OAI: oai:DiVA.org:umu-38842DiVA: diva2:382882
Available from: 2011-01-03 Created: 2011-01-03 Last updated: 2017-12-11Bibliographically approved
In thesis
1. Thermal and mechanical studies of carbon nanotube-polymer composites synthesized at high pressure and high temperature
Open this publication in new window or tab >>Thermal and mechanical studies of carbon nanotube-polymer composites synthesized at high pressure and high temperature
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, thermal and mechanical properties of polymers and carbon nanotubes-polymer composites, which were modified and studied under high pressure, are presented. The results concern the thermal conductivity κ and heat capacity per unit volume ρcp of pure polymers: polyisoprene (PI), polybutadiene (PB), and nylon-6, and their multi-wall and single-wall carbon nanotube (MWCNT and SWCNT) composites both before (untreated) and after high pressure treatments. As shown here, a suitable high pressure high temperature (HP&HT) treatment induces either cross-links in the polymers (PI and PB), i.e. transforms these into elastomers, or increases the crystallinity (nylon-6).

The experiments were done, in situ, in the temperature range 100-520 K for pressures up to 1.5 GPa, and the results show that cross-linking under high pressure can be monitored in data for κ and ρcp. Moreover, κ for a well cross-linked (ebonite-like) polymer near ambient conditions can be up to 50% higher than the untreated states, whereas ρcp becomes similar as the glassy state of the untreated polymer. The glass transition of the cross-linked states becomes broader and shifts to higher temperatures with increasing degree of cross-linking. In the case of nylon-6, the HP&HT treatment causes microstructural changes, viz. increased crystallinity and crystals with a preferred orientation and increased size, which enhances κ and improves the thermal stability.

The thermal property studies of the CNT polymer composite show that k of the composites increases significantly, e.g. 120% for 5wt% SWCNTs in PI, which is attributed to the very high k of CNTs. Moreover, MWCNTs also improve k, but not as much as SWCNTs. This is accounted for by their lower aspect ratio (length/diameter), whereas their lower k is less important. Adding CNTs normally raise the glass transition temperatures of the polymers. More specifically, SWCNTs in PB raise the glass transition temperature slightly more than MWCNTs and, in particular, under the most densified conditions and for a high molecular weight PB, which may be due to more favorable conditions for coating/wrapping of the CNTs.

The mechanical studies of the HP&HT treated polymers and composites show that CNTs strongly enhances the tensile strength and Young’s modulus, e.g. 5 wt% SWCNT in PI synthesized at 1 GPa and 513 K showed 2 times higher tensile strength and 2.3 times higher Young’s modulus than that of similarly treated pure PI. The results indicate that the treatment improves the poor interfacial contact between the CNTs and polymer, which is one of the obstacles for achieving stronger CNT composites

Place, publisher, year, edition, pages
Umeå: Institutionen för fysik, Umeå Universitet, 2011. 52 p.
Identifiers
urn:nbn:se:umu:diva-43477 (URN)978-91-7459-223-8 (ISBN)
Public defence
2011-06-03, Naturvetarhuset, N300, Umeå universitet, Umeå, 10:15 (English)
Opponent
Supervisors
Available from: 2011-05-06 Created: 2011-05-02 Last updated: 2011-05-04Bibliographically approved
2. Studies of novel phases and states produced by means of high pressure: Polymer and polymer based carbon nanocomposites
Open this publication in new window or tab >>Studies of novel phases and states produced by means of high pressure: Polymer and polymer based carbon nanocomposites
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Place, publisher, year, edition, pages
Umeå: Institutionen för fysik, Umeå universitet, 2011
National Category
Materials Engineering
Research subject
Materials Science
Identifiers
urn:nbn:se:umu:diva-49817 (URN)978-91-7459-315-0 (ISBN)
Public defence
2011-12-15, Naturvetarhuset, N200, Umeå universitet, Umeå, 13:30
Opponent
Supervisors
Available from: 2011-11-24 Created: 2011-11-18 Last updated: 2011-11-21Bibliographically approved

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Tonpheng, BounphanhYu, JunchunAndersson, Britt MAndersson, Ove

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