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Studies of novel phases and states produced by means of high pressure: Polymer and polymer based carbon nanocomposites
Umeå University, Faculty of Science and Technology, Department of Physics.
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: urn:nbn:se:umu:diva-49817ISBN: 978-91-7459-315-0 (print)OAI: oai:DiVA.org:umu-49817DiVA: diva2:457743
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
List of papers
1. High-pressure-induced microstructural evolution and enhancement of thermal properties of nylon-6
Open this publication in new window or tab >>High-pressure-induced microstructural evolution and enhancement of thermal properties of nylon-6
2010 (English)In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 43, no 24, 10512-10520 p.Article in journal (Refereed) Published
Abstract [en]

The transition behavior and thermal properties of nylon-6 at elevated pressure, p, have been established by in-situ thermal conductivity, κ, and heat capacity measurements. The glass transition temperature, Tg, of virgin nylon-6 is described well by the empirical equation Tg(p) = 319.60(1 + 1.90 p)0.24 (p in GPa and Tg in K). Moreover, isobaric heating in the 1−1.2 GPa range causes a cold-crystallization transition near 500 K. As a result, κ increased 15% whereas the heat capacity per unit volume decreased 7% slowly with time during 4 h annealing at 530 K. The transformation is associated with a significantly increased crystallinity, from 35% to 55−60%, and a pressure-induced preferred orientation and increased size for the lamellae of monoclinic α crystalline structure. This state has 8−10 K higher melting temperature and better formic acid resistance than that of virgin nylon-6. However, the results show no indication of cross-linking, as reported for similarly treated nylon-1010 and nylon-11, but instead chain scissoring.

Identifiers
urn:nbn:se:umu:diva-38807 (URN)10.1021/ma102273b (DOI)000285429400049 ()
Available from: 2011-01-03 Created: 2011-01-02 Last updated: 2017-12-11Bibliographically approved
2. Thermal properties and transition studies of multi-wall carbon nanotube/nylon-6 composites
Open this publication in new window or tab >>Thermal properties and transition studies of multi-wall carbon nanotube/nylon-6 composites
2011 (English)In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 49, no 14, 4858-4866 p.Article in journal (Refereed) Published
Abstract [en]

Transition behavior and thermal properties of a multi-wall carbon nanotube (MWCNT)/nylon-6 composite (P-composite) made by in situ polymerization and subsequently structurally modified by high-pressure–high-temperature treatment have been established. The thermal conductivity (κ) of nylon-6 improved 27% by the addition of 2.1 wt.% MWCNT filler simultaneously as the heat capacity per unit volume decreased 22% compared with that of nylon-6 at 1 atm and 298 K. Moreover, the MWCNT filler raises the glass transition temperature (Tg) of nylon-6, but the pressure dependence of Tg remains unchanged. A model for κ indicates that the interfacial thermal resistance between the MWCNT filler and the nylon-6 matrix decreases 20% up to 1 GPa and most significantly above 0.8 GPa. P-composite was structurally modified by a sluggish cold-crystallization transition at 1.0 GPa, 530 K, which further increased κ by as much as 37% as the crystallinity of nylon-6 improved from 31% to 58% with a preferred crystal orientation and increased crystal size.

Place, publisher, year, edition, pages
Elsevier, 2011
National Category
Chemical Sciences Physical Sciences
Identifiers
urn:nbn:se:umu:diva-45835 (URN)10.1016/j.carbon.2011.07.006 (DOI)
Available from: 2012-02-07 Created: 2011-08-17 Last updated: 2017-12-08Bibliographically approved
3. Microstructure, nucleation and thermal properties of high-pressure crystallized MWCNT/nylon-6 composites
Open this publication in new window or tab >>Microstructure, nucleation and thermal properties of high-pressure crystallized MWCNT/nylon-6 composites
2011 (English)In: Polymer, ISSN 0032-3861, E-ISSN 1873-2291, Vol. 52, no 24, 5521-5527 p.Article in journal (Refereed) Published
Abstract [en]

Multi-wall carbon nanotube (MWCNT)/nylon-6 composites made by in-situ polymerization and subsequently modified by treatment at 1.0 GPa (or 1.7 GPa) and 530 K have been studied by WAXD, DSC and NMR. The pressure treatment gives an amorphous to crystalline transformation where the crystallinity increases from ∼31% to as much as ∼58% concurrently as the nylon-6 crystals increase in size and attain a preferred orientation relative to the applied pressure. A composite of 2.1 wt% purified MWCNT in nylon-6 shows significantly higher melting temperature than neat nylon-6 after identical pressure treatments. The improved thermal stability of the composite is attributed to crystal growth in the presence of reinforcing MWCNTs. The NMR spectrum of a pressure treated composite is similar to that of nylon-6 single crystals, which suggests a reduction of crystal boundaries after treatment, but there is no indication of covalent bonds between the nylon-6 chains and the MWCNTs.

Place, publisher, year, edition, pages
Elsevier, 2011
Keyword
Multi-wall carbon nanotube, Nylon-6, Thermal property
National Category
Engineering and Technology Natural Sciences
Identifiers
urn:nbn:se:umu:diva-49310 (URN)10.1016/j.polymer.2011.09.036 (DOI)
Available from: 2012-02-07 Created: 2011-11-07 Last updated: 2017-12-08Bibliographically approved
4. Thermal conductivity, heat capacity, and cross-linking of polyisoprene/single-wall carbon nanotube composites under high pressure
Open this publication in new window or tab >>Thermal conductivity, heat capacity, and cross-linking of polyisoprene/single-wall carbon nanotube composites under high pressure
2009 (English)In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 42, no 23, 9295-9301 p.Article in journal (Refereed) Published
Abstract [en]

Polyisoprene (PI)/single-wall carbon nanotube (SWCNT) composites and pure PI have been cross-linked by high-pressure treatment to yield densified elastomeric states. Simultaneously, the SWCNT and cross-linked-induced changes of the thermal conductivity, heat capacity per unit volume, and glass transition were investigated by in situ measurements. The thermal conductivity of both the elastomeric and liquid PI improves ≈120% by the addition of 5 wt % SWCNT filler. The SWCNT filler (5 wt %) increases the glass-transition temperature of liquid PI by ≈7 K and that of the elastomeric state by as much as 12 K, which is due to a filler-induced increase in the cross-link density. Moreover, the 5 wt% filler yields a heat capacity decrease by ≈30% in both the glassy and liquid/elastomeric states, which indicates that SWCNTs cause a remarkably large reduction of both the vibrational and configurational heat capacity of PI. Finally, the consequences of high-pressure densification and the possibilities this provides to help elucidating the nature of the heat conduction in polymer/carbon nanotube composites are discussed.

Place, publisher, year, edition, pages
American Chemical Society, 2009
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
urn:nbn:se:umu:diva-30449 (URN)10.1021/ma902122u (DOI)
Available from: 2009-12-25 Created: 2009-12-25 Last updated: 2017-12-12Bibliographically approved
5. Tensile strength and young's modulus of polyisoprene/single-wall carbon nanotube composites increased by high pressure cross-linking
Open this publication in new window or tab >>Tensile strength and young's modulus of polyisoprene/single-wall carbon nanotube composites increased by high pressure cross-linking
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
Identifiers
urn:nbn:se:umu:diva-38842 (URN)10.1021/ma101484e (DOI)000281883000035 ()
Available from: 2011-01-03 Created: 2011-01-03 Last updated: 2017-12-11Bibliographically approved
6. Effects of cross-links, pressure and temperature on the thermal properties and glass transition behaviour of polybutadiene
Open this publication in new window or tab >>Effects of cross-links, pressure and temperature on the thermal properties and glass transition behaviour of polybutadiene
2011 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 13, no 33, 15047-15054 p.Article in journal (Refereed) Published
Abstract [en]

The thermal conductivity κ, heat capacity per unit volume ρcp and glass transition behaviour under pressure have been established for medium and high vinyl content polybutadiene PB with molecular weights 2600 and 100 000 and their highly cross-linked (ebonite) states obtained purely by high-pressure high-temperature treatments. Cross-linking eliminates the glass transitions and increases κ by as much as 50% at 295 K and 1 atm, and decreases ρcp to a limiting level close to that of the glassy state of PB, which is reached before the ultimate cross-link density is achieved. The pressure and temperature behaviours of κ are strongly changed by cross-links, which increases the effect of temperature but decreases the effect of pressure. We attribute these changes to a cross-linked induced permanent densification and consequential increase of phonon velocity simultaneously as conduction along polymer chains is disrupted. The glass transition temperatures for a time scale of 1 s are described to within 0.5 K by: Tg(p) = 202.5 (1 + 2.94 p)0.286 and Tg(p) = 272.3 (1 + 2.57 p)0.233 (p in GPa and T in K) up to 1 GPa, for PB2600 and PB100000, respectively, and can be estimated for medium and high vinyl content PBs with molecular weights in between by a constant, pressure independent, shift in temperature.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2011
National Category
Physical Sciences
Identifiers
urn:nbn:se:umu:diva-45735 (URN)10.1039/C1CP20785G (DOI)
Available from: 2011-08-15 Created: 2011-08-15 Last updated: 2017-12-08Bibliographically approved
7. Microstructural and property changes in high pressure treated carbon nanotube/polybutadiene composites
Open this publication in new window or tab >>Microstructural and property changes in high pressure treated carbon nanotube/polybutadiene composites
2011 (English)In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 21, no 35, 13672-13682 p.Article in journal (Refereed) Published
Abstract [en]

In a comprehensive investigation of carbon nanotube (CNT) filled liquid and solid polybutadienes of molecular weights 2600 and 100000, respectively, we report results of thermal conductivity (κ), glass transition temperature (Tg), interfacial interaction and microstructure before and after simultaneous high-pressure and high-temperature (HP&HT) treatment. The HP&HT treatment changed polybutadiene from a liquid or solid to a highly cross-linked, ebonite-like, state. Concurrently, the microstructure changed from randomly dispersed CNTs to a web-like structure of coated and/or wrapped CNTs, with a permanent shift in their D*-band by as much as 16 cm−1. Moreover, κ of the recovered state of a 2.9 wt% –COOH functionalized multi-wall carbon nanotube (MWCNT) composite increased by 34% predominantly due to an irreversible densification and a consequentially increased phonon velocity. Results prior to treatment show that single-wall carbon nanotube (SWCNT) fillers promote κ better (17%/wt%) than –SH functionalized MWCNT fillers (8%/wt%), which is accounted for by their higher aspect ratio, whereas their about twice as high κ appears to be unimportant. The SWCNTs also raise Tg slightly more than MWCNTs and, in particular, under the most densified conditions and for the high molecular weight polybutadiene, which may be due to more favorable conditions for coating/wrapping.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2011
National Category
Materials Chemistry
Identifiers
urn:nbn:se:umu:diva-45955 (URN)10.1039/C1JM12187A (DOI)
Available from: 2012-02-07 Created: 2011-08-23 Last updated: 2017-12-08Bibliographically approved

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