Poly(butyl terephthalate)/oxytetramethylene + oxidized carbon nanotubes hybrids: Mechanical and tribological behavior
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Georg Broza Institute of Polymers and Composites, Technical University of Hamburg, 21073 Hamburg, Germany
Tea Datashvili and Haley E. Hagg Lobland Department of Materials Science and Engineering, Laboratory of Advanced Polymers and Optimized Materials; and Department of Physics, Center for Advanced Research and Technology, University of North Texas, Denton, Texas 76207
Agata Kopyniecka Institute of Polymers and Composites, Technical University of Hamburg, 21073 Hamburg, Germany (Received 18 August 2011; accepted 20 March 2012)
We have created hybrids of functionalized single wall carbon nanotubes (fSWCNTs) and also multiwall CNTs (fMWCNTs) with PBT/PTMO, a block copolymer of semicrystalline poly(butyl terephthalate) (PBT) with amorphous oxytetramethylene (PTMO). For both single wall (SW) and multiwall (MW) carbon nanotubes (CNTs) tensile modulus and strain at break as a function of CNTs’ concentration (cCNT) show maxima. Elongation at break is enhanced by the nanotubes, a plasticizing effect—much stronger for SWCNTs because they have less contact points per unit area with the matrix and also are more flexible. Repetitive tensile tests were also performed; each loading cycle resulted in lowering the tensile modulus. Brittleness B(cCNT) diagrams show minima. New results for CNT hybrids fit an earlier general diagram for determination of viscoelastic recovery in sliding wear (f) as a function of brittleness (B); the original equation with unchanged parameters covers also these results. Volumetric wear was determined after abrasion on a pin-on-disk tribometer. Minima are seen on the volumetric wear versus cCNT diagrams, similar to those on the B(cCNT) diagrams.
I. INTRODUCTION
Poly(ether-b-ester) copolymers have numerous applications as engineering materials due to their attractive combination of strength, high elasticity, melt stability and high crystallization rates. These elastomers are block copolymers that contain alternatively crystallizable (hard) and noncrystallizable (soft) chain segments, resulting in a material with high melting temperature crystallites (hard segments)—dispersed in a soft component and low glass transition temperature matrix. High melting temperatures are pertinent in quest for polymers, which can survive temperature cycling over wide temperature ranges for applications in thermoelectric (TE) devices.1,2 Our segmented poly(ether-b-ester) copolymers of poly(butyl terephthalate) (PBT) and oxytetramethylene (PTMO) belong to the family of such thermoplastic elastomers.3 The a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2012.116 J. Mater. Res., Vol. 27, No. 14, Jul 28, 2012
nanometric structure of segregated hard and soft segments is mainly responsible for the outstanding mechanical properties of these materials.4 Generally and as well known, properties of polymers can be modified and improved by addition of fillers with sizes in the nm range5–19 including carbon nanotubes (CNTs).20–33 CNTs exhibit a high elastic modulus, strong electrical and high t
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