The formation of a nanohybrid shish-kebab (NHSK) structure in melt-processed composites of poly(ethylene terephthalate) (PET) and multi-walled carbon nanotubes (MWCNTs)

• Published in: Polymer (Guilford) 2017-05, Vol.117, p.208-219
• Main Authors: Heeley, Ellen L., Hughes, Darren J., Crabb, Eleanor M., Bowen, James, Bikondoa, Oier, Mayoral, Beatriz, Leung, Sandy, McNally, Tony
• Format: Article
• Language: English
• Subjects: Cold extrusion; Crystal structure; Crystalline morphology; Crystallites; Crystallization; Crystals; Epitaxial growth; Ethylene; Extrusion; Fillers; Kinetics; Lamellar structure; Mechanical properties; Morphology; Multi wall carbon nanotubes; Nanocomposites; Nanohybrid shish-kebab structure (NHSK); Nanotechnology; Nanotubes; Nucleation; Polyethylene terephthalate; Polymer matrix composites; Polymer-MWCNT nanocomposites; Polymers; Recrystallization; Scattering; Small angle X ray scattering; Small- and wide-angle X-ray scattering (SAXS/WAXS); Thermal analysis; X-ray scattering; X-rays
• ISSN: 0032-3861; 1873-2291
• DOI: 10.1016/j.polymer.2017.04.033

The combination of synchrotron Small- and Wide-Angle X-ray scattering (SAXS/WAXS), and thermal analysis was used to follow the evolution of crystalline morphology and crystallization kinetics in a series of melt-processed composites of poly(ethylene terephthalate) (PET) and multiwall carbon nanotubes (MWCNT). The as-extruded PET-MWCNT composites underwent both hot and cold isothermal crystallizations where a final oriented nanohybrid shish-kebab (NHSK) crystalline structure was observed. An oriented NHSK structure was seen to persist even after melting and recrystallization of the composites. From the scattering data, we propose a model whereby the oriented MWCNTs act as heterogeneous nucleation surfaces (shish) and the polymer chains wrap around them and the crystallites (kebabs) grow epitaxially outwards during crystallization. However, depending on crystallization temperature, unoriented crystallites also grow in the polymer matrix, resulting in a combination of a NHSK and lamellar morphology. In contrast, the neat PET homopolymer showed the sporadic nucleation of a classic unoriented lamellar structure under the same isothermal crystallization conditions. These results provide a valuable insight into the distinctive modification of the crystalline morphology of melt-processed polymer-MWCNT composites prior to any secondary processing, having a significant impact on the use of MWCNTs as fillers in the processing and modification of the physical and mechanical properties of engineering polymers. [Display omitted] •Morphology and crystalline evolution in PET-MWCNT composite samples was investigated.•Hot and cold isothermal crystallizations of PET-MWCNT composites.•SAXS/WAXS data revealed an unoriented lamellar structure for neat PET composites.•PET-MWCNT composites revealed an oriented nanohybrid shish-kebab (NHSK) morphology.•MWCNTs act as nucleation surfaces for the epitaxial growth of PET crystallites.