Confirmation of a nanohybrid shish‐kebab (NHSK) structure in composites of PET and MWCNTs

Abstract

Additional Supporting Information may be found in the online version of this article.Composites incorporating multiwall and/or single walled carbon nanotube (MWCNT/SWCNT) fillers and a polymer matrix, offer exciting potential for industrial applications. This is due to modification of many properties, e.g. mechanical and electrical compared with the neat homopolymer.1-5 The CNT filler provides not only direct reinforcement due to their outstanding physical properties, but also secondary reinforcement via modification through their influence on the final polymer crystal morphology. Our recent work has shown the value of MWCNTs as a functional nanofiller in poly(ethylene terephthalate) (PET); improvements in mechanical properties were linked to the direct MWCNT reinforcement and its dramatic nucleating effects on the polymer matrix. 6,7 Whilst it has been shown that CNTs act as nucleating agents in polymer crystallization during processing, what is not understood is ABSTRACTHere, the confirmation of an oriented nanohybrid shish-kebab (NHSK) crystalline structure in a series of composites of poly(ethylene terephthalate) (PET) and multiwall carbon nanotubes (MWCNTs) is reported. The combined use of small-and wide-angle X-ray scattering (SAXS/WAXS) and thermal analysis has been used to investigate the morphology development in PET-MWCNT nanocomposites under hot isothermal crystallization conditions. The MWCNTs act as both heterogeneous nucleating agents and surfaces (oriented shish structures) for the epitaxial growth of PET crystallites (kebabs) giving an oriented crystalline morphology. In contrast, the PET homopolymer does not show any residual oriented crystalline morphology during isothermal crystallization but gave a sporadic nucleation of a classic unoriented lamellar structure with slower crystallization kinetics. The results provide a valuable insight into the role of MWCNTs as nano-particulate fillers in the morphology development and subsequent modification of physical properties in engineering polymers.

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

“…This data was recently reported in a short communication [38], where during the hot crystallization process samples, were first heated above Tm to 270 ºC, to erase any crystalline structure from the extrusion process. The samples were then quenched to the crystallization temperature.…”

“…The residual orientation observed in the PET2% and PET4% composites, is likely to be due to the MWCNTs acting as rigid rod-like structures that do not relax in the viscous polymer matrix once aligned in the die head, thus their orientation is 'locked-in' once the polymer is extruded and cooled. [38] The crystalline structure in the polymer composites is also confirmed with WAXS. To investigate the change in the initial structure of the neat PET and PET-MWCNT composites post extrusion, hot and cold isothermal crystallizations were performed.…”

“…This indicates that an oriented residual crystalline structure exists in the polymer post extrusion. [12,38] This oriented crystalline structure is attributed to an oriented NHSK morphology, where due to the design of the extruder die head [11], the MWCNTs are initially aligned in the polymer melt during extrusion. The MWCNTs then act as nucleating sites during the extrusion casting and cooling process (once extruded), and so an initial crystalline structure develops compared with the amorphous neat PET.…”

“…The 1D profiles of the azimuthal peaks were fitted using Gaussian functions to obtain the average full width at half maximum (FWHM) values. [12,38,42] Avrami plots [43,44], using the double logarithmic from of the Avrami equation, were obtained for the isothermal crystallization measurements from Qs:…”

“…[36,38] Differentiating between these scenarios is difficult in polymer-melt composite systems and requires fast and sensitive techniques to follow the time-resolved morphology development during the polymers crystallization process. Recently, in a short communication [38], we reported some preliminary results of the hot isothermal crystallization in a set of melt processed PET-MWCNT composites with MWCNT loadings between 1 and 4 wt%. The…”