Macroscopic CNT fibres inducing non-epitaxial nucleation and orientation of semicrystalline polymers

Hangbo Yue,Javier Llorca,Juan P Fernández-Blázquez,Juan J Vilatela,Alfonso Monreal-Bernal

doi:10.1038/srep16729

Hangbo Yue, Javier Llorca + Show 3 more

Open Access

https://doi.org/10.1038/srep16729

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Abstract

In the presence of macroscopic fibres of carbon nanotubes (CNT), various semicrystalline polymers are shown to present accelerated crystallisation through the formation of a transcrystalline (TC) layer perpendicular to the fibre axis. From differential scanning calorimetry, polarized optical microscopy and X-ray diffraction we establish this to be due to much faster nucleation rates at the fibre surface. The formation of a TC layers is demonstrated for polyvinyldene fluoride, isotactic polypropylene and poly(lactic acid) in spite of the large differences in their chemistry and structure unit cells, suggesting that epitaxy in terms of lattice type or size matching is not a prerequisite. For the three polymers as well as poly(ether ether ketone), the TC layer is identically oriented with the chain axis in the lamella parallel to the CNTs, as observed by wide and small angle X-ray scattering. These results point to polymer chain orientation at the point of adsorption and the formation of a mesomorphic layer as possible steps in the fast nucleation of oriented lamella, with wetting of the CNT fibre surface by the molten semi-crystalline polymer a key condition for heterogeneous nucleation to take place.

Highlights

Conductivity in the graphite basal plane producing a local temperature gradient by dissipation of excess heat from exothermal crystallisation[12]
The fibres have a high surface area (> 250 m2/g) and can be used to produce composites with high volume fraction (> 15%) of aligned carbon nanotubes (CNT), enabling bulk measurements by differential scanning calorimetry (DSC), polarized optical microscopy (POM) and wide and small angle X-ray scattering (WAXS/SAXS) that provide additional information about the heterogeneous nucleation of semi-crystalline polymer, otherwise inaccessible when working with CNTs dispersed in polymer matrices
polyvinyldene fluoride (PVDF) and PP used in this study, as well as other thermoplastics reported (e.g. PS18, Nylon-619, PVA20) show similar affinity with CNT fibres

Summary

Introduction

Conductivity in the graphite basal plane (tube axis) producing a local temperature gradient by dissipation of excess heat from exothermal crystallisation[12]. The fibres have a high surface area (> 250 m2/g) and can be used to produce composites with high volume fraction (> 15%) of aligned CNTs, enabling bulk measurements by differential scanning calorimetry (DSC), polarized optical microscopy (POM) and wide and small angle X-ray scattering (WAXS/SAXS) that provide additional information about the heterogeneous nucleation of semi-crystalline polymer, otherwise inaccessible when working with CNTs dispersed in polymer matrices From these measurements we observe accelerated crystallisation and chain axis parallel to the CNTs (i.e. to the fibre axis) irrespective of polymer type, suggesting that epitaxy is not a prerequisite for the nucleation of the TC layer. In addition to contributing to the discussion on polymer crystal nucleation on CNTs and other nanocarbons, this work intends to set the ground for development of large polymer composite structures based on fibres of CNTs, currently produced on a kilometers/day scale in the laboratory[14] and larger quantities in semi-industrial environments

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