Characterization of the adhesion of single-walled carbon nanotubes in poly (p-phenylene terephthalamide) composite fibres Libo Deng a , Robert J. Young a, * , Sybrand van der Zwaag b , Steven Picken c a Materials Science Centre, School of Materials, University of Manchester, Manchester M1 7HS, UK b Faculty of Aerospace Engineering, Delft University of Technology, 2629 HS, Delft, The Netherlands c Department of Chemical Technology, Delft University of Technology, 2628 BS Delft, The Netherlands article info Article history: Received 21 December 2009 Received in revised form 22 February 2010 Accepted 22 February 2010 Available online 1 March 2010 Keywords: Aramids Carbon nanotubes Raman spectroscopy abstract Poly(p-phenylene terephthalamide)/single-walled carbon (PPTA/SWNT) composite fibres with different draw ratios have been spun using a dry-jet wet spinning process and their structure and deformation behaviour analysed using Raman spectroscopy. The dispersion of nanotube has been examined by Raman scattering intensity mapping along the fibre. The nanotubes improved the polymer orientation in composite fibre with a draw ratio of 2 but degraded the orientation at higher draw ratios. The mechanical reinforcing effect by nanotubes is related to the change of polymer orientation, suggesting a dominant role of polymer orientation in mechanical performance of the composite fibre. High efficiency of stress transfer within the strain range of 0e0.35% and breakdown of the interface at higher strains has been found in the composite fibres through an in situ Raman spectroscopic study during fibre deformation. Cyclic loading applied on the fibre has indicated reversible deformation behaviour at low strain and gradual damage of the interface at high strains. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Poly(p-phenyleneterephthalamide) (PPTA) fibres, which are made up of oriented bundles of rig-rod polymer molecules, are character- ized by high stiffness and tensile strength. For commercial PPTA fibres such as Twaron and Kevlar fibres, however, there is still a gap between the actual modulus (140 GPa) and the crystallite modulus (200 GPa) measured with X-ray diffraction [1,2]. It is desirable but great chal- lenge to enhance the high performance PPTA fibres. Carbon nanotubes (CNTs) are now believed to be the ultimate reinforcing filler for polymers due to their extraordinary mechan- ical properties [3,4]. They have shown mechanical reinforcement in a variety of polymers such as epoxy [5], PVA [6], PMMA [7] and polyamide [8] with very few successful examples on high perfor- mance polymers [9]. More recently, Coleman's group have reported [10] a significant improvement in mechanical properties of Kevlar fibres by incorporating multi-walled carbon nanotubes, in which the Kevlar/nanotube composite fibres were prepared by swelling of Kevlar fibre in a suspension of nanotubes in the solvent N-meth- ylpyrrolidone. Although the conventional dry-jet wet spinning process for preparation of PPTA fibre is believed to be feasible and is suitable for the mass-production of PPTA/NT composite fibres, little work has been published so far. In this present study, we investigate the effect of nanotubes on PPTA/SWNT composite fibres spun with a dry-jet wet spinning process by using Raman spectroscopy, which has proved to be a powerful technique in studying CNT based polymer composites. We demonstrate here that important issues involved in mechanical reinforcement, such as the state of disper- sion and orientation of nanotubes, and the interfacial stress transfer can be assessed using Raman spectroscopy [11]. 2. Experimental 2.1. Materials The neat PPTA and PPTA/SWNT composite fibres were spun with a dry-jet wet spinning process. Fibres with different draw ratios (DRs), which is defined as the ratio of fibre take-up speed and dope extruding speed, have been spun to understand the influence of processing conditions on the properties of the fibres. The nano- tubes in the composite fibres were pristine HiPco SWNTs, and the content of nanotubes was 0.5% by weight for all composite fibres. 2.2. Mechanical testing Single-fibres of PPTA and PPTA/SWNT were mounted across a cardboard window with a gauge length of 50 mm. Both ends of * Corresponding author. Tel.: þ44 161 306 3550. E-mail address: robert.young@manchester.ac.uk (R.J. Young). Contents lists available at ScienceDirect Polymer journal homepage: www.elsevier.com/locate/polymer 0032-3861/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymer.2010.02.040 Polymer 51 (2010) 2033e2039