16th International Conference on Composite Structures ICCS 16

A. J. M. Ferreira (Editor) © FEUP, Porto, 2011

ON THE DISPERSION OF RECYCLED CARBON FIBRE FOR MANUFACTURING RANDOM MAT USING WET-LAID PROCESS

Guozhan Jiang, Stephen J Pickering, Nick A Warrior Division of Materials, Mechanics and Structures

University of Nottingham Nottingahm NG7 2RD, United Kingdom

e-mail: g.jiang@nottingham.ac.uk

Key words: Carbon fibre, recycling, dispersion, random mat. ABSTRACT

Recycling carbon fibre from polymer composites is one of the major research themes at the Polymer Composites Group of the University of Nottingham, aiming at sustainable manufacture of high performance carbon fibre composites. Over the years, we have developed two recycling processes. One involves thermo-oxidative processing of carbon fibre composites in a fluid bed reactor [1], and another process involves the use of supercritical propanol [2]. The polymeric matrices undergo a reaction-extraction process in the supercritical fluids at about 300oC and 50 bar. Recently, Recycling Carbon Fibre Company (UK) has commercialized a pyrolysis process for recycling carbon fibre [3].

Due to the removal of size on the fibre surface during recycling, the recycled carbon fibre is usually in a fluffy form with severe entanglements, as shown in Figure 1. In order to apply the recycled carbon fibres, they have to be transformed into various preforms, such as a random mat or aligned mat. Also, an assessment method needs to be established to evaluate the behaviour of recycled carbon fibre in polymer composites. We are investigating both aspects.

In this context, the dispersion of recycled carbon fibre is first being investigated. Uniform dispersion is a pre-requisite for the transformation of fluffy fibre using wet-laid process, as illustrated in Figure 2 (left). The recycled carbon fibre is mixed with a dispersion medium. By stirring the dispersion medium, shear force is transferred to the carbon fibre agglomerates to separate them into single fibres. The fibre suspension is then processed into mat. An A4 sized random mat we prepared is shown in Figure 2 (right).

We investigated the effects of surfactants, the types of water-soluble polymers (cellosize, poly(ethylene oxide), poly(acrylamide-co-acrylic acid)) and its rheology, the molecular weight of water-soluble polymers and shear force on fibre dispersion. We used mathematical modelling to correlate the dispersability of recycled carbon fibre with surfactant type, the viscosity and surface tension of the dispersion medium, fibre length, fibre surface energy. The main conclusion is that fibre can be dispersed when the contact distance is greater than 5nm.

G Jiang, S J Pickering and N A Warrior.

2

Figure 1 A photograph of recycled carbon fibre from fluid bed process (left) and from RCF Ltd (UK).

Figure 2 (left) A schematic diagram of wet-laid process for transforming recycled carbon fibre into random mat; (right) A random carbon fibre mat (A4 size), the average fibre length is 12mm REFERENCE [1] (a) G Jiang G, S J Pickering, et al. “Study of a fluidised bed process for recycling carbon fibre

from polymer composite”. Paper No. O22-002, Proceedings of 7th World Congress for Chemical Engineering. Glasgow, UK, 14-18 July, 2005. (b) G Jiang, S J Pickering, et al. Thermochimica Acta 2007; 454(2): 109-115.

[2] (a) G Jiang, S J Pickering, et al. Industrial & Engineering Chemistry Research 2010; 49(10): 4535-4541. (b) G Jiang, S J Pickering, et al. Composites Science and Technology 2009; 69: 192-198.

[3] P Price, J Dividson, Recycling carbon fibre, US patent 2010189629, 2010.