Colour as an indicator for stabilization of polyacrylonitrile fibres

Abstract

The conversion of polyacrylonitrile (PAN)-based precursors into high-performance carbon fibres requires careful control of treatment conditions. The stabilization process is a crucial step in this conversion process as the precursor undergoes chemical modifications that will substantially influence the properties of the final product. As the PAN fibre undergoes stabilization, its colour changes from white through various shades of orange and brown until an overall black appearance is achieved as a result of the imine-based chromophores generated from the underlining chemical reactions. In this work, we quantified the colour changes caused by a wide range of stabilization conditions on a reflectance spectrophotometer. Both CIELAB colour space and RGB colour space measurements correlated well with widely adopted stabilization indicators for oxidized PAN fibre (OPF), including fibre density and relative cyclization index. In particular, RGB colour component B showed very good linear and quadratic relationships with OPF density and relative cyclization index, respectively. The method used in this investigation may be further developed into a convenient tool for monitoring the progression of PAN fibre stabilization.