Chemical determination of shive content in flax using the acetyl bromide method

The purity from shives of flax fibre raw materials is an important parameter in several different applications. The utilisation of an exact, quick and easy method for the determination of shive content in different kinds of flax raw materials, would be beneficial for the development of systems ensuring reliable raw materials supply. The methods previously used are gravimetric fibre content determination and air classification. Methods based on the difference in chemical composition between fibres and shives, mainly lignin content, have also been investigated for determining purity, e.g. Klason lignin method and NIRS. The Klason lignin method is insensitive to the physical nature of the sample while NIRS enables quick analysis once the calibration is established, but the methods still have respective drawbacks in terms of response time and lack of simplicity. The acetyl bromide procedure for determining lignin content could have advantages over previously suggested methods for determining shive content. It is quick, does not require the use of expensive equipment and only small samples of pure fibres and shives are needed for calibration. The purpose of this study was therefore to investigate the possibilities of using the acetyl bromide method in determining shive content. Known recombinations of pure flax fibres and shives of different origin were analysed using a simplified acetyl bromide analysis. The linearity and precision of the analytical method was then confirmed. The acetyl bromide response was compared with other lignin analysis based methods (Klason lignin and Kappa number) and an analysis of different sources of errors in a suggested sampling and analytical procedure was made. The results show that the method can be used for determining shive contents for very different raw materials. The method is much less time consuming than Klason lignin method, giving similar experimental errors. A need for much larger samples of absolute purity for calibration is the major drawback for the Kappa number method.