The measurement of opacity and medullation in wool using an optical fibre diameter analyser

The measurement of Opacity, Transmittance and medullation content in wool by the Optical Fibre Diameter Analyser (OFDA) was investigated. The Projection Microscope (PM) was used as the reference method against which OFDA medullation measurement was compared. Three separate but related areas of research were carried out. In the first section of work, comparative measurements were made at the same sites on individual fibres using both OFDA and PM. It was determined that OFDA Transmittance and OFDA % Opacity both varied considerably within a measurement site. OFDA correctly classified the majority (93%) of fibre sites for medullation, but mis-classified a high proportion of sites of low medullation levels. In the second section of work, 58 samples, exhibiting a range of fibre diameters and medullation levels, were measured using the OFDA snippet measurement method for medullation. The OFDA values obtained were compared with PM measurements from the same samples. It was determined that OFDA gave a highly precise measurement of OFDA % Opacity and Number % Medullation. However, OFDA exhibited low accuracy compared with other available methods. In the third section of work, a preliminary investigation into the effect of colouration in wool as an alternative source of opacity on OFDA medullation measurement was carried out. The effect of dyeing on white wool was to inflate OFDA % Opacity and Number % Medullation values. The degree to which these values were affected was related to hue. The effect on the levels of OFDA % Opacity and Number % Medullation were directly proportional to the percentage of dyed fibre present. Both pigmentation and urine-stain increased the levels of OFDA % Opacity and Number % Medullation measured in wool. This research supports the wool industry's decision to utilise OFDA for the measurement of Number % Medullation in wool and highlights the problems associated with coloured fibres.