MEASUREMENT OF FIBRIL ANGLE IN WOOD FIBERS WITH POLARIZATION CONFOCALMICROSCOPY

A new confocal microscopy technique has been developed to determine th e orientation of fibrils in the S-2 layer of wood fibres. This techniq ue is based on fluorescence dichroism of the fibre wall when dyed with specific fluorochromes. The dyed fibres emit the strongest fluorescen ce when the excitation light is polarized parallel to the cellulose fi brils. Optical sectioning with a confocal microscope allows observatio n of the fluorescent intensity from a given layer within the wall with minimal interference from layers above and below, including the oppos ite wall. Thus, the fibril angle of the S-2 layer can be determined si mply from the change in fluorescent intensity as the polarization angl e of the excitation light is varied. Two fluorochromes, Congo red and acridine orange, were used to induce fluorescence dichroism in fibrils . Congo red was more effective than acridine orange. The technique has been successfully applied to softwood and hardwood fibres in wood sec tions and mechanical pulps, and to fibres prepared under different che mical pulping and bleaching conditions. Measurements can be made on fi bres either in the wet or dry state. The results are in excellent agre ement with measurements obtained from other methods.