Study of the paper fibre surface using atomic force microscopy

When wood fibres bond to form a paper sheet, it is their external surface which first comes into contact. The external surface and its properties thus play a very important role in determining the strength of the paper sheet. In this study, an atomic force microscope (AFM) was employed to probe the external surface of the fibre. AFM force curves obtained on never-dried pulp samples indicated the presence of a soft gelatinous fibrillar layer at the surface, the thickness of which was found to increase with beating. Transverse moduli of the gel layer and the cell wall were obtained by fitting the data to the Sneddon's model. Adhesion force measurements between an AFM tip functionalized with cellulose and fibre surfaces indicated that the degree of bonding improved with beating. The presence of a fibrillar layer at the surface was also seen in the total internal reflectance fluorescence microscopy images.