Imaging Kraft pulp fibres in air and water by atomic force microscopy

There is a need for techniques that might provide new insights into the morphology and properties of surfaces of interest to the pulp and paper industry. Atomic Force Microscopy (AFM) is one such technique that may be used to image surfaces under ambient conditions, or even immersed in fluids. Here, we show that unbleached kraft pulp fibre surfaces can be imaged by AFM in air and in water. Images range in size from tens of microns, showing kraft fibres in a paper sheet, down to a few nanometers, showing individual microfibrils detached from the pulp by beating. It is possible to follow directly the changes in dimensions of fibres on wetting and drying. At higher magnifications, the microfibrillar structure of the cell wall surface is readily imaged. Individual microfibrils generated by beating display a range of dimensions down to less than 1.5 nm. Image quality and ultimate resolution are currently less than for some electron microscopic techniques, but the usefulness of AFM is assured by the ease of sample preparation and the ability to image surfaces under ambient conditions.