Effect of fines on fibre bonding: Cross-sectional dimensions of TMP fibres at potential bonding sites

It has been shown that the density and tensile strength properties of handsheets made of the long fibre fraction of a pulp can be significantly improved by the addition of chemical or mechanical fines. This raises questions about how fines affect potential bonding sites, what fibre crossing points look like in wet pressed and dried sheets, and how they appear in cross-sectional view. An attempt has been made to answer these questions using a confocal laser scanning microscope (CLSM) to obtain cross-sectional images of fibre crossing points in wet pressed networks, and then exactly the same areas after drying. Fibre width, thickness and cross-sectional area were measured from these images. Handsheets made of just the long fibre fraction were bulky and had little strength, whilst those containing fines additions were denser and stronger. Sheets containing kraft fines were significantly stronger than those containing TMP fines. Preliminary measurements made from the cross-sectional images showed that, on average, fibres in networks containing a fines addition became flatter on drying than those in networks consisting of only long fibres.