1973 Volume 1

The surface properties of hardwood papers are determined largely by the nature of the fibres and vessel elements (henceforth referred to as vessels) and the possibilities for interfibre and fibre to vessel hydrogen bonding. Experiments with Eucalyptus species and tropical hardwoods covering a wide range of wood densities have shown that surface smoothness as well as bulk mechanical properties depend on the lateral conformability of the fibres and that the response to beating, in terms of surface smoothness, is more marked for pulps with fibres of high Runkel ratio. Effective removal of vessels from pulps was accomplished on a laboratory scale by a method based on that used by Jacquelin for flocculation studies. Vessel removal resulted in a drastic reduction in the vessel IGT pick number. A comparison between the picking tendency of two eucalypt pulps with similar external fibre and vessel dimensions, similar vessel concentrations, but with greatly different fibre lumen diameters, indicated that the bonding strength between fibres and vessels is an important factor in picking, as well as vessel size and concentration. Laterally conformable fibres from low density woods can provide the necessary fibre-to-vessel bonding. Beating has a very pronounced effect in reducing pick number and the question arises whether breaking up of the vessels or improved bonding is mainly responsible. The wider use of hardwood resources for fine papers, particularly for offset printing papers, depends on the surface properties that can be attained.

Dr Page presented an interesting film with an informative commentary upon it, which without the film is not of value in itself and so cannot usefully be reproduced, but the authors have provided the following synopsis. 

A unique apparatus has been built and techniques developed that permit a fresh approach to the study of fibre properties. The apparatus is a stress/strain recorder for testing single fibres under axial tensile load. It is fitted with a high power polarising scopial image and the trace of the stress/strain curve can be recorded on cine film, in synchronism, so that the visual appearance of the fibre and its state of stress and strain at any time can be displayed. The detailed physical events that coincide with initiation of yield and failure are dramatically revealed.

The presentation consisted of a series of cine sequences that demonstrate phenomena that relate to the tensile properties of fibres, including –

1. The effect of fibril angle on fibre strength and stretch-to-break.
2. The initiation of rupture by defects.
3. The tensile behaviour of microcompressed fibres.
4. The phenomena that occur when a fibre dries under tensile stress.
5.  The tensile behaviour of wet fibres.