Dislocations in wood fibres
Aim: The aim of the project is to study formation, properties and ultrastructure of dislocations in spruce wood fibres and to relate this to pulp and paper properties.
dislocation is a structure easily seen in polarised light microscopy and is the
result of a localised change or distorsion of the microfibrils in either the S1
or both S1 and S2 walls. They occur regularly along the spruce fibre. Fibre
deformations in the form of dislocations are less common in fresh spruce wood
mildly treated and delignified. Dislocations, earlier called nodes, can appear
during chipping, pulping and bleaching and if large enough they can decrease
paper strength. Small dislocations, earlier called slip planes, affect fibre
flexibility and are not considered dangerous. Larger dislocations also give
fibre flexibility, but due to the less ordered or more open structure in the
dislocations, they can be the target for chemical, mechanical or enzymatic
attack giving fibre shortening and inferior paper properties.
Project description: Dislocations are induced during industrial conditions and in this case often negatively affect paper strength. In the laboratory, normal stirring in water does not induce dislocations and during shearing they disappear and the fibres are more or less swelled and disintegrated. In HCl fibres are not cleaved at pH 1.8, while at pH 1 or at lower pHs, fibres are cleaved at dislocations. In addition to fibre surface erosion, cellulases also cleave fibres at dislocations giving shorter fibres, while xylanase give delamination. Balloon swelling is obtained in LiCl/DMAc and in phosphoric acid, and the balloon formation and stability reflect the properties of the used pulp fibre. After phosphoric acid swelling stable balloons which can be studied with EM, are obtained in fibres with 3-4% lignin. Cellulase treated, bleached or otherwise mechanically affected fibres give rapid ballooning and also further dissolution of the fibre. Spruce pulp fibres will be further investigated regarding influence of dislocations using cellulases and HCl. Appearance of dislocations in industrial pulps during manufacturing will be investigated and correlated with pulp and paper properties.