CHEMICAL MODIFICATION OF PULP TO REDUCE ITS HORNIFICATION TENDENCY

Pulp undergoes a number of partly irreversible changes during drying. These losses of properties are summarised by the term ''hornification' '. They may have a negative effect on processibility and the quality o f prod-ucts. This pa per addresses the question, whether hornification during the drying process may be avoided by a slight chemical derivat isation (introducing ''spacer groups''). As reactive compounds alpha,b eta- unsaturated substances and amino derivatives were chosen. Attenti on was paid to modify the pulps under mild conditions in aqueous mediu m within short reaction times and to obtain derivatives which are stab le under the conditions of paper making. initial wet sulphite pulp oi spruce was derivatised by the active compounds and the effect oi degre e of substitution and derivatising conditions on hornification was inv estigated. The recycling behaviour of modified fibres was evaluated by a simplified laboratory method measuring paper technological properti es. The results prove that by such an approach the hornification tende ncy may be reduced considerably and the decrease of paper strength pro perties caused by recycling may be diminished. By first experiments it was also demonstrated that an existing hornified structure may be rev ersed by special chemical derivatisation.