Hydrolysis and modification of mechanical pulp using carbohydrate-degrading enzymes

The effects that an inter-stage treatment with enzyme has on pulp quality and energy demands were examined during pilot-scale mechanical pulping. The crude cellulase Novozyme 342 was used to treat primary stage, pressurised refiner mechanical pulp derived, from radiata pine prior to secondary refining. Compared to a control treatment without enzyme, the enzyme treatment increased the energy required for secondary refining to low pulp freeness. After secondary refining, enzyme-treated and control pulps had similar sheet density, tear strength and scattering coefficient at a given freeness. Enzyme treatment did yield an increase in brightness and a decrease in opacity and tensile strength in pulp receiving low levels of secondary refining. Laboratory studies showed that carbohydrate-degrading enzymes, particularly mono-component enzymes, were more aggressive on fines than long fibres. There was evidence that chemical processing can enhance the accessibility of fibres to enzymic attack. The crude cellulase also appeared to be more aggressive because it contained a range of enzyme types. Both the pilot plant and laboratory studies suggest that enzymes might not act on the long fibre fraction when fines are present. Future studies should therefore consider using pulp fractionation to obtain long fibres for enzymic treatment, particularly if these studies are aimed at reducing the energy demands for pulp refining.